Dissertations / Theses: 'Laser frequency noise'

1

De, Syamsundar. "Noise in dual-frequency semiconductor and solid-state lasers." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112114/document.

Full text

Abstract:

Les sources cohérentes de lumière émettant deux fréquences optiques avec une différence largement accordable dans le domaine radiofréquence et un fort degré de corrélation entre leurs fluctuations respectives peuvent être d’un grand intérêt pour de nombreuses applications telles que la photonique micro-onde, les horloges atomiques ultra stables, la physique atomique, la métrologie, etc. C’est le cas des lasers bifréquences émettant deux modes de polarisations linéaires croisées avec une différence de fréquence dans le domaine radiofréquence. Nous comparons les caractéristiques de telles sources bifréquences basées sur des lasers à semiconducteurs (VECSEL: vertical-external-cavity surface-emitting laser) ou des lasers à solide (notamment les solides dopés Nd3+ ou Er3+). Au-delà de la différence évidente entre les mécanismes de gain dans les lasers à semiconducteurs et dans les lasers à solide, le VECSEL bifréquence et le laser Nd:YAG bifréquence ne présentent pas la même dynamique. Le VECSEL bifréquence, comme pour un laser de classe A, a une dynamique dénuée d’oscillations de relaxation puisque la durée de vie des photons dans la cavité est beaucoup plus longue que celle de l’inversion de population. A l’opposé, le laser Nd:YAG bifréquence possède une dynamique présentant des oscillations de relaxation comme pour un laser de classe B, en vertu du fait que la durée de vie des photons dans la cavité est plus courte que celle de l’inversion de population. Dans cette thèse, nous explorons les mécanismes par lesquels cette dynamique, en plus du couplage non linéaire entre les deux modes, gouverne le bruit dans les lasers bifréquences. En particulier, nous analysons à la fois expérimentalement et théoriquement les propriétés spectrales des différents bruits (intensité, phase) ainsi que leurs corrélations dans le cas d’un VECSEL bifréquence de classe A et d’un laser Nd:YAG bifréquence de classe B. Enfin, un modèle de réponse linéaire de deux oscillateurs amortis couplés permet d’interpréter les résultats obtenus sur la corrélation entre ces différents bruits
Coherent sources emitting two optical frequencies with a widely tunable frequency difference lying in the radio-frequency range and having a high degree of correlation between their fluctuations can be useful for numerous applications such as microwave photonics, ultra-stable atomic clocks, atom manipulation and probing, metrology, etc. Dual-frequency lasers, which emit two orthogonal linearly polarized modes with a frequency difference lying in the radio-frequency range, have huge potentials for the above mentioned applications. We compare the characteristics of such dual-frequency oscillation in lasers based on either semiconductor (VECSEL: vertical-external-cavity surface-emitting laser) or solid-state active media (mainly Nd3+, or Er3+ doped crystalline host). Apart from the obvious difference between the gain mechanisms in semiconductor and solid-state laser media, the dual-frequency VECSEL and the dual-frequency Nd:YAG laser exhibit different dynamical behaviors. The dual-frequency VECSELs exhibit relaxation oscillation free class-A dynamics as the photon lifetime inside the cavity is longer than the population inversion lifetime. On the contrary, the dual-frequency Nd:YAG lasers obey class-B dynamics linked with the fact that the photon lifetime inside the cavity is shorter than the population inversion lifetime, leading to the existence of relaxation oscillations. In this thesis, we figure out how the laser dynamics, in addition to the nonlinear coupling between the two laser modes, governs different noise phenomena in dual-frequency lasers. In particular, we demonstrate, both experimentally and theoretically, the influence of the laser dynamics and the nonlinear coupling between the two modes on the laser noise, by analyzing the spectral properties of the different noises (intensity, phase) and their correlation in a class-A dual-frequency VECSEL (vertical-external-cavity surface emitting laser) and a class-B dual-frequency Nd:YAG laser. Moreover, the noise correlation results are interpreted in terms of the linear response of two coupled damped oscillators

APA, Harvard, Vancouver, ISO, and other styles

2

Saxena, Bhavaye. "Noise Characteristics for Random Fiber Lasers with Rayleigh Distributed Feedback." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31766.

Full text

Abstract:

Frequency and intensity noise are characterized for Erbium-Doped Fiber and Brillouin random lasers based on Rayleigh distributed feedback mechanism. We propose a theoretical model for the frequency noise of an Er-doped fiber random lasers using the property of random phase modulations from multiple scattering points in ultra-long fibers. We find that the Rayleigh feedback suppresses the noise at higher frequencies by introducing a Lorentzian envelope over the thermal frequency noise of a long fiber cavity. The theoretical model and measured frequency noise agree quantitatively with two fitting parameters. A similar model, which also includes additional acoustic fluctuations and a distributed gain profile in the fiber, has been speculated for the Brillouin random laser. These random laser exhibits a frequency noise level of < 6 Hz^2/Hz at 2 kHz, which is lower than what is found in conventional narrow-linewidth EDF fiber lasers and Nonplanar Ring Laser oscillators (NPRO) by a factor of 166 and 2 respectively.

APA, Harvard, Vancouver, ISO, and other styles

3

Kolbl, Josef Karl. "Low-noise frequency synthesis and picosecond timing for satellite laser ranging systems." Thesis, University of Central Lancashire, 2001. http://clok.uclan.ac.uk/20201/.

Full text

Abstract:

The main aims of the research are to develop various high-speed hardware circuits based on the latest electronic devices and integrated circuit technologies to provide time measurement with one picosecond accuracy, thereby enabling the development of a satellite laser ranging (SLR) system with submillimeter precision. Different types of oscillators and frequency multipliers have been developed (RF and microwave) in order to provide a synchronous and low phase noise clock signal to the SLR timing system, which is phase-locked to the Universal Time Clock (UTC). A technique to quantify phase noise in signal sources is presented and verified. The development of the ranging system encompasses the analog timing verniers, the digital timing system, acquisition and processing of the ranging data, and the controlling of the peripherals, like the laser. The mixed analog/digital timing system architecture provides a time interval determination of two events with picosecond accuracy. Optical calibration techniques and an electronic timing calibration technique were developed to provide calibration of the timing system down to one picosecond accuracy and femtoseconds of resolution, traceable to the International Standard (speed of light, metric standard). The work done has led to several electronic modules for measuring precisely laser runtimes to artificial satellites and to the Moon which are now in successful and permanent operation in five SLR stations around Tokyo, one SLR station in Australia, and one SLR station in Germany. Furthermore, the work has produced three papers and two patents and won the First Prize of Innovation Awards from Deggendorf Government. The research and development work pushed the picosecond timing technology to an extent where the SLR stations in Australia, Tokyo and Germany now have a significant improvement in their ranging data accuracy in comparison to their previous timing equipment, thereby achieving more precise environmental monitoring.

APA, Harvard, Vancouver, ISO, and other styles

4

Sebastian, Ananthu. "Noise dynamics in multi-Stokes Brillouin laser." Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S068.

Full text

Abstract:

La diffusion Brillouin stimulée (SBS) est un processus d'interaction cohérent, pour lequel la lumière est diffusée à partir des ondes acoustiques générées optiquement. Les lasers Brillouin suscitent un très grand intérêt pour leur capacité à produire des largeurs de raie ultra cohérentes. Cette thèse est consacrée à la compréhension des propriétés de bruit des lasers à fibre Brillouin en anneau, fonctionnant avec de multiples ordres de Stokes. Tout d'abord, nous présentons une technique basée sur la méthode de ringdown de la cavité, qui permet de caractériser le coefficient de gain Brillouin directement à partir du sondage de la cavité laser. Ses avantages sont d'obtenir des paramètres à partir d'une seule expérience avec de faibles puissances optiques (quelques 10 milliwatts) pour des cavités courtes (quelques mètres de long, ou cavités intégrées). Deuxièmement, il est démontré qu'une largeur de raie intrinsèque de quelques dizaines de mHz peut être facilement obtenue en cascadant deux lasers Brillouin non résonants (pour lesquels la pompe effectue un seul passage à l'intérieur de la cavité). Afin d'obtenir ces résultats, la stabilité à long terme a été améliorée en utilisant une boucle d'asservissement de type Pound Drever Hall, ce qui nous permet de comparer nos résultats analytiques et expérimentaux. Malheureusement, nous n'avons pas exploré les limites fondamentales de la réduction du bruit en raison du plancher de bruit de notre banc de mesure. Troisièmement, un des travaux majeurs de cette thèse est l'étude analytique et expérimentale des propriétés du bruit, y compris le bruit de fréquence et le bruit relatif d'intensité, d'un laser Brillouin résonant (pour lequel, les ondes de pompe et de Stokes sont résonantes à l'intérieur de la cavité). En particulier, les impacts du facteur de qualité de la cavité fibrée en anneau, le désaccord de gain Brillouin ont été évalués très précisément sur les caractéristiques du RIN du laser telles que la réduction de l'amplitude du bruit et la fréquence de relaxation. Nous soulignons le fait que de nombreuses caractéristiques du bruit de fréquence sont liées aux propriétés du RIN par un couplage entre l'intensité et la phase. Nous montrons que le processus en cascade modifie la dynamique du laser Brillouin par rapport à celle d'un laser Brillouin monomode avec une seule composante de Stokes de premier ordre. Nos résultats expérimentaux sont en excellent accord avec nos simulations, obtenues grâce à notre système non linéaire décrivant le fonctionnement d'un laser Brillouin multi-Stokes. Cette bonne concordance est principalement due à notre capacité : à obtenir des valeurs très précises des paramètres de la cavité et du coefficient de gain Brillouin en utilisant la technique CRDM ; à atteindre une stabilité à long terme (plusieurs dizaines d'heures) ; à contrôler finement le désaccord entre la résonance de Stokes du laser et la fréquence du maximum de gain Brillouin. Nous démontrons expérimentalement pour la première fois que le bruit de fréquence est dégradé en présence d'une diffusion Brillouin anti-Stokes. Nous montrons également qu'un désaccord de gain de l'ordre de quelques centaines de kHz peut dégrader la réduction du bruit d'intensité ou également augmenter la largeur de raie par un couplage amplitude-phase. Toutes ces observations très fines nous permettent donc de fixer les limites fondamentales de tels systèmes laser comme : l'augmentation du bruit due aux ordres anti-Stokes ; le rôle du bruit de pompe et son interrelation possible avec la finesse de la cavité ; l'effet du désaccord inhérent aux ordres de Stokes plus élevés. Toutes ces conclusions sont les clés de la conception et de l'ingénierie de ces lasers à fibre Brillouin, qui suscitent actuellement beaucoup d'intérêt comme en témoignent les travaux en cours dans la communauté scientifique. Cette thèse de doctorat contribue à une meilleure compréhension des lasers Brillouin multi-Stokes
Stimulated Brillouin Scattering (SBS) is a coherent interaction process in which light is scattered from optically generated acoustic waves. It is a powerful tool for microwave and optical signal processing, distributed sensing and spectroscopy. Brillouin lasers are attracting a lot of interest for their ability to produce ultra coherent linewidths. This thesis is devoted to the understanding of noise properties of Brillouin fiber ring lasers, operating with multiple Stokes orders. First, we present a technique based on the cavity ring-down method, which allows to characterize the Brillouin gain coefficient directly from probing the laser cavity. Its advantages are to obtain parameters from a single experiment with low optical powers (some 10 milliwatts) for short cavities (a few meters long, or integrated cavities). Secondly, it is shown that an intrinsic linewidth of a few tens of mHz can be easily obtained by cascading two non-resonant Brillouin lasers (for which the pump performs a single pass inside the cavity). In order to obtain these results, the long-term stability has been improved by using a Pound-Drever-Hall servo loop, which allows us to compare our analytical and experimental results. Unfortunately, we were unable to explore the fundamental limits of noise reduction due to the noise floor of our bench. Thirdly, one of the major works of this thesis is the theoretical and experimental study of the noise properties, including frequency noise and relative intensity noise, of a resonant Brillouin laser (for which pump and Stokes waves are resonant inside the cavity). In particular, the impacts of the fiber-ring-cavity quality factor, Brillouin gain detuning, are evaluated very precisely on the laser RIN features such as amplitude noise reduction and relaxation frequency. We emphasize the fact that many characteristics of the frequency noise are related to the RIN properties by a coupling between intensity and phase. We show that the cascade process modifies the dynamics of the Brillouin laser when compared to those of a single-mode Brillouin laser with a single first-order Stokes component. Our experimental results are in excellent agreement with our numerical simulations, obtained thanks to our non-linear system describing the operation of a multi-Stokes Brillouin laser. This good match is mainly due to our ability: to obtain very precise values of the cavity parameters and the Brillouin gain coefficient using the CRDM technique ; to achieve long-term stability (hours); to finely control the detuning between the laser Stokes resonance and the frequency of the Brillouin gain maximum. We demonstrate experimentally for the first time that frequency noise is degraded in the presence of anti-Stokes Brillouin scattering. We also show that a gain detuning of the order of a few hundred kHz can degrade the intensity noise reduction or also increase the linewidth by amplitude-phase coupling. All these very fine observations thus allow us to set the fundamental limits of such laser systems such as: the increase in noise due to anti-Stokes orders; the role of pump noise and its possible interrelation with cavity finesse; the effect of the detuning inherent to higher Stokes orders. All these conclusions are key to the design and engineering of these Brillouin fiber lasers, which are currently attracting a great deal of interest as evidenced by the work in progress in the scientific community. This PhD thesis contributes to a better understanding of multi-Stokes Brillouin lasers

APA, Harvard, Vancouver, ISO, and other styles

5

Slagmolen, Bram Johannes Jozef, and BRAM SLAGMOLEN@ANU EDU AU. "Direct Measurement of the Spectral Distribution of Thermal Noise." The Australian National University. Faculty of Science, 2005. http://thesis.anu.edu.au./public/adt-ANU20051128.104552.

