The objective of this work is to develop a near-infrared laser device capable of emitting orbital angular momentum (OAM) light. The prototyped device must be suitable for compact, energy-saving optical communication applications. Integrated OAM lasers will revolutionize high-capacity data transmission over any telecommuni- cation network environment, as OAM light can be guided and transmitted through kilometers of optical fibers and propagated in free space and underwater. Several methods for generating OAM light employing various complex monolithic and hybrid integration methods have been demonstrated. In this work, microscale integrated spiral phase plates (SPPs) are chosen to convert the laser beam output into an OAM mode. The concept and design fundamentals of SPPs are discussed, followed by the SPP fabrication process and their implementation in a high-speed communication setup and then integration with a semiconductor laser. SPPs are fabricated by a novel direct laser writing that provides the possibility to rapidly prototype 3D photonic structures via a two-photon polymerization pro- cess. After fabrication, SPPs are used in a fine-tuned free-space optical experimental setup that requires high-precision intercomponent alignment to test the high-speed OAM communication system and analyze the quality of OAM modes, resulting in high-purity OAM signals at data rates up to 1.8 Gbit/s – limited by the avalanche photodetector (APD) frequency response. The fabricated 20-μm-diameter SPPs were the smallest reported in the literature to date for optical characterization. A proof-of-concept monolithic light-emitting array, as a highly integrated OAM laser source, is further proposed for telecommunications and other applications. SPP-integrated 940-nm vertical-cavity surface-emitting laser (VCSEL) array chips that are relatively low-cost, have a small footprint, and are manufacturable in high volumes are developed. SPPs with topological charge modulus values from 1 to 3 are fabricated on the VCSEL arrays, demonstrating OAM modal purities up to ∼65%. The experimentally evaluated data rates in the OAM setup showed consistently sta- ble links up to 2.0 Gbit/s with a bit error ratio of ∼ 1.6 × 10−8 (APD-limited). The challenges of SPP-laser integration are summarized, with the conclusion that the widespread adoption of OAM is limited by the availability of practical integrated solutions for OAM generation and detection.

Self-heating leads to temperature rise of laser diode and limits the output power, efficiency and modulation bandwidth due to increased loss and decreased differential gain. The main heat sources in laser diode during continuous wave operation are Joule heating and free carrier absorption loss. To control device self-heating, the epi structure needs to be designed with low electrical resistance and low absorption loss, while the heat flux must spread out of the device efficiently. This dissertation presents the control of self-heating of both edge emitting laser diodes and vertical cavity surface emitting lasers (VCSELs). For the 980nm high power edge emitting laser, asymmetric waveguide is used for low free carrier absorption loss. The waveguide and cladding materials are optimized for high injection efficiency. BeO heatsink is applied to spread the heat efficiently. Injection efficiency of 71% and internal loss of 0.3 cm-1 have been achieved. A total output power of 9.3 W is measured from 0.5cm long device at 14.5A injection current. To further reduce the internal loss, the development of 980nm quantum dot active region is studied. Threshold current density as low as 59A/cm2 is reached. For the VCSELs, oxide-free structure is used to solve the self-heating problem of oxide VCSELs. Removing the oxide layer and using AlAs in the DBRs leads to record low thermal resistance. Optimization of the DBRs leads to low resistance and low free carrier absorption. Power conversion efficiency higher than 50% is achieved. To further reduce device voltage and heat generation, the development of intracavity contacts devices is introduced.

