Dissertations / Theses on the topic 'Optical cavity'

An optical cavity comprises a set of mirrors between which light can be reflected a number of times. The selectivity and stability of optical cavities make them extremely useful as frequency references or discri­mi­nators. With light coupled into the cavity, a sample placed inside a cavity will experience a significantly increased interaction length. Hence, they can be used also as amplifiers for sensing purposes. In the field of laser spectroscopy, some of the most sensitive techniques are therefore built upon optical cavities. In this work optical cavities are used to measure properties of gas samples, i.e. absorption, dispersion, and refractivity, with unprecedented precision. The most sensitive detection technique of all, Doppler-broadened noise-immune cavity enhanced optical heterodyne molecular spectrometry (Db NICE-OHMS), has in this work been developed to an ultra-sensitive spectroscopic technique with unprecedented detection sensitivity. By identifying limiting factors, realizing new experimental setups, and deter­mining optimal detection conditions, the sensitivity of the technique has been improved several orders of magnitude, from 8 × 10-11 to 9 × 10-14 cm-1. The pressure interval in which NICE-OHMS can be applied has been extended by deri­vation and verification of dispersions equations for so-called Dicke narrowing and speed dependent broadening effects. The theoretical description of NICE-OHMS has been expanded through the development of a formalism that can be applied to the situations when the cavity absorption cannot be considered to be small, which has expanded the dynamic range of the technique. In order to enable analysis of a large number of molecules at their most sensitive transitions (mainly their funda­mental CH vibrational transitions) NICE-OHMS instrumentation has also been developed for measurements in the mid-infrared (MIR) region. While it has been difficult to realize this in the past due to a lack of optical modulators in the MIR range, the system has been based on an optical para­metric oscillator, which can be modulated in the near-infrared (NIR) range. As the index of refraction can be related to density, it is possible to retrieve gas density from measurements of the index of refraction. Two such instru­men­tations have been realized. The first one is based on a laser locked to a measure­ment cavity whose frequency is measured by compassion with an optical frequency comb. The second one is based on two lasers locked to a dual-cavity (i.e. one reference and one measurement cavity). By these methods changes in gas density down to 1 × 10-9 kg/m3 can be detected. All instrumentations presented in this work have pushed forward the limits of what previously has been considered measurable. The knowledge acquired will be of great use for future ultrasensitive cavity-based detection methods.

Volume Holographic Data Storage Systems (HDSS) has been of interest for almost seven decades, and are now considered as a viable option for Write Once Read Many (WORM) cold data storage applications. Thanks to the Bragg selectivity of thick volume holograms, HDSS stores several hundreds of holograms on top of each other, called multiplexed data pages, by which data recording density can be substantially increased compared to surface recordings. On the other hand, signal intensity upon reconstruction of such multiplexed data pages inversely scales with number of multiplexing squared. Therefore, longer detection time and/or a high power laser along with a large dynamic range material is needed to make HDSS a truly viable "fast and high density" option for WORM applications. Historically, the trade-off between data density and data rate is well recognized. The challenge has been partially solved by continuous efforts such as improvement of materials, optical architectures, opto-mechanical systems and signal processing [1,2]. In this dissertation, we provide an additional pathway for HDSS to further increase both data density and transfer rates which is Cavities Enhancement Techniques for HDSS, to overcome the fundamental tradeoff. Key ideas are: recycling light with cavity to enhance data rate, and increasing number of multiplexing by combining cavity-eigenmode multiplexing, a subset of orthogonal phasecode multiplexing, with angular multiplexing. Based on this idea, we design and demonstrate Cavity-enhanced HDSS in such a way that we increase data rate and/or data density by at least factor of 2 while taking advantage of previous improvements as they are, or only with the minimum amount of modifications. In Section 1, we review history of HDSS and summarize the latest research results of HDSS and requirements on modern optical data storage systems as they relate to our solutions. In Section 2, theory of volume holography is reviewed by emphasizing understanding of angular and orthogonal phase code multiplexing. In Section 3 the theory of cavity enhanced reference arms is presented. We discuss how cavities provide a coherent boost to the beam power, which can be used in recording to alleviate source power requirements and/or increase the data recording rate and demonstrate the enhancement experimentally. Beyond basic enhancement, cavities also enable orthogonal phase code multiplexing via cavity eigenmodes. In Section 4, we experimentally demonstrate angular and orthogonal phase code hybrid multiplexing to overcome the limitation of the maximum number of multiplexing imposed by the geometrical constraints of angular multiplexing. In Section 5, novel aspects of the research are discussed in conjunction with the application of the technology for commercial use. Conclusions and future research direction are addressed in Section 6.

The optical ring cavity has been studied for about ten years, both theoretically and experimentally. In these studies the uniform plane wave approximation has been used. In this work we investigate effects which result from the retention of the transverse diffraction. We establish that transverse structure is inevitable since plane wave fixed points are susceptible to transverse instabilities (modulational instability). We show that this instability is a universal mechanism for initiating various interesting and complicated, yet understandable, dynamical responses in a one and a two transverse dimensional cavity.

xv, 204 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
This thesis reports on progress made toward realizing strong cavity quantum electrodynamics coupling in a novel micro-cavity operating close to the hemispherical limit. Micro-cavities are ubiquitous wherever the aim is observing strong interactions in the low-energy limit. The cavity used in this work boasts a novel combination of properties. It utilizes a curved mirror with radius in the range of 40-60 µm that exhibits high reflectivity over a large solid angle and is capable of producing a diffraction limited mode waist in the approach to the hemispherical limit. This small waist implies a correspondingly small effective mode volume due to concentration of the field into a small transverse distance. The cavity assembled for this investigation possesses suitably low loss (suitably low linewidth) to observe vacuum Rabi splitting under suitable conditions. According to best estimates for the relevant system parameters, this system should be capable of displaying strong coupling. The dipole coupling strength, cavity loss and quantum dot dephasing rates are estimated to be, respectively, g = 35µeV, κ = 30µeV, and γ = 15µeV. A survey of two different distributed Bragg reflector (DBR) samples was carried out. Four different probe lasers were used to measure transmission spectra for the coupled cavity-QED system. The system initially failed to display strong coupling due to the available lasers being too far from the design wavelength of the spacer layer, corresponding to a loss of field strength at the location of the quantum dots. Unfortunately, the only available lasers capable of probing the design wavelength of the spacer layer had technical problems that prevented us from obtaining clean spectra. Both a Ti:Al 2 O 3 and a diode laser were used to measure transmission over the design wavelength range. The cavity used here has many promising features and should be capable of displaying strong coupling. It is believed that with a laser system centered at the design wavelength and possessing low enough linewidth and single-mode operation across a wide wavelength range strong coupling should be observable in this system.
Committee in charge: Hailin Wang, Chairperson, Physics; Michael Raymer, Advisor, Physics; Jens Noeckel, Member, Physics; Richard Taylor, Member, Physics; Andrew Marcus, Outside Member, Chemistry

Today's information and communication industry is confronted with a serious bottleneck due to the prohibitive energy consumption and limited transmission bandwidth of electrical interconnects. Silicon photonics offers an alternative by transferring data optically and thereby eliminating the restriction of electrical interconnects over distance and bandwidth. Due to the inherent advantage of using the same material as that used for the electronic circuitry, silicon photonics also promises high volume and low cost production plus the possibility of integration with electronics. In this thesis, I introduce an all-silicon optical interconnect architecture that promises very high integration density along with very low energy consumption. The basic building block of this architecture is a vertically coupled photonic crystal cavity-waveguide system. This vertically coupled system acts as a highly wavelength selective filter. By suitably designing the waveguide and the cavity, at resonance wavelength of the cavity, large drop in transmission can be achieved. By locally modulating the material index of the cavity electrically, the resonance wavelength of the cavity can be tuned to achieve modulation in the transmission of the waveguide. The detection scheme also utilizes the same vertically coupled system. By creating crystal defects in silicon in the cavity region, wavelength selective photodetection can be achieved. This unique vertical coupling scheme also allows us to cascade multiple modulators and detectors coupled to a single waveguide, thus offering huge channel scalability and design and fabrication simplicity. During this project, I have implemented this vertical coupling scheme to demonstrate modulation with extremely low operating energy (0.6 fJ/bit). Furthermore, I have demonstrated cascadeability and multichannel operation by using a comb laser as the source that simultaneously drives five channels. For photodetection, I have realized one of the smallest wavelength selective detector with responsivity of 0.108 A/W at 10 V reverse bias with a dark current of 9.4 nA. By cascading such detectors I have also demonstrated a two-channel demultiplexer.

