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In developing a compact electro-optic sampling system for industrial use it is desirable to utilize a semiconductor laser diode as the light source since these devices are compact and economical. This thesis investigates several novel laser driver techniques for generating extremely short optical gain switched pulses from a semiconductor laser diode. These techniques include a novel bias control scheme in which the bias to a semiconductor laser diode, that is being driven with a step recovery diode pulse generator circuit, is turned on and off in order to switch the gain switched optical pulses on and off as desired. The second technique involves a mono-cycle scheme that allows a step recovery diode pulse generator circuit, which is customarily driven by a fixed frequency oscillator, to be driven by a mono-cycle pulse train of variable repetition rate. An equivalent circuit model of a laser diode based on the mono-mode rate equations is discussed and implemented in SPICE for the purpose of studying the interaction of the laser driver circuit electronics and the laser diode. The laser diode equivalent circuit is benchmarked against analytical solutions of the rate equations. A qualitative agreement between the measurements of the laser diode optical and terminal voltage responses and the SPICE simulations of the laser diode equivalent circuit model are demonstrated. / Thesis / Master of Engineering (ME)

In this thesis, a red green and blue (RGB) laser diode driver (LDD) is designed, assembled and tested, which can work as a standalone device or an internal component fully controlled by a laser projector. In particular, the thesis explores a multi-channel RGB LDD for a retrofitted laser projector, targeting projectors for home, business and education. If laser diodes (LDs) with the same color are connected in series, a higher forward voltage is required, making most commercial LDDs unsuitable for this application due to their insufficient compliance voltages. If the connections of all the LDs are in parallel, issues on size and cost arise since many LDs are used in this case. Another problem to use the commercial LDDs for RGB laser projection is that there are no proper communication interfaces to link the LDDs to the laser projector. In order to solve these problems by taking advantage of all the features of iC-HTG, an integrated circuit with automatic current control functionality, both the hardware circuits and the software for an eight-channel LDD are designed. Experimental results show that all the RGB channels can achieve compliance voltage of 23 V within the required working current range, which can drive up to 5 blue, 4 green or 10 red LDs in series in each single channel. It is confirmed experimentally that the designed LDD can fulfill the requirements on driving current (i.e. 1% accuracy and 1% stability). The protection functions of the developed LDD are also explored and verified experimentally. It can detect the open laser connection before the LDD channels are enabled. Fast over-current protection can be achieved within 1.5 µs. Circuit interfaces and protocols of the communications enable the multi-channel RGB LDD to work as a standalone device or an internal component of the laser projector. / Thesis / Master of Applied Science (MASc)

En chirurgie plastique, le succès des lambeaux libres et des replantations dépend largement de la qualité des microanastomoses vasculaires. Ce travail complète les bases scientifiques de la technique de microanastomoses assistées par laser diode 1950 nm par la mise au point d’une méthode standardisée et l’étude post-opératoire du débit sanguin sur des séries animales. Il pose les jalons des premières séries cliniques. Dans une première série animale (S1), 30 anastomoses terminoterminales carotidiennes et 30 anastomoses jugulaires sont effectuées par la technique laser diode 1950 nm chez des rats Wistar. Les paramètres lasers suivants sont utilisés: taille du spot 400 µm, temps 1s, puissance délivrée de 100 mW à 150 mW (carotides) et de 90 mW à 140 mW (veines jugulaires). Elles sont comparées à J0 puis après 1, 4 et 12 semaines postopératoires, à un groupe contrôle de 30 anastomoses artérielles et de 30 anastomoses veineuses dans les mêmes proportions réalisées à l’aide de la technique conventionnelle par fils. Deux autres séries animales S2 et S3 sont ensuite entreprises à l’aide des paramètres lasers mis en évidence dans l’étude S1. Une série S2 regroupant vingt microanastomoses terminoterminales carotidiennes de rats Wistar est réalisée par la technique laser (n=10, P=120mW, spot 400 μm, durée du spot 1s, 5 spots par paroi, fluence 95 J/cm²) et la technique conventionnelle par fils 10/0 (groupe contrôle, n=10). Pour les deux groupes, la carotide controlatérale non opérée sert de référence pour le calcul du débit sanguin par IRM de flux : Une séquence de positionnement, une séquence anatomique, une séquence angiographique et une séquence de flux sont réalisées un jour après l’opération puis après une, quatre et huit semaines. Une série S3 regroupant vingt microanastomoses terminoterminales jugulaires de rats Wistar est réalisée par la technique laser (n=10, P=110mW, spot 400 μm, durée du spot 1s, 4 spots par paroi, fluence 90 J/cm²) et la technique conventionnelle (groupe contrôle, n=10). De même la jugulaire controlatérale sert de référence dans les diverses séquences IRM. Au total, 40 actes microchirurgicaux comprenant 38 lambeaux libres et 2 replantations digitales sont réalisés à l’aide du laser diode 1950 nm. Les microanastomoses artérielles sont terminoterminales dans 36 cas et terminolatérales pour 4 autres. Les microanastomoses veineuses sont toutes terminoterminales. Les microanastomoses sont réalisées par un laser diode 1,95 µm après mise en place de 2-5 points de rapprochement. Les paramètres suivants sont utilisés : taille du spot 400µm, puissance 125mW, 4 à 8 spots sur chaque face, temps d’application (0,7-2s) suivant le diamètre des vaisseaux : la fluence varie de 70 à 200 J/cm². Les études du débit sanguin par les nouvelles techniques d’IRM de flux avec les paramètres maintenant standardisés mettent en évidence l’excellente perméabilité des anastomoses laser sur un modèle animal. Le taux de succès de cette première grande série clinique apparait excellent lorsque comparé à celui des grandes séries de la littérature. Les innovations technologiques devraient conduire à une utilisation plus large de cet outil au bloc opératoire. / In the field of plastic surgery, the most important factor for successful free flap transfer and replantations is a well executed vascular microanastomosis. The aim of these studies is to complement the scientific basis of the 1950 nm diode laser assisted microanastomosis (LAMA) by standardising the technique and studying the postoperative blood flow in animal series. This work introduces the first clinical series. In the first animal series (S1), 30 end-to-end microanastomoses of the carotidis and 30 end-to-end microanastomoses of the external jugular were performed with a 1950 nm diode LAMA technique in Wistar rats. The following laser parameters were used: spot size=400µm, spot duration=1s, Power varying between 100 to 150 mW for arterial microanastomoses and between 90 to 140 mW for venous microanastomoses. They were compared at D0 and at 1, 4 and 12 weeks with 30 conventional arterial microanastomoses and 30 conventional venous microanastomoses.Two other animal series (S2 and S3) were performed using the standardised parameters of the initial studies. In the S2 series, LAMA was performed on a group of 10 carotidis on Wistar rats. Two 10/0 stay sutures and a standard laser tissue welding technique (P=120mW, spot size=400 μm, t=1s, 5 spots for each wall, fluence=95 J/cm²) were used (LAMA group). They were compared with a group of 10 conventional arterial anastomosis (CSMA group). A MRI-positioning sequence (Magnetic Resonance Imaging), an anatomical sequence, an angiographic sequence and a flow sequence were performed 1 day after operation and then after 1, 4 and 8 weeks. Similarly, the series S3 included 20 microanastomoses of the external jugular performed with LAMA (n=10, P=110mW, spot size=400 μm, spot duration= 1s, 4 spots for each wall, fluence 90 J/cm²) or the conventional technique (n=10). For the two groups, contralateral non-operated external jugular were used as control.In total, 40 clinical procedures, including 38 free flaps and 2 finger replantations have been performed with the LAMA technique. End-to-end arterial microanastomoses were performed in 36 cases and end-to-side in 4 cases. All venous microanastomoses were performed end-to-end. LAMA was performed with a 1950 nm diode laser after placement of 2-5 stitches. The following laser parameters were used: spot size=400 μm, spot duration=0.7-2s, 4-8 spots for each wall, power=125 mW, fluence=70-200 J/cm². The animal series S1 demonstrates excellent bloodless patency at fluences ranging from 90 to 100 J/cm² (Power between 110-130mW) for arterial LAMA, and between 80 and 95 J/cm² (Power between 100-120mW) for venous LAMA. The flow-MRI further demonstrates that 1950 nm diode laser-assisted microanastomoses performed with our standardised parameters is a consistent, reliable and reproducible technique. The success rate of the clinical series appears promising. Technical innovation will most likely lead to greater ease of use of the laser handpiece in the operating room.

