Dissertationen zum Thema „Amplified spontaneous emission (ASE)“

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2002.
Includes bibliographical references.
This thesis details efforts in using cadmium selenide (CdSe) nanocrystallites (NCs) as a novel lasing media. We begin with the synthesis of polymer/NC composites, in which the NCs are stabilized within a long-chain methacrylate polymer. This chapter serves to highlight the processing flexibility afforded by the NCs as well as some of the salient linear optical properties of NCs. The wide range of colors that are accessible using these NCs and the ability to excite them simultaneously are emphasized and provide an incentive to use them as a gain medium. Chapter 3 summarizes work done in developing a NC-based gain media and lists the stringent requirements for observing amplified spontaneous emission (ASE), a signature manifestation of gain. Then the synthesis of a robust NCs-titania, sol-gel matrix is described which satisfies these requirements. We exploit the stability and processability of these matrices to study the optical properties of the NC gain media.
(cont.) True temperature independent gain and ASE thresholds are shown to present, thus confirming early theoretical predictions of strongly-confined, zero dimensional gain media. Chapter 4 considers the incorporation of such structures with a suitable feedback structure and presents evidence for the first NC based distributed feedback laser. Room-temperature operation of such devices is shown to follow naturally from the unique gain features of the constituent NCs. Chapter 5 emphasizes the flexibility inherent in using these NCs as a gain media. We combine the processability of NC-titania films with soft-lithographic techniques to construct more complicated lasing structures. Simultaneous, mixed-colored lasing is shown to be possible, which might allow for new devices that operate within a wide gain window.
by Vikram C. Sundar.
Ph.D.

Surface plasmon-polaritons are optical surface waves formed through the interaction of photons with free electrons at the surface of metals. They offer interesting applications in a broad range of scientific fields such as physics, chemistry, biology, and material science. However, many of such applications face limitations imposed by the high propagation losses of these waves at visible and near-infrared wavelengths, which result mainly from power dissipation in the metal. In principle, the propagation losses of surface plasmon-polaritons can be compensated through optical amplification. The objective of this thesis is to provide deeper insights on the physics of surface plasmon-polariton amplification and spontaneous emission in surface plasmon-polariton amplifiers through theoretical and experimental vehicles applied (but not necessarily restricted) to a particular plasmonic mode termed long-range surface plasmon-polariton. On the theoretical side, the objective is approached by developing a realistic theoretical model to describe the small-signal amplification of surface plasmon-polaritons in planar structures incorporating dipolar gain media such as organic dye molecules, rare-earth ions, and quantum dots. This model takes into account the inhomogeneous gain distribution formed near the metal surface due to a non-uniform excitation of dipoles and due to a position-dependent excited-state dipole lifetime that results from near-field interactions between the excited dipoles and the metal. Also, a theoretical model to describe the amplified spontaneous emission of surface plasmon-polaritons supported by planar metallic structures is developed. This model takes into account the different energy decay channels into which an exited dipole located in the vicinity of the metal can relax. The validity of this model is confirmed through experimentation. On the experimental side, the objective is approached by providing a direct experimental demonstration of complete loss compensation in a plasmonic waveguide. The experiments are conducted using the long-range surface plasmon-polariton supported by a symmetric thin gold waveguide incorporating optically pumped organic dye molecules in solution as the gain medium. Also, an experimental study of spontaneous emission in a long-range surface plasmon-polariton amplifier is presented. It is shown that this amplifier benefits from a low spontaneous emission into the amplified mode, which leads to an optical amplifier with low noise characteristics. The experimental setup and techniques are explained in detail.

