This thesis outlines two advancements in the field of limited data absorption tomography. First, a novel reconstruction algorithm integrating the use of level set methods is presented that incorporates the additional a priori knowledge of a distinct interface between the species of interest and co-flow. The added a priori further reduces the ill-posedness of the system to produce a final concentration distribution that explains the laser absorption measurements and is qualitatively consistent with advection/diffusion transport. The algorithm is demonstrated by solving a simulated laser tomography experiment on a turbulent methane plume, and is compared with the current state-of-the-art reconstruction algorithm. Given the limited number of attenuated measurements, accurate reconstructions are also highly dependent on the locations sampled by the measurement array. This thesis displays how the mathematical properties of the coefficient matrix, A, formed by the locations of the lasers, are related to the information content of the attenuation data using a Tikhonov reconstruction framework. This formulation, in turn, becomes a basis for a beam arrangement design algorithm that minimizes the reliance on additional assumed information about the concentration distribution. Using genetic algorithms, beam arrangements can be optimized for a given application by incorporating physical constraints of the beam locations. The algorithm is demonstrated by optimizing unconstrained and constrained arrangements of light sources and detectors. Simulated experiments are performed to validate the optimality of the arrangements.

The excellent pseudoelasticity, shape memory and biocompatibility of Nitinol have made it a leading candidate for applications in various fields, including aerospace, micro-electronics and medical devices. Challenges associated with laser processing need to be resolved before its full potential in practical applications can be realized. The current thesis details the effects of pulsed Nd:YAG laser processing on Ni-rich (Ni-49.2. at.% Ti) Nitinol. First, the mechanical, pseudoelastic and cyclic loading properties for varying process parameters have been compared to those of the base metal. Process parameters were shown to greatly influence the mechanical performance. This was due to local yielding occurring within the processed material during tensile straining. In addition, laser processed samples showed higher permanent residual strain and exhibited a slightly higher efficiency for energy storage during the initial 5 cycles compared to base material. Fracture surfaces of base material revealed ductile dimpled surfaces while welded specimens exhibited both brittle (low peak power) and ductile (high peak power) failure modes. DSC analyses conducted on the processed metal revealed additional high temperature transformation peaks. These peaks were attributed to the local phase conversion induced by laser processing. Further corroboration was made with room temperature XRD analysis, showing only austenite in the base metal and added martensite peaks in the melted metal. Temperature controlled TEM observations confirmed high temperature transformation peaks to be associated with processed metal. Furthermore, TEM analysis aided in identifying the submicron second phase particles observed in fracture surfaces as Ti2Ni. Finally, local phase conversion was correlated to change in local chemical composition. Preferential vaporization of nickel was determined to cause the change in Ni/Ti ratio. This in turn explained the altered mechanical performance and presence of the Ti-rich intermetallic (Ti2Ni). Consequently, a novel method using a high power density energy source to alter transformation temperature of shape memory alloys (SMA’s) was developed. Results were used to successfully demonstrate a novel technology that can embed additional memories in Nitinol and other SMA’s. Possessing the ability to control local transformation temperatures and as a result the shape memory effect of SMA’s promises to enhance their functionality while enabling new applications to be realized.

The goal of the thesis is Ring Laser Integrated Taper-directional Coupler Using Deep Etching to Fabricate Total Internal Reflection Mirrors. In order to total internal reflection, we make deep etching for the total reflection mirror. We use the tapered waveguide coupler, if unidirectional traveling-wave oscillation can be achieved, spatial hole burning effects seen in DFB laser can be avoided. In this paper, two types of ring laser structures are fabricated and discussed, in which (1) 90 degrees total reflection mirrors and (2) circular retro-mirrors. In fabrication process, we get smooth waveguide and highly perpendicularity waveguide by Self-Alignement wet etch method. In order to reduce bending loss and waveguide loss, we make deep etching for the total reflection mirror and circular retro-mirrors.

Photonic crystal is the periodic structure with different refractive index media. Its photonic-bandgap characteristics could be used to make the photonic crystal lasers. Because of the difficulty of fabrication, the development of three-dimensional photonic crystal is far behind the two-dimensional and one-dimensional photonic crystals. Blue phase liquid crystals are formed by periodic lattice structure with double-twisted cylinder, therefore it is a three-dimensional self-assembled photonic crystal. The objective in this study is to fabricate the three-dimensional photonic crystal blue phase liquid crystal laser by investigating the materials and the fabricating conditions. In this thesis, we doped the laser dye in the blue phase liquid crystal to make the laser device. Firstly, we studied blue phase temperature range and Bragg reflection wavelength under different material ratio. The blue phase lattice structures under different cool rate and surface treatment could be investigated by observing Kossel diagram . According to the experiment results, three-dimensional blue phase photonic crystal laser under room temperature could be achieved through appropriate material ratio, and its Bragg reflection wavelength is corresponds to the emission spectrum of the doped laser dye. By decreasing the cooling rate and the adapting homogeneous alignment of the substrates, the laser output will become more stable. As the result, we successfully fabricated the three-dimensional liquid crystal blue phase laser device at room temperature, and measured three-dimensional laser output. In addition, We study the relations between the laser emission direction and the alignment direction, and the temperature tuning characteristics of the laser wavelength. These results are very useful for the development of the three dimension tunable laser.

