Optical control in GaAs microwave semiconductor devices

Abstract

New types of Traveling Wave Photodetectors (TWPDs) are designed using coplanar stripline structures, fabricated on semi-insulating GaAs substrates, and characterized by microwave and optical methods. In this traveling wave photodetector structure the incident light interacts continuously with the optically generated microwave signal while they propagate along their own waveguides. Therefore, when the phases between the optical and microwave signals are matched, a strong traveling wave signal can be detected without losing its high speed and high quantum efficiency. Two types of photoconductive TWPDs, that is, symmetrical and asymmetrical TWPDs, are studied in this dissertation. DC and RF characterizations are carried out for these devices. Also, the interference effects are investigated with multiple input beams. Since these TWPDs have planar structures, it is easy to integrate the TWPDs with other elements in Microwave and Millimeter wave Hybrid (MIC) and Monolithic (MMIC) Integrated Circuits such as GaAs Field-Effect Transistors (GaAs FETs). In this dissertation, an optical receiver is constructed by hybrid integration of the TWPD with a commercial low noise GaAs FET amplifier. A network, to match device impedances to the appropriate source or load impedances are designed and fabricated in microstrip on a semi-insulating GaAs substrate. Microwave ring resonators for optoelectronic application are designed using CAD tools such as LINECALC and TOUCHSTONE, fabricated in our laboratory using photolithography process, and optically characterized using a modulated laser diode light source and a spectrum analyzer. A microstrip ring resonator and a new type of CPW-to-Slotline ring resonator monolithically integrated with a Schottky photodetector are investigated for optical excitation and nonlinear behavior. Harmonic signals are generated by optical excitation of the resonators at the fundamental mode. By mixing a local microwave signal with an optically generated RF signal in the vicinity of resonant frequencies of the resonator, new signals, which contain the sum and difference frequency of the two input signals, are generated. Also, nonlinear parametric amplification of optical RF input signal is investigated in both of the ring resonators with a local microwave pump signal.