On trouve sur la plateforme de thèses en ligne Pastel le résumé suivant : Le développement du laser a ouvert la voix à l'exploration de nouveaux domaines scientifiques et industriels. Les impulsions laser à haute intensité sont un outil unique pour les études d'interaction lumière/matière et leurs applications. Mais elles sont générées par des systèmes laser reposant sur l'utilisation de milieux à gain en verre pompés par des lampes flashes et sont donc intrinsèquement limitées en termes de cadence et d'efficacité. Le développement, au cours de ces dernières années, des lasers semi-conducteurs a attiré l'attention sur une nouvelle classe de lasers, les « laser solides pompés par diodes » (DPSSL). Ils possèdent une grande efficacité et sont des candidats de choix pour les systèmes compacts à haute puissance moyenne requis pour des applications industrielles, mais aussi en tant que sources de pompe à haute puissance pour des lasers ultra-intenses. Les travaux décrits dans cette thèse s'inscrivent dans le cadre du système laser Lucia (1 kilowatt de puissance moyenne), actuellement en construction au «Laboratoire d'Utilisation des Intenses lasers» (LULI) à l'Ecole Polytechnique, France. La génération d'impulsions laser de durée sub-10 nanosecondes avec des énergies allant jusqu'à 100 joules et des taux de répétition de 10 hertz est principalement limitée par l'émission spontanée amplifiée (ASE) et les effets thermiques. L'étude de ces limitations est le thème central de ce travail. Leur impact est discuté dans le cadre d'un premier jalon énergétique fixé vers 10 joules. Le système laser mis au point est présenté en détails depuis l'oscillateur jusqu'à la fin de la chaine d'amplification. Une discussion complète de l'impact de l'ASE et des effets thermiques est complétée par des vérifications expérimentales. Les modèles de simulation informatique développés sont validés puis utilisés pour prédire les performances du système laser qui, lors d'une première activation, à atteint un niveau d'énergie de 7 joules en régime mono-coup et de 6,6 joules pour un taux de répétition de 2 hertz. Les limitations actuelles sont discutées ainsi que les approches envisagées pour des développements futurs
On trouve sur la plateforme de thèses en ligne Pastel le résumé suivant : The development of the laser triggered the birth of numerous fields in both scientific and industrial domains. High intensity laser pulses are a unique tool for light/matter interaction studies and applications. However, current flash-pumped glass-based systems are inherently limited in repetition-rate and efficiency. Development within recent years in the field of semiconductor lasers and gain media drew special attention to a new class of lasers, the so-called Diode Pumped Solid State Laser (DPSSL). DPSSLs are highly efficient lasers and are candidates of choice for compact, high average-power systems required for industrial applications but also as high-power pump sources for ultra-high intense lasers. The work described in this thesis takes place in the context of the 1 kilowatt average-power DPSSL program Lucia, currently under construction at the ‘Laboratoire d'Utilisation des Laser Intenses' (LULI) at the Ecole Polytechnique, France. Generation of sub-10 nanosecond long pulses with energies of up to 100 joules at repetition rates of 10 hertz are mainly limited by Amplified Spontaneous Emission (ASE) and thermal effects. These limitations are the central themes of this work. Their impact is discussed within the context of a first Lucia milestone, set around 10 joules. The developed laser system is shown in detail from the oscillator level to the end of the amplification line. A comprehensive discussion of the impact of ASE and thermal effects is completed by related experimental benchmarks. The validated models are used to predict the performances of the laser system, finally resulting in a first activation of the laser system at an energy level of 7 joules in a single-shot regime and 6. 6 joules at repetition rates up to 2 hertz. Limitations and further scaling approaches are discussed, followed by an outlook for the further development