Diese Arbeit beschreibt eine ausfŸhrliche Untersuchung der physikalischen Eigenschaften von Mikrokugelresonatoren aus Quarzglas. Diese Resonatoren unterstŸtzen sogennante whispering-gallery Moden (WGM), die GŸten so hoch bis 109 bieten. Als experimentelle Hilfsmittel wurden ein Nahfeld- und ein Konfokalmikroskop benutzt, um die Struktur der Moden bezŸglich der Topographie des Resonators eindeutig zu identifizieren, oder um einzelne Quantenemitter zu detektieren und anzuregen. Die resonante †berhšhung des elektromagnetischen Feldes in den Moden des Resonators wurde ausgenutzt, um stimulierte Raman-Streuung mit extrem niedrigem Schwellenwert im Quarzglas zu beobachten. Ein Rekordschwellenwert von 4.5 Mikrowatts wurde gemessen. Mittels einer Nahfeldsonde wurde die Modenstruktur des Mikro-Ramanlasers gemessen. Mikroresonatoren stellen einen Grundbaustein der Resonator-Quantenelektrodynamik dar. In dieser Arbeit wurde die Kopplung von einem einzelnen strahlenden Dipol an die WGM sowohl theoretisch als auch experimentell untersucht. Die kontrollierte Kopplung von einem einzelnen Nanoteilchen an die WGM eines Mikrokugelresonators wurde nachgewiesen. Erste Ergebnisse in der Kopplung eines einzelnen Emitters an die Moden des Resonators wurden erzielt. Die resonante Wechselwirkung mit Resonatormoden wurde ausgenutzt, um den Photonentransfer zwischen zwei Nanoteilchen dramatisch zu verstŠrken. Schlie§lich wurde die bislang unbeachtete Analogie zwischen dem Quantensystem eines einzelnen Emitters in Wechselwirkung mit einer einzelnen Resonatormode und dem klassischen System zweier gekoppelten Moden experimentell untersucht. Es wurde bewiesen, wie die aus der Resonatorquantenelektrodynamik bekannten Kopplungsregime der starken und schwachen Kopplung in Analogie auch an einem klassischen System beobachtet werden kšnnen. Der †bergang von schwacher zu starker Kopplung wurde beobachtet, und bislang gemessene unerwartet hohe Kopplungsraten konnten einfach erklŠrt werden.
This work presents an extensive study of the physical properties of silica microsphere resonators, which support whispering-gallery modes (WGMs). These modes feature Q-factors as high as 109 corresponding to a finesse of 3 millions for spheres with a diameter of about 80 micrometers. These are to date among the highest available Q-factors, leading to cavity lifetimes of up to few microseconds. A near-field microscope and a confocal microscope are used as tools to unequivocally identify the mode structure related to the sphere topography, and for excitation and detection of single quantum emitters. The high field enhancement of the cavity modes is exploited to observe ultra-low threshold stimulated Raman scattering in silica glass. A record ultra-low threshold of 4.5 microwatts was recorded. The mode structure of the laser is investigated by means of a near-field probe, and the interaction of the probe itself with the lasing properties is investigated in a systematic way. Microcavities also one of the building blocks of Cavity QED. Here, the coupling of a radiative dipole to the whispering-gallery modes has been studied both theoretically and experimentally. The controlled coupling of a single nanoparticle to the WGMs is demonstrated, and first results in coupling a single quantum emitter to the modes of a microsphere are reported. The resonant interaction with these modes is exploited to enhance photon exchange between two nanoparticles. Finally a novel analogy between a system composed of a single atom interacting with one cavity mode on one side and intramodal coupling in microsphere resonators induced by a near-field probe on the other side is presented and experimentally explored. The induced coupling regimes reflect the different regimes of weak and strong coupling typical of Cavity QED. The transition between the two coupling regimes is observed, and a previously observed unexpectedly large coupling rate is explained.

In this thesis we study (theoretically and experimentally) various aspects of the classical and quantum dynamics of the non-isolated cavity-optomechanical system formed by a high-finesse Fabry-Pa'©rot (FP) cavity with a thin semitransparent highmechanical-quality vibrating membrane at its center. This optomechanical setup is called the Membrane-In-the-Middle (MIM) setup. In particular we show the subsequent five main results. 1. We determine to what extent optical absorption by the membrane hinders reaching a quantum regime for the cavity-membrane system. We show that even though membrane absorption may significantly lower the cavity finesse and also heat the membrane, one can still simultaneously achieve ground state cooling of a vibrational mode of the membrane and stationary optomechanical entanglement with state-of-the-art apparatuses. 2. We show that the coupling between the optical cavity modes and the vibrational modes of the membrane can be tuned by varying the membrane position and orientation. In particular, we demonstrate a large quadratic dispersive optomechanical coupling in correspondence with avoided crossings between optical cavity modes weakly coupled by scattering at the membrane surface. The experimental results are well explained by a first order perturbation treatment of the cavity eigenmodes. 3. We present an experimental study of dynamical back-action cooling of the fundamental vibrational mode of the membrane. We study how the radiation-pressure interaction modifies the mechanical response of the vibrational mode, and the experimental results are in agreement with a Langevin equation description of the coupled dynamics. The experiments are carried out in the resolved sideband regime, and we have observed cooling by a factor of 350. We have also observed the mechanical frequency shift associated with the quadratic term in the expansion of the cavity mode frequency versus the effective membrane position, which is typically negligible in other cavity optomechanical devices. 4. We demonstrate the analog of electromagnetically induced transparency in our setup at room temperature. Due to destructive interference, a weak probe field is completely reflected by the cavity when the pump beam is resonant with the motional red sideband of the cavity. Under this condition we infer a significant slowing down of light of hundreds of microseconds, which is easily tuned by shifting the membrane along the cavity axis. We also observe the associated phenomenon of electromagnetically induced amplification which occurs due to constructive interference when the pump is resonant with the blue sideband. 5. We show a phase/frequency noise cancellation mechanism due to destructive interference which can facilitate the production of ponderomotive squeezing in the kHz range and we demonstrate it experimentally, in collaboration with the University of Florence and the University of Trento, in an optomechanical system formed by a Fabry-Pa'©rot cavity with a micro-mechanical mirror.

