Stephen Drew

Date of Award

8-2009

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

Advisor

Nuri W. Emanetoglu

Second Committee Member

Rosemary Smith

Third Committee Member

David E. Kotecki

Abstract

An optoelectronic mixing (OEM) device detects an intensity-modulated optical signal, and simultaneously mixes it with a modulated electrical signal to obtain the baseband signal. OEM devices have applications in optical communications and sensors such as laser assisted detection and ranging (LADAR) systems. InGaAs metal-semiconductor-metal (MSM) detectors, which are symmetric devices, have been demonstrated to work as OEMs in LADAR systems. The development of an OEM device with gain would improve overall system performance when used in the receiver of a LADAR system. Symmetric heterojunction phototransistors (HPTs) are candidates for OEMs with gain. This thesis investigates the development of a symmetric gain optoelectronic mixer (SG-OEM) for chirped-FM LADAR operating in the "eye-safe" 1.55um wavelength range. Signal processing of a chirped-FM LADAR system is simplified if the photodetector in the receiver is used as an OEM device. Adding gain to the optoelectronic mixer allows the following transimpedance amplifier's gain to be reduced, increasing bandwidth and improving the system's noise performance. The symmetric gain optoelectronic mixer is based on a symmetric heterojunction phototransistor. The base layer material is Ino.53Gao.47As (InGaAs), and the emitter/collector layer material is Ino.52Alo.48As (InAlAs). One- and two-dimensional simulation programs are used to model the behavior of these structures. Characteristics such as responsivity, symmetric response and noise performance of these OEMs are analyzed. Two sample heterostructures were grown using molecular beam epitaxy. The process is currently in the prototype development stage. Simulation results and preliminary results from the initial batch of devices are presented. These devices show an improvement in responsivity of at least two orders of magnitude over the previously demonstrated InGaAs MSM OEM devices. The incorporation of these devices into a LADAR system should greatly improve performance. These symmetric gain optoelectronic mixer devices can lead to miniaturized LADAR-on-chip systems. Such systems will have many military and civilian applications, such as range finding, terrain mapping, reconnaissance, and face recognition.

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