We investigate the post-weld-shift(PWS) induced fiber alignment shift in butterfly laser packaging. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A novel measurement and compensation technique employing a high-magnification camera with image capturing system (HMCICS) to probe the post-weld-shift (PWS) induced fiber alignment shifts in high-performance butterfly-type laser module packages is studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The increased coupling efficiency after this PWS compensation was from 3% to 10%. This HMCICS technique has provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

The fiber grating external cavity laser (FGECL) module packaged with fiber bragg grating and FP laser diode is investigated. The optical spectrum of FGECL is single longitudinal mode. In order to get stable single longitudinal mode, the FP laser diode coated with an AR-coating (reflectivity is 0.5%). To achieve higher coupling efficiency between laser diode and fiber, the hyperbolic-end lensed fiber is used. A coupling efficiency of up to 86% has been demonstrated. The alignment and fix between laser diode and fiber are accomplished by laser welding technology. The results of FGECL module show that the output power and side-mode suppression ratio (SMSR) are more than 2mW and 44dB, respectively. Comparing to the non-AR coated FGECL, the result of SMSR is 5 dB improved. Dynamic tests of the FGECL module operate at 2.5Gbps, including the eye diagram, bit error rates, impedance matching of laser diode, signal current, and the limit of the dispersion in the optical communication system has been measured. The FGECL module can meet the ITU-T G.957 standard.

A notch clip approach to compensate post-weld-shift(PWS) induced by laser welding process in butterfly type laser module packages is investigated. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the laser welding process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A notch clip approach and measurements employing a high-magnification camera with image capturing system (HMCICS) to probe the PWS induced fiber alignment shifts and welding compensation on notch in high-performance butterfly-type laser module packages are studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The overall coupling efficiency after this PWS compensation was from 80¢H to 90¢H. This notch approach and HMCICS technique have provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

The coupling of Fabry-Perot laser and fiber-grating for single frequency operation was studied experimentally and theoretically. A 1.55

ABSTRACT The spectral characteristics for non-AR coated fiber grating lasers were studied theoretically and experimentally. The lensed fiber was used to improve coupling efficiency between laser and fiber. The tapered fibers were fabricated by using the mixture of HF and oil with different density to increase etched taper angle. The coupling efficiency could reach more than 60%. A single-mode operation for a fiber grating external cavity laser (FGECL) was simulated. The results showed that the SMSR, emitted power, and wavelength drift were dependent on the related device parameters. Our calculations showed that the strong current-dependent SMSR oscillation was from the mode selection by the fiber grating external cavity and the heating effect in the Fabry-Perot (FP) laser. A 1.55mm FP laser chip that one facet was coated a high reflectivity (HR) of 90% and another facet was uncoated. In our experiment and simulation of FGECL, the reflectivity of fiber gratings were 50% and 70% and 86%, and the length of external cavity was about 0.9cm. The measured result of FGECL showed that the side-mode suppression ratio (SMSR) was more than 35dB and the output power was larger than 1.5mW at the injected current 2 to 3 times of threshold current. Furthermore, the spectrums of fiber grating external cavity lasers were studied in order to understand the external laser characteristics.

This paper presents design and fabrication of ring cavity semiconductor lasers with simple fabrication processes and good potential for integration. A 1.55-£gm symmetric quantum well InGaAsP epi-layer wafer is used to fabricate the lasers. The fabrication processes involve a bi-level deep etching to reduce the bending losses. Two geometric types of ring cavity semiconductor lasers have been investigated. For the type 1 ring cavity in the form of race tracks, two different designs are presented. One has a single ring resonator (SRR) design and the other has a coupled double ring resonators (DRR) design. The resonator of the type 2 ring cavity is formed between a cleaved facet and a loop mirror. Both a single ring resonator (SRR) design and a double ring resonator (DRR) design are presented for this type of cavity also. The maximum saturation output light powers of 0.479 and 0.409 mW are observed in room temperature L-I measurements for type 1 and type 2 ring cavity semiconductor lasers respectively. The spontaneous emission spectra of the type 1 ring cavity semiconductor lasers show a red-shift phenomenon under increasing drive currents. The type 1 ring cavity semiconductor lasers with ring resonators of 100 and 200 £gm radii have also been found to exhibit an interesting wavelength clamping phenomenon of the output light.