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed February 3, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Cavity enhanced optical frequency comb spectroscopy is a technique that allows for quick and sensitive measurements of molecular absorption spectra. Locking the comb lines of an optical frequency comb to the cavity modes of an enhancement cavity and then extracting the spectral information with a Fourier transform spectrometer grants easy access to wide segments of absorption spectra. One of the main obstacles complicating the analysis of the measurements is the inevitable dispersion occurring inside the cavity. In this project, absorption measurements of CO2 were performed using an existing and well established setup consisting of a near-infrared optical frequency comb locked to a Fabry- Pérot enhancement cavity using the Pound-Drever-Hall technique, and a Fourier transform spectrometer. The purpose was to improve theoretical models of the measured absorption spectra by creating and verifying a model for the cavity dispersion, stemming mostly from the cavity mirrors but also from the normal dispersion of the intracavity medium. Until now, the cavity dispersion has been treated as an unknown and was included as a fitting parameter together with the CO2 concentration when applying fits to the absorption measurements. The dispersion model was based on previously performed precise measurements of the positions of the cavity modes. The model was found to agree well with measurements. In addition, pre-calculating the dispersion drastically reduced computation time and seemed to improve the overall robustness of the fitting routine. A complicating factor was found to be small discrepancies between the locking frequencies as determined prior to the measurements and the values yielding optimum agreement with the model. These apparent shifts of the locking points were found to have a systematic dependence on the distance between the locking points. The exact cause of this was not determined but the results indicate that with the locking points separated by more than about 10nm the shifts are negligible.

This dissertation contains a study of ultracold atoms in optical cavities. We particularly focus on two aspects of the coupled atom-cavity systems. In the first aspect, we implement the quantum nature of the light field to probe the quantum state of the atoms. This is interesting due to the nondestructive nature of the characterization of many-body atomic states. In the second aspect we study the cavity optomechanics that investigates the coupling of mechanical and optical degrees of freedom via radiation pressure. The optomechanical cavity provides an interesting nonlinear system to study the coupling between atoms and the intracavity field.In the context of cavity quantum electrodynamics we study the reflection of two counter-propagating modes of the light field in a high-Q ring cavity by ultracold atoms either in the Mott insulator state or in the superfluid state of an optical lattice. We find that the dynamics of the reflected light strongly depends on both the lattice spacing and the state of the matter-wave field. By using the Monte Carlo wave-function method to account for the cavity damping we also determine the two-time correlation function and the time-dependent physical spectrum of theretroreflected field. We find that the light field and the atoms become entangled if the latter are in a superfluid state. We also analyze quantitatively the entanglement between the atoms and the light.In cavity optomechanics the mechanical effect can either comes from a vibrating macroscopic oscillator or a collective density excitation of a Bose-Einstein condensate. First we use a Fabry-Perot-type cavity to study the opto-mechanically-induced bistable quantum phase transitions between superfluid and a Mott insulator states of an ultracold bosonic gases trapped inside the cavity. Secondly, we study the symmetricand antisymmetric collective density side modes of the BEC which results from the optomechanical effects of the light fields in a ring cavity.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 179-185).
Optical parametric amplifiers have emerged as important optical sources by extending the properties of few-cycle laser sources, which exist only in materials with sufficiently large gain bandwidths, to wide array of spectral ranges. The work reported in this thesis relates to two areas for the continued development of optical parametric amplification based sources. First, we present a white light seeded, carrier-envelope stable, degenerately pumped OPA producing near tranform-limited sub 7 fs , 3 [mu]J pulses at the driver wavelength from a long pulse, non-CEP stable Ti:sapphire regenerative amplifier. Problems to the spectral phase jump at the driver wavelength, 800 nm, were avoided by using a near infrared OPA to produce white light continuum down to 800 nm where the spectral phase is smooth. Secondly, enhancement cavities are used in conjunction with parametric amplifiers resulting in a new technique entitled, cavity-enhanced optical parametric chirped-pulse amplification (C-OPCPA). C-OPCPA increases the capabilities of nonlinear crystals and can allow continued scaling of parametric amplifier systems to high repetition rate. This work contains the first theoretical and experimental investigation of C-OPCPA. Numerically, passive pump pulse shaping of the intracavity pump power is shown to enable octave spanning gain. Experimentally, a first proof-of-principle experiment demonstrates a 78 MHz C-OPCPA with more than 50% conversion with under 1 W of incident pump power. A comparison to a single pass system shows improvements in the C-OPCPA of orders of magnitude in conversion efficiency and 3 fold increase in phase matching bandwidth in 10 and 20 mm periodically poled lithium niobate phase matched for parametric amplification with 1030 nm pump wavelength and a 1550 nm signal wavelength. A Yb-fiber laser based CPA system producing up to 5 W of 500 fs pulses comprises the pump source, and a Er-fiber laser the signal.
by Aleem Mohammad Siddiqui.
Ph.D.

This thesis presents two contrasting implementations of the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) technique. OF-CEAS com- bines passive optical-feedback locking of semiconductor lasers with cavity-enhanced absorption spectroscopy, and is well suited to sensitive detection of pressure- broadened trace gases. Chapters 1 and 2 set the work in this thesis in context, by describing the theory and discussing the motivations behind trace gas sensing by tuneable laser spectroscopy in the near- and mid-IR. Chapter 3 reviews the theory of OF-CEAS, prior to presenting the results of an experimental implementation based on a near-IR DFB diode laser setup following the traditional V-cavity methodology to spatially decouple the optical- feedback beam from the direct back reflection. The capabilities of the system are demonstrated by accurate determination of a self-broadened half-width at half- maximum of a CO 2 transition, and by detection of acetylene in a car exhaust sample. Chapter 4 describes the design and implementation of the linear cavity method- ology for QCL OF-CEAS, which is the significant contribution of this work. Successful OF-CEAS locking with the linear cavity is shown for two different DFB-QCLs, with close operating wavelengths (5.5 and 5.2 µm) but quite different operating powers and facet size. Chapter 5 presents quantitative spectroscopic results from the linear cavity OF-CEAS instrument, using both lasers. Spec- troscopy on mixes of N 2 O and NO returned sensitivities, quantified by the α min , of 2.7 × 10 −8 cm −1 in 1 s at 0.28 atm and 2.4 × 10 −8 cm −1 in 1 s at 0.19 atm respectively. Limited by etalon fringing on the baseline, the α min compared well with those obtained with V-cavity QCL OF-CEAS instruments. The temporal stability was investigated by Allan variance calculations and the best minimum detectable concentrations for the linear QCL OF-CEAS instrument were 32 ppm for N 2 O (35 s) and 5 ppb for NO (2 s). For NO, this detection limit compares favourably with other mid-IR QCL-based NO sensors, and is sufficient for mon- itoring NO in polluted urban environments. With the Maxion DFB-QCL, mon- itoring of NO in air outside the laboratory was attempted, and an air sample drying system benchmarked. Although this experiment proved unsuccessful, it was possible detect trace amounts of NO desorbing from the walls of the gas cell. Over the course of one hour the concentration rose from 3.8 ± 0.7 ppb to 28.4 ± 0.2 ppb, leading to a rate of desorption of 6.76 ± 0.01 × 10 −3 ppb s −1 . The sensitivity (α min ) of these spectra was 7.0 × 10 −9 cm −1 in 1 s, improved due to the higher mirror reflectivity at the lasing wavelength of the Maxion DFB-QCL, although still limited by etalon fringing.