Full text

Abstract:

This thesis investigates the direct measurement of the thermal noise spectral distribution. Long base line gravitational wave detectors, being commissioned around the world, are limited in sensitivity in the intermediate frequencies by the thermal noise. These detectors are utilising suspended test mirrors for the detection of gravitational waves by measuring their relative displacement. One of the fundamental noise sources in these detectors is the thermally induced displacement of the suspension onto and within the mirrors. This thermally induced motion of the test mirrors limits the displacement sensitivity of the gravitational wave detectors. Knowledge of the spectral behavior of thermal noise over a wide frequency range will improve predictions and understanding of the behavior of the suspension and test mirrors.¶ In this thesis the direct measurement of the thermal noise spectral distribution of a mechanical flexure resonator is described. The mechanical flexure resonator is an unidirectional ’wobbly table’ made from copper-beryllium, which hinges around four thin flexures 15 mm wide, 1 mm high and ~116 µm thick. The mechanical flexure resonator has a resonant frequency of 192 Hz, with a quality factor of ~3000.¶ The thermal noise induced displacement of the mechanical flexure resonator was measured using an optical cavity. The end mirror of a two mirror optical cavity was mounted on the mechanical flexure resonator. A laser was made resonant with the test cavity by use of a locking control system. Thermal noise induced displacement moved the test cavity away from resonance. By measuring the error-signal in the control system, the equivalent thermal noise displacement was obtained.¶ The thermal noise induced displacement of the mechanical flexure resonator was predicted to be in the order of 10^(−12) to 10^(−17) m/sqrtHz over a frequency range of 10 Hz to 10 kHz. All other external noise sources needed to be suppressed to below this level. A major noise source was the laser frequency fluctuations. When the test cavity was locked to the laser, the laser frequency fluctuations dominated the read out signal. To suppress the frequency fluctuations, the laser was locked to a rigid long optical reference cavity. This allowed the frequency fluctuations to be suppressed to below the equivalent thermal noise displacement of the test cavity over the frequency range of interest.¶ Acoustic noise was suppressed by placing the whole experiment inside a vacuum chamber, and evacuating the air inside the chamber down to a pressure level of 10^(−4) mbar. A seismic vibration isolation system was used to suppress the seismic noise in the laboratory to below 10^(−14) m/sqrtHz at frequencies above 4 Hz.¶ With the experimental set up, the thermal noise displacement of the mechanical flexure resonator has been measured. Due to the degradation of the isolator performance, measurement of the thermal noise behavior over a wide frequency range of the mechanical flexure resonator was unsuccessful. By using an analytical curve fitting routine around the fundamental and first order resonant modes of the resonator, a loss factor of (3.5 ± 1.5 − 3.7 ± 1.5) × 10^(−4) for the copper-beryllium mechanical flexure resonator was obtained and structural damping was inferred.

APA, Harvard, Vancouver, ISO, and other styles

6

Quinlan, Franklyn. "LOW NOISE, HIGH REPETITION RATE SEMICONDUCTOR-BASED MODE-LOCKED LASERS FOR SIGNAL PROCESSING AND COHERENT COMMUNICATIONS." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3393.

Full text

Abstract:

This dissertation details work on high repetition rate semiconductor mode-locked lasers. The qualities of stable pulse trains and stable optical frequency content are the focus of the work performed. First, applications of such lasers are reviewed with particular attention to applications only realizable with laser performance such as presented in this dissertation. Sources of timing jitter are also reviewed, as are techniques by which the timing jitter of a 10 GHz optical pulse train may be measured. Experimental results begin with an exploration of the consequences on the timing and amplitude jitter of the phase noise of an RF source used for mode-locking. These results lead to an ultralow timing jitter source, with 30 fs of timing jitter (1 Hz to 5 GHz, extrapolated). The focus of the work then shifts to generating a stabilized optical frequency comb. The first technique to generating the frequency comb is through optical injection. It is shown that not only can injection locking stabilize a mode-locked laser to the injection seed, but linewidth narrowing, timing jitter reduction and suppression of superfluous optical supermodes of a harmonically mode-locked laser also result. A scheme by which optical injection locking can be maintained long term is also proposed. Results on using an intracavity etalon for supermode suppression and optical frequency stabilization then follow. An etalon-based actively mode-locked laser is shown to have a timing jitter of only 20 fs (1Hz-5 GHz, extrapolated), optical linewidths below 10 kHz and optical frequency instabilities less than 400 kHz. By adding dispersion compensating fiber, the optical spectrum was broadened to 2 THz and 800 fs duration pulses were obtained. By using the etalon-based actively mode-locked laser as a basis, a completely self-contained frequency stabilized coupled optoelectronic oscillator was built and characterized. By simultaneously stabilizing the optical frequencies and the pulse repetition rate to the etalon, a 10 GHz comb source centered at 1550 nm was realized. This system maintains the high quality performance of the actively mode-locked laser while significantly reducing the size weight and power consumption of the system. This system also has the potential for outperforming the actively mode-locked laser by increasing the finesse and stability of the intracavity etalon. The final chapter of this dissertation outlines the future work on the etalon-based coupled optoelectronic oscillator, including the incorporation of a higher finesse, more stable etalon and active phase noise suppression of the RF signal. Two appendices give details on phase noise measurements that incorporate carrier suppression and the noise model for the coupled optoelectronic oscillator.
Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD

APA, Harvard, Vancouver, ISO, and other styles

7

Foltynowicz, Aleksandra. "Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-22269.

Full text

Abstract:

Noise-immune cavity-enhanced optical heterodyne molecular spectro-metry (NICE-OHMS) is one of the most sensitive laser-based absorption techniques. The high sensitivity of NICE-OHMS is obtained by a unique combination of cavity enhancement (for increased interaction length with a sample) with frequency modulation spectrometry (for reduction of noise). Moreover, sub-Doppler detection is possible due to the presence of high intensity counter-propagating waves inside an external resonator, which provides an excellent spectral selectivity. The high sensitivity and selectivity make NICE-OHMS particularly suitable for trace gas detection. Despite this, the technique has so far not been often used for practical applications due to its technical complexity, originating primarily from the requirement of an active stabilization of the laser frequency to a cavity mode. The main aim of the work presented in this thesis has been to develop a simpler and more robust NICE-OHMS instrumentation without compro-mising the high sensitivity and selectivity of the technique. A compact NICE-OHMS setup based on a fiber laser and a fiber-coupled electro-optic modulator has been constructed. The main advantage of the fiber laser is its narrow free-running linewidth, which significantly simplifies the frequency stabilization procedure. It has been demonstrated, using acetylene and carbon dioxide as pilot species, that the system is capable of detecting relative absorption down to 3 × 10-9 on a Doppler-broadened transition, and sub-Doppler optical phase shift down to 1.6 × 10-10, the latter corresponding to a detection limit of 1 × 10-12 atm of C2H2. Moreover, the potential of dual frequency modulation dispersion spectrometry (DFM-DS), an integral part of NICE-OHMS, for concentration measurements has been assessed. This thesis contributes also to the theoretical description of Doppler-broadened and sub-Doppler NICE-OHMS signals, as well as DFM-DS signals. It has been shown that the concentration of an analyte can be deduced from a Doppler-broadened NICE-OHMS signal detected at an arbitrary and unknown detection phase, provided that a fit of the theoretical lineshape to the experimental data is performed. The influence of optical saturation on Doppler-broadened NICE-OHMS signals has been described theoretically and demonstrated experimentally. In particular, it has been shown that the Doppler-broadened dispersion signal is unaffected by optical saturation in the Doppler limit. An expression for the sub-Doppler optical phase shift, valid for high degrees of saturation, has been derived and verified experimentally up to degrees of saturation of 100.

APA, Harvard, Vancouver, ISO, and other styles

8

Hofmann, Peter. "Monolithic Soft Glass Single Frequency Fiber Lasers." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/268515.

Full text

Abstract:

Envisioning novel fully monolithic fiber-optical devices, this dissertation investigates four fiber optical devices both, active and passive, that contribute to the goal of further integrating and miniaturizing fiber optics. An all phosphate glass fiber laser was designed in an effort to reduce laser intensity noise by reducing cavity losses and low mechanical strength that arise from intra-cavity fusion splices between silica fiber Bragg gratings (FBG) and phosphate active fiber in state of the art phosphate single frequency fiber lasers. Novel phosphate glass based FBGs have been fabricated utilizing high intensity laser pulses at 193 nm and a phase-mask. Net reflectivities of up to 70 % and a bandwidth of 50 pm have been achieved in the FBGs. The laser design comprised two of the novel FBGs and a short section of Er³⁺Yb³⁺ phosphate fiber to form a distributed Bragg reflector (DBR) laser. The performance of the new laser has been compared to a conventional phosphate fiber laser. Particular focus was put on the laser intensity noise due to its dependence on intra-cavity losses. Relative intensity noise (RIN) amplitudes of -80 dB/Hz have been measured for both lasers when operating at comparable output powers. For similar levels of absorbed pump power the relaxation oscillation frequencies (ROF) were shifted towards lower frequencies in the new laser. ExcessFBG scattering losses and mode-field miss-match between the active and passive fiber limited the output power of the new laser to 16 mW compared to 140 mW in the conventional laser. A monolithic all-phosphate glass fiber laser with up to 550 mW output power that is operating at a single longitudinal mode and exhibiting narrow linewidth is presented. The laser cavity has been formed by inscribing FBGs directly into heavily Er³⁺Yb³⁺ doped phosphate glass fiber using femtosecond laser pulses and a phase mask, completely eliminating the need for intra-cavity fusion splices. A linewidth of less than 60 kHz and relaxation oscillation peak amplitudes below -100 dB/Hz without active suppression of RIN have been measured. The compact form factor and higher output power combined with the low noise and narrow linewidth characteristic make this laser an ideal candidate for ranging, interferometry and sensing applications. Strong and robust Bragg gratings in optical fiber fabricated from highly photosensitive photo-thermo-refractive (PTR) glass are demonstrated. The fibers were drawn at 900 °C from a machined PTR-glass preform. A low power two beam interference pattern from a continuous wave (cw) He-Cd laser with a wavelength of 325 nm was used to write gratings into the fibers, achieving peak grating strengths of 20 dB and a spectral width of 45 pm. The gratings showed no sign of degradation when exposed to a high temperature environment of 425 °C for several hours. This is significantly higher when compared to standard Telecom FBGs which are rated for operation temperatures below 200 °C. A detailed study of novel mode-field adapters (MFA) based on multi-mode interference in graded index multi-mode fibers (GIMF) is presented. MFAs are often used in cases when low coupling losses between single mode fibers with very different mode-field diameters are needed. Here a new type of MFAs has been fabricated and characterized from a selection of commercially available single mode and graded index fibers. Compared to existing techniques the presented MFAs can be fabricated very quickly and are not limited to certain fiber types. Insertion losses of 0:5 dB over a spectral range of several hundred nm have been obtained with an ultra compact MFA with a length of 275 μm.

APA, Harvard, Vancouver, ISO, and other styles

9

Audo, Kevin. "Étude théorique et expérimentale des lasers solides bi-fréquences auto-régulés en bruit d'intensité via des non-linéarités intracavité." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S002/document.

Full text

Abstract:

Les lasers à état solide bi-fréquences constituent des sources de choix pour de nombreux domaines (métrologie, photonique micro-onde, Lidar-Radar, horloges atomiques). Cependant, de tels lasers souffrent d'excès de bruit d'intensité difficiles à supprimer avec les méthodes habituelles. Dans ce contexte, nous développons une nouvelle approche baptisée « buffer reservoir » pour la réduction de l'excès de bruit d'intensité des lasers à état solide. Cette méthode repose sur le changement du comportement dynamique du laser par insertion d'un mécanisme d'absorption non-linéaire faiblement efficace dans la cavité. Tout d'abord, nous étudions cette approche dans des lasers solides mono-fréquence en exploitant deux types d'absorption non-linéaire : l'absorption à deux photons (TPA) et l'absorption par génération de seconde harmonique (SHGA). Nous montrons qu'il est possible de réduire de 50 dB le bruit d'intensité à la fréquence des oscillations de relaxation d'un laser Er,Yb:verre sans en dégrader la puissance de sortie ni le bruit de phase. Nous explorons les mécanismes physiques sous-jacents en développant un modèle analytique décrivant le comportement dynamique du laser. L'effet de l'absorbant non-linéaire sur les pics de bruit à haute fréquence à l'intervalle spectrale libre de la cavité est également étudié. Nous démontrons l'intérêt de telles sources lasers auto-régulées en intensité pour la distribution d'oscillateurs locaux sur porteuse optique. Nous mettons ensuite en application l'approche « buffer reservoir » dans des lasers bi fréquences. En développant un modèle analytique prédictif, nous montrons expérimentalement que l'utilisation de TPA engendre, sous certaines conditions, une réduction de 40 dB de l'amplitude des pics de bruit en-phase et en anti-phase. Nous vérifions en outre les propriétés de couplage des modes dans le milieu actif lorsque les pertes non-linéaires sont présentes. Enfin, nous abordons l'utilisation de SHGA comme ''buffer reservoir'' dans les lasers bi-fréquences. Plus particulièrement, nous explorons expérimentalement et théoriquement le comportement du laser lorsque les pertes non-linéaires ne sont introduites que sur un seul mode propre du laser. Dans cette configuration, nous montrons qu'il est possible d'obtenir pour les deux modes à la fois une forte diminution des pics de bruit d'intensité résonants
Dual-frequency solid-state lasers are attractive for numerous domains (metrology, microwave photonics, Lidar-Radar, optical clocks). However, such lasers suffer from excess intensity noise which is difficult to cancel with usual methods. In this context, we develop a new approach called “buffer reservoir” for reducing the excess intensity noise. This method relies on the change of the laser’s dynamical behavior by inserting a low efficient nonlinear absorption mechanism in the cavity. First, this approach is studied on single frequency solid-state lasers by using two types of non-linear absorption: two-photon absorption (TPA) and second harmonic generation absorption (SHGA). We show a possible reduction of the intensity noise at the relaxation oscillations frequency of an Er,Yb:glass laser up to 50 dB without degrading neither its power nor its phase noise. We explore the underlying physics by developing an analytical model describing the laser dynamical behavior. The effect of the nonlinear absorber on the noise peaks lying at high frequency at the free spectral range of the cavity is also studied. We demonstrate the relevance of such self-regulated lasers for the distribution of optically carried local oscillators. We then extend the “buffer reservoir” approach to dual-frequency lasers. By developing a predictive analytical model, we show experimentally that the use of TPA enables 40 dB reduction of both in-phase and anti-phase noise under certain conditions. The mode coupling in the active medium is analyzed when the nonlinear losses are present. Finally, we address the use of SHGA as a ''buffer reservoir'' in dual-frequency lasers. In particular, we experimentally and theoretically explore the laser behavior when the nonlinear losses are inserted on one eigen-mode of the laser only. This configuration enables a strong reduction of resonant noise peaks for both modes

APA, Harvard, Vancouver, ISO, and other styles

10

Lally, Evan M. "A Narrow-Linewidth Laser at 1550 nm Using the Pound-Drever-Hall Stabilization Technique." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/34739.