GaAs-based nitride is found to be sensitive to growth conditions and ex-situ annealing processes. The critical thickness is almost one order thicker than the theoretical prediction by force balance model. The growth process could be sped up by the nitrogen incorporation itself, while the nitrogen incorporation could be affected by Beryllium doping. The incorporated nitrogen atoms partly occupy substitutional sites for Arsenic. Some nitrogen atoms are at interstitial sites. Annealing could drastically increase the optical quality of GaAs-based nitrides. As an end of this paper, some preliminary results of InGaAsN/GaAsN/AlGaAs laser diodes are also presented. / Singapore-MIT Alliance (SMA)

GaAs-based InGaAsN/GaAs quantum well is found to be very sensitive to growth conditions and ex-situ annealing processes. Annealing could drastically increase the optical quality of GaAs-based InGaAsN/GaAs quantum well. As an end of this paper, some results on InGaAsN/GaAsN/AlGaAs laser diodes are also presented. / Singapore-MIT Alliance (SMA)

A simulation scheme is proposed to analyze the effects of elliptic-conical lensed fiber parameters on the coupling efficiency between a 980nm laser diode and single-mode fiber(SMF). The variation of fiber tip shapes with different melting zone volumes was investigated in this thesis. The heat-transfer finite element model in MARC package is employed to simulate the temperature distribution during the melting process. The free convection is considered in predicting the melting zone. Due to the surface tension, a round tip may be solidificated. In this study an elliptical tip lens is expected to improve the coupling efficiency. The microlens shapes with different radius of curvature is simulated with the software of Surface Evolver. The coupling efficiency of 980nm laser source and different elliptic-conical lensed fiber is calculated by utilizing the ZEMAX optical analysis software. The Taguchi method is employed to evaluate the effect of tip shape parameters on the coupling efficiency. The optimal elliptic-conical lensed fiber parameters has also been proposed. The efficiency loss introduced from the misalignments in laser module packaging has also been discussed in this study.

This thesis details an innovative laser diode packaging method to improve the accuracy of the laser locator by modifying the location method and packaging process. This method features its simplicity in the packaging process, the capability in tweaking the rotary angle of the laser diode, and an effective solution to the scaling effect as well as the enhancement in yield. The gripping micro-unit,consisting of a refined micro gripper together with the piezoelectric actuator and coupler,integrates a self-designed rotary adjustment and release unit to enable the micro-rectangle unit such as a laser unit to fine tune the location of the object. It works with the linear stage, platform, and image acquisition system to become the core of the proposed location system. A series of experiments are designed to verify the functionality. A precise linear stage without the rotary axis is applied to control the locator,adjust the location of the laser, and minimize the error from equipment. The result demonstrates its feasibility.