The Vertical-Cavity Surface-Emitting Laser (VCSEL) is a new type of microcavity semiconductor laser with new and unusual characteristics. It is designed to have very high reflectivity mirrors with cavity length on the order of the wavelength of light, making possible dynamical studies in the smallest of laser cavities. Only one single longitudinal mode is supported within the gain spectrum of the active semiconductor material, thus requiring the cavity length to be an integer multiple of the emission wavelength. This short cavity length and a wide output aperture, on the order of five microns, provide for a high Fresnel number. The combination of the high Fresnel number and of the richness of nonlinear effects in GaAs makes the VCSEL an ideal candidate for the study of spatio-temporal dynamics in nonlinear optics. In this dissertation we report on the longitudinal and transverse characteristics of VCSELs under injection-locking. Unique features appear experimentally in the longitudinal nonlinear dynamics of this system including beam coupling, four-wave mixing, new frequency generation, subharmonic bifurcation, and enhanced relaxation oscillations, opening a route to chaos. Coherent Energy Transfer (CET) takes place between a strong monochromatic injection frequency and all the frequencies contained in the VCSEL's laser emission just above threshold, leading to asymmetric gain. The high Fresnel number of the VCSEL makes it an interesting candidate for the study of transverse pattern behavior under injection-locking. We have forced high-order transverse modes and observed transverse instabilities including optical vortices. We have found three ways of generating vortices in VCSELs; these are the helicoidal phase mask, the Gaussian-beam-induced vortices, and the injection-locked TEM*₀₁ mode.

A feasibility study of an "Extended Cavity, Self Focussing Laser Optical Head" for optical data storage applications is presented. A general description of the proposed device is discussed followed by a prediction of its dynamic operation. This is verified by a one dimensional computer model, simulating dynamic laser head behavior. Transient laser phenomena such as longitudinal mode competition and laser frequency modulation are investigated as applicable to the device operation. The self-focussing concept is confirmed by the passive cavity experiment and a geometrical computer model of the cold cavity (i.e. no gain medium).