Full text

Abstract:

Linewidth is a measure of the frequency stability of any kind of oscillator, and it is a defining characteristic of coherent lasers. Narrow linewidth laser technology, particularly in the field of fiber-based infrared lasers, has progressed to the point where highly stable sources are commercially available with linewidths on the order of 1-100 kHz. In order to achieve a higher level of stability, the laser must be augmented by an external frequency stabilization system. This paper presents the design and operation of a frequency locking system for infrared fiber lasers. Using the Pound-Drever-Hall technique, the system significantly reduces the linewidth of an input laser with an un-stabilized linewidth of 2 kHz. It uses a high-finesse Fabry-Perot cavity, which is mechanically and thermally isolated, as a frequency reference to measure the time-varying frequency of the input laser. An electronic feedback loop works to correct the frequency error and maintain constant optical power. Testing has proven the Pound-Drever-Hall system to be highly stable and capable of operating continuously for several seconds at a time.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

11

Capocasa, Eleonora. "Optical and noise studies for Advanced Virgo and filter cavities for quantum noise reduction in gravitational-wave interferometric detectors." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC080/document.

Full text

Abstract:

L'astronomie gravitationnelle a débuté en septembre 2015 avec la première détection de la fusion de deux trous noirs par LIGO. Depuis lors, plusieurs fusions de trous noirs et une fusion d'étoiles à neutrons ont été observées. Advanced Virgo a rejoint les deux observatoires LIGO dans la prise de données en août 2017, augmentant fortement les capacités de localisation du réseau. Afin d'exploiter pleinement le potentiel scientifique de ce nouveau domaine, un énorme effort expérimental est nécessaire pour améliorer la sensibilité des interféromètres. Cette thèse, développée dans ce contexte, est composée de deux parties. La première concerne Advanced Virgo : nous avons développé un budget de bruit automatique pour le bruit de fréquence du laser et nous avons effectué des mesures de caractérisation optique pour les cavités de bras kilométriques. Des pertes aller-retour aussi faibles que 80 ppm ont été mesurées. Elles sont parmi les plus basses jamais mesurées avec un faisceau de cette taille. La deuxième partie concerne la conception et le développement d'une cavité de filtrage de 300 m, un prototype pour démontrer la production de lumière squeezing dépendante de la fréquence avec les propriétés nécessaires pour une réduction du bruit quantique à large bande dans KAGRA, Advanced Virgo et Advanced LIGO. Nous avons contribué à la fois aux phases de conception et d'intégration du projet. Nous avons d'abord fait le design optique de la cavité, y compris les spécifications pour l'optique de la cavité et une estimation détaillée des sources de dégradation pour le squeezing. Nous avons donc développé un système de contrôle pour les miroirs, assemblé les suspensions et finalement aligné et mis la cavité en résonance avec la lumière laser
Gravitational wave astronomy has started in September 2015 with the first detection of a binary black-hole merger by LIGO. Since then, several black-hole mergers and a binary neutron star merger have been observed. Advanced Virgo joined the two LIGO detector in the observation run, in August 2017, highly increasing the localization capabilities of the network. In order to fully exploit the scientific potential of this new-born field, a huge experimental effort is needed to bring the instruments at their design sensitivity and to further improve them. This thesis, developed in this context, it is composed of two parts. The first is about Advanced Virgo: we have developed an automatic noise budget for the laser frequency noise and we have performed optical characterization measurements for the kilometric arm cavities. Round trip Losses as low as 80 ppm have been measured. They are among the lowest ever measured for beams of these size. The second part is about the design and development of a 300 m filter cavity, a prototype to demonstrate the frequency dependent squeezing production with properties needed for a broadband quantum noise reduction in the future upgrades of KAGRA, Advanced Virgo and Advanced LIGO. We have contributed to the design and integration phases of the project. We have first made the optical design of the cavity, including the the specifications for the main cavity optics and a detailed estimation of the squeezing degradation sources. We have then developed a local control system for the mirrors, assembled the suspensions, and finally aligned and brought the cavity in resonance with the laser light

APA, Harvard, Vancouver, ISO, and other styles

12

Wang, Ziyang. "Next Generation Ultrashort-Pulse Retrieval Algorithm for Frequency-Resolved Optical Gating: The Inclusion of Random (Noise) and Nonrandom (Spatio-Temporal Pulse Distortions) Error." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-04122005-224257/unrestricted/wang%5Fziyang%5F200505%5Fphd.pdf.

Full text

Abstract:

Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2005.
You, Li, Committee Member ; Buck, John A., Committee Member ; Kvam, Paul, Committee Member ; Kennedy, Brian, Committee Member ; Trebino, Rick, Committee Chair. Vita. Includses bibliographical references.

APA, Harvard, Vancouver, ISO, and other styles

13

Von, Bandel Nicolas. "Development and study of low noise laser diodes emitting at 894 nm for compact cesium atomic clocks." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS003/document.

Full text

Abstract:

Ce travail de thèse porte sur la conception, la réalisation et l'étude de sources laser à semi-conducteur de haute cohérence, émettant à 894 nm, pour application aux horloges atomiques Césium compactes pompées optiquement, dans un contexte de développement industriel. Nous nous intéressons plus particulièrement aux lasers à émission par la tranche, dits "Distributed-Feedback" (DFB), pompés électriquement. L'objectif est d'obtenir un laser monomode en fréquence, à faible seuil, à rendement optique élevé et de largeur de raie inférieure à 1 MHz. Nous traitons d'abord de la conception et de la caractérisation au 1er ordre des diodes DFB, jusqu'à leur mise en modules pour horloge, puis nous effectuons une étude approfondie des propriétés physiques de l'émission laser en terme de cohérence temporelle, en introduisant une nouvelle méthode universelle de caractérisation du bruit de fréquence optique. Enfin, nous nous intéressons aux propriétés spectrales de l'émission en configuration d'asservissement sur une raie de fluorescence du Césium ("Dither-Locking"). Nous montrons que les propriétés intrinsèques du composant satisfont aux exigences du système industriel tel qu'il a été défini lors de l'étude
This PhD work deals with the design, the fabrication and the study of high-coherence semiconductor laser sources emitting at 894 nm, for application to compact, optically-pumped cesium atomic clocks in an industrial context. We are particularly interested in the electrically pumped "Distributed-Feedback" in-plane laser diodes (DFB). The aim is to obtain a low-threshold, single-mode laser with high optical efficiency and a linewidth of less than 1 MHz. We first deal with the design and first-order characterization of the DFB diodes until they are put into modules for the clock. We then carry out an in-depth study of the physical properties of the laser emission in terms of coherence time. For that purpose, a new universal method for characterizing the optical frequency noise is introduced. Finally, we look further into the spectral properties of the emission in a servo configuration on a fluorescence line of the cesium ("Dither-Locking"). We show that the intrinsic properties of the component satisfy the requirements of the industrial system as defined in the study

APA, Harvard, Vancouver, ISO, and other styles

14

Mousa, Pasandi Mohammad. "Adaptive decision-directed channel equalization and laser phase noise induced inter-carrier-inteference mitigation for coherent optical orthogonal frequency division multiplexing transport systems." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114464.

Full text

Abstract:

The explosive growth of global Internet traffic has placed tremendous strain on both op-tical networks and optical transmission systems, underscoring the need for not only high-capacity transmission links but also for flexible, reconfigurable, and adaptive networks. Re-cent progress in complementary metal–oxide–semiconductor (CMOS) technology has fa-cilitated the use of digital signal processing (DSP) in optical communication systems. Blessed with the revival of coherent optical transmission systems, over the past few years, DSP-enabled, software-defined optical transmission (SDOT) systems have led the funda-mental paradigm shift from inflexible optical networks to robust, reconfigurable, plug-and-play optical networks.Recently, coherent optical orthogonal frequency division multiplexing (CO-OFDM) has been intensively investigated as a promising modulation format for realizing coherent transmission systems. Although CO-OFDM has attracted significant interest in the research community, it has yet to leave a tangible impact on the commercial front due to implemen-tation shortcomings, such as excessive overhead, and susceptibility to fibre nonlinearities and frequency/phase noise.This thesis explores DSP-based solutions for CO-OFDM transmission systems, including two key original contributions. The first contribution is a novel adaptive decision-directed channel equalizer (ADDCE) that aims to reduce the required overhead in CO-OFDM transmission systems. ADDCE retrieves an estimation of the phase noise value after an initial decision making stage, by extracting and averaging the phase drift of all OFDM sub-channels, demonstrating zero-overhead phase noise compensation. Moreover, it updates the channel transfer matrix on a symbol-by-symbol basis, thus enabling a reduction in the associated overhead with pilot symbols. The second original contribution of this thesis focuses on the mitigation of the effect of the laser phase noise induced inter-carrier interfer-ence (ICI) in CO-OFDM systems. This interpolation-based ICI compensator estimates the time-domain phase noise samples using linear interpolation between the common-phase-error (CPE) estimates of consecutive OFDM symbols.The performances of the aforementioned DSP equalization schemes are numerically and experimentally studied in reduced-guard-interval dual-polarization CO-OFDM (RGI-DP-CO-OFDM) transmission systems, and are found to demonstrate superior performance over conventional equalizers (CEs). In addition, a computational complexity analysis of the pro-posed equalizers is provided, which confirms a low implementation complexity.
La croissance explosive du trafic globale sur Internet a crée une pression importante sur les réseaux optiques et les systèmes de transmission optiques; ce qui suggère le besoin de liens de transmission de haute capacité ainsi que de réseaux adaptables, reconfigurables et flexible. Les récents progrès dans les technologies de semiconducteurs métal-oxyde com-plémentaire (CMOS) ont facilité l'usage des traitements de signaux numériques (DSP) dans les systèmes de transmission optique. Grâce au retour en force du système de transmission optique cohérent ces dernières années, les systèmes de transmission optique régis par logiciel et supportés par les traitements de signaux numériques ont mené la transition fondamentale des réseaux optique inflexible vers des réseaux optique robuste, reconfigurable, prêt à brancher et utiliser.Depuis peu, le format de modulation par multiplexage fréquentiel orthogonale en optique cohérente (CO-OFDM) est profondément étudier comme format de modulation particu-lièrement prometteur pour réaliser des systèmes de transmission cohérents. Malgré le fait que les CO-OFDM aient réussi à susciter un grand intérêt dans la communauté de recherche, ils leur restent encore à avoir un impact plus tangible dans le secteur commercial. Ce non-déploiement commercial est attribué aux difficultés d'implémentations, notamment à l'information superflue excessive nécessaire et à la susceptibilité accrue aux nonlinéarités de la fibre optique et aux bruits de fréquence et de phase.Cette thèse explore certaines idées de DSP pour des systèmes de transmission CO-OFDM, incluant deux contributions originales. La première étant un égalisateur de canaux à adaptation dirigée par décision (ADDCE) qui vise à réduire l'information superflue nécessaire aux systèmes de transmission CO-OFDM. ADDCE récupère une estimation de la valeur du bruit de phase après un stage initiale de décision en extrayant et en moyennant la dérive de phase de tout les sous-canaux OFDM, ce qui démontre une compensation du bruit de phase sans information superflue. De plus, cela ajourne la matrice de transfère du canal optique symbole par symbole, offrant une réduction de l'information excédante associés avec les symboles pilotes. La seconde contribution de cette thèse se concentre sur la mitiga-tion de l'interférence inter-canaux (ICI) induite par le bruit de phase du laser dans les systèmes CO-OFDM. Ce compensateur de ICI basé sur l'interpolation estime le bruit de phase des échantillons dans le temps en utilisant une interpolation linéaire entre les estimations d'erreur de phase commune (CPE) de symboles OFDM consécutifs. Les performances des algorithmes d'égalisations appliqués en DSP mentionnés ci-haut sont étudiées en simulations et expérimentalement dans un système de transmission en CO-OFDM sur double polarisation à intervalle de garde réduite (RGI-DP-CO-OFDM), ce qui démontre une performance supérieure vis-à-vis de l'égalisateur conventionnel (CEs). Plus encore, l'analyse de la complexité des algorithmes d'égalisateurs proposées sera fournit; confirmant une implémentation à faible complexité.

APA, Harvard, Vancouver, ISO, and other styles

15

Schiemangk, Max. "Ein Lasersystem für Experimente mit Quantengasen unter Schwerelosigkeit." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/19826.