In this work, we study the nonlinear propagation of light in liquid crystals (LCs) and the optical gain provided by LCs when they are polymer- or dye-doped.We will focus on nematic LCs, which are characterized by a mean orientation (also called director) of the elongated molecules and by a subsequent birefringence. After a general introduction on LCs, we focus on the nonlinear propagation of light in nematic LCs, and in particular the soliton-like propagation (nematicon). Indeed, if the light injected in the cell is intense enough, it can create a waveguide that counteracts the diffraction of the light. The light then propagates with an almost constant (or periodic) transverse profile.Our contribution to the subject starts with the numerical modeling of the thermal noise that characterizes the nematic LCs and the study of spatial instabilities of the soliton propagation caused by that noise. In Ch.3 we show that, by explicitly implementing the spatial correlation of the director in the LC thermal noise, it is possible to reproduce some of the features that characterize the LC response, such as the speckle generation or the fluctuating trajectory of the spatial optical soliton in LCs. Indeed, when the nematicon diameter is of the same order ofmagnitude as or smaller than the refractive index perturbations caused by the thermal noise, the nematicon starts to fluctuate in space. These fluctuations are not present when the noise is not correlated, indicating that the long-range interactions in LCs are crucial to explain the fluctuations. The model also allows us to introduce the propagation losses experienced by the nematicon without the use of an ad-hoc term. The simulations are in agreement with the experimental results. This method could also help the modeling of complex nonlinear phenomena in LCs that rely on noise, such as modulation instabilities or filamentation.Then, the optical gain is included in the LCs by dissolving photoluminescent polymers or dyes in it. In particular, we show that a particular polymer, the polyfuorene, when dissolved in nematic LCs, creates an intricate supramolecular pattern composed by homogeneous LC-rich regions surrounded by polymer-rich boundaries. The study of these structures through an ultra-fast spectroscopic technique (the pump-probe technique) and confocal microscopy reveals that the boundaries are composed by ordered and isolated chains of polymers. This particular morphology allows the observation of the optical gain from an oxidized unit of the polymeric chain (keto defects). This signal is usually covered by the absorption caused by the chain aggregation in solid state samples, while in LCs it is clearly visible. The optical gain from the keto defects appears also to be polarized orthogonal to the LC director, which is also the orientation of most of the boundaries. When a dye, one of the pyrromethenes, is dissolved in the LCs, the sample appears to be homogeneous. The optical gain from the dye ispolarized along the LC director and it shows an important spectral blue-shift (10 nm) passing from a polarization parallel to orthogonal to the LC director. The amplified spontaneous emission (ASE) shows the same shift when changing the direction of the sample excitation.When the ASE and the nematicon are generated in the same sample, it is possible to study the interaction between the two. In particular, the waveguide induced by the soliton can be used to guide another signal at another wavelength. We show that the nematicon can collect the ASE generated in the same device and guide it to the same fiber used to inject the nematicon in the LC cell. The extraction of the ASE from the device increases almost one order of magnitude when the soliton is present. However, due to the nematicon spatial fluctuations in LCs, an optimal nematicon power has to be found. Indeed, by increasing the soliton power, the light guiding is improved since the refractive index contrast of the nematicon-induced waveguide is increased. However, very high soliton powers have to be avoided, since the power-dependent soliton fluctuations prevent an optimal collection of the light. The nematicon is also found to increase the spectral purity and the polarization degree of the guided signal.Another LC system is studied, the chiral nematic LCs. In this system, the molecules are disposed following an helicoidal distribution. Due to their optical anisotropy and the periodic distribution, the system presents an optical band-gap. If the LC is also dye-doped, the combination of optical band-gap and gain generates laser emission. We are interested in a fast (sub-ms) reorientation of the helix, with the aim of studying the effect of this reorientation on the laser emission. The first step is the alignment of the LC helix (without the dye) with its axis parallel to the glass plates that constitute the cell, which is difficult to obtain with a high optical quality. For this reason, an innovative method is developed to align LCs through directional solvent evaporation. The solvent-induced method allows us to obtain particularly homogeneous textures, with a contrast ratio between the bright and the dark states that is a factor of 4 greater than that obtained with traditional methods. The LC samples based on solvent-induced alignment are then stabilized via two-photon photo-polymerization. This technique allows us to polymerize small regions of the device while the rest of the sample can be washed out in a solvent bath. When an achiral material is used to refill the device, it assumes a chiral alignment in the polymerized regions and an achiral nematic distribution in the rest. The first characterization of the laser emission is then presented in the last Chapter, with the aim of achieving sub-ms electrical tuning in future works.In this work a wide range of aspects have been investigated, leading to the realization of novel techniques for the fabrication of liquid crystal devices, the demonstration of novel phenomena for light amplification in liquid crystals and the experimental verification of new numerical modeling tools for light propagation in liquid crystals. The three key aspects of the work are nonlinear propagation, optical amplification and electrical response of different LC-based mixtures. Although the first few chapters deal with some of the aspects separately, in the last chapter these aspects are combined, revealing interesting new phenomena and pointing out a number of new aspects that could be part of future work. The results in this work have potential applications in fast tunable lasers, optical communication systems and lab-on-chip components.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

Le développement du laser a ouvert la voix à l'exploration de nouveaux domaines scientifiques et industriels. Les impulsions laser à haute intensité sont un outil unique pour les études d'interaction lumière/matière et leurs applications. Mais elles sont générées par des systèmes laser reposant sur l'utilisation de milieux à gain en verre pompés par des lampes flashes et sont donc intrinsèquement limitées en termes de cadence et d'efficacité. Le développement, au cours de ces dernières années, des lasers semi-conducteurs a attiré l'attention sur une nouvelle classe de lasers, les « laser solides pompés par diodes » (DPSSL). Ils possèdent une grande efficacité et sont des candidats de choix pour les systèmes compacts à haute puissance moyenne requis pour des applications industrielles, mais aussi en tant que sources de pompe à haute puissance pour des lasers ultra-intenses. Les travaux décrits dans cette thèse s'inscrivent dans le cadre du système laser Lucia (1 kilowatt de puissance moyenne), actuellement en construction au «Laboratoire d'Utilisation des Intenses lasers» (LULI) à l'Ecole Polytechnique, France. La génération d'impulsions laser de durée sub-10 nanosecondes avec des énergies allant jusqu'à 100 joules et des taux de répétition de 10 hertz est principalement limitée par l'émission spontanée amplifiée (ASE) et les effets thermiques. L'étude de ces limitations est le thème central de ce travail. Leur impact est discuté dans le cadre d'un premier jalon énergétique fixé vers 10 joules. Le système laser mis au point est présenté en détails depuis l'oscillateur jusqu'à la fin de la chaine d'amplification. Une discussion complète de l'impact de l'ASE et des effets thermiques est complétée par des vérifications expérimentales. Les modèles de simulation informatique développés sont validés puis utilisés pour prédire les performances du système laser qui, lors d'une première activation, à atteint un niveau d'énergie de 7 joules en régime mono-coup et de 6,6 joules pour un taux de répétition de 2 hertz. Les limitations actuelles sont discutées ainsi que les approches envisagées pour des développements futurs.