Optical microcavities can find broad application areas, like tunable and compact sources, dynamic filters for optical communications, biological and chemical sensors, etc. Optical microcavities are key component allowing one to obtain compact laser devices exhibiting small cavity volume and low threshold. Among the different resonators architectures for microcavities laser, photonic crystal (PC) structures are one of the most promising. These structures feature the periodicity in one or more dimensions, and are resonant for light waves of a specific wavelength. Two-dimensional PCs are planar dielectric waveguide where photons are vertically confined by the vertical profile of the optical index, while the crystal periodicity acts only in the slab plane. In photonic crystals the refractive index contrast of the periodic structure is high enough to open a full band gap, and thus to fully confine light at very small scale. Strong coupling is theoretically feasible, and quality factor of more than 106 have been experimentally achieved for small modal volumes. Substantial additional gains are possible with confinement improvement in microfabrication techniques and with implementation of low loss design. Photonic crystal whose index contrast is lower can be used as DFB gratings. In a DFB device, the laser modes receive feedback at one specific wavelength, determined by the grating period of the structure. The feedback strength is related to the coupling constant, ?, which in turn depends on the grating index contrast, and to the grating length, L. The ?L product must be high enough to ensure the feedback required for lasing. In an optically pumped laser, an external source supplies the excitation energy necessary to get the population inversion. To do that, it must be on resonance with one of the absorption transitions of the active medium. When the external source provides enough energy, the active material exhibits gain: more photons are generated than lost. For intense incoming beams, i.e. intense laser sources, multiple-photon absorption processes become appreciable. It is thus possible to have absorption also by pumping with sources having photon energies lower than the resonance energy of the active medium. The two-photon absorption (TPA), described from the 3rd order susceptibility, involves the simultaneous absorption of two photons with energy: E_exc-E_ground=2?? The absorption of the first photon causes the promotion of the electron to the virtual level. Here the simultaneous absorption of the second photon promotes the electron to the real excited state. The system can then decay to the ground state emitting an up-converted photon, i.e., a photon having energy higher than that of the exciting ones. A large part of this work is devoted to the realization and characterization of active microresonators behaving as laser sources. Two main research subjects will be pursued: An integrated InP semiconductors photonic crystal microcavity laser, operating in the telecommunication wavelength. A distributed feedback laser for two-photon induced IR-to-visible up-conversion lasing. Within the second subject, particular attention will be devoted to the characterization of the two-photon induced emission properties of organic push-pull dyes and II-VI semiconductors quantum dots (QDs) to evaluate their potentiality as candidates for all-solid-state up-converted laser devices. The third reported research subject is the exploitation of hybrid silica-titania sol-gel films for UV lithography application, finalized to the production of surface relief gratings. MICROLASER BASED ON EFFECTIVE INDEX CONFINED, SLOW-LIGHT MODES IN PC WAVEGUIDES This research regards the study of photonic crystal microcavity having small mode volume V and high quality factor Q, for the production of low threshold integrated laser devices. The light propagation inside the PC is modified because of its periodicity. In this study we exploit the low-light guided modes at the high symmetry point of the dispersion curve of a PC-W1 waveguide. The PC-W1 waveguide is a PC having triangular symmetry with a missing row of hole along the ?K direction. The linear defect entails the appearance of defect modes with frequencies localized inside the unperturbed PC band gap, and thus modes that exponentially decay inside the PC. The band associated with the defect mode becomes flat at the K point of the band diagram, leading to slow-modes whose group velocity goes to zero. The lateral confinement of low-group velocity modes is controlled by locally changing the refractive index of the two dimensional photonic crystal waveguides. The index modulation is induced by post-processing a dielectric strip on top of the two-dimensional PC waveguide. This results in a photonic heterostructure whose confinement properties are the result of the effective index shift and the local curvature of the band associated with the waveguide mode. In this thesis the results of the device simulation, experimental realization and characterization will be reported. Computational tools, such as MPB and 3D-FDTD software have been used for the device design and for the study the electromagnetic field behavior inside the cavity. The realization of the PC structure has been accomplished through lithography techniques like e-beam lithography and reactive ion etching. Intense clean-room activities have been necessary to reach optimized structure quality. The characterization of the microcavity laser has been pursued with a proper optical set-up, in such a way to determine its performance. UP-CONVERTED LASING The up-converted lasing is an alternative method to convert the emission of a cheap, easily available IR laser into that of a more technological valuable visible laser. It involves the two photon pumping (TPP) mechanism, i.e., the NLO system is excited through the simultaneously absorption of two photons in the near-IR range. In this work we report our effort towards the realization of a solid-state visible laser device based on a TPP induced emission. The starting point of this technology is to find a system able to efficiently convert the IR incoming radiation to a visible one. We have studied the up-conversion process both in push-pull organic dyes embedded in sol-gel hybrid films and in semiconductor core-shell CdSe-CdS-ZnS quantum dots embedded in zirconia films. The excitation source is an amplified Ti:Sapphire laser at 800 nm. Concerning the organic compounds, it has been possible to characterize the emission properties only in solution, because of their poor photostability when they are embedded in sol-gel matrices. On the opposite, quantum dots embedded in zirconia films show promising amplified emission properties, with interesting gain value and extremely long time stability. We have investigated the possibility to implement this material with a distributed feedback optical resonator for obtaining compact and integrated laser devices. The grating parameters have been determined with MPB software, and first attempts of e-beam lithography of the pattern have been done. We have also prepared a devoted optical set-up for the optical characterization of the laser devices. SILICA-TITANIA SOL-GEL FILM FOR DIRECT PHOTOPATTERNIG APLICATIONS The possibility to exploit the photocatalytic action of hybrid silica-titania sol-gel film towards the decomposition of their organic component, for the direct patterning of surface structure has been investigated. These films have been characterized to study their microstructural properties, and to confirm the presence of crystalline titanium oxo-clusters. Their photocatalytic efficiency has been measured using stearic acid as reference material. To test the potentiality of this system for UV-lithography, it has been exposed to a UV-lamp. The organic component decomposition leads to a film shrinkage of about 60%, accompanied by a refractive index increases of about 0.1 By irradiating the spin-coated films through an UV-mask, structures of different shapes and micrometer dimension have been achieved.
Lo studio delle microcavità ottiche riveste un grande interesse per applicazioni in svariati campi, quali la ricerca di sorgenti laser tunabili e compatte, filtri per le telecomunicazioni, sensori chimici e biologici, etc. Le microcavità ottiche sono fondamentali per l’ottenimento di dispositivi laser compatti, aventi bassa soglia di emissione laser, ove il campo elettromagnetico è confinato in volumi estremamente ridotti, con conseguente aumento dell’interazione radiazione-materia,. Tra le possibili architetture della cavità risonante, per dispositivi pompati otticamente, i cristalli fotonici rappresentano una delle soluzioni più promettenti. Questi ultimi sfruttano la periodicità in una o più direzioni e sono risonanti con determinate lunghezze d’oda della radiazione elettromagnetica. In un cristallo fotonico bidimensionale il confinamento verticale è garantito dal profilo verticale dell’indice di rifrazione, mentre il confinamento nel piano del cristallo è opera della strutture periodica. Nei cristalli fotonici il contrasto di indice di rifrazione della struttura periodica è tale da aprire un intervallo completo di energie proibite per la propagazione della radiazione nel mezzo. Essa può quindi essere confinata in volumi molto piccoli, dell’ordine del cubo della lunghezza d’onda, con fattori di qualità sperimentali superiori a 106. Inoltre i valori ottenuti sperimentalmente sono inferiori a quelli previsti teoricamente, e ulteriori passi in avanti saranno possibili con lo sviluppo delle tecniche litografiche e di produzione del materiale attivo. I cristalli fotonici nei quali il contrasto di indice di rifrazione è insufficiente per aprire un band-gap completo si comportano come reticoli distributed feedback, DFB. In un dispositivo DFB, i modi risonanti ricevono il feedback a lunghezze d’onda specifiche, determinate dal periodo del reticolo. La forza dell’accoppiamento è legata alla costante di accoppiamento ?, la quale, a sua volta, dipende dal contrasto di indice nel reticolo e all’estensione totale del reticolo. Il prodotto ?L deve essere sufficiente per garantire il feedback richiesto per l’emissione laser. In un laser a pompaggio ottico, una sorgente esterna fornisce al mezzo attivo l’energia di eccitazione richiesta per raggiungere l’inversione di popolazione, requisito necessario per ottenere il guadagno all’interno del mezzo e quindi l’amplificazione. Affinché si verifichi assorbimento, l’energia del fascio di pompa deve essere in risonanza con una delle transizioni del mezzo attivo. Per campi incidenti molto intensi, come possono essere quelli legati a fasci laser focalizzati, diventano tuttavia apprezzabili anche fenomeni di assorbimento multi fotonici. Si può quindi avere assorbimento anche utilizzando sorgenti di pompa aventi energie inferiori all’energia di risonanza del mezzo attivo. L’assorbimento a due fotoni (TPA), legato alla suscettibilità non lineare al terzo ordine, comporta l’assorbimento simultaneo di due fotoni, con energia: E_exc-E_ground=2?? L’assorbimento del primo fotone promuove l’elettrone dallo stato fondamentale a uno stato virtuale, dal quale esso passa immediatamente allo stato eccitato attraverso l’assorbimento simultaneo di un secondo fotone incidente. Infine il sistema può tornare allo stato fondamentale, attraverso l’emissione di un fotone a energia superiore rispetto ala pompa. Gran parte del lavoro di dottorato è incentrato sulla realizzazione e caratterizzazione di microcavità attive per l’ottenimento di sorgenti laser. All’interno di tale attività sono stati studiati due sistemi differenti: Una microcavità laser a semiconduttore, realizzata sfruttando le proprietà dei cristalli fotonici bi-dimensionali, che emette alla lunghezza d’onda delle telecomunicazioni. Un dispositivo laser DFB, pompato oticamente a due fotoni, per la conversione di emissione laser dall’infrarosso al visibile. All’interno della seconda tematica, particolare attenzione è stata rivolta alla caratterizzazione delle proprietà di emissione indotta a due fotoni di un cromoforo organico e di quantum dots di un semiconduttore II-VI, il CdSe, entrambi inglobati in matrice sol-gel. Un terzo soggetto è costituito dallo studio delle proprietà foto catalitiche di film sol-gel ibridi a base di silica e titania, in vista di possibili applicazioni per il patterning diretto tramite radiazione UV. CONFINAMENTO DI MODI LENTI IN GUIDA D’ONDA A CRISTALLO FOTONICO PER L’OTTENIMENTO DI MICROCAVITA’ LASER Questa ricerca riguarda lo studio di cavità, ottenute sfruttando cristalli fotonici bidimensionali, a basso volume modale e alto fattore di qualità Q, finalizzate all’ottenimento di dispositivi laser integrati a bassa soglia. Questo lavoro si basa sull’utilizzo dei modi guidati lenti corrispondenti al punto ad elevata simmetria K della curva di dispersione di una guida d’onda W1-PC. Una guida d’onda W1-PC si ottiene da un cristallo fotonico a simmetria triangolare, attraverso la rimozione di una fila di buche lungo la direzione ?K. In questo modo si introduce un difetto lineare, il quale si riflette nella comparse di modi del difetto, aventi frequenze localizzate all’interno del band-gap del cristallo fotonico, che pertanto decadono esponenzialmente all’interno del cristallo. Le bande associate ai modi del difetto hanno curvatura nulla in corrispondenza dei punti a elevata simmetria, e ciò implica una velocità di gruppo del modo nulla in corrispondenza di tali punti. L’estensione laterale dei modi lenti viene controllata agendo sull’indice di rifrazione del cristallo fotonico, in modo da creare una etero struttura in grado di confinarli efficacemente. L’indice effettivo della guida viene modificato localmente depositando un film di polimero all’interfaccia superiore della guida. La forza del confinamento dipende dall’entità della variazione dell’indice e dalla curvatura della banda associata al modo lento. L’attività svolta all’interno di questo progetto consiste nel design della struttura, nella sua realizzazione sperimentale e infine nella caratterizzazione ottica del dispositivo. Per ottimizzare i parametri del dispositivo e comprendere il comportamento della radiazione elettromagnetica all’interno della cavità, sono stati impiegati strumenti di calcolo computazionale, quali i software MPB e TESSA 3D-FDTD. I parametri delle simulazioni sono stati poi utilizzati per la realizzazione del cristallo fotonico, effettuata tramite tecniche litografiche, quali la litografia con fascio elettronico e l’etching ionico. La caratterizzazione ottica del dispositivo è stata effettuata con un apposito set-up, al fine di determinarne le prestazioni. EMISSIONE LASER CON CONVERSIONE DI FREQUENZA La conversione di frequenza laser fornisce l’interessante possibilità di convertire una sorgente laser economica e di facile reperibilità nell’infrarosso, in una sorgente laser nel visibile di enorme interesse tecnologico. Essa si basa sull’emissione indotta a seguito di processi di assorbimento a due fotoni nel vicino IR. In questo lavoro verranno presentati gli sforzi profusi e i risultati preliminari ottenuti nella ricerca di un dispositivo laser allo stato solido per la conversione di frequenza. A tal fine sono state investigate le proprietà di conversione di un cromoforo push-pull organico disperso in matrici sol-gel ibride, e di quantum dots di semiconduttore II-VI, CdSe-CdS-ZnS, dispersi in una matrice inorganica a base di zirconia. Il composto organico presenta interessanti proprietà di emissione indotta a due fotoni in soluzione. Tuttavia la sua scarsa resistenza al pompaggio ottico in matrice solida preclude un suo possibile impiego e rende estremamente problematica la stessa caratterizzazione ottica. Al contrario i film di QDs-ZrO2 mostrano una buona efficienza di conversione di frequenza, con valori di guadagno per l’emissione spontanea amplificata interessanti, e elevata stabilità del segnale emesso nel tempo. E’ stata pertanto studiata la possibilità di implementare i film di QDs-ZrO2 all’interno di una cavità risonante di tipo distributed feedback per ottenere un dispositivo laser compatto e integrabile. I parametri del reticolo sono stati determinati con il software MPB e sono stati fissati in modo da avere amplificazione in corrispondenza del massimo di emissione dei QDs. Sono tutt’ora in corso delle prove di realizzazione del reticolo DFB tramite litografia elettronica su film sol-gel appositamente sviluppati per il patterning diretto. Infine è stato messo appunto un set-up dedicato per la caratterizzazione ottica dei dispositivi prodotti. FILM SOL-GEL IBRIDI A BASE DI SILICA-TITANIA PER IL PATTERNING DIRETTO CON LUCE UV E’ stata studiata l’attività fotocatalitica di film sol-gel ibridi a base di silica-titania, promossa dalla radiazione UV. I film sono stati caratterizzati a livello micro strutturale tramite spettroscopia infrarossa, e sono stati osservati al microscopio elettronico per confermare la presenza di cluster di titanio cristallino al loro interno. L’efficienza del processo di fotocatalisi è stata determinata mediante test standard che si avvalgono dell’acido stearico come materiale di riferimento. Quest’ultimo infatti è in grado di simulare efficacemente i comuni inquinanti organici, è può essere depositato facilmente per spin-coating. Successivamente è stata valutata la possibilità di sfruttare l’attività foto catalitica per il patterning diretto dei film. Tale studio parte dall’osservazione che la fotocatalisi si manifesta anche nei confronti della componente organica dei film sol gel ibridi.. Questo fenomeno è accompagnato da una diminuzione dello spessore del film, fino al 60% sullo spessore iniziale, e può pertanto essere sfruttato per la realizzazione di strutture a rilievo. Test di patterning diretto sono stati effettuati irradiando il film con una lampada UV attraverso una maschera in quarzo, ottenendo strutture di dimensione micrometrica ben definite.

