The Space Interferometry Mission, scheduled for launch in 2008, is an optical stellar interferometer with a 10 meter baseline capable of micro-arcsecond accuracy astrometry. A mission-enabling technology development program is underway at JPL, including the design and test of heterodyne interferometer metrology gauges to monitor the separation of optical components of the stellar interferometer. The gauges are required to have a resolution of 15 picometers and to track the motion of mirrors over several meters. We report laboratory progress in meeting these goals.
We report a new familiy of polarimetric imaging cameras based on tunable liquid crystal components. Our camera designs use a dual frequency liquid crystal tunable filter that rotates the polarization of incoming light, in front of a single linear polarizer. The unique features of this approach include fast switching speed, high transmission throughput, no mechanical moving parts, broad bandwidth, high contrast ratio, wide viewing angle, and compact/monolithic architecture. This paper discusses these tunable liquid crystal polarimetric imaging camera architectures (time division, amplitude division), the benefits of our design, the analysis of laboratory and field data, and the applicability of polarization signatures in imaging.
Recent investigations in holographic mass memory systems have produced proof of concept demonstrations that have highlighted their potential for providing unprecedented capacity, data transfer rates and fast random access performance. The exploratory nature of most such investigations have been largely confined to benchtop experiments in which the practical constraints of packaging and environmental concerns have been ignored. We have embarked on an effort to demonstrate the holographic mass memory concept by developing a compact prototype system geared for avionics and similar applications which demand the following features (mostly interdependent factors): (1) solid state design (no moving parts), (2) fast data seek time, (3) robust with respect to environmental factors (temperature, vibration, shock). In this paper, we report on the development and demonstration of two systems, one with 100 Mbytes and the other with more than 1 Gbyte of storage capacity. Both systems feature solid state design with the addressing mechanism realized with acousto- optic deflectors that are capable of better than 50 microseconds data seek time. Since the basic designs for the two systems are similar, we describe only the larger system in detail. The operation of the smaller system has been demonstrated in various environments including hand-held operation and thermal/mechanical shock and a photograph of the smaller system is provided as well as actual digital data retrieved from the same system.
We introduce a multichannel RF correlator that is capable of simultaneously computing the correlations between a given input signal and a set of stored reference waveforms. The system relies on angularly multiplexed volume holograms to store the reference waveforms and is a new example of an emerging class of RF systems that use photonics to solve complex problems. Preliminary experimental data derived from a demonstration system are presented and discussed.
Although the concept of using multiplexed holography for data storage has been considered for some time, recent advances in several critical device technologies along with developments in storage materials have greatly enhanced the likelihood of successful implementations. We review several basic architectural concepts along with various multiplexing options and associated techniques for holographic data storage.
Radio frequency signal processing systems that use photorefractive crystals to provide key functions are described. Some new experimental results obtained with a time-integrating correlator developed to support the acousto-optic null steering processor effort are presented that demonstrate the effectiveness of the photorefractive time-integrating approach. We also describe a new adaptive notch filtering system that provides effective and flexible excision of narrowband interference. The system architecture makes optimal use of the unique properties of the photorefractive effect to provide a simple yet highly effective solution for the adaptive signal processing problem.
We describe recent results from our efforts in characterizing a photorefractive device to be used as a time integrator in the Acousto-optic Null Steering Processor. This processor is being developed for the ARPA Transition of Optical Processing to Systems Program under Rome Laboratory contract F30602-91-C-0044. We present frequency response data for the BSO crystals which were measured using a novel acousto-optic apparatus. We also present measured dynamic range data for the candidate BSO crystals.
Results of an experimental investigation of the dynamic range of the photorefractive effect in several ferroelectric crystals are described in the context of adaptive filtering applications. The results indicate a very large (greater than 80 dB) dynamic range for several samples; the dynamic range is shown to be limited by noise processes inherent in the crystals. The large photorefractive dynamic range of the ferroelectric signals investigated should prove useful for signal processing and computing applications.