In this dissertation, a novel semiconductor mode-locked oscillator which is an extension of eXtreme Chirped Pulse Amplification (XCPA) is investigated. An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity also based on a semiconductor gain is presented for generating more than 30ns frequency-swept pulses with more than 100pJ of pulse energy and 3.6ps compressed pulses directly from the oscillator. The XCPO shows the two distinct characteristics which are the scalability of the output energy and the mode-locked spectrum with respect to repetition rate. The laser cavity design allows for low repetition rate operation < 100MHz. The cavity significantly reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in a Semiconductor optical Amplifier (SOA). Secondly, a functional device, called a Grating Coupled Surface Emitting Laser (GCSEL) is investigated. For the first time, passive and hybrid mode-locking of a GCSEL is achieved by using saturable absorption in the passive section of GCSEL. To verify the present limitation of the GCSEL for passive and hybrid mode-locking, a dispersion matched cavity is explored. In addition, a Grating Coupled surface emitting Semiconductor Optical Amplifier (GCSOA) is also investigated to achieve high energy pulse. An energy extraction experiment for GCSOA using stretched pulses generated from the colliding pulse semiconductor mode-locked laser via a chirped fiber bragg grating, which exploits the XCPA advantages is also demonstrated. Finally, passive optical cavity amplification using an enhancement cavity is presented. In order to achieve the interferometric stability, the Hänsch-Couillaud Method is employed to stabilize the passive optical cavity. The astigmatism-free optical cavity employing an acousto-optic modulator (AOM) is designed and demonstrated. In the passive optical cavity, a 7.2 of amplification factor is achieved with a 50 KHz dumping rate.

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Frequency domain functional near infrared spectroscopy (FD-fNIRS) is a tissue optical measurement technique used to measure absolute haemoglobin concentrations in brain tissue. This work is intended to be the first step in the development of a wearable, low-cost FD-fNIRS device for neurofeedback applications. The system requirements were generated from a review of relevant literature. A simplified system architecturewas developed based on the various instrumentation methodologies proposed by various authors. The functional blocks of this system were prototyped and their performance was evaluated. The developed vertical-cavity surface-emitting laser (VCSEL) current source was found to have a span of 10uA which meets the design specifications. Challenges exist in optimally biasing silicon photomultiplier (SiPM), which is susceptible to optical and electronic noise sources.

Ce travail de thèse porte sur l'étude et le développement de composants à cavité verticale dans le contexte des réseaux courtes et moyennes distances multiplexés en longueur d'onde autour de 1,55 μm. Pour fabriquer de telles structures, nous avons tout d'abord développé des miroirs de Bragg diélectriques constitués de silicium amorphe et de nitrure de silicium. La différence d'indice (1,9) élevée entre ces matériaux a permis d'atteindre les hautes réflectivités (R = 99,5%) nécessaires au bon fonctionnement des VCSELs. A la suite du développement de ces miroirs, nous avons réalisé un VCSEL, reporté sur substrat silicium par collage métallique AuIn2, comprenant deux miroirs diélectriques et une zone active à base de puits quantiques InGaAs/InGaAsP. Les caractérisations et les études par simulation du VCSEL ont engendré plusieurs optimisations, et ont permis d'obtenir une émission laser continue sous pompage optique jusqu'à une température de 35°C. Ces résultats encourageants ont validé notre processus de fabrication ainsi que la fiabilité et la bonne qualité des miroirs de Bragg diélectriques. Pour s'affranchir du caractère instable de la polarisation de ces VCSELs nous avons proposé l'utilisation de nanostructures quantiques InAs/InP anisotropes se présentant sous forme de fils. L'étude de ces structures et leur mise en cavité ont démontré leur intérêt pour introduire une anisotropie du gain permettant d'assurer une polarisation stable. Nous avons développé un VCSEL accordable suivant une nouvelle approche. Le principe repose sur l'insertion d'une couche de phase électro-optique à base de nano-PDLC (Polymer Dispersed Liquid Crystal) dans la cavité du VCSEL. Le nano-PDLC, permet d'obtenir une variation isotrope de l'indice de réfraction sous l'action d'une tension. La réalisation d'un prototype pompé optiquement a permis une première démonstration de faisabilité d'un VCSEL accordable par voie électro-optique. Une accordabilité de 10-nm autour de 1.55-μm a été mesurée pour une tension de 170V, et le temps moyen de commutation sur la gamme spectrale est de 30 μs.

