The concept of in-vivo multi-spectral confocal microscopy is introduced. A slit-scanning multi-spectral confocal microendoscope (MCME) was built to demonstrate the technique. The MCME employs a flexible fiber-optic catheter coupled to a custom built slit-scan confocal microscope fitted with a custom built imaging spectrometer. The catheter consists of a fiber-optic imaging bundle linked to a miniature objective and focus assembly. The design and performance of the miniature objective and focus assembly are discussed. The 3mm diameter catheter may be used on its own or routed though the instrument channel of a commercial endoscope. The confocal nature of the system provides optical sectioning with 3μm lateral resolution and 30mum axial resolution. The prism based multi-spectral detection assembly is typically configured to collect 30 spectral samples over the visible chromatic range. The spectral sampling rate varies from 4nm/pixel at 490nm to 8nm/pixel at 660nm and the minimum resolvable wavelength difference varies from 7nm to 18nm over the same spectral range. Each of these characteristics are primarily dictated by the dispersive power of the prism. The MCME is designed to examine cellular structures during optical biopsy and to exploit the diagnostic information contained within the spectral domain. The primary applications for the system include diagnosis of disease in the gastro-intestinal tract and female reproductive system. Recent data from the grayscale imaging mode are presented. Preliminary multi-spectral results from phantoms, cell cultures, and excised human tissue are presented to demonstrate the potential of in-vivo multi-spectral imaging.

To study propagation in bent waveguides numerically the most common technique used is the Beam Propagation Method (BPM), with either the split-step procedure and Fast Fourier Transform algorithm, or a finite difference approach. Most versions are based on a first order modification of the permittivity profile for scalar or full vector wave equations. Others are based on a longitudinally variant index profile and wide angle beam propagation techniques. New device applications are well beyond the limitations of the present numerical approaches. An example of these applications are polymer and semiconductor ring lasers, (de)multiplexing systems, and polarization converters based on bent waveguides. They will require more accurate and novel numerical approaches to solve more complex problems at smaller radii. Important issues are characteristics such as: the modal spectra, total loss and loss rates, and modal field distributions.

This dissertation investigates the nonlinear optics of circular-grating distributed-feedback (CGDFB) semiconductor lasers. Included are gain saturation, index saturation, and self- and cross-phase modulation third-order nonlinearities. After a brief review of the historical and technical background needed to understand our results, a numerical model is developed for gain saturation. This model includes a radially-varying nonlinear gain and a uniformly-distributed grating loss in the solution of the coupled-mode equations. The results show that lossy, high-power operation results in an optimum coupling strength for efficient conversion of pump power into useful output pourer. Results also show a multi-mode spectrum for large coupling strengths, a consequence of mode selection governed by a spatially-varying gain distribution. Single-mode selection entails operating at approximately the optimum coupling coefficient determined for efficient pumping. These results are extended by including the gain/index coupling described by the linewidth enhancement factor. A unique feature of this coupling is the possibility of above-threshold, single-mode operation over a limited power range, even for the case of large coupling coefficients. Similar results are obtained for the circular-grating distributed-Bragg-reflector (CGDBR) laser. The excess spontaneous emission rate associated with the nonuniform CGDFB radial (longitudinal) field profiles is also calculated. The resulting above-threshold linewidth closely follows the inverse-power dependence predicted by the Schawlow-Townes relation. To include third-order nonlinearities, we derive coupled-mode equations which describe self- and cross-phase modulation effects via an intensity-dependent refractive index. It is then shown that the circular-grating structure acts as an all-optical switch. We also find that an additional pi/2 phase shift at the center of the grating permits the possibility of self-pulsing cylindrical gap solitons. For a positive nonlinearity (n2 it is shown numerically that these solitons are not physically allowable. That is, for a passive structure, time-dependent self-pulsing behavior is damped by the 1/beta r factor in the self- and cross-phase modulation terms. This damping can be compensated for by the addition of gain. In this case, self-pulsing with an excellent contrast ratio is obtained. The numerical methods used to obtain both steady-state and time-dependent solutions are also described. The steady-state results are obtained using a multi-dimensional Newton-Raphson technique known as the "shooting" method. Time-dependent data use a fourth-order predictor-corrector technique. The stability of the time-dependent solutions to the exact coupled-mode equations is reviewed. Coupled-mode equations based on a large-radius approximation for the Hankel functions are found to be stable over a wider range of variables. Numerical tests used to verify the time-dependent software are described.