Thesis (Ph. D.)--University of Oregon, 2008.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 147-163). Also available online in ProQuest, free to University of Oregon users.

Ever since the first laser demonstration in 1960, applications for laser systems have increased to include diverse fields such as: national defense, biology and medicine, entertainment, imaging, and communications. In order to serve the growing demand, a wide range of laser types including solid-state, semiconductor, gas, and dye lasers have been developed. For most applications it is critical to have lasers with both high optical power and excellent beam quality. This has traditionally been difficult to simultaneously achieve in semiconductor lasers. In the mid 1990's, the advent of an optically pumped semiconductor vertical-external-cavity surface-emitting laser (VECSEL) led to the demonstration of high (multi-watt) output power with near diffraction limited (TEM00) beam quality. Since that time VECSELs covering large wavelength regions have been developed. It is the objective of this dissertation to investigate and explore novel cavity designs which can lead to increased functionality in high power, high brightness VECSELs. Optically pumped VECSELs have previously demonstrated their potential for high power, high brightness operation. In addition, the "open" cavity design of this type of laser makes intracavity nonlinear frequency conversion, linewidth narrowing, and spectral tuning very efficient. By altering the external cavity design it is possible to add additional functionality to this already flexible design. In this dissertation, the history, theory, design, and fabrication are first presented as VECSEL performance relies heavily on the design and fabrication of the chip. Basic cavities such as the linear cavity and v-shaped cavity will be discussed, including the role they play in wavelength tuning, transverse mode profile, and mode stability. The development of a VECSEL for use as a sodium guide star laser is presented including the theory and simulation of intracavity frequency generation in a modified v-cavity. The results show agreement with theory and the measurement of the sodium D1 and D2 lines are demonstrated. A discussion of gain coupled VECSELs in which a single pump area accommodates two laser cavities is demonstrated and a description of mode competition and the importance of spontaneous emission in determining the lasing condition is discussed. Finally the T-cavity configuration is presented. This configuration allows for the spatial overlap of two VECSEL cavities operating with orthogonal polarizations. Independent tuning of each cavity is presented as well as the quality of the beam overlap and demonstration of Type II intracavity sum frequency generation. Future applications to this configuration are discussed in the generation of high power, high brightness lasers operating from the UV to far-infrared and even terahertz regimes.

Previously, we proposed and experimentally demonstrated enhanced recording speeds by using a resonant optical cavity to semi-passively increase the reference beam power while recording image bearing holograms. In addition to enhancing the reference beam power the cavity supports the orthogonal reference beam families of its eigenmodes, which can be used as a degree of freedom to multiplex data pages and increase storage densities for volume Holographic Data Storage Systems (HDSS). While keeping the increased recording speed of a cavity enhanced reference arm, image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe: LiNbO3 medium with a 532 nm laser at two Bragg angles for expedited recording of four multiplexed holograms. We experimentally confirmed write rates are enhanced by an average factor of 1.1, and page crosstalk is about 2.5%. This hybrid multiplexing opens up a pathway to increase storage density while minimizing modifications to current angular multiplexing HDSS.

Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed November 21, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

The subject of this master's thesis is stabilizing a frequency comb laser to an external cavity using a couple of servo controllers. The aim of the project was to build a pair of servo controllers, replacing parts of the existing commercial and proprietary solution already in use. The system under control is an optical frequency comb, which is locked to an external cavity and is used for trace gas detection and spectroscopy. The comb is a broadband light source and needs to be locked to the external cavity in order to achieve maximum transmission through the cavity. The goal was to replace two of the original controllers and try to improve the locking capabilities of the system. The controllers were also supposed to be customizable and for that reason the control system with all its components was built on breadboards and confined in an aluminium box. Control circuits were built for the purpose, one for controlling the comb offset frequency by modulating the pump diode current, the other for controlling the repetition rate of the comb laser by altering the length of the laser cavity using a piezo-electric transducer (PZT). A commercial and proprietary servo controller was also in the system, controlling an intra-cavity electro-optic modulator. It was kept for controlling the higher frequency region, for which the PZT no longer worked. In order to simulate and design the system, Matlab was used with functions described by both theoretically and experimentally obtained mathematical equations. The controllers were tested thoroughly in order to make sure they acted according to the intended design, before they were tested with the laser. After an initial lock was obtained, the controllers were optimized further using both experimental and theoretical methods until the lock was optimized and the transmission through the cavity was maximized. The error signals that were used for controlling the system were monitored with both an oscilloscope and a spectrum analyser, the latter producing a spectrum with the power ratio plotted versus frequency. The transmission intensity through the cavity was measured when a good lock had been achieved and the results were analysed by applying a Fourier transform to the measured data. This was done with both the old controllers and the new controllers and the resulting plots were compared. Analysis showed that the new control system yielded a transmission signal with a slightly reduced noise level compared to the signal resulting from using the old controllers. The results from the spectrum analyser also showed slightly reduced error signals for the new controllers compared to those of the old controllers. When summarising this work it can be concluded that the goals set up at the start were achieved with results living up to the expectations. The results also verified that such a control system can be built for locking an optical frequency comb to an external cavity with simple and rather cheap components and with good results.