The aim of this thesis is the preparation and characterization of model components for organic thin-film solid-state lasers. The theses focuses on comparing different methods of determining the threshold energy, which leads to an amplified spontaneous emission of the studied derivative diketo-pyrrolo-pyrrole. The theoretical part is devoted to a summary of knowledge on the interaction of light with matter and lasers with a focus on organic solid-state lasers. The practical part is focused on preparation of model components for organic solid-state lasers, modification of apparatus for their characterization, comparison of evaluation methods for determining the threshold energy and study of the effect of different conditions of components preparation.

V oblasti nových nízkomolekulárních organických materiálů patří deriváty difenyldiketopyrrolopyrrolu (DPP), používané dříve jako barviva a pigmenty, k objektům vysokého zájmu pro jejich potencionální aplikace v moderních technologiích. Studium jejich optických vlastností ve vztahu k jejich chemické struktuře umožní využití jejich vysokého potenciálu ve vývoji pokročilých inteligentních materiálů. Přehled chemických a fyzikálních vlastností DPP derivátů a zhodnocení současného stavu řešené problematiky jsou uvedeny v teoretické části této práce. Tři hlavní procesy studované v této práci jsou: klasická absorpce a emise, dvoufotonová absorpce (TPA) a zesílená spontánní emise (ASE). Výsledky budou diskutovány a shrnuty ve dvou částech: první zahrnuje první dvě výše zmíněné oblasti a druhá problematiku zesílené spontánní emise.

L'interaction matière-lumière dans des milieux opaques donne lieu à des phénomènes collectifs nécessitant le couplage d'équations atomiques et d'une équation de transport. Le piégeage de la lumière dans un système atomique multi-niveaux sera étudié expérimentalement dans une vapeur froide et théoriquement avec le couplage des paramètres atomiques à une équation de diffusion. Ensuite, du gain sera ajouté dans ce nuage d'atomes froids multi niveaux. Nous montrerons théoriquement qu'un seuil laser existe dans ce type de système combinant gain et diffusion et qu'expérimentalement le gain Raman associé à de la diffusion sur une raie résonante a permis l'observation d'un laser aléatoire à atomes froids. La validité de l'équation de diffusion nécessite une non redistribution en fréquence et donc des atomes suffisamment froids pour s'affranchir de l'effet Doppler. Finalement nous étudierons le transport dans une vapeur atomique chaude (20°C-180°C) opaque. L'effet Doppler invalide la loi de Beer-Lambert pour la longueur des pas des photons entre des diffusions qui suivent alors une statistique de Lévy.

碩士
國立清華大學
光電工程研究所
101
Deoxyribonucleic acid (DNA) has a unique helix structure and exhibits interesting material properties, which have found many applications in biochemistry and nanotechnology. Recently, DNA biopolymer has also been implemented in optoelectronics. As DNA is rich in nature and is an environmental-friendly material, research in DNA photonics has drawn much attention. Most research efforts have emphasized on manipulation of DNA host and dyes. However, the surfactant used to modify DNA also plays in important role in system performance. In this work, we use aromatic surfactants vinylbenzyltrimethylammonium chloride and benzyltrimethylammonium chloride to modify DNA doped withrhodamine 6G dye, and study the amplified spontaneous emission.The experiment results are compared to the commonly used lipid surfactant (hexadecyltrimethylammonium chloride)-based DNA biopolymer. It is found that the DNA biopolymer modified by aromatic surfactants exhibitslower threshold. The possiblemechanism is discussed and this property may be promising for the applications of organic dye laser. The second part of this thesis present the synthesis of an IR dye. We use 4,8-dibromobenzo-[1,2-c;4,5-c’]bis[1,2,5]thiadiazole as the core structure and synthesize a new organic infrared dye. The synthesized infrared dye emits 1245 nm lightwhen excited at805 nm and 1210 nm. This dye may bepotential to be employed in optical communication.