This dissertation describes an investigation into the use of computer generated holograms to implement free-space optical interconnects. Computer generated holograms are discussed in terms of their theory of operation, design principles, fabrication techniques, optical performance, and sources of error. To motivate the research, discussion of an optoelectronic computing module is included; the device uses computer generated holograms to implement large-fanout optical interconnects. The emphasis of this dissertation is not on a specific application, rather it is focused on understanding the abilities and limitations of computer generated holograms. New contributions are made in the area of hologram design, both individual and multifaceted elements. These design techniques were built into a computer aided design tool (SPIDER 3.0), which was developed to promote the use of computer generated holograms. Hologram fabrication techniques and optical performance are also carefully characterized. Measurements show that performance is poorer than what is expected. Several significant sources of error are identified in the design and fabrication of computer generated holograms, and these effects are shown to explain most of the measured results. The dissertation concludes that computer generated holograms are currently limited by errors in fabrication and in the approximate diffraction theories employed in the design process. While the optical performance of the holograms is not as good as expected, the results are shown to be adequate for successful use in real applications.

The butt-coupling of a Fabry-Perot semiconductor laser diode and a singlemode optical fiber was realized and characterized in the near field. A novel butt-coupling model was developed and found very effective in describing all physical phenomena that occur when the butt-coupling parameters are varied over a wide range. The strong external optical feedback to the laser diode cavity that is present at extremely-short separations between the laser diode and the fiber is advantageously used to realize an extremely-short external cavity laser diode. By varying the length of the external cavity, the operational characteristics of this external cavity laser diode are controlled in a predictable and repeatable manner; a wavelength tunable laser diode source based on this effect was developed and analyzed. Another realization of an extremely short external cavity tunable laser diode, based on a closely spaced external filter with variable characteristics, was demonstrated. A potential application of the butt-coupling technique for light collection in an optical recording head is discussed. The work presented here is a research tool that can be used to facilitate the design of extremely-short external cavity laser diodes, which in many ways are technologically novel.

A method to predict modal noise in short distance (30 m), high temporal bandwidth (hundreds of MHz) multimode optical links is proposed. In order to accommodate low cost, mechanical alignment, the link medium is modified from single mode fiber (used routinely in telecommunication systems) to multimode fiber. Modal dispersion in multimode fiber calls for a reduction in link length to preserve a relatively high temporal bandwidth. The source is a vertical cavity surface emitting laser (VCSEL), which is well suited for the high packaging density, high temporal bandwidth, and low power dissipation requirements of short distance optical communication systems. Coherence properties of several different types of VCSELs are experimentally examined with constant and modulated injection current with a bandwidth typical of that used in data communications systems. A fluctuation in the spatial irradiance output pattern of the VCSEL is identified as the dynamic component responsible for significant modal noise effects. The effect of finite system coherence length has been applied to the simulation process. The reduction in output fiber face speckle contrast, due to a broader source power spectrum and/or due to fiber modal dispersion with increasing fiber length, mitigates the effect of modal noise in the transmission link.

A theory, based on material parameters, is developed for colloidal-crystal Bragg filters. The coupling constant, for coupled-wave equations, is derived to produce filter spectra. The spectra are modified by convolving with a Gaussian function to represent crystal defects. Scattering losses are calculated to attenuate the out-of-band transmission. The theory is tested by comparing theoretical spectra with experimental spectra from colloidal-crystal Bragg filters fabricated with polystyrene and poly(methyl methacrylate) colloid spheres. A novel cell, for containing the colloidal crystal, is presented in addition to crystal growing techniques. Coupled-wave theory spectra are compared with experimental filter spectra for filters with variable colloid sphere diameters, filter thicknesses, liquid refractive indices, and Bragg wavelengths. Spectral comparisons are based on the notch bandwidth, optical density, and out-of-band scattering losses. The bandwidths agree to within one nanometer provided the criteria for the Rayleigh-Gans scattering approximation are satisfied. The optical densities correlate with spectrophotometer-measured optical densities. And, scattering losses correspond to within 10 percent for all material parameters. Thus, the coupled-wave theory is consistent with the data and provides an excellent tool for evaluating colloidal-crystal Bragg filter performance.