L’objectif de cette thèse est de développer un nouveau matériau photopolymère pouvant être microstructuré dans la gamme de longueur d'onde du proche infrarouge (NIR). Le but final de ce travail est de proposer des solutions innovantes pour l'intégration de micro-optique sur les VCSELs (Vertical-Cavity Surface-Emitting Laser), sources lumineuses miniaturisées utilisées dans de nombreuses applications en optique, photonique, capteurs ou biologie. Le verrou technologique principal a consisté à développer et étudier le photopolymère adéquat pour la microfabrication déclenchée par le VCSEL. La difficulté principale tient à la longueur d'onde de photopolymérisation qui est fixé par le VCSEL et qui a obligé à développer un système moléculaire nouveau pour une polymérisation radicalaire à 780 et 850 nm. Une part importante du travail a consisté à étudier les mécanismes photophysiques et photochimiques des matériaux permettant de proposer des systèmes efficaces, sur le plan de la photophysique, de la photochimie de photopolymérisation et également une approche originale a été développée pour appréhender de façon quantitative les phénomènes de diffusion du colorant dans la matrice polymère. Sur la base des systèmes moléculaires proposés, la démonstration de l'intégration de microlentilles sur VCSEL par ce procédé innovant a pu être démontré. Les VCSELs lentillés ont été caractérisés et des propriétés très intéressantes pour la focalisation ont été démontrées. / The objective of this thesis is to develop a new photopolymer material that can be microstructured in the wavelength range of near-infrared (NIR). The ultimate aim of this work is to propose innovative solutions for micro-optical integration on VCSELs (Vertical-Cavity Surface-Emitting Laser). These miniaturized light sources are used in many applications in optics, photonics, sensors or biology. The main technological challenge was to develop and explore a new photopolymer compatible with a microfabrication initiated by the VCSEL. The main difficulty was to develop a new molecular system for radical polymerization at 780 and 850 nm, which is the wavelength emitted by the VCSEL. An important part of the work consisted to study the photophysical and photochemical mechanisms of this photopolymer in order to provide efficient systems in terms of photophysics, photochemistry of the photopolymerization. An original approach was developed to quantitatively apprehend the phenomena dye diffusion in the polymer matrix. Based on the proposed molecular systems, demonstrating the integration of microlenses on VCSELs by this innovative process could be shown. The lensed VCSELs have been characterized and very interesting properties for focusing have been demonstrated.

The vertical-cavity surface-emitting laser or VCSEL is a special type of diode laser, which has established itself in optoelectronic applications asa low-cost, high-quality miniaturized light source. The development of VCSELs can be largely promoted with support from computer simulations. In this study, we have used such simulations, on one hand to understand and improve the VCSEL performance, and on the other hand to prepare for analyzing new device concepts such as transistor-VCSELs. This thesis starts with a background introduction to the principle idea of VCSELs and then states the significance of this simulation work.Then it briefly introduces the previously used simulation workbench Sentaurus and explains the mathematical approach and the computation methods of the finally chosen simulator PICS3D. The case study of a fabricated and characterized epitaxially regrown VCSEL is the major component of this work. First the device configuration is demonstrated with detailed discussion on several design features. Second the physical models of electrical, optical and thermal phenomena along with their key parameters are presented and so are the advanced models for the active region. The main results of simulation, including steady-state characteristics and small-signal modulation, show good agreement with the experimental results and reveal some imperfections of the device design and processing, such as the overestimated stability of the regrown junction and the variation of cavity length caused by over-etch. This work is also treated as an evaluation of the simulator PICS3D, and two problems are identified: one is the troublesome way to construct a 3D device by coupling several 2D layer structures together, requiring the mesh for each layer structure to be compatible; the other would be the tricky boundary setting for the adopted method, Effective Index Method (EIM), for the transverse field calculation when only a weak index guiding effect exits in the cavity. Finally, we summarize this work and suggest some tasks for further simulations.