Full text

Abstract:

Bereits Galilei untersuchte, ob verschiedene frei fallende Körper im Schwerefeld der Erde gleich stark beschleunigt werden, die sogenannte Universalität des freien Falls. Die Genauigkeit der experimentellen Überprüfungen konnte seitdem beständig gesteigert werden. Einen neuen Ansatz, die Messgenauigkeit noch weiter zu verbessern, bilden quantenmechanische Messmethoden, die auf Materiewelleninterferometrie beruhen. Die dabei genutzten Apparaturen verwenden Laserstrahlung zur Kühlung, Manipulation und Detektion der Atome. Ziel der vorliegenden Arbeit war die Entwicklung des Lasersystems für ein neues Experiment, das erstmals Zwei-Spezies-Atominterferometrie (mit Rb & K) in Mikrogravitation demonstrieren soll. Ein Lasersystem, das sowohl die funktionalen Anforderungen als auch die aus dem Einsatz auf dem Katapult des Fallturms resultierenden Anforderung (Volumen < 44 l, Masse < 35 kg und voll funktionsfähig sofort nach einem Katapultstart mit Beschleunigungen von 30 g) erfüllt, wurde funktional konzipiert und mechanisch designt. Zur Demonstration wurde der Rubidium-Teil des Lasersystems funktional sowie mechanisch qualifiziert. Inzwischen wird er routinemäßig für Experimente am Fallturm eingesetzt. Für das Lasersystem wurden kompakte und robuste schmalbandigen Lasermodule entwickelt. Diese liefern bei einer Grundfläche der optischen Bank von nur 10 mm x 50 mm Ausgangsleistungen von bis zu 3,7 W. Am Arbeitspunkt (1 W Ausgangsleistung) besitzen die Strahlquellen Linienbreiten im Bereich von 100 kHz (Lorentz) bzw. 1 MHz (-3 dB, 10 µs). Zum Nachweis der spektralen Stabilität der Lasermodule wurde ein Messverfahrens zur Charakterisierung des Frequenzrauschens freilaufender Laser entwickelt. Dieses basiert auf einer Schwebungsmessung mit anschließender Analyse der Quadraturkomponenten des Signals im Zeitbereich. Durch den Einsatz geeigneter Filter erlaubt es die Unterdrückung der für Diodenlaser typischen Frequenzdrifts.
Galileo, already, investigated whether different free falling bodies in the gravitational field of the Earth are accelerated at the same rate, the so-called universality of the free fall. The accuracy of the experimental tests has been steadily increased ever since. A new approach to further increase the measurement accuracy is provided by quantum mechanical measurements based on matter wave interferometry. The apparatuses used for this purpose employ laser radiation for cooling, manipulation, and detection of the atoms. The aim of this thesis’ work was the development of the laser system for a new experiment intended to demonstrate two-species atom interferometry (utilizing Rb & K) in microgravity for the first time. A laser system, which fulfills the functional requirements as well as the requirements resulting from the deployment on the catapult of the drop tower (volume < 44 l, mass < 35 kg, and fully functional immediately after a catapult launch with accelerations of 30 g), has been functionally conceived and mechanically designed. For demonstration, the rubidium part of the laser system was functionally and mechanically qualified. By now, it is routinely used for experiments at the drop tower. For the laser system, compact and robust spectrally narrow laser modules have been developed. These provide an output power up to 3.7 W at a footprint of the optical bench of only 10 mm × 50 mm. At the operating point (1 W output power), the radiation sources exhibit linewidths in the range of 100 kHz (Lorentzian) and 1 MHz (−3 dB, 10 μs). To validate the spectral stability of the laser modules a measuring method for the characterization of the frequency noise of free-running lasers has been developed. This method is based on a beat note measurement with subsequent analysis of the quadrature components of the signal in the time domain. By utilizing appropriate filters, it allows for the suppression of the frequency drifts that are typical for diode lasers.

APA, Harvard, Vancouver, ISO, and other styles

16

Danion, Gwennaël. "Synthétiseur micro-onde à térahertz ultra-stable." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S014/document.

Full text

Abstract:

Le but de cette thèse est la synthèse optique d'ondes millimétriques et submillimétriques avec un très bas bruit de phase. La première partie concerne la réalisation d'un laser biaxe bifréquence dont chacune des deux fréquences est accordable indépendamment et continûment sur 1 THz. Ce laser est caractérisé en bruit d'amplitude et de phase. Nous avons mis en évidence un facteur de couplage entre les fluctuations de puissance de la diode de pompe et le bruit de phase du laser. La deuxième partie concerne le développement d'un système amplificateur qui se compose d'un amplificateur EDFA et d'un SOA par polarisation. Ce système amplificateur permet d'obtenir une puissance de l'ordre de 17 dBm, tout en réduisant le bruit relatif d'intensité (RIN) d'une vingtaine de dB sur 1 GHz. Cet amplificateur est également un actionneur pour la stabilisation de puissance permettant un RIN de l'ordre de -150 dB/Hz de 3 Hz à 5 kHz. La dernière partie concerne la mise en place du banc cavité et de l'asservissement des fréquences du laser sur une cavité ultra-stable. Nous obtenons un bruit de phase, à 10 kHz pour une porteuse à 10 GHz, meilleur que le plancher de bruit d'un analyseur de bruit de phase hautes performances de l'ordre de -115 dBc/ Hz. Le bruit de phase du système est indépendant de la fréquence de battement
The aim of this thesis is the optical synthesis of millimeter and submillimeter waves with a very low phase noise. The first part concerns the development of a dual-axis dual frequency laser, whose the two frequencies are tuneable independently and continuously on 1 THz. This laser is characterized in amplitude noise and phase noise. We have identified a coupling factor between the diode pump and the power fluctuations of the laser phase noise. In the second part, we report the development of an amplifier system which consists of an EDFA and a SOA per polarisation axis. This amplifier system delivers 17 dBm of power and reduces the relative intensity noise (RIN) by 20 dB on a 1 GHz bandwidth. This amplifier is also an actuator for the power stabilization to a RIN of the order of -150 dB/Hz from 3 Hz to 5 kHz. The last part concerns the setup of the cavity bench and the stabilization of the laser frequency on a ultrastable cavity. We obtain a phase noise at 10 kHz of frequency offset on a 10 GHz carrier better than the noise floor of a phase noise analyser with high performance of the order of -115 dBc/Hz. The system phase noise is independent of the beatnote frequency

APA, Harvard, Vancouver, ISO, and other styles

17

Fresnel, Schadrac. "Lasers à fibre Brillouin multi-stokes : cohérence et caractérisation en bruit." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S032/document.

Full text

Abstract:

La diffusion Brillouin est la diffusion inélastique de la lumière par les ondes acoustiques d'un milieu. Dans une fibre optique, la diffusion Brillouin stimulée (DBS) se manifeste, à partir d'une certaine intensité lumineuse incidente (Pompe), par la génération d'une onde Stokes rétrodiffusée dont la fréquence est décalée de celle de la Pompe d'une valeur directement proportionnelle à la vitesse de propagation des ondes acoustiques. Le décalage Brillouin présente une grande sensibilité à tous les effets qui peuvent modifier la vitesse de l'onde acoustique. Cette propriété permet d'étudier la composition des fibres et confère à la DBS la potentialité pour la réalisation de capteurs à fibres optiques. Le processus de DBS s'accompagne aussi d'un gain pour l'onde Stokes rétrodiffusée, puisque presque toute la puissance de l'onde Pompe y est transférée. Il peut donc être utilisé pour la réalisation d'amplificateurs et de lasers à fibres optiques. Dans le cadre de ce travail de thèse, nous avons étudié expérimentalement les propriétés statiques et dynamiques du laser à fibre Brillouin (LFB). Dépendamment du taux d'amortissement de l'onde acoustique et du taux de pertes de la cavité, le LFB peut être très cohérent et très peu bruité, favorisant ainsi son utilisation dans de multiples domaines comme la défense, la métrologie et les télécommunications. Lorsque la Pompe ne fait qu'un tour dans la cavité Brillouin, le LFB étudié présente un bruit de fréquence 10 000 fois plus faible que celui du laser de Pompe tout en gardant un bruit d'intensité similaire. Lorsque la Pompe est résonante, il est possible d'obtenir un LFB à multiples ondes Stokes en cascadant l'effet non-linéaire Brillouin dans la fibre optique. Limités par nos bancs de mesures, nous avons mesuré un bruit de fréquence 1 000 fois plus faible que celui de la Pompe et un bruit d'intensité plus de 100 fois plus faible
Brillouin scattering is the inelastic scattering of light by the acoustic waves of a medium. In an optical fiber, stimulated Brillouin scattering occurs, from a certain incident light intensity (pump), for generating a backscattered "Stokes" wave, whose frequency is shifted from that of the pump by a value directly proportional to the acoustic wave propagation velocity in the fiber. The Brillouin shift has a high sensitivity to all effects that can change the speed of the acoustic wave. This property makes it possible to study the composition of the fibers and gives to the SBS the potential for the production of optical fiber sensors. The SBS process is also accompanied by a gain for the backscattered Stokes wave since almost all the power of the Pump wave is transferred there. It can, therefore, be used for the production of optical fiber amplifiers and lasers. As part of this thesis work, we experimentally studied static and dynamic properties of the Brillouin fiber lasers (BFLs). Depending on the damping rate of the acoustic wave and the loss rate of the cavity, the BFL can be very coherent and less noisy, thus promoting its use in multiple fields such as defense, metrology, and telecommunications. When the Pump makes only one turn in the Brillouin cavity, the studied BFL has a frequency noise 10,000 times lower than that of the Pump laser while keeping a similar intensity noise. When the Pump is resonant, it is possible to obtain a BFL with multiple Stokes waves by cascading the Brillouin non-linear effect in the optical fiber. Restricted by our measurement benches, we measured a frequency noise 1000 times lower than that of the Pump and an intensity noise more than 100 times lower

APA, Harvard, Vancouver, ISO, and other styles

18

Eloy, Aurélien. "Étude des fluctuations temporelles de la lumière diffusée par des atomes froids." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4063/document.

Full text

Abstract:

Dans cette thèse, nous nous intéressons aux propriétés des fluctuations de la lumière diffusée par un nuage d'atomes froids, que ce soit les variations temporelles de l'intensité ou les fluctuations spectrales du champ électrique dans le régime de diffusion simple ou multiple de la lumière. Bien que notre analyse soit réalisée sur un système passif, l'ajout de gain dans le système peut conduire à l'obtention d'un laser aléatoire dont l'étude des corrélations temporelles de l'intensité émise peut permettre une étude détaillée de ses propriétés de cohérence.La première étape de cette caractérisation est l'étude du bruit de fréquence de lasers conventionnels. La mesure est réalisée grâce à un discriminateur de fréquence, pouvant être une cavité Fabry-Pérot ou une transition atomique, utilisé pour convertir le bruit de fréquence en bruit d'intensité mesuré. Un modèle simple est présenté montrant que, alors que les résultats obtenus pour la cavité ou la transition atomique soient identiques à faibles fréquences de Fourier, de nouvelles structures apparaissent à hautes fréquences, permettant de réaliser de la spectroscopie de bruit en analysant les fluctuations de la lumière transmise.Les propriétés de cohérence peuvent aussi être étudiées grâce à la fonction de corrélation g(2) de l'intensité, offrant un accès à la statistique des photons de la lumière émise. Nous mesurons cette fonction dans un milieu passif en expansion balistique en contrôlant finement le régime de diffusion de la lumière. Nous analysons en détails l'évolution du contraste, la perte de cohérence ainsi que le changement de forme de g(2) dans le régime de diffusion multiple. Ces résultats sont combinés à des études numériques et analytiques pour mettre en évidence le rôle de la diffusion multiple dans les changements de la fonction g(2). Cette mesure est la première réalisation expérimentale de spectroscopie des ondes diffuses sur un nuage d'atomes froids en mouvement balistique.La caractérisation de la cohérence temporelle d'un laser aléatoire passe par l'étude de la fonction g(2) sur un milieu actif sous le seuil d'émission. Nous implémentons alors un schéma de gain Raman hyperfin, combinant efficacement gain et diffusion. Nous présentons les premiers tests de la quantification du gain dans le nuage par spectroscopie pompe-sonde, montrant l'apparition d'une fenêtre de transparence électromagnétiquement induite. Enfin, par une méthode hérérodyne, nous sommes en mesure d'accéder au spectre optique de la lumière diffusée en présence de gain
In this thesis, we are interested in studying the properties of the fluctuations of the light scattered by a cloud of cold atoms, namely temporal fluctuations of the intensity or spectral fluctuations of the electric field in the single or multiple scattering of light. Although our analysis is focused on a passive medium, gain can be added in the system leading to a random laser whose the study of the temporal correlations of the emitted intensity allows to better characterize its coherence properties.The first step towards this characterization is the study of the frequency noise power spectral density of conventional lasers. This measurement is made using a frequency discriminator, being a Fabry-Pérot cavity or an atomic transition, used to convert frequency noise into measurable intensity noise. A simple model is developed showing that, while results obtained with the Fabry-Perot cavity and the atomic transition are the same at low Fourier-frequency, new features appear at high Fourier-frequency showing the influence of the atoms in the noise conversion, allowing to perform spectroscopic measurements by analyzing the intensity fluctuations of the transmitted light.Coherence properties can also be studied with the correlation function g(2) of the intensity, giving access to the photon statistics of the emitted light. We measure this function in a passive medium ballistically expanding while controlling the regime of scattering of light. We analyze in detail the evolution of contrast, the loss of coherence and the change of shape in the multiple scattering regime. Those results are combined with numerical and analytical studies showing the role of multiple scattering in the changes of the g(2)-function. This measurement is the first experimental demonstration of diffusing wave spectroscopy on cold atoms in ballistic motion.The characterization of the temporal coherence of a random laser requires the study of the g(2)-function in an active medium below threshold. We implement a scheme based on hyperfine Raman gain, combining effectively gain and scattering. We present our first results to quantify the amount of gain in the cloud with pump-probe spectroscopy, showing the appearance of an electromagnetically induced transparency window. Finally, based on a heterodyne method, we are able to access the optical spectrum of the scattered light in presence of gain

APA, Harvard, Vancouver, ISO, and other styles

19

Barč, Andrej. "Přenos radiofrekvenčního signálu optickým vláknem." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442409.

Full text

Abstract:

This work deals with the transmission of optical radiation modulated by a radio frequency signal through an optical fiber. Furthermore, it describes the principles of communication and area coverage. It points out the practical use of components located in the communication chain of this system. Explains the functionality of the properties and the division of individual components. It introduces the benefits and limitations of this system. It further describes the creation of a topology suitable for laboratory measurement of RoF technology. Provides experimental measurement of C-band parameters. Indicates the possible use of RoF technology using a wireless optical link. A part of the work is also a sample laboratory protocol.