Munition development has always been driven by the necessity of delivering enough explosives to a targeted object to destroy it. Targets that are protected by steel reinforced concrete housings have become increasingly more difficult to destroy. Improvements must be made in munitions engineering design to either deliver more payload to the target or to make the weapon more potent. In most cases, due to aircraft weight limitations, the delivery of more payload is not an option. Therefore, improving the destructive power of a weapon of a given payload requires the use of more powerful explosives. However, when the potency of an explosive is increased, its sensitivity to premature detonation also increases. The characteristics of the metal casing containing the explosive contribute significantly to the weapon's detonation sensitivity. Casing experience significant heating during weapon penetration. This heating can cause the weapon to detonate before it reaches its target location. In the past, computer codes used to model detonating weapons have not taken heating into account in their performance predictions. Consequently, the theoretical models and the actual field tests are not in agreement. New models, that include temperature information, are currently being developed which are based on work done in the area of computational fluid dynamics. In this research, a remotely located, high-speed, infrared (IR) camera is used to obtain detailed measurements of the passive radiation from an object in an energetic environment. This radiation information is used to determine both the emissivity and the temperature of the surface of an object. However, before the temperature or emissivity was determined, the functional form of the emissivity was calculated to be an Mth degree polynomial with respect to wavelength dependence. With the advent of large, high-speed, IR detector arrays, it has now become possible to realize IR imaging spectrometers that have very high spatial resolution. The IR spectrometer system developed in this research utilized a large detector array to allow multiple spectral images to be formed simultaneously on the image plane. In conjunction with the correct emissivity model, this imaging IR spectrometer can determine temperature to within ±5 degrees Celsius. These experimentally verified temperature maps were then integrated into the newly developed computer models. This additional information will result in more accurate computer codes for modeling the energetic environment. In turn, this will allow the weapon designer to accurately optimize weapon performance with respect to different materials, geometries and kinetics.

Experimental data often contains curious and unexplained results. In the course of experimental investigations of Raman shifting and the Co:MgF₂ laser, results were obtained which would not have been expected from the typical theoretical picture. In the case of Raman shifting, the forward Stokes conversion was found to depend upon the pump bandwidth. Numerical modeling suggests that coupling between the Stokes directions may be the root cause of the phenomena. In the case of the Co:MgF₂ laser, the laser output was observed to have large amounts of spectral structure. This amount of structure should not be expected in a room temperature vibronically broadened laser. Further experiments point to adsorbed water vapor for the cause of the structure, and this hypothesis is supported by a numerical model. Additionally, a unique method for treating the effects of arbitrary gain distribution on the propagation of the lowest order laser cavity mode is expanded to cover new distributions and new coordinate systems. An extension to parametric gains is also made. The extensions are then used to predict unstable regions in real laser cavities. These instabilities are observed in diffraction calculations. Guidelines for observing this intriguing result are presented.

This dissertation addresses both fundamental aspects of the coherent exciton kinetics in single semiconductor quantum wells and more application-oriented aspects of the collective excitonic optical properties in quantum well Bragg structures. We use a bosonic theory to investigate the ultrafast coherent exciton dynamics after an optical excitation in a single semiconductor quantum well. It is shown that, on intermediate time scales, nonlinear mean-field interactions between excitons lead to a coherent, wave-like evolution in the momentum distribution of optically inactive excitons, which can survive for some time before dephasing sets in. Driven by two-exciton correlations, this coherent quantum kinetic effect bridges the well-known kinetics associated with optical excitation on the one hand and incoherent relaxation on the other. We also study more general dynamical properties of bosonic mean field systems with N-species of excitons (in a single semiconductor quantum well). We find that the momentum-conserving exciton mean field equations, including the coupling to external fields and fermionic corrections, have the dynamical structure su(N,N). We show that one can define a non-real generalized "Bloch vector" and a non-hermitian "density matrix" description, which allow us to explicitly obtain all the constants of motion associated with the su(N,N) symmetry. The many-body effects and correlations of excitons in a single quantum well are mainly induced by the Coulomb interactions. In the case of a semiconductor quantum well Bragg structure, the light induced coupling between different quantum wells also dramatically affects the excitons' behavior, especially through the collective excitations of excitons in the whole structure. We investigate the linear excitonic optical properties of the quantum well Bragg structure induced by the collective excitations using the transfer matrix approach. We show that the so called "intermediate band" (IB) created by the exciton resonance, which does not exist in conventional photonic crystals, can be used for the stopping, storing and releasing of light, which is important in information processing devices. We also discuss the compensation of the dispersive distortion in the light delay process through reversing the IB band structure. Other conceptual and practical issues such as the decay rate of the IB modes and the generalized anti-reflection coating are also investigated.