This thesis focuses on the construction and development of an experiment to study cold potassium atoms in an optical ring cavity. Firstly we load a potassium-39 magneto optical trap (MOT) inside the ring cavity. To achieve this a laser system, rectangular magnetic coils system and vacuum system are designed and constructed. To stabilise the laser system, a detailed study of various potassium spectroscopy techniques is undertaken and the reference laser is suitably locked to the magnetically induced spectroscopy. We load an ensemble of 10\(^5\) potassium atoms inside the ring cavity mode and study their collective strong coupling with the cavity field. In the collective strong coupling regime, the photons are coherently exchanged between the atomic ensemble and cavity field. This rate of exchange is determined by the singlephoton Rabi frequency `2\(g\)' which must be larger than the cavity field decay rate `2\(k\)' and atomic spontaneous emission rate `2\(ᵧ\)'. As a result of this coupling, the peak in the cavity transmission signal undergoes a splitting known as `vacuum Rabi splitting' (or `normal mode splitting'). The vacuum Rabi splitting has been realised and measured to be ~ 2\(π\). 18 MHz in our system.

Le contrôle des états quantiques de la lumière est une étape nécessaire pour la transmission et le traitement quantiques des informations. Un nuage d'atomes froids constitue un milieu optiquement non-linéaire très intéressant pour créer et manipuler des états photoniques. Le sujet de cette thèse est l'étude expérimentale de telles non-linéarités, induites entre des photons optiques par leur couplage avec des atomes de Rydberg. Les états de Rydberg sont des états atomiques très excités (n>30), qui permettent de créer des interactions photon-photon par l'intermédiaire de leurs interactions dipôle-dipôle à longue distance (>10µm). Nous utilisons une cavité de faible finesse pour transformer ces interactions en effets observables sur un faisceau de très faible intensité, ce qui peut permettre de produire des états non-classiques de lumière
The control of quantum states of light is a necessary step for quantum information transportation and processing. Cold atomic memories are one of the prime candidates for storing and manipulating photonic states. This thesis is a study of optical non-linear effects created using Rydberg states. Rydberg states are highly excited states (n>30) of atoms, which are useful in realizing photon-photon interactions because of their long distance (>10µm) dipole-dipole interactions. We utilize a low finesse cavity to transform phase shifts into intensity correlations which would allow one to generate arbitrary non-classical states of light

Among the number of optical sources, vertical-cavity surface-emitting lasers (VCSELs) are relatively recent type of semiconductor laser devices, which are attractive for a number of applications particularly for free space optical (FSO) communication systems. In such systems reliable optical devices with lower power consumption and low cost are among the key requirements. VCSELs typically operate with unstable output polarization modes, and there is a need to improve their output power regarding to the polarization instability, particularly when introducing the optical feedback (OF). This thesis investigates a number of key properties of VCSEL including the polarization instability, hysteresis loop (HL), relative intensity noise (RIN) and how to control the polarization switching (PS). The investigations are based on the analytical studies and extensive experimental work. PS properties of VCSEL are investigated by introducing variable polarization optical feedback (VPOF) with the modulation frequency and modulation depth. The dependency conditions for the HL, RIN and PS are determined with VPOF. Under OF, the threshold current (Ith) of VCSEL is reduced by 11.5% and the PS, which is demonstrated theoretically and experimentally, is completely suppressed. The PS positions are depending on the polarization angle of OF, OF levels and the bias current. The PS disappeared with the modulation depth of 78.66%, whereas it is entirely vanished with the modulation frequency of 200 MHz. The hysteresis width of the VCSEL polarization modes is reduced by increasing the feedback level. The minimum RIN value of -156 dB/Hz is achieved at a zero degree of the polarization angle for the dominant polarization mode of VCSEL under VPOF. For the first time, a novel technique based on employing orthogonal polarization OF is proposed to supress the nonlinearity associated with the modulated VCSEL, where the second, third, and fourth harmonics are completely suppressed to the noise floor. Finally, optimal operating conditions for a high-quality polarization-resolved chaos synchronization of the polarization modes of VCSEL with VPOF are experimentally and theoretically studied. A perfect value of 99% of the correlation dynamics for the chaotic synchronization of the polarization modes of VCSEL is found with a zero time delay over a wide range of polarization angle. Finally, Simulink and Origin software version 6.1 are used in this work to simulate and plot the results. The simulation results are agreed with the experimental results, which show that the chaotic synchronization dynamic of the polarization modes can be achieved by VPOF.

Die verlässliche Erzeugung einzelner Photonen mit wohldefinierten Eigenschaften in allen Freiheitsgraden ist entscheidend für die Entwicklung photonischer Quantentechnologien. Derzeit basieren die wichtigsten Einzelphotonenquellen auf dem Prozess der spontanen parameterischen Fluoreszenz (SPF), bei dem ein Pumpphoton in einem nichtlinearen Medium spontan in ein Paar aus Signal und Idlerphotonen zerfällt. Resonator-überhöhte SPF, also das Plazieren des nichtlinearen Mediums in einem optischen Resonator, ist ein weit verbreitetes Verfahren, um Einzelphotonenquellen mit erhöhter Helligkeit und angepassten spektralen Eigenschaften zu konstruieren. Das Anpassen der spektralen Eigenschaften durch gezielte Auswahl der Resonatoreigenschaften ist besonders für hybride Quantentechnologienvon Bedeutung, welche darauf abzielen, unterschiedliche Quntensysteme so zu kombinieren, dass sich deren Vorteile ergänzen. Diese Arbeit stellt eine umfassende theoretische und experimentelle Analyse der dreifach resonanten SPF vor. Das aus der Literatur bekannte theoretische Modell wird diesbezüglich verbessert, dass der Einfluss sämtlicher Eigenschaften des Resonators auf die wichtigen experimentellen Größen (z.B. die Erzeugungsrate) gezielt ausgewertet werden kann. Dieses verbesserte und hoch genaue Modell stellt eine wichtige Grundlage für die Entwicklung und Optimierung neuartiger Photonenpaarquellen dar. Im experimentellen Teil dieser Arbeit wird der Aufbau und die Charakterisierung einer dreifach resonanten Photonenpaarquellen präsentiert. Die neu entwickelte digitale Regelelektronik sowie ein hochstabiler, schmalbandiger Monochromator welcher auf monolitischen, polarisationsunabhängigen Fabry-Pérot Resonatoren basiert, werden vorgestellt. Indem diese temperaturstabilisierten Resonatoren als Spetrumanalysator verwendet werden, wird zum ersten Mal die Frequenzkammstruktur des Spektrums der erzeugten Signal- und Idlerphotonen nachgewiesen. Des Weiteren wird der Einfluss der Pumpresonanz auf die Korrelationsfunktion und die Zweiphotoneninterferenz von Signal- und Idlerphotonen simuliert und vermessen. Abschließend werden Experimente aus dem Bereich der hybriden Quantennetzwerke präsentiert, in welchen Quantenfrequenzkonversion verwendet wird um die erzeugten Signalphotonen in das Telekommunikationsband zu transferieren. Dabei wird nachgewiesen, dass das temporale Wellenpaket durch die Konversion nicht beeinflusst wird und aufgezeigt, wie Quantennetzwerke von kommerziellen Telekommunikationstechnologien profitieren können.
The consistent generation of single photons with well-defined properties in all degrees of freedom is crucial for the development of photonic quantum technologies. Today, the most prominent sources of single photons are based on the process of spontaneous parametric down-conversion (SPDC) where a pump photon spontaneously decays into a pair of signal and idler photons inside a nonlinear medium. Cavity-enhanced SPDC, i.e., placing the nonlinear medium inside an optical cavity, is widely used to build photon-pair sources with increased brightness and tailored spectral properties. This spectral tailoring by selective adjustment of the cavity parameters is of particular importance for hybrid quantum technologies which seek to combine dissimilar quantum systems in a way that their advantages complement each other. This thesis provides a comprehensive theoretical and experimental analysis of triply-resonant cavity-enhanced SPDC. We improve the theoretical model found in the literature such that the influence of all resonator properties on the important experimental parameters (e.g., the generation rate) can be analyzed in detail. This convenient and highly accurate model of cavity-enhanced SPDC represents an important basis for the design and optimization of novel photonpair sources. The experimental part of this thesis presents the setup and characterization of a triply-resonant photon-pair source. We describe the digital control system used to operate this source over days without manual intervention, and we present a highly stable, narrow-linewidth monochromator based on cascaded, polarization-independent monolithic Fabry-Pérot cavities. Utilizing these temperature-stabilized cavities as a spectrum analyzer, we verify, for the first time, the frequency comb spectral structure of photons generated by cavity-enhanced SPDC. We further simulate and measure the impact of the pump resonance on the temporal wave-packets and the two-photon interference of signal and idler photons. Finally, we present a series of experiments in the context of hybrid quantum networks where we employ quantum frequency conversion (QFC) to transfer the generated signal photons into the telecommunication band. We verify the preservation of the temporal wave-packet upon QFC and highlight how quantum networks can benefit from advanced commercial telecommunication technologies.

