Keyvan Sayyah

Dynamic IR scene projection using the Hughes liquid crystal light valve

This paper reviews recent development and application of the infrared version of the liquid crystal light valve (LCLV). We describe delivered IR image projectors for advanced end-to- end laboratory testing of IR seeker and sensor systems. System performance characteristics are given. A newly developed version of the device has much higher contrast with low IR background image capability.

High performance single crystal silicon liquid crystal light valve with good image uniformity

This paper is composed of two distinct portions. In the first part, we introduce modified versions of the Hughes silicon liquid crystal light valve with wavefront distortions of better than lambda/4, a resolution of 16 line pairs/mm at 50% modulation concurrent with a contrast ratio of 20:1. In the second portion, we present the results and analysis of a thorough study of the dependence of the performance of this device on its various operating parameters. The contrast ratio of this device was found to be very sensitive to the accumulation phase voltage and pulse width of the driving waveform, while the resolution is strongly dependent on the depletion phase pulse width.

OPTICALLY ADDRESSED SPATIAL LIGHT MODULATOR WITH A HIGH PHOTOSENSITIVITY AND INTENSITY ADAPTATION RANGE

An optically addressed spatial light modulator based on a single-crystal silicon Schottky diode array photoreceptor and nematic liquid crystals with a high photosensitivity (better than 1microW/cm(2)) and input light intensity adaptation range (greater than 3 orders of magnitude) is demonstrated. This photosensitivity and intensity adaptation range is concurrent with a spatial resolution of 25 line pairsymm, contrast ratios greater than 200:1, and response times less than 10 ms in a wide photosensing wavelength range of 400-1100 nm.

High-resolution liquid-crystal-based spatial light modulator with a thin crystalline silicon photosubstrate structure.

We report an optically addressed, liquid-crystal-based spatial light modulator demonstrating a resolution of 25 line pairs/mm at 50% modulation transfer function and more than 40-line-pair/mm limiting resolution by using a 25-μm-thick silicon Schottky diode-array photosubstrate. This resolution is obtained concurrent with a high photosensitivity of approximately 20 μW/cm(2) and a contrast ratio of over 200:1. The high resolution and photosensitivity obtained with the thin photosubstrate are explained by a fringing field and an equivalent-circuit model, respectively.

Conformal pixellated MQW modulator structure for modulating retroreflector applications

We have developed a conformal optical modulator structure comprising pixellated InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption modulators embedded in a polymer membrane for operation in the 1550-nm optical region. The MQW modulators retain their electrical and optical characteristics after the polymer embedding process, with leakage currents of less than 50 nA and modulation contrast ratios of 2 : 1. The radio frequency response of these modulators was shown to be dependent on the pixel size, with a 3-dB modulation frequency of over 200 MHz for a 225/spl times/125 /spl mu/m/sup 2/ pixel. The conformal MQW modulator structure developed here can be used in applications requiring placement on a curved surface, such as in cats eye modulating retroreflectors.

Anomalous liquid crystal undershoot effect resulting in a nematic liquid crystal‐based spatial light modulator with one millisecond response time

We report here, a single crystal silicon‐based spatial light modulator demonstrating a millisecond response time using a nematic liquid crystal operated in the surface mode configuration. This unexpected fast response time can be explained by a combination of liquid crystal voltage undershoot and the transient nematic effect. The fast response time measured is concurrent with high spatial resolution and gray scale capability which make this device unique in its class.

Two-dimensional pseudo-random optical phased array based on tandem optical injection locking of vertical cavity surface emitting lasers.

We demonstrate, both theoretically and experimentally, a pseudo-random, two-dimensional optical phased array (OPA) concept based on tandem injection locking of 64-element vertical cavity surface emitting laser (VCSEL) arrays. A low cavity-Q VCSEL design resulted in an injection locking optical power of less than 1 μW per VCSEL, providing large OPA scaling potential. Tandem injection locking of two VCSEL arrays resulted in measured controllable optical phase change of 0-1.6π. A high quality beam formed with suppressed grating lobes due to the pseudo-random array design was demonstrated with performance close to simulated results. A preliminary 2.2° x 1.2° beam steering example using the tandem arrays was also demonstrated.

Multitone photonic oscillator

A photonic oscillator that can generate multi-tone oscillations in both the RF and optical domains is demonstrated. The oscillator consists of a simple closed optoelectronic loop comprising a CW laser source, an optical modulator, a photodetector, a low noise electrical amplifier, an electrical bandpass filter and single or multiple optical delay elements. Multi-tone oscillations with independent control of tone spacing and phase noise is demonstrated using two optical fiber delay lines as optical delay elements. The phase noise of the oscillator is systematically measured as a function of its parameters such as the photodetector current, the amplifier gain and oscillation frequency. Phase noise values better than -125 dBc/Hz at 100 kHz offset frequency are measured at various combinations of the above parameters. Multi-tone photonic oscillators using Mach-Zender or electroabsorption modulators are theoretically analyzed and experimentally demonstrated with the relative merits compared.

Schottky diode silicon liquid-crystal light valve

The authors report the operation of the Hughes Schottky diode-based silicon liquid crystal light valve (SLV) using readout light in the visible region. Limiting resolutions of 28 lp/mm limited by the Schottky diode periodicity, contrast ratios of >100:1, visible input light sensitivities of better than 50 (mu) W/cm2, and response times as fast as 5 ms have been measured. Both standard twisted nematic and homeotropically-aligned liquid crystal configurations have been utilized. The main parameter of this device is the leakage current of the Schottky diodes.

One-dimensional equivalent circuit simulation of a photodiode-based spatial light modulator

A one-dimensional (1-D) equivalent circuit model for an optically addressed, photodiode-based spatial light modulator (SLM) is presented. The model is first verified for a liquid crystal (LC)-based SLM via a 1-D experimental version of the device followed by a detail simulation using SPICE. It was found that the optical performance of the LC-SLM was most sensitive to the liquid crystal thickness, substrate doping concentration, and the photodiode leakage current. This model can be a useful tool for the analysis of the optical performance (such as photosensitivity and image uniformity) of a variety of photodiode-based SLMs as a function of their structural and operating parameters.