APA, Harvard, Vancouver, ISO, and other styles

20

Verolet, Théo. "Hybrid semiconductor lasers for advanced coherent formats in datacenter interconnects." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST006.

Full text

Abstract:

Alors que le trafic de donnée intra-datacenter augmente exponentiellement, de nouvelles générations de transpondeurs optiques sont étudiées. Ces transpondeurs doivent délivrer un fort débit, tout en restant faible consommation. Les technologies cohérentes –sur lesquelles sont établies les liens intercontinentaux- doivent voir leur taille et bilan énergétique réduits. L’utilisation de formats cohérents avancés améliorera les performances des systèmes cohérents tout en les gardant compacts et efficaces énergétiquement. Cependant ces formats peuvent être déployés seulement si des lasers faibles bruits sont utilisés. C’est dans ce cadre que cette thèse étudie la réduction du bruit de phase de trois types de diodes lasers. Premièrement, nous étudions un nouveau type de laser à rétroaction distribué ayant une faible largeur de raie. Des simulations montrant les paramètres de conceptions optimaux de ce type de laser III-V/Si sont présentées. Dans le chapitre suivant, nous analysons les propriétés de reconfiguration rapide de lasers accordables faible bruit. Ici, nous proposons d’abord une nouvelle méthode de mesures permettant d’analyser précisément un saut de mode, ensuite nous présentons des résultats record de transmission cohérentes de paquets optiques. Dans un dernier chapitre, nous montrons que la rétroaction optique permet de stabiliser un laser à verrouillage de mode. Après avoir analysé les différents régimes de fonctionnement, nous confirmons les hautes performances de lien de communication cohérente utilisant ces lasers peigne de fréquence
As data traffic is exponentially increasing in datacenters, new generation of mass producible optical transceivers delivering high data throughput at very low energy consumption are required. Optical coherent technology has been widely used in the past decade to support intercontinental data traffic, as it benefits from higher performance over direct modulation systems though at the cost of complexity and price. To be efficiently used in datacenters, the size and energy consumption of coherent transceivers need to be scaled down while keeping relatively high data throughput. This could be achieved using higher order coherent formats, improving the transmission link spectral efficiency. However, these advanced communication formats can only be supported by low noise lasers. This thesis hence focuses on the phase noise optimization of three types of compact laser diodes using passive/active integration suitable for datacenter interconnects. First, a novel design of III-V/Si narrow linewidth high quality factor DFB laser based on a chirped grating is thoroughly studied. Detailed numerical simulations that yield grating parameters leading to optimal performances are presented for the first time to our knowledge. In a second study, we investigate the fast switching properties of a newly designed narrow linewidth extended cavity III-V/Si laser. After detailing the laser operating principles, we propose an experimental method to precisely characterize laser switching dynamics. Record coherent slot switching experiments are then demonstrated using this new laser. In the final part, we first investigate optical feedback regimes in single section quantum dash MLL and show that coherent feedback can induce a drastic phase noise reduction of the MLL longitudinal modes. The potential use of this comb source in a DWDM coherent link is demonstrated through highly spectrally efficient transmission experiments

APA, Harvard, Vancouver, ISO, and other styles

21

Gredat, Grégory. "Propriétés de bruit et dynamique de lasers à semiconducteurs en régime d'émission bifréquence pour l'optique micro-ondes et la métrologie." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS109.

Full text

Abstract:

L'émission cohérente de deux fréquences optiques présentant un battement radio-fréquence accordable trouve son application dans les liaisons opto-hyperfréquences, utiles aux radars ou radio-télescopes, mais également dans le domaine de la métrologie avec le déport optique de références temps-fréquence ultra-stables. Grâce à un cristal biréfringent à l'intérieur de leur cavité, les lasers à semiconducteurs de type VECSEL (vertical-external-cavity surface-emitting lasers) permettent de générer deux faisceaux corrélés de bonne pureté spectrale, avec une différence de fréquence accordable et polarisés linéairement dans des directions orthogonales. De telles sources lasers ont été développées à la longueur d'onde de la transition D₂ du césium dans le but d'élaborer une horloge atomique exploitant une résonance par CPT (coherent population trapping). L'objectif est de proposer un compromis inédit entre performance et compacité. En plus de caractériser les bruits (intensité et phase) de ces sources lasers, nous exploitons la modélisation de leur dynamique grâce à des équations d'évolution couplées pour minimiser dans un premier temps le transfert de bruit provenant de la pompe et optimiser dans un second temps leur asservissement. Une nouvelle architecture de la pompe optique produisant deux faisceaux corrélés est mise en place pour cette minimisation. La contribution du niveau de bruit mesuré à l'instabilité à court terme de l'horloge CPT est ensuite prédite. Aux basses fréquences, le spectre de bruit de phase du battement généré par le VECSEL bifréquence est dominé par des effets thermo-optiques, principalement causés par le bruit de la pompe. Nous établissons un modèle tenant compte des détails microscopiques du milieu à gain, de l'anisotropie de la diffusion de chaleur, des effets de lentille thermique ou encore des fluctuations thermodynamiques. Nous analysons la matrice de covariance spectrale des bruits d'intensité. Les modes propres des fluctuations sur les polarisations croisées sont alors comparés aux modes symétriques et anti-symétriques. Enfin, une méthode est élaborée pour obtenir une caractérisation et un tri des processus non-stationnaires de bruit particulièrement présents aux basses fréquences
Coherent emission of two optical tones with a radiofrequency (RF) tunable beatnote can spur many microwave photonics applications. Indeed, it can be useful for radars, remote sensing, or in the metrological context of ultra-stable RF frequency standards. A birefringent crystal can be inserted inside the external cavity of a VECSEL (vertical-external-cavity surface-emitting lasers) to produce a tunable very low-noise RF beatnote out of two orthogonal linear polarizations. Such dual-frequency semiconductor lasers operating along the D₂ line of cesium have been developed for CPT (coherent population trapping) atomic clocks. The development of these clocks corresponds to a need to find a trade-off between size and performance. First, intensity and RF beatnote phase noise investigations in these dual-frequency VECSELs are reported. A model based on coupled rate equations allows us to find minimization strategies for the noise transfer from the pump to the laser thanks to a new pumping architecture, which produces two correlated pump spots to feed the laser modes. The laser dynamics is then optimized for efficient noise active suppression. We predict a contribution to the short term relative frequency stability of the CPT clock compatible with an Allan deviation of 5x10⁻¹³ at 1s. Pump induced thermo-optic effects are dominating the low-frequency part of the dual-frequency VECSEL beatnote phase noise spectrum and require to be better understood. A new thermal model is thus established. This model takes into account the details of the gain medium, heat diffusion spatial anisotropy, thermal lens effects and also thermodynamic fluctuations. Besides, an analysis of the spectral intensity noise covariance matrix is initiated. We evidence that the eigen modes of the cross-polarized intensity fluctuations are close to in-phase and anti-phase noise mechanisms. Eventually, we elaborate a novel characterization and ranking method for non-stationary noises, which are often related to low-frequency spurious peaks

APA, Harvard, Vancouver, ISO, and other styles

22

Dascalu, Gabriela Cristina. "Frequency Noise in Widely Tunable Lasers for Coherent Communication." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-143209.

Full text

Abstract:

The objectives of this thesis are to measure the frequency noise of a widely tunable semiconductor laser, determine the main causes for the frequency uctuations and investigate the requirements for laser frequency noise for mQAM modulation formats by means of simulations. The following theoretical aspects are covered: the derivation of the frequency noise spectrum and the detuned loading effect from the rate equations; the shape and the causes of the frequency noise power spectral density; the derivation of the linewidth spectrum from white and 1/f frequency noise; the functionality of the laser and feedback loop used for the measurements. Measurements using the feedback loop showed substantial improvements in the -3 dB laser line width, but further investigation is needed in order to obtain a laser that is suitable both as a transmitter and as a local oscillator in coherent communication. Simulations outlined the dependence of linewidth, constellation diagrams and symbol error rates on frequency noise, for BPSK, QPSK, 8PSK modulation formats and their respective differential formats.

APA, Harvard, Vancouver, ISO, and other styles

23

Greenhalgh, P. A. "Direct frequency modulation of semiconductor lasers by acoustic waves." Thesis, University of Kent, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354573.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Olyaei, Maryam. "Low-frequency noise in high-k gate stacks with interfacial layer engineering." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177911.

Full text

Abstract:

The rapid progress of complementary-metal-oxide-semiconductor (CMOS) integrated circuit technology became feasible through continuous device scaling. The implementation of high-k/metal gates had a significantcontribution to this progress during the last decade. However, there are still challenges regarding the reliability of these devices. One of the main issues is the escalating 1/fnoise level, which leads to degradation of signal-to-noise ratio (SNR) in electronic circuits. The focus of this thesis is on low-frequency noise characterization and modeling of various novel CMOS devices. The devices include PtSi Schottky-barriers for source/drain contactsand different high-kgatestacksusingHfO2, LaLuO3 and Tm2O3 with different interlayers. These devices vary in the high-k material, high-k thickness, high-k deposition method and interlayermaterial. Comprehensive electrical characterization and low-frequency noise characterization were performed on various devices at different operating conditions. The noise results were analyzed and models were suggested in order to investigate the origin of 1/f noise in these devices. Moreover, the results were compared to state-of-the-art devices. High constant dielectrics limit the leakage current by offering a higher physical dielectric thickness while keeping the Equivalent Oxide Thickness (EOT) low. Yet, the 1/f noise increases due to higher number of traps in the dielectric and also deterioration of the interface with silicon compared to SiO2. Therefore, in order to improve the interface quality, applying an interfacial layer (IL) between the high-k layer and silicon is inevitable. Very thin, uniform insitu fabricated SiO2 interlayers with HfO2 high-k dielectric have been characterized. The required thickness of SiO2 as IL for further scaling has now reached below 0.5 nm. Thus, one of the main challenges at the current technology node is engineering the interfacial layer in order to achieve both high quality interface and low EOT. High-k ILs are therefore proposed to substitute SiOx dielectrics to fulfill this need. In this work, we have made the first experiments on low-frequency noise studies on TmSiO as a high-k interlayer with Tm2O3 or HfO2 on top as high-k dielectric. The TmSiO/Tm2O3 shows a lower level of noise which is suggested to be related to smoother interface between the TmSiO and Tm2O3. We have achieved excellentnoise performancefor TmSiO/Tm2O3 and TmSiO/HfO2 gate stacks which are comparableto state-of-the-art SiO2/HfO2 gate stacks.

QC 20151130

APA, Harvard, Vancouver, ISO, and other styles

25

Hallal, Ayman. "Génération d'ondes millimétriques et submillimétriques sur des systèmes fibrés à porteuses optiques stabilisées." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S005/document.

Full text

Abstract:

Je rapporte dans ce manuscrit une étude théorique et expérimentale d’une source compacte, fiable et bas coût d’ondes électromagnétiques continues et cohérentes de 30 Hz de largeur de raie, accordables de 1 GHz à 500 GHz par pas de 1 GHz. Ces ondes sont générées par un photo-mélange de deux diodes lasers DFB (Distributed Feedback) très accordables autour de 1550 nm, stabilisées avec des polarisations orthogonales sur une même cavité Fabry-Perot optique fibrée. J’ai conçue des électroniques de correction très rapides pour chaque laser permettant d’avoir une bande passante d’asservissement de 7 MHz limitée par la longueur de la boucle. Je démontre des suppressions de bruit de phase jusqu’à -60 dBc/ Hz à 1 kHz et de -90 dBc/Hz à 100 kHz d’écart d’une porteuse électrique à 92 GHz. Je mesure aussi une dérive de fréquence de ~170 kHz d’un battement à 10 GHz à long terme sur 7,5 heures de verrouillage continu. Je montre une conception optimisée d’une boucle d’asservissement intégrée de quelques dizaines de cm de longueur qui réduit le bruit de phase de 18 dB à 1 MHz d’écart à la porteuse optique et des couplages phase-amplitude réduits dans la cavité d’un facteur 50 par rapport à ceux estimés expérimentalement. L’ajout d’un troisième laser DFB stabilisé en phase sur un oscillateur local permettrait d’avoir une source continûment accordable sur 1 THz. La source d’ondes continues permettrait également de générer à partir de fibres hautement non linéaires et dispersives des impulsions pico- ou femtosecondes à un taux de répétition fixe en remplacement les lasers DFB par des lasers plus stables. Je calcule par simulation une gigue temporelle de 7,2 fs sur un temps d’intégration de 1 ms à 40 GHz de taux de répétition
I report in this manuscript a theoretical and experimental study of a compact, reliable and low cost source of 30 Hz linewidth, continuous and coherent electromagnetic waves tunable from 1 GHz to 500 GHz in steps of 1 GHz. These waves are generated by photomixing two distributed feedback (DFB) laser diodes at 1550 nm which are frequency stabilized with orthogonal polarizations on the same optical fibered Fabry-Perot cavity. I have designed very fast electronic control filters for each laser allowing a 7 MHz servo bandwidth limited by the loop length. I demonstrate phase noise suppressions down to -60 dBc/Hz at 1 kHz and -90 dBc/Hz at 100 kHz offset frequencies from a 92 GHz electrical carrier. I also measure a ~170 kHz frequency drift of the beat note at 10 GHz on the long term over a continuous 7.5 hour locking period. I show an optimized design of an integrated servo loop of few tens of cm length which reduces the phase noise by 18 dB at 1 MHz optical carrier offset frequency and the phase-amplitude couplings in the cavity by a factor of 50 compared to the experimental one. The addition of a third DFB laser phase stabilized on a local oscillator allows the possibility to have continuously tunable source over 1 THz. The continuous wave source also makes it possible to generate fixed repetition rate pico- or femtosecond pulses from highly non-linear and dispersive fibers, replacing the DFB lasers by further stable lasers. I have calculated by simulation 7.2 fs temporal jitter at 40 GHz repetition rate over a 1 ms integration time

APA, Harvard, Vancouver, ISO, and other styles

26

Sahni, Mohamed Omar. "Contribution à l'étude de techniques pour l'affinement spectral de lasers : application aux diodes à blocage de modes destinées aux télécommunications optiques cohérentes." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S121/document.