In this study, the design and fabrication of a monolithic InP-based 1550-nm photonic-crystal surfaceemitting laser (PCSEL) is reported. The device is composed by an InGaAsP multi-quantum well (MQW) active layer and InP photonic crystal (PhC) formed by metal organic chemical vapour deposition (MOCVD). A theoretical study based mainly on the Fourier modal method using Stanford Stratified Structure Solver (S 4) and finite element analysis using COMSOL Multiphysics was carried out in order to optimize the emission at 1550 nm due to the two-dimensional band-edge resonance effect at the Γ point.The device design and modeling, materials testing (annealing and MOCVD regrowth), process optimization and the fabrication of light emitting diodes (LEDs) based on the same structure as the PCSELs (without the PhC) is reported. The fabricated devices show a low series resistance of 8.19 Ω and a turn-on voltage of 0.84 V. The average differential output power is 41 mW/A with an electroluminescent peak at 1511 nm. The full assembly of the final PCSEL devices is beyond the scope of the present thesis and corresponds to an ongoing project expected to be finalized within the coming year. However, detailed guidelines and fabrication instructions, including the manufacturing of an appropriate lithographic mask set, are provided. / Föreliggande examensarbete rapporterar designen och tillverkningsprocessen för en monolitisk InPbaserad 1550-nm så kallad Photonic-Crystal Surface-Emitting Laser (PCSEL). Komponenten bestå r av en aktiv kvantbrunnsstruktur i InGaAsP och ett fotoniskt-kristall (PhC)-lager i InP, bägge odlade med hjälp av metalorganisk gasfasepitaxi (MOCVD). En teoretisk studie baserad på Fourier-modalmetoden med användning av Stanford Stratified Structure Solver (S4) och finit elementanalys-metoden med med hjälp av av COMSOL Multiphysics utfördes för att optimera emissionen vid 1550 nm genom en tvådimensionell bandkantsresonanseffekt vid Γ punkten.Rapporten går igenom komponentdesign och modellering, materialtestning (värmebehandling och MOCVDåterväxt), processoptimering och tillverkning av lysdioder (LED) baserade på samma struktur som PCSELkomponenterna (men utan PhC-strukturering). De tillverkade lysdioderna uppvisar en låg serieresistans på 8.19 Ω och en framspänning på 0.84 V. Den genomsnittliga differentiella utgångseffekten är 41 mW/A med en luminescenstopp vid 1511 nm. Den slutliga tillverkningen av färdiga PCSEL-enheter ligger utanför ramen för detta examensarbete och motsvarar istället ett pågående projekt som förväntas bli slutfört inom det kommande året. Däremot ges detaljerade riktlinjer och tillverkningsinstruktioner, för vilket ett fotolitografiskt mask-set även tagits fram.

The aim of this project was to produce an integrate-able free space optical transceiver for Specks. Specks are tiny computing units that together can form a powerful network called a SpeckNet. The SpeckNet platform is developed by the SpeckNet consortium, which consists of five Scottish Universities and combines computer science, electrical engineering and digital signal processing groups. The principal goal of creating an optical transceiver was achieved by integrating in-house fabricated VCSELs (with lasing thresholds below 400 uA) and custom designed detectors on the SpeckNet platform. The transceiver has a very low power consumption (approximately 100 uW), which removes the need for synchronous communication through the SpeckNet thus making the network more efficient. I describe both static and dynamic beam control techniques. For static control, I used micro-lenses. I fabricated the lenses by greyscale electron beam lithography and integrated them directly on VCSEL arrays. I achieved a steering angle of 10 degrees with this design. I also looked at integrated gratings etched straight into a VCSEL and observed beam steering with an efficiency of 60% For dynamic control, I implemented a liquid crystal (LC) design. I built a LC cell with 30 individually controlled pixels, but I only achieved a steering angle of 1 degree. Furthermore, I investigated two different techniques for achieving beam steering by interference, using coupled VCSELs (a phased array approach). Firstly, using photonic crystals etched into the surface of the VCSEL, I built coupled laser cavities. Secondly, I designed and built bow-tie type VCSELs that were optically coupled but electrically isolated. These designs work by differential current injection causing an interference effect in the VCSELs far field. This technique is the first stepping stone towards realising a phased optical array. Finally, I considered signal detection. Using the same VCSEL material, I built a resonant-cavity detector. This detector had a better background rejection ratio than commercially available silicon devices.