Brian K. Jones

Modulation characteristics of the Epson liquid crystal television

The amplitude- and phase-modulating properties of liquid crystal televisions (LCTVs) are becoming increasingly well known. The Epson Crystal Image video projector is a relatively new TV and uses three liquid crystal panels to encode the red, green, and blue components of the video signal onto the projector light. These panels can be removed for use in optical systems. We present the results from measurements of the phase- and amplitude-modulation properties of one of these LCTV panels.

Real-time, full-resolution liquid crystal-based stereoscopic display

Wheatstone invented the first stereoscopic display on record in 1834. Numerous approaches to the display of stereo imagery have been demonstrated since; however, all suffer from various drawbacks. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays typically have tight limitations on the position of the viewers head. We investigate an architecture consisting of two readily available, inexpensive twisted nematic liquid crystal display (TN-LCD) panels sandwiched together to form a compact, rugged stereoscopic display. We describe the theory of operation, the experimental determination of the liquid crystal display modulation characteristics, and modifications to the theory of operation, as a consequence of the experimental results.

Optical image correlation using high-speed multiple quantum well spatial light modulators

We review GaAs Fabry-Perot vertical cavity multiple quantum well (MQW) spatial light modulators (SLMs) developed at Sanders, a Lockheed Martin Company, and demonstrate their use in optical image correlation. These MQW SLMs are reflective- mode modulators using electrically-tunable absorption to modulate the reflected intensity. The operation of the MQW SLMs with a newly-developed Labview graphical user interface is described. A compact Vander-Lugt image correlator is described which was configured using MQW SLMs: binary 128 X 128 pixel image input with a binary filter plane. In addition, the architecture of 8-bit gray-scale MQW-SLM module developed at Sanders is discussed. The performance of the image correlator was characterized using amplitude-encoded binary phase-only filters and various test targets including test imagery supplied by US Army AMCOM, and is compared with simulations for peak-to-secondary efficiencies on these data. Finally, high-speed (250,000 frames per second) target recognition of 128 X 128 pixels binary input imagery is demonstrated.

Improvements in the dual LCD-based stereo display (Invited Paper)

The benefits of stereo vision are numerous and quickly become apparent when attempting to perform simple tasks without the aid of stereo cues. The proliferation of remotely operated vehicles and indirect viewing applications has resulted in an increased need to see the operational environment in stereo. Several approaches to the display of stereo imagery have been demonstrated. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays require no headgear but typically have tight limitations on the position of the viewers head. Previous papers have described a new type of stereoscopic display based on dual liquid crystal displays. The new display provides a stereo view without temporal or spatial multiplexing. Several prototype displays have been built and demonstrated to potential users with favorable reviews. With a successful proof-of-principle prototype completed, the effort is focusing on improvements to the image quality, consolidating the electronics, and packaging the display for use in rugged environments. The results of this effort should produce a rugged, compact, multiuse stereo display.

Design and evaluation of a multiple quantum well SLM-based optical correlator

A vanderLugt correlator is under construction using two Sanders binary Multiple Quantum Well Spatial Light Modulators. This correlation is part of the U.S. Army Aviation and Missile Commands three-year program to evaluate the latest generation hardware available for image processing. The Sanders modulators offer extremely high frame rates that make them attractive for image processing applications. The limiting factor in this correlator will actually be the output detector rather than the spatial light modulator. The correlator will be evaluated using infrared imagery to determine its performance in a target cueing/target screening applications. The results from these experiments as well as future plans will be presented.

Optical characterization of the InFocus TVT-6000 liquid crystal television (LCTV) using custom drive electronics

Liquid crystal televisions are popular low-cost spatial light modulators. One LCTV of interest is found in the InFocus TVT-6000 television projector. A wavefront splitting interferometer has been constructed and analyzed for measuring the complex characteristics of these modulators, including phase and amplitude coupling. The results of this evaluation using the TVT-6000 projector drive electronics have been presented in a previous work. This work will present results of the complex characterizations of these modulators using custom drive electronics.

Compact 3D display using dual LCDs

Stereo imagery has been a goal in optics research since the invention of the stereoscope in 1834. While the market has been inundated with displays of various types, sizes, and formats, no general purpose, easy to use, inexpensive method for the display of imagery in stereo has been developed. The benefits of stereo vision are numerous and quickly become apparent when attempting to perform simple tasks without the aid of stereo cues. Numerous approaches to the display of stereo imagery have been demonstrated. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays, so named because they do not require the headgear, typically have tight limitations on the position of the viewers head. The research proposed here will investigate the application of two readily available, inexpensive liquid crystal panels sandwiched together to form a compact, rugged stereoscopic display. The appropriate drive signals are provided to the two stacked panels, which encode in polarization, the left and right images. Standard polarized 3D glasses can then be used to view the image in stereo. The proposed display will provide stereo pairs without loss of resolution or frame rate and without strict limitations on the placement of the viewer’s head.

New architectures and components for optical target recognition at the U.S. Army Aviation and Missile Command

Poor performance in key components has limited the development of optical target recognition systems. New components are now available, however, that exhibit size and speed characteristics compatible with image processing applications. The U.S. Army Aviation & Missile Command has recently begun a program to exploit the new devices for both homing and imagery analysis applications. New architectures and algorithms which exploit the modulation characteristics of the new devices are being developed and tested. Part of the program is also aimed at funding improvements in the devices to better meet the requirements for optical target recognition. This paper will discuss the overall program, specific devices under consideration, and present the architectures and algorithms under development. Any experimental results available at the time will also be presented, with more detailed results to be presented at a later conference.

Investigation of phase-encoded inputs to VanderLugt correlators

Extremely light efficient optical correlators can be built if both the input and filter are displayed on phase modulating devices. Problems may exist, however, since changes in the input scene intensity cause changes in the phase encoding. An analysis is presented here for the VanderLugt correlator architecture. Experimental results comparing the correlator response to phase-encoded and amplitude-encoded inputs are also presented for varying input scene intensities.

JWST NIRCam pick-off mirror grounding

The optics train of the Near Infrared Camera (NIRCam) instrument for NASAs James Webb Space Telescope (JWST) includes a pick-off mirror (POM) mounted in the focus and alignment mechanism (FAM). Over the course of the mission, the POM will have a narrow view of the L2 space environment. Charged particles will impinge and collect on the mirror surface increasing the possibility of arcing to the adjacent baffle. A technique to ground the POM and remove accumulated charge has been qualified and implemented on the flight instrument. This paper will provide an overview of the qualification process including cryogenic resistance measurements, vibration testing and optical surface error measurements. To measure the efficiency of this grounding technique, a POM engineering model was exposed to representative mission electron fluence and results with the POM grounded and ungrounded will be presented.