Full text

Abstract:

Les peignes de fréquences optiques, issus de diodes à blocage de modes, font partie des candidats potentiels pour les réseaux de transmission à multiplexage en longueurs d’onde (WDM). Cependant, les modes composant leur peigne, exhibent généralement des largeurs de raie optiques relativement élevées ( 1-100 MHz), rendant ainsi incompatible leur utilisation sur un réseau WDM employant des formats de modulation avancés d’ordre supérieur. Cette thèse étudie, une solution pour palier à cette limitation. La technique utilisée, dite d’asservissement à correction aval hétérodyne, effectue un traitement du flux lumineux en sortie du laser sans agir sur ce dernier, permettant de réduire le bruit de fréquence présent sur chacune des raies et par conséquent leur largeur de raie optique. Dans une première approche, la technique est appliquée à un laser mono-fréquence. Cela a permis d’une part de valider son fonctionnement et d’autre part d’identifier les limites intrinsèques du dispositif expérimental mis en place. Ainsi, nous démontrons que le niveau de bruit de fréquence minimum permis par notre système, correspond à un spectre optique de largeur de raie optique instantanée de 50 Hz et une largeur de raie de 1,6 kHz pour un temps d’observation de 10 ms. La technique est par la suite appliquée à une diode à blocage de modes actif. Le peigne de fréquences optiques ainsi généré, est composé de 21 modes, ayant tous une largeur de raie optique intrinsèque inférieure à 7 kHz, dont 9 modes sont sub-kHz. Pour un temps d’observation du spectre optique de 10 ms, ces modes exhibent tous une largeur de raie d’environ 37 kHz. Nous démontrons ainsi l’impact de la gigue d’impulsions sur les performances de la technique et nous soulignons l’intérêt d’une telle cohérence, pour le domaine des télécommunications optiques cohérentes (transmissions WDM cohérentes de type m-QAM avec des constellations d’ordre élevé, compatibles avec des débits multi-Tbit/s par raie). En dernier lieu, nous abordons une seconde technique consistant à pré-stabiliser la fréquence d’un laser par asservissement en boucle fermée. Elle repose sur l’utilisation d’un interféromètre à fibre déséquilibré comme référence pour réduire le bruit de fréquence d’un laser, situé particulièrement en basses fréquences. Appliquée à un laser mono-fréquence, elle a permis de réduire son bruit de fréquence technique conduisant ainsi à une nette amélioration de sa largeur de raie intégrée sur 3 ms, de 224 kHz à 37 kHz. Ce premier résultat représente un bon support vers l’exploration du potentiel des diodes à blocage de modes pour des applications métrologiques
Optical frequency combs obtained from mode-locked laser diodes are potential candidates for WDM networks. However, their lines exhibit usually a broad optical linewidth ( 1-100 MHz). Thus their use is incompatible for high order modulation formats WDM based systems. This thesis investigates one solution to overcome this limitation. It consists of using a feed-forward heterodyne technique to reduce the frequency noise of each comb-line and consequently their optical linewidths. In a first approach, the technique is applied to a single-mode laser. This allowed us to validate its proper working and to identify the intrinsic limits of the experimental device set up. The latter analysis enabled us to reveal that the minimum achievable frequency noise level by our system, corresponds to a 50 Hz intrinsic optical linewidth spectrum and a 1,6 kHz optical linewidth based on 10 ms observation time. This technique is then applied to an actively mode-locked laser diode demonstrating, at our system output, a 21-line optical frequency comb with intrinsic optical linewidths reduced to below 7 kHz. It is worth noting that 9 among them, exhibit sub-kHz linewidths. For an observation time of 10 ms, all lines share the same optical linewidth, almost equal to 37 kHz. We thus show that the timing jitter impacts the technique performances. We also highlight the relevance of such coherence level for coherent optical communication. Lastly, we study a laser frequency pre-stabilization technique based on a locking to an unbalanced fiber interferometer. When applied to a single-mode laser, the technique showed a reduction of its technical frequency noise, thus leading to a clear improvement of its integrated optical linewidth from 224 kHz to 37 kHz for 3 ms observation time. This first result provides a good support towards the exploration of mode-locked laser diodes potential for metrological applications

APA, Harvard, Vancouver, ISO, and other styles

27

Dumont, Paul. "Laser à semiconducteur pompé optiquement bifréquence pour les horloges à atomiques à piégeage cohérent d'atomes de Césium." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLO012/document.

Full text

Abstract:

Les horloges atomiques à piégeage cohérent de population (CPT) constituent aujourd'hui un outil idéal pour la réalisation de références de fréquence stables, compactes et à faible consommation énergétique. Dans le cas des horloges à base de césium, elles nécessitent l'utilisation d'un champ laser bifréquence à 895 nm (raie D1) ou à 852 nm (raie D2) et dont la différence entre les fréquences optiques est égale à 9,19 GHz, soit l'écart entre les niveaux hyperfins du niveau fondamental. Nous proposons une nouvelle solution pour générer ce champ laser, à partir d'un unique laser à semiconducteur pompé optiquement et à émission bipolarisée et bifréquence.Dans ce manuscrit, nous étudions la conception d'une telle source dont l'émission est accordable en fréquence sur la transition D2 du césium. Nous détaillons tout particulièrement le choix des éléments intracavité et de la structure semiconductrice utilisée. Nous décrivons ensuite la mise en oeuvre expérimentale et la caractérisation d'un prototype. Nous présentons les deux boucles d'asservissement que nous avons mises en place pour verrouiller la fréquence optique du laser sur la transition du césium, et la différence de fréquence sur la fréquence délivrée par un oscillateur local. Nous effectuons une modélisation et une caractérisation complète des trois types de bruits du laser, à savoir le bruit d'intensité, le bruit de fréquence optique, et le bruit de phase du signal généré par battement entre les modes laser. Enfin, nous montrons les premiers résultats expérimentaux de piégeage cohérent d'atomes de césium réalisé avec le prototype et étudions les caractéristiques du signal obtenu. Finalement nous établissons un budget de bruit d'une horloge CPT, en nous appuyant sur l'estimation de l'impact de chacun des bruits laser précédemment étudiés. Après avoir identifié les limites du système actuel, nous proposons quelques pistes d'améliorations du laser bifréquence, reposant sur la réduction du bruit d'intensité laser et sur la modification de la structure semiconductrice
Atomic clocks using the coherent population trapping (CPT) technic are ex-cellent candidates to obtain frequency references that are stable, compact and with a low powerconsumption. In the case of cesium atomic clocks, this technic require a dual-frequency laserfield either at 895 nm (D1 transition) or 852 nm (D2 transition) whose frequency difference isequal to 9.19 GHz, the frequency splitting between the two hyperfine levels of the fundamentalstate. Here we present a new concept for generating this type of laser field using a unique dualfrequency and optically-pumped laser with a dual-polarized emission.In this manuscript, we study the conception of such a laser source at a wavelength of 852 nm.We detail the design of the intracavity elements and the semiconductor active structure. Thenwe describe the experimental set-up and characterization of a first prototype. We present thestabilization set-up of the laser based on two different servo-loops, one used to lock the opticalfrequency onto the cesium transition and the other to lock the frequency difference onto thefrequency generated by a local oscillator. We report a complete simulation and characterizationof the main laser noises: the laser intensity noise, the optical frequency noise, and the phase noiseof the radiofrequency signal generated by the beatnote of the two laser modes. We show the firstexperimental results of coherent population trapping obtained with the prototype. Finally weestablish a noise budget of a CPT atomic clock by estimating the impact of each laser noises.After we identify the system limits, we propose different ways to improve the dual-frequencywhich rely on the reduction of the intensity noise and the modification of the semiconductorstructure design

APA, Harvard, Vancouver, ISO, and other styles

28

Ozdur, Ibrahim Tuna. "Low noise, narrow optical linewidth semiconductor-based optical comb source and low noise RF signal generation." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5009.

Full text

Abstract:

Recently optical frequency combs and low noise RF tones are drawing increased attention due to applications in spectroscopy, metrology, arbitrary waveform generation, optical signal processing etc. This thesis focuses on the generation of low noise RF tones and stabilized optical frequency combs. The optical frequency combs are generated by a semiconductor based external cavity mode-locked laser with a high finesse intracavity etalon. In order to get the lowest noise and broadest bandwidth from the mode-locked laser, it is critical to know the free spectral range (FSR) of the etalon precisely. First the etalon FSR is measured by using the modified Pound-Drever-Hall (PDH) based method and obtained a resolution of 1 part in 106, which is 2 order of magnitude better than the standard PDH based method. After optimizing the cavity length, RF driving frequency and PDH cavity locking point, the mode-locked laser had an integrated timing jitter of 3 fs (1 Hz- 100 MHz) which is, to the best of our knowledge, the lowest jitter ever reported from a semiconductor based multigigahertz comb source. The mode-locked laser produces ~ 100 comb lines with 10 GHz spacing, a linewidth of ~500 Hz and 75 dB optical signal-to-noise ratio. The same system can also be driven as a regeneratively mode-locked laser with greatly improved noise performance. Another way of generating a low noise RF tone is using an opto-electronic oscillator which uses an optical cavity as a high Q element. Due to the harmonic nature of OEOs, a mode selection element is necessary. Standard OEOs use an RF filter having drawbacks such as broad pass band, high loss, and high thermal noise. In our work, a novel optoelectronic scheme which uses an optical filter (Fabry-Perot etalon) as the mode filter instead of an RF filter is demonstrated. This method has the advantage of having ultra-narrow filtering bandwidths ( ~ 10 kHz for a 10 GHz FSR and 10[super6] finesse) and an extremely low noise RF signal. Experimental demonstration of the proposed method resulted in a 5-10 dB decrease of the OEO noise compared to the conventional OEO setup. Also, by modifying the etalon-based OEO, and using single side band modulation, an optically tunable optoelectronic oscillator is achieved with 10-20 dB lower noise than dual side band modulation. Noise properties of the OEO as a function of optical frequency detuning is also analyzed theoretically and the results are in agreement with experimental results. The thesis concludes with comments on future work and directions.
ID: 029808830; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 98-106).
Ph.D.
Doctorate
Optics and Photonics

APA, Harvard, Vancouver, ISO, and other styles

29

Suresh, Saurabh. "Transmission Loss Analysis of Laminated Glass with Porous Layers using Transfer Matrices for Automotive Applications." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1305893843.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Davila-Rodriguez, Josue. "External cavity mode-locked semiconductor lasers for the generation of ultra-low noise multi-gigahertz frequency combs and applications in multi-heterodyne detection of arbitrary optical waveforms." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5621.

Full text

Abstract:

The construction and characterization of ultra-low noise semiconductor-based mode-locked lasers as frequency comb sources with multi-gigahertz combline-to-combline spacing is studied in this dissertation. Several different systems were built and characterized. The first of these systems includes a novel mode-locking mechanism based on phase modulation and periodic spectral filtering. This mode-locked laser design uses the same intra-cavity elements for both mode-locking and frequency stabilization to an intra-cavity, 1,000 Finesse, Fabry-P&"233;rot Etalon (FPE). On a separate effort, a mode-locked laser based on a Slab-Coupled Optical Waveguide Amplifier (SCOWA) was built. This system generates a pulse-train with residual timing jitter of <2 fs and pulses compressible to <1 ps. Amplification of these pulse-trains with an external SCOWA lead to 390 mW of average optical power without evident degradation in phase noise and pulses that are compressible to the sub-picosecond regime. Finally, a new laser is built using a 10,000 Finesse Fabry-P&"233;rot Etalon held in a vacuum chamber. The fluctuations in the optical frequency of the individual comb-lines over time periods longer than 12 minutes are shown to be significantly reduced to <100 kHz in a measurement that is limited by the linewidth of the reference source. The use of these comb sources as local oscillators in multi-heterodyne detection of arbitrary optical waveforms is explored in three different cases. 1) Sampling of mode-locked pulses, 2) sampling of phase modulated continuous wave light and 3) periodically filtered white light. The last experiment achieves spectral interferometry with unprecedented resolution.
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics

APA, Harvard, Vancouver, ISO, and other styles

31

Collombon, Mathieu. "Résonance noire à trois photons sur un nuage d'ions calcium confinés." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0017.