碩士
國立中山大學
光電工程研究所
89
In this thesis, we investigate the single-pumped L-band (1570-1610 nm) amplified spontaneous emission fiber source by employing 1480 nm single pumping configuration. Using the 1480 nm-pumped laser, we chose the adequate fiber length and adjusted the pump power to optimize the characteristics of the ASE source. The characteristics are experimentally examined and compared in terms of the output power, mean wavelength, spectral linewidth, and pumping conversion efficiency in four configurations with single-pass forward (SPF), single-pass backward (SPB), double-pass forward (DPF), and double-pass backward (DPB) structures. Among them, the DPF configuration with low mirror reflectance of 8% is the better one to be an L-band ASE fiber source with output power of 13.8 mW, mean wavelength of 1585.7 nm, spectral linewidth of 40.9 nm and pumping efficiency of 13.8%.

Low-cost, high-speed quantum random number generators (QRNGs) are imperative to develop in order to have a widespread application in areas ranging from cryptography and stochastic simulations to banking and internet. Amplified spontaneous emission (ASE) based QRNGs offer a great advantage in this pursuit. However, most ASE-based QRNGs use costlier and more complex components compared to their speed. In this work, we discuss two QRNG schemes where we alleviate this problem. We also develop a comprehensive theoretical study to understand then in detail. In our ASE-ASE beating based QRNG, random numbers are generated by performing balanced detection of two independent ASE signals. Our second QRNG scheme is based on mixing a laser and an ASE of similar power and measuring the beat noise using a balanced detector. Our theoretical analysis shows that introducing the laser improves the standard deviation of the raw data, which can result a higher minimum entropy in the later QRNG. This fact is corroborated by the experiments as well. Our first experimental implementation of ASE based QRNGs use a balanced detector of 1.6GHz bandwidth and clock in bit generation rates of 7.44Gbps (ASE-ASE) and 7.9898Gbps (ASE-Laser) using an 8-bit ADC. Then we reduce the bandwidth of the detector to 100MHz since most available ADCs with higher bit resolution have bandwidths of few hundreds of MHz. In this case also, we achieve half a Gbps speeds for our QRNGs using the aforementioned 8-bit ADC - 546.03Mbps (ASE-ASE), 507.94Mbps (ASE-Laser). Furthermore, we develop two multiplexed QRNG schemes to double the speed of the QRNGs. Our experimental implementations of them show that multiplexing can achieve 1Gbps speed with a very slow detector (bandwidth of 100MHz). All the random numbers are verified using industry-standard statistical tests - NIST and DIEHARD - and obtain satisfactory results. Moreover, they can be easily integrated on a chip for commercial use.

碩士
國立中山大學
光電工程研究所
90
In this thesis, we investigate the double-pumped L-band (1570-1610 nm) amplified spontaneous emission (ASE) fiber source by employing the 1480 nm bi-directional pumping configuration. First, we chose the adequate fiber length, and then adjusted the pump power to optimize the characteristics of the ASE source in different reflectance. The characteristics are experimentally examined and compared in terms of output power, mean wavelength, linewidth, flatness and conversion efficiency in three configurations with forward-forward (FF), forward-backward (FB) and backward-forward (BF) structures. In our experiments, FB configuration with EDF length of 93 m and reflectance of 30 ％ is the best one to be an L-band ASE fiber source with an output power(POUT) of 71.8 mW, a mean wavelength(λm) of 1584.3 nm, a linewidth(Δλ) of 41.6 nm, the flatness(ΔP) of 1 dB, and the pump conversion efficiency(η) of 42.2 ％.

