Three-dimensional confinement of carriers eliminates the problem of thermal spreading of carriers observed in higher-dimensional systems. Uniform self-assembled quantum dots (QDs) are obtained using the spontaneous islanding of highly strained III-V semiconductors grown with standard epitaxy. Visible stimulated emission has been obtained with red-emitting AlInAs QDs in AlGaAs barriers. Continuous (CW) threshold current densities below 100A/cm2 have been measured at low temperatures and QD material gain larger than 1.7 x 104 cm-1 demonstrate good material quality. Room temperature lasing has also been observed for higher threshold current densities. For longer wavelengths where the thermionic emission problem is less important, InAs/GaAs lasers can operate at room temperature for current densities below ∼100A/cm2 for wavelengths around 950 nm. The zero-dimensional transitions between confined electrons and holes in artificial atoms allow the observation of state-filling at relatively low level of material excitation. Lasing is observed in the upper QD shells for small gain media, and progress towards the QD ground states for longer cavity lengths. Gain may also be increased by including multiple layers of QDs in the active region. To understand the shell structure of AlInAs/AlGaAs QDs, we present results of interband spectroscopy of single Al0.36In0.64As/Al 0.33Ga0.67As self-assembled QDs. The single dot spectroscopy has been carried out at low temperature as a function of the excitation power and magnetic field up to 8 T. The emission spectra as a function of excitation power show two distinct groups of transitions which we associate with the recombination from ground and excited QD levels with a spacing of ∼70 meV. The application of magnetic field allows to identify the exciton emission as well as the emission from the bi-exciton, and charged exciton complexes with binding energies of ∼5 meV. The binding energies compare favorably with results of calculations. Artificial molecules are studied using coupled QD ensembles and single QD spectroscopy. The coupling between the zero-dimensional states is varied by changing the distance between two layers of stacked InAs/GaAs QDs. Energy level splitting larger than 30 meV of the symmetric and anti-symmetric states of the lowest confined shell are measured and are compared to theory.

The thesis consists of two research directions: Optical fiber applications in gas concentration and radiation dose measurements; and polarization effects in fiber optic communication systems. Part I of the thesis presents two optical fiber applications. (1) An infrared (IR) fiber bundle has been designed and fabricated to measure gas concentrations in a chemical vapor deposition (CVD) chamber using Fourier transform infrared spectroscopy. This fiber bundle covers the IR range from 0.5 to 20 mum and reduces the light beam divergence in the CVD chamber, which makes it possible to measure gas concentrations in a region near the substrate surface. Semi-ellipsoid mirrors have been designed and used to increase the collection efficiency of infrared radiation and to compensate the loss introduced by the fiber bundle. (2) A fiber optic radiation sensor based on radiation-induced fiber loss is reported. The gamma radiation-induced loss spectra in various fibers have been studied. Among all the fibers tested, 5% P-doped fiber shows the highest sensitivity to gamma radiation. The wavelength and dose rate dependence of radiation-induced loss in 5% P-doped fiber are investigated and the possibility of using this fiber as a radiation sensor for radiation therapy is discussed. Part II of the thesis examines two polarization effects, polarization mode dispersion (PMD) and polarization dependent loss (PDL), in fiber optic communication systems based on the waveplate models. A new waveplate model, capable of generating any PMD and PDL values, is proposed to overcome the limitations of the conventional waveplate model. Using both models the statistical distributions of PDL and differential group delay (DGD) have been studied considering the presence of biased elliptical birefringence. The principal state of polarization (PSP) of an optical pulse is proposed for a fiber having both PMD and PDL. PMD and PDL of a pulse for a fiber consisting of two polarization maintaining fiber segments are calculated, and the pulse distortions due to PMD and PDL are analyzed. PMD and PDL impact on digital communication systems have been studied in terms of system Q factor, bit error rate (BER) and system outage probability. The acceptable PMD values in a system with PDL are discussed for various power margins. The Q factor distributions due to PDL and its combination with PMD have been measured experimentally and compared to numerical simulations.

High peak power 10 ns near-infrared coherent radiation has been obtained from frequency conversion of a dye laser beam in a LiNbO$\sb3$ crystal. The observed tuning range spanned the 0.734 to 2.853 $\mu$m wavelength range. An examination of optical parametric oscillator frequency conversion revealed that the production of the monochromatic laser radiation at the signal wavelength was only obtainable for a limited portion of the accessible pump wavelengths. In contrast, optical parametric amplifier frequency conversion resulted in the production of bichromatic infrared radiation for the entire accessible pump wavelength range. It appears that the crystal pump acceptance bandwidth leading to reduce power conversion can be described by a model in which the signal wave is assumed to have zero bandwidth.