Full text

Abstract:

Les travaux présentés dans cette thèse décrivent l’ensemble de la démarche expérimentale qui a été mise en place afin d’observer un piégeage cohérent de population à trois photons sur un nuage d’ions calcium confinés en piège radio-fréquence. La réalisation d’un tel processus cohérent repose sur des contraintes expérimentales fortes concernant la relation de phase entre les trois lasers impliqués dans le processus d’interrogation ainsi que sur leurs finesses spectrales. Notre approche est basée sur l’optimisation des performances d’un laser stabilisé à 411 THz (729 nm) pour atteindre une stabilité de fréquence relative inférieure à 10⁻¹⁴ à 1 s. Ces performances ont ensuite été transférées vers un peigne de fréquence optique. Le comportement de cet instrument ainsi que les performances du transfert sont présentés dans ces travaux. Le peigne est alors utilisé comme oscillateur de transfert pour asservir les deux autres lasers impliqués dans l’interrogation des ions (866 nm et 794 nm). Grâce à ce travail sur la mise en relation des trois sources laser, ainsi que l’optimisation de leur qualités spectrales nous avons pu observer les premières résonances noires à trois photons dans le spectre de fluorescence des ions 40 Ca⁺. Ces résultats originaux ainsi que les premières études systématiques du comportement de la résonance en fonction de différents paramètres expérimentaux sont présentés. L’analyse de ces résultats a permis de définir clairement les conditions expérimentales à respecter pour une potentielle utilisation métrologique de cette résonance qui émane d’une superposition cohérente d’état stable ou métastable
The work presented in this thesis describes the complete experimental set-up and approach to realize three-photon coherent population trapping in a cloud of radiofrequency confined calcium ions. The realization of such a population trapping relies on a stringent conditions of the phase relationship between the three lasers involved in the interrogation process, and also their spectral linewidths. Our experimental approach is based on the optimization of the performance of a frequency-stabilized titanium-sapphirelaser at 411 THz (729nm) at the 10⁻¹⁴ level, in term of relative frequency uncertainties. This laser’s fre-quency stability is subsequently transfered to a optical frequency comb by means of a phase-locked loop. Then the two other lasers involved (866 nm and 794 nm) are phase-locked to the optical frequency combwith the same technique. This work describes the transfer method along with its measured performances. With all the three lasers sharing the same ultra-stable frequency reference we have been able to experi-mentally observe for the first time a 3-photon dark resonance in the fluorescence spectra of the 40 Ca⁺, signature of a coherent population trapping in a 3-photon scheme. The dependence of this resonance at experimental parameters, such as laser powers, laser detunings and local magnetic field, have been studied and are presented in this work. The preliminary results have allowed to explain the behaviour of the dark resonance and explored conditions for the use of the 3-photon dark line as a THz frequency standard

APA, Harvard, Vancouver, ISO, and other styles

32

Panapakkam, Venkatesan Vivek. "Optical frequency comb generation using InP based quantum-dash/ quantum-well single section mode-locked lasers." Thesis, Evry, Institut national des télécommunications, 2016. http://www.theses.fr/2016TELE0024/document.

Full text

Abstract:

Les interconnections optiques dans les fermes de données (data centers) nécessitent la mise au point de nouvelles approches technologiques pour répondre aux besoins grandissants en composants d’interface respectant des cahiers de charge drastiques en termes de débit, coût, encombrement et dissipation d’énergie. Les peignes de fréquences optiques sont particulièrement adaptés comme nouvelles sources optiques, à mêmes de générer un grand nombre de porteuses optiques cohérentes. Leur utilisation dans des systèmes de transmission en multiplexage de longueurs d’onde (WDM) et exploitant de nouveaux formats de modulation, peut aboutir à des capacités jamais atteintes auparavant. Ce travail de thèse s’inscrit dans le cadre du projet européen BIG PIPES (Broadband Integrated and Green Photonic Interconnects for High-Performance Computing and Enterprise Systems) et a pour but l’étude de peignes de fréquences générés à l’aide de lasers à verrouillage de modes, à section unique, à base de bâtonnets quantiques InAs/InP et puits quantiques InGaAsP/InP. Nous avons entrepris l’étude de nouvelles couches actives et conceptions de cavités lasers en vue de répondre au cahier des charges du projet européen. Une étude systématique du bruit d’amplitude et de phase de ces sources a en particulier été menée à l’aide de nouvelles techniques de mesure afin d’évaluer leur compatibilité dans des systèmes de transmission à très haut débit. Ces peignes de fréquences optiques ont été utilisées avec succès dans des expériences de transmission sur fibre optique avec des débits records dépassant le Tbit/s par puce et une dissipation raisonnable d’énergie par bit, montrant leur fort potentiel pour les applications d’interconnections optiques dans les fermes de données
The increasing demand for high capacity, low cost, high compact and energy efficient optical transceivers for data center interconnects requires new technological solutions. In terms of transmitters, optical frequency combs generating a large number of phase coherent optical carriers are attractive solutions for next generation datacenter interconnects, and along with wavelength division multiplexing and advanced modulation formats can demonstrate unprecedented transmission capacities. In the framework of European project BIG PIPES (Broadband Integrated and Green Photonic Interconnects for High-Performance Computing and Enterprise Systems), this thesis investigates the generation of optical frequency combs using single-section mode-locked lasers based on InAs/InP Quantum-Dash and InGaAsP/InP Quantum-Well semiconductor nanostructures. These novel light sources, based on new active layer structures and cavity designs are extensively analyzed to meet the requirements of the project. Comprehensive investigation of amplitude and phase noise of these optical frequency comb sources is performed with advanced measurement techniques, to evaluate the feasibility of their use in high data rate transmission systems. Record Multi-Terabit per second per chip capacities and reasonably low energy per bit consumption are readily demonstrated, making them well suited for next generation datacenter interconnects

APA, Harvard, Vancouver, ISO, and other styles

33

McGuire, John Andrew. "Femtosecond nonlinear spectroscopy at surfaces Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy." Berkeley, Calif. : Oak Ridge, Tenn. : Lawrence Berkeley National Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/836810-xRj01W/native/.

Full text

Abstract:

Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); 24 Nov 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56751" McGuire, John Andrew. USDOE Director. Office of Science. Office of Basic Energy Sciences. Materials Science and Engineering Division (US) 11/24/2004. Report is also available in paper and microfiche from NTIS.

APA, Harvard, Vancouver, ISO, and other styles

34

Sanjuán, Muñoz Josep. "Development and validation of the thermal diagnostics instrumentation in lisa pathfinder." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/6366.

Full text

Abstract:

This thesis focuses on the issues related to the thermal diagnostics aboard the space mission LISA Pathfinder (LPF). LPF is a technological mission devoted to put to test critical subsystems for the LISA mission. LISA will be the first space born gravitational wave (GW) observatory with the main objective of detecting GWs. GWs are ripples of the space-time geometry caused by acceleration of masses in an asymmetric way. Their detection requires put test masses (TMs) in an almost perfect inertial frame (or free fall).

Non-inertial forces perturbing the TMs must be less than 6 fN/sqrt(Hz) in the frequency range of 0.1 mHz to 0.1 Hz and the noise in the measurement between the TMs (separated by 5 Gm) must be of 40 pm/sqrt(Hz) in the same band. To reduce the risks of a direct launch of LISA, ESA has decided to first launch LPF to put all the LISA technologies to test.
The payload of LPF, the LISA Technology Package (LTP), contains two TMs placed in two cylinders inside a single spacecraft (SC) and an interferometric system that measures the relative distance between them. The SC isolates the TMs from the external disturbances but internal stray forces will still perturb the TMs. Their levels must be bounded not to challenge the free fall accuracy. One of these disturbances is temperature fluctuations and the aspects related to their measurement are the leitmotif of this thesis.

In chapter 1 we have presented how temperature fluctuations couple into the key subsystems of the LTP to degrade their performance. The foreseen effects are radiation pressure, radiometer effect, temperature coefficient of optical components, etc. Onground estimations conclude that the temperature stability in the LTP must be less than 100 microK/sqrt(Hz) in the frequency range of 1 mHz to 30 mHz (LTP band). Since temperature fluctuations are an important issue in LPF and in LISA, a thermal diagnostic subsystem is needed aboard both missions.

The task of the thermal diagnostics in the LTP is twofold: on the one hand, temperature fluctuations in different subsystems must be measured with noise levels of 10 microK/sqrt(Hz) in the LTP band. On the other hand, a set of heaters will generate heat pulses that in conjunction with temperature measurements will be used to estimate the actual coupling between temperature and systems performance. These actions will provide information on the behaviour of the system and will permit to identify the fraction of noise in the system coming from temperature issues. The main function of LPF, as precursor mission of LISA, is the understanding of all the noise sources in the system. This will provide clues to the final leap from LPF sensitivity to LISA one.

The main investigations carried out during this thesis can be split into three main categories: (i) the design and validation of the LTP temperature measurement subsystem (TMS); (ii) the extension of the system to the LISA requirements; and (iii) the analysis of the in-flight thermal experiments in the LTP. The thesis is organised as follows: in chapter 2 we describe the designed electronics and the temperature sensors chosen. Aspects related to the coupling of the TMS with other subsystems nearby are discussed in chapter 3. Chapter 4 focuses on the design of the testbed needed for the validation of the TMS. Two different testbeds are described: one for the LTP measurement bandwidth (MBW) and another one for the LISA MBW, 0.1 mHz. In chapter 5 we present the results of the test campaigns: the prototype, the engineering model and the flight model systems were put to test. The results of the investigations in the LISA band are also shown. Chapter 6 contains investigations in view of LISA requirements to reduce excess noise at very low frequency and to reduce the floor noise of the measurement. Chapter 7 focuses on the thermal experiment on-board LPF: a set of thermal excitations are proposed to extract information of the thermal behaviour of the key subsystems of the LTP.

APA, Harvard, Vancouver, ISO, and other styles

35

Muñoz-Arcos, Christian Daniel. "Optical Microwave Signal Generation for Data Transmission in Optical Networks." Thesis, Toulouse, ISAE, 2020. http://www.theses.fr/2020ESAE0013.

Full text

Abstract:

La croissance des services de télécommunications et l’augmentation du trafic de données àl’échelle mondiale favorise le développement et l’intégration de différents réseaux de transmissionde données. Un exemple de ce développement est constitué par les réseaux defibres optiques, qui sont actuellement chargés d’interconnecter les continents par des liaisonslongues avec des taux de transfert importants. Les réseaux optiques, ainsi que les réseauxsupportés par d’autres moyens de transmission, utilisent des signaux électriques à certainesfréquences pour la synchronisation des éléments du réseau. La qualité de ces signaux est unfacteur décisif dans la performance globale du système, c’est pourquoi leur bruit de phasedoit ˆetre aussi faible que possible.Ce document décrit la conception et la mise en œuvre d’un système optoélectronique pour lagénération de signaux micro-ondes à l’aide de diodes laser à cavité verticale (VCSEL) et sonintégration dans un système de transmission optique de données. Compte tenu du fait que lesystème proposé intègre un laser VCSEL directement modulé, une caractérisation théoriqueet expérimentale a été élaborée sur la base des équations d’évolution du laser, de mesuresdynamiques et statiques, et d’un modèle électrique équivalent de la région active. Cetteméthode a permis l’extraction de certains paramètres intrinsèques du VCSEL, ainsi que lavalidation et la simulation de ses performances dans différentes conditions de modulation.Le VCSEL utilisé émet en bande C et a été sélectionné en considérant que cette bande estcouramment utilisée dans les liaisons à longue distance.Le système proposé est constitué d’une boucle fermée qui déclenche l’oscillation grâce auxsources de bruit des composants et module le VCSEL en fort signal pour générer des impulsionsoptiques (gain switching). Ces impulsions optiques, qui dans le domaine des fréquencescorrespondent à un peigne de fréquences optiques, sont détectées pour générer simultanémentune fréquence fondamentale (déterminée par un filtre passe-bande) et plusieurs harmoniques.Le bruit de phase mesuré à10 kHz de la porteuse à1,25 GHz est de -127,8 dBc/Hz, etconstitue la valeur la plus faible signalée dans la littérature pour cette fréquence et cette architecture.La gigue et la largeur d’impulsion optique ont été déterminées lorsque différentescavités résonantes et différents courants de polarisation étaient utilisés. La durée d’impulsion
The massive growth of telecommunication services and the increasing global data traffic boostthe development, implementation, and integration of different networks for data transmission.An example of this development is the optical fiber networks, responsible today for theinter-continental connection through long-distance links and high transfer rates. The opticalnetworks, as well as the networks supported by other transmission media, use electricalsignals at specific frequencies for the synchronization of the network elements. The qualityof these signals is usually determined in terms of phase noise. Due to the major impact ofthe phase noise over the system performance, its value should be minimized.The research work presented in this document describes the design and implementation ofan optoelectronic system for the microwave signal generation using a vertical-cavity surfaceemittinglaser (VCSEL) and its integration into an optical data transmission system. Consideringthat the proposed system incorporates a directly modulated VCSEL, a theoreticaland experimental characterization was developed based on the laser rate equations, dynamicand static measurements, and an equivalent electrical model of the active region. This proceduremade possible the extraction of some VCSEL intrinsic parameters, as well as thevalidation and simulation of the VCSEL performance under specific modulation conditions.The VCSEL emits in C-band, this wavelength was selected because it is used in long-haullinks. The proposed system is a self-initiated oscillation system caused by internal noise sources,which includes a VCSEL modulated in large signal to generate optical pulses (gain switching).The optical pulses, and the optical frequency comb associated, generate in electricaldomain simultaneously a fundamental frequency (determined by a band-pass filter) and severalharmonics. The phase noise measured at 10 kHz from the carrier at 1.25 GHz was -127.8dBc/Hz, and it is the lowest value reported in the literature for this frequency and architecture.Both the jitter and optical pulse width were determined when different resonantcavities and polarization currents were employed. The lowest pulse duration was 85 ps andwas achieved when the fundamental frequency was 2.5 GHz. As for the optical frequencycomb, it was demonstrated that its flatness depends on the electrical modulation conditions.The flattest profiles are obtained when the fundamental frequency is higher than the VCSELrelaxation frequency. Both the electrical and the optical output of the system were integrated into an optical transmitter.The electrical signal provides the synchronization of the data generating equipment,whereas the optical pulses are employed as an optical carrier. Data transmissions at 155.52Mb/s, 622.08 Mb/s and 1.25 Gb/s were experimentally validated. It was demonstrated thatthe fundamental frequency and harmonics could be extracted from the optical data signaltransmitted by a band-pass filter. It was also experimentally proved that the pulsed returnto-zero (RZ) transmitter at 1.25 Gb/s, achieves bit error rates (BER) lower than 10−9 whenthe optical power at the receiver is higher than -33 dBm. la plus faible, 85 ps, a été obtenue lorsque la fréquence fondamentale du système était de 2,5 GHz. En ce qui concerne le peigne de fréquences optiques, il a été démontré que la formedu peigne dépend des conditions de modulation électrique et que les profils les plus platssont obtenus lorsque la fréquence fondamentale est supérieure à la fréquence de relaxationdu VCSEL. Les sorties électrique et optique du système ont été intégrées dans un émetteur optique. Lesignal électrique permet la synchronisation de l’équipement responsable de la génération desdonnées, tandis que les impulsions optiques sont utilisées comme porteuse optique. La transmissionde données à 155,52 Mb/s, 622,08 Mb/s et 1,25 Gb/s a été validée expérimentalement

APA, Harvard, Vancouver, ISO, and other styles

36

Chou, Hui-Ling, and 周慧玲. "A Study of Reducing Laser Feedback Noise by High Frequency Modulation." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/80829248175908261767.