Most of today’s optical networks, use reconfigurable optical add/drop multiplexers (ROADMs) as nodes. To become more dynamic and flexible, these nodes architectures evolved over the years. The colorless, directionless and contentionless functionalities are now standard, however, current architectures have poor scalability due to limitations on wavelength selective switches dimensions. Hence, due to constant increase in data traffic, current architectures might become a bottleneck to manufacture future large-scale ROADMs. In this work, the hardware cost and in-band crosstalk generation inside different large-scale ROADM architectures, is compared with conventional architectures. Moreover, an analysis of optical filtering, amplified spontaneous emission (ASE) noise and in-band crosstalk impact in the performance of an optical network, with nodes based on the most promising large-scale architecture, the interconnected A architecture, is performed. This performance is assessed through Monte-Carlo simulation with 16 point quadrature amplitude modulation with polarization-division multiplexing (PDM-16QAM) and PDM- 32QAM signals with 200 Gb/s and 250 Gb/s, respectively. Two architectures are considered for the interconnected A express structure, Broadcast and Select (B&S) and Route and Select (R&S). For the add/drop structure, a bank-based structure is considered. The maximum number of cascaded ROADMs, considering all the studied impairments, is 5 and 7 nodes for a 32 GBaud 16QAM signal, respectively, for B&S and R&S architectures. A 32QAM signal reaches 3 and 4 nodes, respectively, for B&S and R&S architectures. The main penalty in transmission is the ASE noise generated by optical amplifiers throughout the network, having the in-band crosstalk and optical filtering penalties a lower contribution.
A maioria das redes óticas são atualmente compostas por multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs, em inglês) nos nós, cuja arquitetura tem evoluído para se tornarem mais dinâmicos e flexíveis. As funcionalidades colorless, directionless e contentionless estão hoje normalizadas, no entanto, as arquiteturas atuais tornam-se pouco escaláveis para ROADMs de elevada dimensão, devido a limitações nos comutadores seletivos no comprimento-de-onda. Neste trabalho, a comparação entre os custos associados e a geração de crosstalk homódino em diferentes arquiteturas propostas para ROADMs de elevada dimensão e as arquitecturas tradicionais é efetuada. É também analisado o impacto da filtragem ótica, ruído de emissão espontânea amplificada (ASE, em inglês) e crosstalk homódino no desempenho de uma rede com nós baseados na arquitetura denominada "Interconnected A". A avaliação é feita através de simulação Monte-Carlo com sinais multiplexados por divisão na polarização e modulação de amplitude em quadratura, PDM-16QAM e PDM-32QAM a 200 Gb/s e 250 Gb/s, respetivamente. Foram consideradas duas configurações para os ROADMs estudados, Broadcast and Select e Route and Select (B&S e R&S, em inglês) e uma estrutura de inserção/extração denominada "bank-based". Quando considerados todos os efeitos, o alcance máximo da rede é de 4 e 7 nós para um sinal 16QAM, respetivamente, para configurações B&S e R&S. Para um sinal 32QAM, é de 3 e 4 nós, respetivamente, para configurações B&S e R&S. A principal penalidade na transmissão deve-se ao ruído ASE gerado nos amplificadores óticos ao longo da rede, tendo a penalidade devido ao crosstalk homódino e a filtragem ótica uma menor contribuição.

True-green wavelength emitters at 555 nm are currently dominated by III-V semiconductor-based inorganic materials. Nevertheless, due to high lattice- and thermal-mismatch, the overall power efficiency in this range tends to decline for high current density showing the so-called efficiency droop in the green region (“green gap”). In order to fill the research green gap, this thesis examines the low cost solution-processability of organometal halide perovskites, which presents a unique opportunity for light-emitting devices in the green-yellow region owing to their superior photophysic properties such as high photoluminescence quantum efficiency, small capture cross section of defect states as well as optical bandgap tunability across the visible light regime. Specifically, the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material were investigated using low-temperature, power-dependent (77 K), temperature-dependent photoluminescence (PL) measurements. We noted three recombination peaks at 77K, one of which originated from bulk defect states, and other two from surface defect states. The latter were identified as bound-excitonic (BE) radiative transitions related to particle size inhomogeneity or grain size induced surface state in the sample. Both transitions led to PL spectra broadening as a result of concurrent blue- and red-shifts of these excitonic peaks. The blue-shift is most likely due to the Burstein-Moss (band filling) effect. Interestingly, the red-shift of the second excitonic peak becomes pronounced with increasing temperature leading to a true-green wavelength of 553 nm for CH3NH3PbBr3. On the other hand, red-shifted peak originates from the strong absorption in the second excitonic peak owed to the high density of surface states and carrier filling of these states due to the excitation from the first excitonic recombination. We also achieved amplified spontaneous emission around excitation threshold energy of 350 μJ/cm2 when optically pumped using 475 nm laser pulses, thus supporting the assignment of carrier absorption and re-excitation mentioned above. This dissertation work led to the following article: D. Priante, I. Dursun, M. S. Alias, D. Shi, V. A. Melnikov, T. K. Ng, O. F. Mohammed, O. M. Bakr, and B. S. Ooi, "The recombination mechanisms leading to amplified spontaneous emission at the true-green wavelength in CH3NH3PbBr3 perovskites", Applied Physics Letters, 106, 081902, 2015. DOI: 10.1063/1.4913463

博士
國立臺灣科技大學
電子工程系
87
This thesis presents simple methods to extract system parameters and to analyze the erbium-doped fiber amplifier (EDFA) for the applications of fibers to communications and sensor systems. First, a simple method to determine, in a quantitative way, the degree of the influence of ASE is presented. Through the study of the effect of ASE on EDFA gains, it is and found that the ASE can be neglected when the nearly-no-ASE factor (NNAF) is large enough. It is proposed as an ASE indicator. Furthermore, a formula for computing the error of output power due to the neglecting of ASE in calculation is also presented. 　　Second, an EDFA parameter extraction method is proposed of obtaining simultaneously the pump absorption cross section, signal emission cross section and signal absorption cross section, the fluorescence lifetime of metastable level, the Er-ion concentration, and the pump and signal absorption coefficients. Based upon the measured dc and ac gains, these parameters can be obtained simultaneously without cutting the fibers or disassembling the EDFA system. They can be computed very easily by the use of our close-form expressions without complicated numerical method. The calculations are in good agree with experimental data. 　　Then, the close-form expressions of nonlinear Fourier transfer functions are presented for the analyses of distortions and cross modulations in EDFA systems. Based upon Volterra series and the time-dependent perturbation theory, the transfer functions have been obtained after taking account of both the EDFA nonlinearity and chirping effect. Their applications to an AM-SCM and an eight-channel wavelength-division-multiplexed (WDM) systems are demonstrated. 　　Moreover, the performance of the EDFA system in thermodynamically and electromagnetically harsher environments have been studied. It is found that the SMF-to-EDFA connection suffers the most from temperature effect when the fiber length is not long. The gain variation amounts to -0.023dB/ . Besides, the eletromagnetic interference effect on the photodiode and its light power and wavelength dependences are discussed.

碩士
國立臺灣大學
光電工程學研究所
95
Based on white-light interferometry, optical low coherence reflectometry (OLCR) has emerged as a promising technique for obtaining high-axial-resolution measurements for fiber optic, integrated optic, and thin film structures. Recent OLCR modules incorporating superluminescent diodes have achieved high resolution of 10-15 um. However, for applications to biological and medical diagnostics, higher imaging resolution is required. We have successfully developed a novel broadband light source, on the basis of a double-clad Cr+4:YAG crystal fiber, generating broadband ASE centered at 1.38 um with a bandwidth of 265 nm by an 1064-nm Yb fiber pump laser. In the research, the light source of the OLCR system was implemented with the Cr:YAG fiber. The point spread function (PSF) of the system was obtained by placing a gold-plated mirror as a sample, and a 5.1-um axial resolution in free space was experimentally demonstrated. Simulation was performed to analyze the relationship between the lineshape of the light source to the corresponding PSF. Finally we prepared a 3-um thick TiO2 coated sample for depth scanning, and successfully distinguished the adjacent refractive index interfaces.

碩士
國立清華大學
電機工程研究所
81
The effect of accumulated optical-amplifier-induced noise on the pulse propagation in a dispersive single-mode optical fiber is theoretically investigated . Due to such effect , the pulse is weakened at the central part and quite long dispersive tails are produced , resulting in significant loss of signal power in a time slot of a bit . This situation becomes more severe as the bandwidth of the noise spectrum increases . Also , the performance degradation of a long-haul IM/DD system with cascaded in-line optical amplifiers due to the effect of cumulative amplified-spontaneous-emission noise is demonstrated.

