This thesis describes the design, fabrication and characterisation of an infrared optical waveguide phase modulator. The modulator was fabricated in GaAs utilizing a carrier-concentration-reduction rib waveguide structure with a Schottky diode contact to allow the application of an electric field across the waveguide region. Measurements of the phase modulation are presented with results agreeing with the theoretical predictions of an electrooptic coefficient of 1.2 x 10-12 m/V at 1.15 //m. Fabrication techniques and problems are thoroughly discussed. The second part of this thesis consists of measurements of the quantum confined stark shift in an AlGaAs-GaAs multiple quantum well p-i-n diode structure. The results show useful changes in absorption with applied electric field. Transmission measurements as a function of applied field are presented for TE polarized light in a waveguiding geometry as well as photocurrent measurements in the same geometry and with light incident perpendicular to the MQW layers. Reasonable agreements for the relative field induced shifts of the excitonic feature are found but the absolute position of the feature is blue shifted by 7 meV with respect to the theoretically predicted position. / Thesis / Master of Engineering (ME)

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / A Phase Modulator combining digital techniques with non-traditional analog circuitry can minimize the shortcomings of a traditional (purely analog) Phase Modulator. These shortcomings are: nonlinear response from input modulating signal to output modulated signal; parameters (frequency and modulation index) that are difficult to set; and the need for complex filters. The design approach discussed in this paper uses a combination of Direct Digital Synthesis (DDS) and analog devices operating in their linear range to generate a Phase Modulated RF (140 MHz) signal. A Numerically Controlled Oscillator (NCO) digitally generates the first IF yielding a very accurate, repeatable and linear signal with easily adjustable parameters such as frequency and modulation index. Linear multipliers (instead of saturated diode mixers or step recovery diodes) are used for up-conversion to RF. Using linear multipliers eases the filtering requirements due to the significantly reduced harmonics and IM (Inter-Modulation) terms. The resulting RF signal is easily translated to higher frequency bands such as L, S, C, X or K.

In this dissertation, the response time issue of the liquid crystal (LC) devices is investigated in meeting the challenges for display and photonic applications. The correlation between the LC director response time and the optical response time is derived theoretically and confirmed experimentally. A major contribution of this thesis is that, based on the small angle approximation, we derive rigorous analytical solutions for correlating the LC director response time to its consequent optical response times (both rise and decay) of a vertical-aligned nematic LC cell. This work successfully fills the gap in the literature of LCD switching dynamics. An important effect related to response time, backflow is analyzed using a homogeneous LC cell in an infrared wavelength. The Leslie viscosity coefficients can hardly be found in the literature. A new effective approach to estimate the Leslie coefficients of LC mixtures based on MBBA data is proposed in this dissertation. Using this method, the Leslie coefficients of the LC material under study can be extracted based on its order parameters. The simulation results agree with the experimental data very well. This method provides a useful tool for analyzing the dynamic response including backflow. Cell gap is an important factor affecting the LC response time. Usually a thinner cell gap is chosen to achieve faster response time, since normally both rise and decay times are known to be proportional to d2. However, they are valid only in the region. In the large voltage region where , the optical decay time is independent of d. In this thesis, we find that between these two extremes the response time is basically linearly proportional to d. Our analytical derivation is validated by experimental results. Therefore, in the whole voltage region, the physical picture of the optical response time as a function of the cell gap is completed. This analysis is useful for understanding the grayscale switching behaviors of the LC phase modulators. In conclusion, this dissertation has solved some important issues related to LC optical response time and supplied valuable tools for scientists and engineers to numerically analyze the LC dynamics.

Sensing rotation has been an essential topic in navigation and many other applications. Gyroscopes based on propagation of light beams over fixed distances have gained interest with the development of the laser. Since the 1970s, with the development of fiber optics these laser based gyroscopes have developed into compact devices, which can fit in the palm of your hand. In this thesis, we describe and analyze the development of a fiber-optic gyroscope. Fiber optic gyroscopes (also called fiber gyro or FOG) have been under development for different types of applications for more than 30 years all around the world. The physical basis of the fiber gyro is the Sagnac effect that was discovered in the early 1900s and is named after its discoverer. In this work, we first explain the principle of operation of the Sagnac effect and we derive the fundamental formulations in order to have an analytical understanding of the theory. Then, we examine the fiber optic gyro configuration component by component, starting with the laser diode pumped broadband light emitting Erbium-doped superfluorescent source. In addition, the principle of phase modulation, electro-optic phase modulators, fiber optic cables and fiber winding techniques, such as quadrupolar winding is explained within the context of development of the FOG. v The FOG that was assembled was based on circulation and sensing of broadband light centered around 1550nm. The fiber coil was 5km long in order to increase sensitivity in the FOG device. Since single-mode fibers were used steps were taken to ensure successful operation even with polarization dependent errors. The constructed system demonstrated a low sensitivity with a large uncertainty while sensing typical rotation rates. Reasons behind the errors and low sensitivity, as well as improvements that can be made are discussed.

This paper reports a reciprocal Mach-Zehnder interferometer in a dual Sagnac ring configuration, and one of two arms in Mach-Zehnder interferometer is used for underwater optic fiber hydrophone. Two Mach-Zehnder interferometers operated in opposite sense are simultaneously induced from the underwater acoustic wave and the PZT phase modulation. Thus, at the output, four interferometric beams occur such that the intensity of interferometric beams will enhance. In general, one stage of a double Mach-Zehnder interferometer is just used as a sensor, another one for compensation. Specially, this paper presents two stages of a double Mach-Zehnder interferometer sense the measurand at the same time due to the topology structure of Sagnac ring pairs. In the other words, the characteristic is to win the affection of two beauties at the same time. Two rings in the same direction make a Mach-Zehnder interferometer. Besides, the inner ring in the clockwise direction and the outer one in the counterclockwise direction also make a Mach-Zehnder interferometer. So as to the unbalanced arms of the Mach-Zehnder interferometer, the underwater acoustic wave induces the light beam phase difference in optic fiber hydrophone interrogator to demodulate the acoustic wave signal by PGC circuit.