The theory surrounding plasmon-polariton wave propagation on infinitely wide thin metal film structures was rederived, understood and is presented. Mode dispersion curves as a function of metal thickness were obtained for various metals and wavelengths. Field distributions for various structures of interest were computed and are presented. Fresnel coefficients have been derived for an n -layer structure to simulate the expected reflectance measurements of attenuated total reflectance (ATR) experiments. ATR experiments have been performed to excite surface plasmon-polaritons on a 20 nm thick titanium (Ti)-gold (Au)-Ti film embedded in SiO2. Measurements of the sensitivity of the thin metal film infinite in width to incident polarisation were performed experimentally confirming the transverse magnetic (TM) nature of surface plasmon-polaritons. A first mask was designed to experimentally verify the optical mode confinement of a thin metal film finite in width. A second mask was designed with the knowledge acquired from the first one. (Abstract shortened by UMI.)

Static and modulated reflectance measurements were made on samples of some III-V compounds and their alloys. Multiplet structures resolved in the reflectance spectra of III-V compounds in the energy range 3.5--7.5 eV led to the determination of the spin orbit splittings Delta0', Delta 2, Delta1', DL3V and ▵L3C . Structure was observed in the thermoreflectance spectra of III-V compounds in the energy range 1.5--6.0 eV and it was assigned to interband transitions. Results enabled comparison with previous data obtained using other techniques. Static and modulated reflectance measurements confirmed the nonlinear variation of energy gaps with composition in GaxIn 1-xSb alloy. Similar data was obtained for InAs1-xP x and InSb1-xAsx alloys from electroreflectance measurements. Results on five III-V alloys were analysed, fitting a quadratic equation to the energy gap variation with composition curves. The total bowing parameters determined experimentally were compared with theoretical values. The spin orbit splitting Delta1 was also found to vary nonlinearly with composition in the five alloy systems investigated and the bowing parameters were related to the atomic spin orbit splittings of the alloying elements.

Abstract not available.

Brillouin scattering based fibre optic sensors have been actively researched over the past decade due to their enhanced sensitivity to environmental parameters such as temperature and strain. Applications range from dynamic health monitoring of civil structures such as bridges, pipelines, and nuclear reactors to real-time threshold applications such as fire detection. As temperature and strain changes often represent the first symptoms of structural degradation, the development of Brillouin scattering based technology will bear considerable scientific as well as economic benefit. Brillouin sensors employing the probe-pump amplification technique obtain distributed spatial information along a fibre using narrow pulses. In this study, the impact of pulse width and extinction ratio on the overall Brillouin spectrum shape is investigated. From independent theoretical and experimental investigations, a comprehensive curve fitting method is proposed to reveal the physical nature of Brillouin scattering in the transient regime.

This thesis is composed of two main sections. The first section is the development of an optical fiber sensor. This new sensor system has been simulated by a Matlab program that considers the distributed feedback lasers' broader linewidth compared with that of frequency stabilized Nd:YAG lasers. The second section involves research on polarization effects in the optical fiber. In this thesis it is proven that only three states of polarization are required to determine the principle state of polarization vector. In addition, polarization effects in fiber Bragg gratings are investigated in this work. To measure the polarization dependent loss of the fiber Bragg grating for the reflection wavelength, an optical circulator is used. A problem arises since the circulator's polarization dependent loss contributes to the measurement result; this effect is often ignored. In this thesis, a test set has been developed to eliminate this uncertainty effect through a three-step procedure using the Jones Matrix method.

This work deals primarily with measurements of molecular line's frequency shifts induced by pressure, laser power and applied frequency modulation. The subjects of the study were infrared transitions in acetylene (C2 H2) and ammonia (NH3) molecules, which are important from the point of view of telecommunications and metrology researchers. In addition, the measurements of saturated line power broadening were carried out for selected lines of 12C2H2 and 13C2H2 as well as for the recently discovered saturated absorption line in 14NH3. This study led to experimentally establishing the molecular dipole moments for a given transition even without proper ro-vibrational assignment.

A new and simple approach was optimized for stabilizing a harmonic active mode-locked fiber laser at 40GHz. A computer tunes the modulation frequency in a 500kHz band near 40GHz to follow variations in the optical cavity length. A second approach based on a Proportional-Integral ( PI) controller and a piezo fiber stretcher was also developed and optimized. This approach uses a circuit-controlled piezo (PZT) device to physically counteract optical cavity length variations. The optimized circuit-controlled and computer-controlled approaches were compared to draw conclusions on their performance. Results for the pulse characteristics, the side mode suppression ratio and the time jitter show that both approaches provide an efficient method for stabilizing a harmonic FM active mode-locked fiber laser at 40GHz. Finally, the versatility of both approaches was used to attempt to generalize the two methods for use at any modulation frequency up to 40GHz.