Full text

Abstract:

碩士
元智大學
電機工程研究所
88
In the optical storage equipments , we use laser diode as our working light source . Because of feedback signal bring out laser diode’s mode hopping , destroy the optical pickup head’s performance . There are several methods to reduce laser feedback noise . This thesis use〝High Frequency Modulation〞producing a sequence of oscillation signal to reduce〝Relative Intensity Noise , RIN〞from —130 dB above to 10~20 dB below . According to the results of adding HF modulation , we do reduce the damage of laser feedback noise successfully .

APA, Harvard, Vancouver, ISO, and other styles

37

Slagmolen, Bram Johannes Jozef. "Direct Measurement of the Spectral Distribution of Thermal Noise." Phd thesis, 2004. http://hdl.handle.net/1885/48192.

Full text

Abstract:

This thesis investigates the direct measurement of the thermal noise spectral distribution. Long base line gravitational wave detectors, being commissioned around the world, are limited in sensitivity in the intermediate frequencies by the thermal noise. These detectors are utilising suspended test mirrors for the detection of gravitational waves by measuring their relative displacement. One of the fundamental noise sources in these detectors is the thermally induced displacement of the suspension onto and within the mirrors. This thermally induced motion of the test mirrors limits the displacement sensitivity of the gravitational wave detectors. Knowledge of the spectral behavior of thermal noise over a wide frequency range will improve predictions and understanding of the behavior of the suspension and test mirrors. ¶ In this thesis the direct measurement of the thermal noise spectral distribution of a mechanical flexure resonator is described. The mechanical flexure resonator is an unidirectional ’wobbly table’ made from copper-beryllium, which hinges around four thin flexures 15 mm wide, 1 mm high and ~116 µm thick. The mechanical flexure resonator has a resonant frequency of 192 Hz, with a quality factor of ~3000. ¶ ...

APA, Harvard, Vancouver, ISO, and other styles

38

Kim, Dongwan. "Frequency Noise Control of Heterogeneous Si/III-V Lasers." Thesis, 2018. https://thesis.library.caltech.edu/10540/13/Dongwan_thesis_2017_final_print.pdf.

Full text

Abstract:

Narrow-linewidth lasers have many applications including optical telecommunication, laser spectroscopy, atomic clocks, and light detection and ranging. Conventionally, narrow linewidth lasers have been realized in the form of fiber-based or solid-state lasers. These lasers are bulky and relatively expensive, limiting their usage as bench-top systems in laboratory environments. Historically, semiconductor lasers, also known as laser diodes, have served applications where size and cost are important factors, including fiber optic communications. The linewidth of the semiconductor lasers, however, has been limited to the MHz-level, due to high loss in laser cavities and small size.

Recently, reduction of the frequency fluctuations in the semiconductor lasers has been achieved, obtaining tens of kHz linewidth, using the heterogeneous Silicon/III-V platform with a new design strategy. In this design, the majority of the optical energy is stored in the low-loss high-Q silicon resonator away from the high-loss III-V active region, requiring the minimal gain from the active region to overcome the reduced modal loss.

This work explores the new design strategy further, and demonstrates theoretically and experimentally that the strategy eliminates the frequency fluctuations arising from the amplitude-phase coupling by placing a relaxation resonance frequency at frequencies of a few hundred MHz. Consequently, it becomes possible to obtain a semiconductor laser device possessing sub-kHz quantum-limited linewidths at frequencies of a few GHz (the frequencies of interest in optical telecommunication).

In addition to the frequency noise reduction, the strategy turns out to have the additional benefit of accomplishing a coherent and stable lasing operation, even under external reflections. Thus, the new design strategy has the potential to replace the costly, but currently indispensable external optical isolators, which have been traditionally used to maintain the consistent performance of semiconductor lasers in the presence of external reflection.

This work paves the way for the design of narrow-linewidth and stable semiconductor lasers that can function without the use of the bulky and costly external components, such as external cavities or optical isolators.

APA, Harvard, Vancouver, ISO, and other styles

39

Lam, Timothy T.-Y. "Frequency noise mitigation in advanced interferometric fibre strain sensors." Phd thesis, 2011. http://hdl.handle.net/1885/151358.

Full text

Abstract:

Frequency noise greatly limits the resolution of high resolution fibre optic strain sensors. The experiments presented in this thesis provide an effective way of obtaining better strain resolution in systems limited by laser frequency noise. In this thesis two main methods are utilised; active frequency noise suppression through feedback control, and post processing noise removal. In chapters 2, 3, and 4, we explore different methods to reduce the frequency noise in lasers used to interrogate fibre interferometric strain sensing systems. We investigate the use of local fibre lasers and their applicability to high resolution strain sensing. We use radio frequency read out techniques to provide a high resolution read out of strain and frequency fluctuations. Then using active feedback, we lock the laser to a stable Mach-Zehnder interferometer. We demonstrate, with active feedback, ultra-high strain resolutions of 14 f{u220A}/{u221A}Hz at infrasonic frequencies. To allow for more flexibility and ease of use, we used a field programmable gate arrays for digital locking and signal processing systems. We present an analysis of the potential performance of a digital feedback system using the Pound-Drever-Hall technique. In this analysis, we discuss the noise sources and their affect on a digital feedback loop. We then experimentally characterise and verify the theoretical analysis. With this digital system we then explore the use of an absolute frequency reference. An interrogation system was designed and implemented that extends the range of an absolute sensing systems. Using this method, we are able to improve a free running system by up to 1.5 orders of magnitude whilst improving the range by a factor of 10 over standard pre-stabilised systems. We then propose and implement a frequency noise insensitive sensing system based on post processing techniques. We utilise time-delay interferometry, a technique developed for gravitational wave detection to eliminate frequency noise through post processing. The technique is combined with digitally-enhanced interferometry, and slightly modified to account for, and remove, several noise sources, including lead fibre phase noise, that is common to fibre optic strain sensors. The design and performance considerations are discussed and analysed, and a first time proof of concept experiment is reported. The design implemented has shown to significantly improve the performance of a frequency noise limited strain sensor.

APA, Harvard, Vancouver, ISO, and other styles

40

Sun, Chung-Chyuan, and 孫忠銓. "A STUDY ON DOUBLE-LAYER PERFORTED STRUCTURE MUFFLER TO IMPROVE LOW – FREQUENCE NOISE." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/49948448994290217412.

Full text

Abstract:

碩士
中華大學
科技管理學系碩士班
100
Noise control of operational environment in industry has become increasingly stringent in recent years. As a common means to control the noise levels, mufflers use absorptive materials and/or structural configuration design to achieve the goal of noise reduction. In this study, three mufflers with different configurations in structure were designed and fabricated to improve the noise emission of a 40Hp Roots blower. Perforated and micro-perforated structures have very good performance in reducing the noise of lower frequency ranges. The muffler with three chambers and double-layer micro-perforated structures has reduced the noise of the blower from 111dBA to 76.8dBA. Also, using extra fine absorptive fibers in the mufflers exhibits good reduction effects for high-frequency noise. The results of simulation and experiment were in agreement. Due to the excellent effects of the double-layer micro-perforated structures in reducing low-frequency noise, multiple-layer micro-perforated structures will be developed in enhancing the performance of the mufflers.

APA, Harvard, Vancouver, ISO, and other styles

41

Yang, Yu-Sen, and 楊育森. "Low-Frequency Noise of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Poly(4-vinylphenol) Insulating Layer." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/cu8yd6.

Full text

Abstract:

碩士
國立中興大學
奈米科學研究所
101
We investigated the low-frequency noise (LFN) of amorphous Indium-Gallium-Zinc-Oxide thin film transistors (a-IGZO TFTs) with various channel width (W) and length (L). The W/L ratios of our samples are 500μm/100μm and 1000μm /200μm, respectively. We placed the device in a dark vacuum chamber during measurement. We found that a-IGZO TFTs exhibit not only 1/f noise but also the Lorentzian noise in some cases. At the same gate-source voltage (Vgs), the higher the drain-source voltage (Vds), the lager the magnitude of the 1/f noise, which increases as Vgs increases at the same Vds . The Lorentzian noise was found in the drain current range about 10-7~10-8 A. We also observed that the illumination has influences on the Lorentzian noise. This indicates that the trapping levels of the a-IGZO film can be affected by the light. The device is sensitive to the environment and becomes unstable for a long-term measurement.

APA, Harvard, Vancouver, ISO, and other styles

42

Δαγρές, Ιωάννης. "Σχεδιασμός αλγορίθμων προσαρμοστικής διαμόρφωσης και αντιμετώπισης θορύβου φάσης σε ασύρματα τηλεπικοινωνιακά συστήματα πολλαπλών φερουσών." Thesis, 2011. http://nemertes.lis.upatras.gr/jspui/handle/10889/4466.

Full text

Abstract:

Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η μελέτη και ο σχεδιασμός καινοτόμων αλγορίθμων φυσικού επιπέδου σε ασύρματα συστήματα επικοινωνίας που χρησιμοποιούν διαμόρφωση με πολύπλεξη συχνότητας ορθογωνίων φερουσών (Orthogonal Frequency Division Multiplexing - OFDM). Η έρευνα επικεντρώθηκε σε δύο κατηγορίες προβλημάτων, στον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης καθώς και αλγορίθμων αντιμετώπισης ισχυρού θορύβου φάσης. Αναπτύχθηκαν αλγόριθμοι εκτίμησης φάσης με γραμμική πολυπλοκότητα, μέσω ενός καινούργιου εναλλακτικού μοντέλου περιγραφής του συστήματος. Το μοντέλο αυτό επιτρέπει την επέκταση των κλασικών αλγορίθμων εκτίμησης της κοινής φάσης με στόχο την εκτίμηση του συνολικού διανύσματος θορύβου φάσης. Επιπλέον, η τεχνική διαγώνιας φόρτωσης (diagonal-loading) προσαρμόστηκε κατάλληλα για τη βελτίωση σύγκλισης της προτεινόμενης λύσης. Τέλος, προτάθηκε και αξιολογήθηκε ένα συνολικό σύστημα OFDM όπου η εκτίμηση του καναλιού, της διαταραχής φάσης και των δεδομένων βασίζονται στο κριτήριο ελαχίστων τετραγώνων, διατηρώντας έτσι τη συνολική πολυπλοκότητα σε χαμηλά επίπεδα. Στο πλαίσιο του σχεδιασμού αλγορίθμων προσαρμοστικής διαμόρφωσης προτείνεται ένα γενικό μοντέλο περιγραφής απόδοσης συστήματος ικανό να περιγράψει τα αναπτυσσόμενα πρωτόκολλα μετάδοσης. Η πρόταση αυτή εντάσσεται στην οικογένεια των τεχνικών ισοδύναμης σηματοθορυβικής απεικόνισης (Εffective SNR Μapping - ESM). Χρησιμοποιώντας τις τεχνικές ESM και κατάλληλους περιορισμούς στην παραμετροποίηση των μεταβλητών μετάδοσης, αναπτύχθηκαν αλγόριθμοι προσαρμοστικής διαμόρφωσης χαμηλής πολυπλοκότητας που ικανοποιούν διαφορετικά κριτήρια βελτιστοποίησης. Επιπρόσθετα, προτείνεται ένα γενικό πλαίσιο για τον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης, χρησιμοποιώντας προσεγγιστικά μοντέλα απόδοσης. Ορίστηκαν οι κατάλληλες μετρικές για την ποσοτικοποίηση της σπατάλης ενέργειας που επιφέρει η χρήση προσεγγιστικών μοντέλων. Μελετήθηκε η επίδραση της καθυστέρησης ανατροφοδότησης πληροφορίας καναλιού στους αλγορίθμους και παρήχθησαν κατάλληλα μοντέλα περιγραφής απόδοσης που συμπεριλαμβάνουν το χρόνο καθυστέρησης. Το συνολικό αποτέλεσμα της εργασίας είναι αλγόριθμοι που καταφέρνουν υψηλή απόδοση συστήματος, με χαμηλή πολυπλοκότητα, κάτι το οποίο τους κάνει υλοποιήσιμους σε ρεαλιστικά συστήματα.
The objective of this thesis is to study and develop novel, low complexity physical layer algorithms for Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The study aims at two algorithmic categories, namely adaptive modulation and coding and compensation of severe phase noise (PHN) errors. A parameterized windowed least-squares (WLS) decision directed phase error estimator is proposed via proper (alternative) system modeling, applied to both channel estimation and data detection stage in OFDM systems. The window is optimized so as to minimize the post-compensation error variance (PCEV) of the residual phase, analytically computed for arbitrary PHN and frequency offset (FO) models. Closed-form expressions for near-optimal windows are derived for zero-mean FO, Wiener and first-order autoregressive PHN models, respectively. Furthermore, the diagonal-loading approach is properly employed, initially proposed for providing robustness to a general class of estimators in the presence of model mismatch, to enhance convergence of the iterative estimation scheme, in those high-SNR regions where the effect of data decision errors dominates performance. In the proposed OFDM scheme, channel, IFO estimation and data equalization are also based on the LS criterion, thus keeping the overall system complexity low. A generic performance description model is proposed and used for AMC algorithmic design, capable of describing most of current and under preparation communication protocols. This model proposition is incorporated to a larger family of performance modelling techniques named Effective SNR Mapping techniques (ESM). Using the ESM techniques and proper parameter adaptation constraints, a number of low-complexity AMC algorithms are developed under a chosen set of optimization scenarios. A framework for the design of AMC algorithms using approximate performance description models is proposed. Specific bounds are derived for quantifying the power loss when using approximate models. The effect of outdated channel state information is also studied by statistically characterizing the effective SNR at the receiver. This description allows parameter adaptation under mobility scenarios. The main value of this collective procedure is the development of low complexity- high performance algorithms, implementable on pragmatic OFDM systems.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Laser frequency noise'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles