Vertical-cavity lasers (VCLs) are of great interest as lightsources for fiber-optic communication systems. Such deviceshave a number of advantages over traditional in-plane laserdiodes, including low power consumption, efficient fibercoupling, on-chip testability, as well as potential low-costfabrication and packaging. To date, GaAs-based VCLs operatingat 850 nm are the technology of choice for short-distance,high-speed data transmission over multimode fiber. Forlong-distance communication networks, long-wavelength (LW) VCLsoperating in the 1.3 and 1.55-&#956m transmission windowsof standard singlemode fibers are desired. However, despiteconsiderable worldwide development efforts, the commercialbreakthrough of such devices has still to be achieved. This ismainly due to shortcomings of the intrinsic material propertiesof InP-based material systems, traditionally employed in LWlaser diodes. While LW quantum well (QW) active regions basedon InP are well established, efficient distributed Braggreflectors (DBRs) are better built up in the AlGaAs/GaAsmaterial system. Therefore, earlier work on LW VCLs has focusedon hybrid techniques such as bonding between InP-based QWs andAlGaAs/GaAs DBRs using waferfusion. More recently, however, themain interest in this field has shifted towards all-epitaxialGaAs-based devices employing novel 1.3-&#956m activematerials with strained GaInNAs QWs as one of the mostpromising candidates. The main focus of this thesis is on the characterization andanalysis of LW VCLs and building blocks thereof, based on bothInP and GaAs substrates. This includes a theoretical study on1.3-&#956m InGaAsP/InP multiple QW active regions, as wellas an experimental investigation of novel, highly strained1.2-&#956m InGaAs/GaAs single QWs. Two high-accuracyabsolute reflectance measurement setups were built for thecharacterization of various DBRs. Reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs/GaAs DBRs than previously anticipated.Near-room temperature operation of a single-fused1.55-&#956m VCL with an InP/InGaAsP bottom DBR wasobtained. A thermal analysis of this device structure clearlyindicated its limited capabilities in terms of high-temperatureoperation. As a result, further efforts were directed towardsall-epitaxial GaAs-based VCLs. Record-long emission wavelengthsto above 1260 nm were obtained from InGaAs VCLs based on anextensive gain–cavity detuning. These devices showed verypromising performance characteristics in terms of thresholdcurrent and light output power, indicating good potential forbeing a viable alternative to GaInNAs-based VCLs.

<p>Vertical-cavity lasers (VCLs) are of great interest as lightsources for fiber-optic communication systems. Such deviceshave a number of advantages over traditional in-plane laserdiodes, including low power consumption, efficient fibercoupling, on-chip testability, as well as potential low-costfabrication and packaging. To date, GaAs-based VCLs operatingat 850 nm are the technology of choice for short-distance,high-speed data transmission over multimode fiber. Forlong-distance communication networks, long-wavelength (LW) VCLsoperating in the 1.3 and 1.55-&#956m transmission windowsof standard singlemode fibers are desired. However, despiteconsiderable worldwide development efforts, the commercialbreakthrough of such devices has still to be achieved. This ismainly due to shortcomings of the intrinsic material propertiesof InP-based material systems, traditionally employed in LWlaser diodes. While LW quantum well (QW) active regions basedon InP are well established, efficient distributed Braggreflectors (DBRs) are better built up in the AlGaAs/GaAsmaterial system. Therefore, earlier work on LW VCLs has focusedon hybrid techniques such as bonding between InP-based QWs andAlGaAs/GaAs DBRs using waferfusion. More recently, however, themain interest in this field has shifted towards all-epitaxialGaAs-based devices employing novel 1.3-&#956m activematerials with strained GaInNAs QWs as one of the mostpromising candidates.</p><p>The main focus of this thesis is on the characterization andanalysis of LW VCLs and building blocks thereof, based on bothInP and GaAs substrates. This includes a theoretical study on1.3-&#956m InGaAsP/InP multiple QW active regions, as wellas an experimental investigation of novel, highly strained1.2-&#956m InGaAs/GaAs single QWs. Two high-accuracyabsolute reflectance measurement setups were built for thecharacterization of various DBRs. Reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs/GaAs DBRs than previously anticipated.Near-room temperature operation of a single-fused1.55-&#956m VCL with an InP/InGaAsP bottom DBR wasobtained. A thermal analysis of this device structure clearlyindicated its limited capabilities in terms of high-temperatureoperation. As a result, further efforts were directed towardsall-epitaxial GaAs-based VCLs. Record-long emission wavelengthsto above 1260 nm were obtained from InGaAs VCLs based on anextensive gain–cavity detuning. These devices showed verypromising performance characteristics in terms of thresholdcurrent and light output power, indicating good potential forbeing a viable alternative to GaInNAs-based VCLs.</p>

Submitted by Maike Costa (maiksebas@gmail.com) on 2016-03-16T11:48:24Z No. of bitstreams: 1 arquivototal.pdf: 3030423 bytes, checksum: 121b1c06c249f60685f65714d1f26c0e (MD5) / Made available in DSpace on 2016-03-16T11:48:24Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3030423 bytes, checksum: 121b1c06c249f60685f65714d1f26c0e (MD5) Previous issue date: 2014-08-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Here we present a systematic analysis of the dynamics in the frequency of semiconductor lasers in systems under orthogonal optical feedback or external injection, with and without frequency discriminator. We measure the parameter of proportionality between the change of frequency and the power level of the orthogonally polarized light injected into the cavity. We perform an application of this injection technique for frequency sweep that allows varying the frequency in a range of tens of GHz and apply it in an experience of spectroscopy. This technique allows frequency sweep without changing the main laser power, which is fed by another, control laser, whose wavelength is di erent from the principal. We have analyzed the dynamics of the semiconductor laser frequency subject to orthogonal optical feedback and injection in a con guration where a di raction grating works as a spectral lter. Using a di raction grating as frequency discriminator in these systems, we observe a dynamical behavior in the laser emission frequency. / Apresentamos neste trabalho uma an alise sistem atica em rela c~ao a din^amica em frequ^encia de lasers semicondutores em sistemas sob realimenta c~ao e inje c~ao otica ortogonal com e sem discriminador de frequ^encia. Medimos o par^ametro de proporcionalidade entre o deslocamento em frequ^encia e a varia c~ao da pot^encia injetada ortogonalmente na cavidade. Montamos alguns sistemas com a nalidade de varrer a frequ^encia de emiss~ao de um laser semicondutor, explorando con gura c~oes sob inje c~ao otica ortogonal. Entre elas, zemos uma aplica c~ao de uma t ecnica que permite obter uma varia c~ao de dezenas GHz em uma experi^encia de espectroscopia, sem variar a pot^encia de sa da do laser principal o qual e alimentado por outro laser de controle com comprimento de onda diferente do principal. Analisamos a dinamica em frequencia do laser semicondutor sujeito a realimenta cao e inje cao otica ortogonal com uma grade de difra cao empregada como ltro espectral. Usando uma grade de difra cao como discriminador de frequencia nesses sistemas, observamos um comportamento semelhante a uma oscila cao na frequencia.

This master´s thesis deals with a solution of the driving circuits of semiconductor laser. In the beginning of the thesis there is an analysis of semiconductor lasers and its characteristics. Then the principle of laser diodes and its excitation is described. This thesis is focused on semiconductor laser excitation through the use of direct and modulating current. Several circuits are described, designed and simulated. The best resulting circuit is realized and measured in the laboratory.

Thesis deals with the optimization of process parameters during laser welding of aluminum alloys 5000 series. The theoretical part describes the types of lasers and their applications in industry, further discusses the properties of aluminum alloys, laser welding theory and principles of monitoring and diagnostics of laser process. In the experimental part the samples were welded using a semiconductor laser. For those samples were evaluated mechanical properties, welded defects and structure depending on the process parameters. Using the photodetector was observed stability of laser process by sensing the plasma plume. The link between stability and the formation of structural defects in the weld joint was observed from the measurement results.

La photo-isomérisation de l’azopolymère cause des mouvements de masse permettant d'inscrire des figures d'interférences à la surface de films minces. Les films sont répliqués sur un substrat en PDMS transparente t étirable. Il forme des réseaux de phase. Les figures de diffraction décrivent les surfaces, elles sont utilisées pour modéliser numériquement les réseaux, quelles que soient les contraintes.Le projet WOLF vise à fabriquer des nano lasers blancs à colorants organiques. Un montage complexe de caractérisation est développé. Le module d’excitation permet d’illuminer les nanotubes un à un. Le pompage tente de maximiser l’émission laser d’un unique nano objet. La collection du signal repose pricipalement sur l’utilisation d’une fibre optique ouvrant la porte de la microscopie confocale. La spectroscopie associée au montage révèle la formation de cavités au sein des nano bâtonnets organiques. Malgré la faible puissance du signal, les modes sont étudiés,mettant en évidence des nano-cavités. Les nano-objets sont parfois étudiés dans des liquide. La micro-fluidique est développée au laboratoire. Sans salle blanche une méthode photolithographique est développée à bas coûts. Les puces nouvellement créées sont testées dans le mélange de deux fluides et lors de la caractérisation de nanoparticules en suspension par leur mouvement Brownien. Cette thèse à permis de mettre en place les outils d’observation de nano-objets uniques / Azopolymer photo-isomerization causes matter motion. This phenomena is responsible for the inscription of the interference pattern on surface of thin films. The films are replicated by pouring PDMS on it. PDMS is a transparent and stretchable polymer. The diffraction pattern of these gratings describes the surface. These informations are used to numerically simulate the surface irrespective of the mechanical constraints.The WOLF project try to synthetize white lightorganic nanolasers. For that purpose, a complex setup has been realised. The excitation part of the setup illuminates a single nano-laser or a few. The pump source is designed to optimise the amplified emission of the nanolasers. The collection of the signal is based on an optical fiber.This fibre has given us the chance to use confocal microscopy. Spectroscopy combined with our setup show the existence of nanocavities among nanotubes. In spite of the low signal power, the emitting modes are studied and show the cavity effect of these lasers. In another context, nano-objets are sometimes studied in solution. For that reason, a new experiment has been setup, namely, microfluidic. Without the use of a clean room, a low cost photolithograpic method is developped. The microfluidic chips are tested during the mixing of to liquids and during the obsevation of the brownian motion of particules. This PhD thesis has given the tools needed for the characterization of single nano-objects.

Complex optical pulse shapes are typically generated from ultrashort laser pulses by manipulating the optical spectrum of the input pulses. This generates complex but periodic time-domain waveforms. Optical Arbitrary Waveform Generation (OAWG) builds on the techniques of ultrashort pulse-shaping, with the goal of making non-periodic, truly arbitrary optical waveforms. Some applications of OAWG are coherently controlling chemical reactions on a femtosecond time scale, improving the performance of LADAR systems, high-capacity optical telecommunications and ultra wideband signals processing. In this work, an array of Vertical Cavity Surface Emitting Lasers (VCSELs) are used as modulators, by injection-locking each VCSEL to an individual combline from an optical frequency comb source. Injection-locking ensures that the VCSELs' emission is phase coherent with the input combline, and modulating its current modulates mainly the output optical phase. The multi-GHz modulation bandwidth of VCSELs updates the output optical pulse shape on a pulse-to-pulse time scale, which is an important step towards true OAWG. In comparison, it is about a million times faster than the liquid-crystal modulator arrays typically used for pulse shaping! Novel components and subsystems of Optical Arbitrary Waveform Generation (OAWG) are developed and demonstrated in this work. They include: 1. Modulators An array of VCSELs is packaged and characterized for use as a modulator for rapid?update pulse?shaping at GHz rates. The amplitude and phase modulation characteristics of an injection-locked VCSEL are simultaneously measured at GHz modulation rates. 2. Optical Frequency Comb Sources An actively mode-locked semiconductor laser was assembled, with a 12.5 GHz repetition rate, ~ 200 individually resolvable comblines directly out of the laser, and high frequency stability. In addition, optical frequency comb sources are generated by modulation of a single frequency laser. 3. High-resolution optical spectral demultiplexers The demultiplexers are implemented using bulk optics, and are used to spatially resolve individual optical comblines onto the modulator array. 4. Optical waveform measurement techniques Several techniques are used to measure generated waveforms, especially for spectral phase measurements, including multi-heterodyne phase retrieval. In addition, an architecture for discriminating between ultrashort encoded optical pulses with record high sensitivity is demonstrated.

1.55-µm high-speed modelocked semiconductor lasers are theoretically and experimentally studied for various coherent photonic system applications. The modelocked semiconductor lasers (MSLs) are designed with high-speed (>5 GHz) external cavity configurations utilizing monolithic two-section curved semiconductor optical amplifiers. By exploiting the saturable absorber section of the monolithic device, passive or hybrid mode-locking techniques are used to generate short optical pulses with broadband optical frequency combs. Laser frequency stability is improved by applying the Pound-Drever-Hall (PDH) frequency stabilization technique to the MSLs. The improved laser performance after the frequency stabilization (a frequency drifting of less than 350 MHz), is extensively studied with respect to the laser linewidth (~ 3 MHz), the relative intensity noise (RIN) (< -150 dB/Hz), as well as the modal RIN (~ 3 dB reduction). MSL to MSL, and tunable laser to MSL synchronization is demonstrated by using a dual-mode injection technique and a modulation sideband injection technique, respectively. Dynamic locking behavior and locking bandwidth are experimentally and theoretically studied. Stable laser synchronization between two MSLs is demonstrated with an injection seed power on the order of a few microwatt. Several coherent heterodyne detections based on the synchronized MSL systems are demonstrated for applications in microwave photonic links and ultra-dense wavelength division multiplexing (UD-WDM) system. In addition, efficient coherent homodyne balanced receivers based on synchronized MSLs are developed and demonstrated for a spectrally phase-encoded optical CDMA (SPE-OCDMA) system.

Advantage of the single QD active layer is its potential for very low threshold current density, which in turn can produce low internal optical loss. The low threshold current density and low internal loss thus enable a significant increase in laser diode cavity length. Because of the importance of the threshold current density in heatsinking, future technology of broad-area monolithic laser diodes can be implemented. The dissertation describes the development and the unique characteristics of single QD active layer laser with long cavity. The data are presented on single layer QD laser diodes that reach threshold current densities values of 11.7 A/cm2 in a p-up mounted 2 cm long cavity and as low as 10 A/cm2, with CW output power of 2 W in a p-down mounted 1.6 cm long cavity. The 8.8 A/cm2 in a p-down mounted 2 cm long cavity is reported. To our knowledge the value 8.8 A/cm2 is the lowest threshold current density ever reported for a room temperature laser diode. These single layer QD laser diodes reach an internal loss of ~0.25 cm-1, which is also the lowest ever reported for a room temperature laser diode. These unique characteristics of single layer QD and laser diode size are potentially promising for the monolithic mode-locked laser because of relatively high peak power with a low repetition rate that is on the order of a few GHz, which can be the novel device for external clocking in the optical interconnect applications. In this dissertation, the stable optical pulse train in a 40 µm wide stripe with a repetition rate of 3.75 GHz with 1.1 cm cavity length through the passive mode-locked onto the monolithic two-section device fabricated from this single layer QD laser is observed.

<p>Semiconductor laser diode has been a popular research topic for longer than half a century and plays a crucial role in optical communication systems. The work in this thesis focuses on the development of the semiconductor laser diode with rapid-evolving nanotechnologies: by incorporating specific semiconductor or metal structures in the nanometer scale into the laser cavity, several key advantages are achieved.</p> <p>One category of the nano-materials is semiconductor quantum dots (QD). QD laser is a promising product by providing three-dimensional confinement to the injected electrons and holes. However, in order to realize the single-longitudinal-mode operation, which is critical to optical communications in purpose of reducing the dispersion and partition noise, the Fabry-Perot (FP) QD laser still needs further development to suppress the gain-broadening effects; otherwise the mode-selective structure must be adopted, such as the distributed feedback (DFB) cavity. In this thesis, the QD FP laser and QD DFB laser are both researched by advanced modelling techniques and the work is summarized as follows.</p> <p>1) For the QD FP laser, a comprehensive rate-equation model has been applied for simulation, with the emphasis on describing the interplay of inhomogeneous and homogeneous gain-broadening effects. According to the laser-behaviour simulations, it is found that for each given inhomogeneous broadening, the optimum homogeneous broadening can be obtained for the single longitudinal-mode selectivity. Based on the optimal gain-broadening parameters, the single-mode QD FP laser is designed and analysed. The quantitative conditions for the performance feasibility are examined with respect to the gain-broadening parameters.</p> <p>2) A one-dimensional (1D) standing wave model is developed for the QD DFB laser. This model can provide more information for the laser operation and better describe the dynamic behaviour compared with the rate-equation model. Based on it, the statistic operation and output spectrum of a typical QD DFB laser are simulated; and then the dynamic properties of the laser are analysed.</p> <p>The other category is the metal nano-structure, including the metal nano-particle and the metal nano-strip Bragg grating. The related work is summarized as follows.</p> <p>1) The optical properties of a single metal nano-particle with different size, composition and shape are researched by Mie theory, with respect to the localized surface plasmon polariton (LSPP) effect. It shows that both the resonance wavelength and Q-factor can be tuned in a large scale by proper methods.</p> <p>2) A novel metal nano-strip distributed Bragg grating (DBR) laser is proposed and investigated theoretically. Firstly the metal nano-strip Bragg grating is simulated by the couple-mode theory and the mode-matching method. It shows that the coupling constant and reflection spectrum can be tuned to meet different requirements when varying the grating parameters. Then for the designed metal-grating DBR laser, the rate-equation simulation results show that it works under the single-mode operation for a broad range of the design parameters.<br /> <strong></strong></p> / Doctor of Philosophy (PhD)