O renovado interesse nas comunicações ópticas com modulação de fase diferencial DPSK (differential phase-shift keying) provém do facto de esta superar o formato convencional de modulação de intensidade, OOK (on-off keying) em certos aspectos, tais como, sensibilidade do receptor, robustez às limitações da transmissão e tolerância às flutuações da potência do sinal. O crescimento exponencial do tráfego de dados e as vantagens do DPSK levam à necessidade da sua utilização no contexto das redes ópticas, sendo uma das principais limitações físicas das redes ópticas, o crosstalk. O crosstalk homódino incoerente, devido ao isolamento imperfeito dos componentes ópticos utilizados nos nós da rede óptica, tem sido identificado como uma das maiores limitações existentes no nível físico das redes ópticas. Esta dissertação apresenta um estudo do impacto do ruído de emissão espontânea amplificada, gerado pela amplificação óptica do sinal, e do crosstalk no desempenho de um sistema de comunicação óptico DPSK com detecção directa e assumindo um receptor balanceado. O desempenho do sistema é avaliado usando uma simulação estocástica baseada no método de Monte Carlo e comparado com o desempenho obtido a partir de formulações analíticas. Diferentes combinações de filtros ópticos e eléctricos são considerados no receptor óptico DPSK. A influência de imperfeições do receptor óptico DPSK no desempenho é também estudada. Investiga-se também a influência do nível de potência do sinal de crosstalk, o atraso entre o sinal original e o sinal de crosstalk e diferentes sequências de bits no sinal de crosstalk DPSK no desempenho do sistema de comunicação óptico.
The renewed interest in optical communications on the differential phase-shift keying (DPSK) modulation format comes from the fact that it outperforms the conventional format on-off keying (OOK), in such aspects, such as receiver sensitivity, robustness to transmission impairments and tolerance to signal power fluctuations. The exponential growth of data traffic and the DPSK advantages over OOK lead to its use on the optical networks environment, where physical limitations, such as crosstalk, may impair significantly the network performance. In-band crosstalk, due to the imperfect isolation of optical components used in the optical network nodes, has been identified as one of the most severe physical layer limitation in optical transparent network. This dissertation proposes to study the impact of amplified spontaneous emission noise, generated by the signal optical amplification, and of in-band crosstalk in the performance of an optical DPSK communication system with direct detection using a balanced receiver. A stochastic simulation based on the Monte Carlo method is used to evaluate the system performance and comparisons with the results obtained using theoretical works are also performed. Different combinations of optical and electrical filters at the optical DPSK receiver are considered. The influence of DPSK receiver imperfections on the system performance is also studied. The influence of the crosstalk level, the delay between the original and the crosstalk signal and different bits sequence on the DPSK crosstalk signal on the system performance is also investigated.

Current transport optical networks are approaching its capacity limits, mainly due to new applications and services that require a huge amount of resources. To increase the network capacity, multiband solutions, that exploit the unused capacity of actual fibers, in particular the L-band, are being currently commercially explored. However, this strategy is assumed as a short to medium term solution. A long-term solution is to use spatial-division multiplexing (SDM) in the optical domain, which leads to the concept of SDM-based optical networks. In this work, different SDM switching architectures (spatial, spatial-wavelength, wavelength, fractional space-full wavelength) are studied and compared in terms of cost per bit, power consumption and flexibility. For the switching architectures with spatial and spatial-wavelength granularities (the architectures that have superior performance), the most relevant physical impairments (PLIs) (amplifiers noise, non-linear interference, narrowing penalty due to filtering and in-band crosstalk) are analytically studied, for a SDM reconfigurable optical add-drop multiplexer (ROADM) cascade. Furthermore, a Monte Carlo simulation is used to assess more rigorously the PLIs effects on the performance of SDM ROADMs, with spatial-wavelength switching architecture, in cascade. The main difference, regarding PLIs, between the single spatial channel ROADM architecture and the SDM ROADM architectures is the enhanced effect of in-band crosstalk. For cascaded ROADMs with 16 directions, 19 spatial channels and filtering isolation of -25 dB, the in-band crosstalk can lead to a 2 dB optical signal-to-noise ratio penalty. Due to this penalty, the signal crosses less 9 ROADMs than in a single spatial channel ROADM architecture.
As redes óticas de transporte atuais estão a aproximar-se do seu limite de capacidade devido às novas aplicações e serviços que requerem uma maior quantidade de recursos de rede. Uma possível solução de curto a médio prazo para a falta de recursos é o uso de múltiplas bandas da fibra, para além da banda C. Uma solução a longo prazo será o uso de multiplexagem com divisão no espaço (SDM) no domínio óptico. Neste trabalho são estudados, o custo por bit, consumo de energia e flexibilidade, das diferentes arquiteturas SDM (no espaço, no espaço e comprimento de onda, no comprimento de onda, fracionada no espaço e completa no comprimento de onda). Para as arquiteturas com granularidades no espaço e no espaço e comprimento de onda estuda-se analiticamente os efeitos das principais limitações do nível físico (PLIs) (ruído dos amplificadores, interferência não-linear, penalidade de filtragem e diafonia homódina), para cascatas de multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs). Usa-se uma simulação Monte Carlo para calcular mais rigorosamente os efeitos das PLIs na arquitetura com granularidade no espaço e comprimento de onda. A principal diferença, em termos de PLIs, entre uma rede SDM e uma rede com um único canal espacial é o efeito da diafonia homódina. Para uma rede com 16 direções, 19 canais espaciais e isolamento dos filtros de -25 dB, a diafonia homódina causa uma penalidade na relação sinal-ruído óptica de 2 dB e o sinal atravessa menos 9 ROADMs que numa rede com apenas um canal espacial.