Augmenting the level of integration for a lower cost and enhancing the performance of the optical devices have turned out to be the focus of many research studies in the last few decades. Many distinct approaches have been proposed in a significant number of researches in order to meet these demands. Optical planar waveguides stand as one of vital employed approach in many studies. Although, their low propagation loss, and low dispersion, they suffers from high power losses at sharp bends. For this reason, large radius of curvature is required in order to achieve high efficiency and compromise the high level of integration. For the purpose of this research, in this thesis different ways to improve the performance of optical microcavity ring resonators (MRRs) have been thoroughly investigated and new configurations have been proposed. The Multiresolution Time Domain (MRTD) technique was further developed and employed throughout this thesis as the main numerical modelling technique. The MRTD algorithm is used as a computer code. This code is developed and enhanced using self built Compaq Visual Fortran code. Creating the structure and Post-processing the obtained data is carried out using self built MATLAB code. The truncating layers used to surround the computational domain were Uniaxial Perfectly Matched Layers (UPML). The accuracy of this approach is demonstrated via the excellent agreement between the results obtained in literature using FDTD method and the results of MRTD. This thesis has focused on showing numerical efficiency of MRTD where the mesh size allowed or the total number of computed points is about half that used with FDTD. Furthermore, the MRR geometry parameters such as coupling gap size, microring radius of curvature, and waveguide width have been thoroughly studied in order to predict and optimise the device performance. This thesis also presents the model analysis results of a parallel-cascaded double-microcavity ring resonator (PDMRR). The analysis is mainly focus on the extraction of the resonant modes where the effect of different parameters of the structure on transmitted and coupled power is investigated. Also, accurate analysis of 2D coupled microcavity ring resonator based on slotted waveguides (SMRR) has been thoroughly carried out for the purpose of designing optical waveguide delay lines based on slotted ring resonator (SCROW). The SCROW presented in this thesis are newly designed to function according to the variation of the resonance coupling efficiency of a slotted ring resonators embedded between two parallel waveguides. The slot of the structures is filled with SiO2 and Air that cause the coupling efficiency to vary which in turn control both the group velocity and delay time of SCROW structures results from the changing the properties of the bent slotted waveguide modes which strongly depends on the slot’s position. Significant improvements on the quality factor and greater delay time have been achieved by introducing sub-wavelength-low-index slot into conventional waveguide.

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.

A photonic crystal (PC) structure for trapping a 50nm radius dielectric particle at a precise location on a silicon surface in an organic solvent environment has been designed and all of its key components have been fabricated. The high gradient of electric field intensity in a PC cavity mode, with wavelength ~ 1.5 microns, exerts a radiation force toward the center of the cavity. The Finite Difference Time Domain (FDTD) modeling method was used to design a symmetric (input/output) structure that consists of two grating couplers, two parabolic tapered waveguides, two single mode ridge waveguides, two photonic crystal waveguides and a single three-missing-hole (L3) PC cavity. The radiation force on the dielectric sphere was exactly calculated using FDTD simulations to evaluate the Maxwell Stress Tensor (MST) in the presence of the particle to be trapped. This result was compared to that obtained using the simpler dipole approximation, and good agreement between them was found. The fabrication of the structure was done by electron beam lithography and chlorine plasma etching. The Q factors for some of the fabricated samples were measured from the cavity enhanced photoluminescence emission of PbSe quantum dots deposited on the sample surface. A vertical Q factor of 3600 (in vacuum environment) was measured for an isolated cavity, which corresponds to a Qv of 3800 ( in solvent environment) in the FDTD simulations. Also, the Q, of the overall structure (cavity and the waveguides) was measure to be 1050 in vacuum, which from simulations is equivalent to a Q of 1800 in a solvent. These Q values and the resonant frequencies of the modes are in close, but not perfect agreement with the simulation results.

In this work, I detail the reconstruction and upgrades performed on the axial cavity ion trap in the ITCM group at the university of Sussex, and the measurement of the coupling of multiple ions to the cavity mode. This enables the optimal coupling between the ions and the cavity by adjusting the ions position in the radial and axial positions. This covers new ground in extending the optimal coupling beyond two ions which is of great importance for experiments with several ions in an optical cavity. The thesis outlines the background theory of light-matter interaction and cavity QED, before describing the physical ion trap hardware and its assembly. A description of the laser and cavity systems is provided, including techniques for locking both to stable references. A number of novel measurement techniques for measuring and maximising the stability of the ions and cavities are presented, including micromotion minimisation, spectroscopy, magnetic field compensation using the ground state Hanle effect, and Raman spectroscopy. These techniques enable the measurement of crucial parameters of the atomic transitions and the cavity. The work culminates in a description of the optimisation of the coupling between ion strings and the cavity first by adjusting the radial trap position by means of variable capacitors attached to RF electrodes, and then axially by means of adjusting the endcap potentials and therefore the spacing between ions to obtain the greatest localisation while still positioning the ions close to the antinodes of the cavity field.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 103-109).
Atomic interferometers have a resolution limit set by the projection noise in measurements on ensembles of uncorrelated atoms. To overcome this classical limit and extend precision measurements into the quantum regime, we need to generate complex entangled states of large atomic ensembles and measure the atomic states with high-quality detection. This thesis describes two experiments in this context. The first experiment demonstrates single-atom resolution and detection sensitivity more than 20 dB below the projection noise limit for hyperfine-state-selective measurements on mesoscopic ensembles containing 100 or more atoms. The measurement detects the atom-induced shift of the resonance frequency of an optical cavity containing the ensemble. The second experiment generates entangled states of 3,000 atoms with non-Gaussian spin distributions. Atoms interact with a weak cavity field, and the heralded detection of a single photon with certain polarization prepares the entangled states. By measuring the non-Gaussian spin distributions using the atom-cavity interaction, we construct a negative Wigner function, manifestly demonstrating that the atoms are entangled. We also show that nearly all of 3000 atoms are involved in the entanglement using an entanglement measure known as the entanglement depth.
by Hao Zhang.
Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 51).
It is currently well-known how to lock an optical cavity on resonance using the Pound- Drever-Hall technique. It is also possible to lock a cavity at a single detuned length using an amplitude modulated laser beam. However, there are many interesting applications, that would benefit from the use of a Universally Tunable Modulator (UTM), because it can create any ratio of amplitude to phase modulation. The unique transfer function of the UTM allows for cavity locking at any of the intermediate points between resonance and about half a linewidth of detuning. In this thesis, we construct such a UTM and verify experimentally that the modulator can indeed be used for continuous detuning of optical cavities.
by Emily Davis.
S.B.