Duncan Tsuen-Hsi Liu

Optical links for cryogenic focal-plane array readout

An optical link can provide an interface channel for a focal plane array that is immune to electro-magnetic interference (EMI) and can lower the heat load on the dewar. Our approach involves the use of fiber optics and an on-focal-plane optical modulator to provide an interface to the focal plane array (FPA). The FPA drives the modulator with an electrical signal. We evaluated specially fabricated AlGaAs/GaAs multiple-quantum-well (MQW) optical modulators, operating near 840 nm, for analog modulation, and we have used the results to calculate the performance of an optical interface link using experimentally determined device parameters. Link noise and dynamic range for an analog link were estimated from a separate experiment using pigtailed fiber components. The performance of the MQW modulator system is compared to alternative strategies. Significant improvement in performance in comparison to conventional electronic interfaces appears to be possible.

Resolution of a target-tracking optical novelty filter

The resolution of a target-tracking optical novelty filter is discussed in terms of the response time of the nonlinear medium, the speed of the target, and the resolution of the input device. Optical novelty filters using a faster nonlinear medium may have a higher output resolution. This is particularly true in the case of tracking high-speed targets. The potential of implementing high-resolution optical novelty filters using photorefractive GaAs is investigated experimentally.

Optical links for cryogenic focal plane array readout

An optical link can provide an interface channel for the focal-plane array that is immune to electromagnetic interference (EMI) and can lower the heat load on the dewar. Our approach involves the use of fiber-optics and an on-focal-plane optical modulator to provide an interface to the focal-plane array (FPA). The FPA drives the modulator with an electrical signal. We evaluated specially fabricated AlGaAs/GaAs multiple quantum well (MQW) optical modulators, operating near 840 nm, for analog modulation, and we have used the results to calculate the performance of an optical interface link using experimentally determined device parameters. Link noise and dynamic range for an analog link were estimated from a separate experiment using pigtailed fiber components. The performance of the MQW modulator system is compared to alternative strategies. Significant improvement in performance in comparison to conventional electronic interfaces appears to be possible.

Space adaptive optics coronography

We present the latest developments on the concept of space adaptive optics coronography. We review the principle of deformable mirror used to suppress the scattered light in a dark hole region around the optical axis. We describe the main limitations of this concept. A description of the experiment which has been built at JPL and its first results are given.

Novelty filtered optical correlator using photorefractive crystal

We demonstrate a new optical correlator in which the correlation peak intensity is increased when the matched input object is moving. The basic configuration of the correlator is the same as a VanderLugt optical correlator consisting of a photorefractive crystal. The principle of this new correlator is based on the dynamic grating erasure property of photorefractive materials. The detail of this principle is described.

GaAs-based photorefractive time-integrating correlator

A potential application of the photorefractive time-integrating correlator is the real-time radar jamming interference rejection system, using the adaptive filter method; a fast photorefractive crystal is needed for adapting a rapidly changing jamming signal. An effort is presently made to demonstrate and characterize a GaAs-based photorefractive time-integrating correlator, since GaAs crystals are 2-3 orders of magnitude faster than most other alternatives.

Real-time optical correlator using photorefractive GaAs

A real-time optical correlator based on GaAs and liquid-crystal TV (LCTV) is demonstrated. The demonstrated system has a video-frame rate limited by the speed of the LCTVs; if faster spatial-light modulators are used, the potential frame rate of a GaAs-based correlator can be as fast as 1000 frames/sec under experimental conditions. Comparisons are made between VanderLugt and joint transform and between degenerate and nondegenerate four-wave mixing. The edge-enhancement effect and the Bragg diffraction effect are discussed.

Power-over-fiber sensor network

We present the characteristics of a prototype all-fiber sensor network that is useful in structure-health management and distributed sensor data acquisition. In this network, each remote sensor node is powered over a fiber by a laser in the base station. The sensor data are sent back to a base station through a different fiber. Issues concerning power consumption per node, data rate, fault-tolerance, packaging, cost, and network expandability will be discussed.

Theory of radiation-induced absorption in optical fibers

A new and simple mathematical model for describing radiation-induced absorption in optical fibers is presented. It treats the radiation-induced defect-generation and the decay process as a series of superposable infinitesimal growth and decay events. Unlike the existing power law growth equation, the new equation is non-empirical, dose-rate dependent, and describes the growth and decay of the induced defect at the same time. It is capable of predicting long-exposure, low-dose-rate induced fiber loss normally taking place in a space mission, using short-exposure, high-dose-rate results produced in a ground-based laboratory. Numerically, the derived equation is also capable of simulating those effects caused by irregular radiation events such as solar-flare radiation burst. In the case of constant dose rate, the general equation reduces to a simple analytical form which agrees reasonably well with the experiment.

Optical processing using photorefractive GaAs and InP

The unique features of photorefractive compound semiconductors are presented. The advantages of this class of nonlinear optical materials for optical processing are illustrated with examples using GaAs and InP. The difference between GaAs and InP in the laser power density requirement is discussed.