Monolithically integrated low-power phototransceivers and photoreceivers for application in an optoelectronic eye.

Abstract

There is a need to develop an artificial optoelectronic eye for surveillance, detection and image recognition. Such a chip should be able to detect, process and transmit near-perfect optical images and related information that would adapt automatically to changing scenarios and environments. A densely packed, two-dimensional array of phototransceivers and photoreceivers is an essential element in such system. In this thesis, several discrete and monolithically integrated components for the optoelectronic chip have been developed and optimized. For discrete devices, new types of lasers and modulators have been investigated. A novel InP-based 1.55mum patterned VCSEL with defect-free mismatched GaAs/AlGaAs top mirrors have been developed. The VCSEL demonstrates state-of-the-art performance characteristics. Quantum dot-based coupled-cavity lasers have also been developed. An efficient, externally controlled, wavelength switching was obtained with wavelength shift of 20nm, and wavelength switching speed of more than 25GHz. For modulating the visual signals, two kinds of modulators have been investigated. A SiGe/Si quantum well modulator, based on the weak confinement of the electron wavefunction in type I SiGe/Si quantum wells, was studied theoretically and experimentally. The modulator promises operation at very low bias. The second modulator employs InGaAs/GaAs self-organized quantum dots in the active region and demonstrates very large electro-optic coefficient (<italic>r</italic> = 2.58 x 10<super>-11</super>m/V, which is comparable to the value of the coefficient in lithium niobate). In the second area, two monolithically integrated optoelectronic integrated circuits are described, namely a low-power phototransceiver and a SiGe/Si photoreceiver array. The low-power phototransceivers, incorporating a microcavity light emitting diode and a phototransistor, demonstrates high optical gain (7dB) and very low power dissipation (40muW). Multichannel photoreceivers realized with SiGe/Si technology were designed and fabricated. The array demonstrates state-of-the-art performance characteristics and is suitable for massively parallel applications. Low power dissipation of 6mW/channel and low crosstalk of -26dB were achieved. The array demonstrates 0.8WHz -3dB bandwidth with 2V applied voltage.