Phase correction of a spatial light modulator displaying a binary phase-only filter

Real-time optical aberration correction with a ferroelectric liquid-crystal spatial light modulator

Real-time correction of an optically aberrated wave front by use of a 10 x 10 ferroelectric liquid-crystal spatial light modulator as the correction device and a point-diffraction interferometer as the wave-front sensor is demonstrated. This type of interferometer requires no reference arm and so can be used, in theory, in an astronomical adaptive-optics system. We discuss some of the unusual features of the point-diffraction interferometer for wave-front sensing.

Astigmatic phase correction for the magneto-optic spatial light modulator

We report a simple low-cost technique for evaluating the phase distortion in a magneto-optic spatial light modulator. We find that the dominant distortion is caused by astigmatism and is easily compensated by encoding of the complex-conjugate pattern onto the device. Two experimental results are shown. First, the focused spot size from a Fresnel lens is sharpened when the aberrations are corrected. Second, we show that the pattern that generates a first-order Bessel-function nondiffracting beam does not work unless the aberrations are corrected.

Interaction of multiple distortions in spatial light modulators

Spatial light modulators are the key components in real-time optical image-processing systems. The phase and the intensity of their outputs will often depart from ideal behavior. An experimental method is described that permits the effects of multiple distortions, present simultaneously, to be modeled. A computer simulation of a bismuth silicon oxide-based correlator is presented, with spatial light modulators subject to three types of distortion, including phase and amplitude. The experimental method permits both the main effects of the distortions and their interactions to be predicted. Combining all the distortions simultaneously gives a more accurate assessment of the suitability of a spatial light modulator for a given optical processing task. Images of 256 × 256 pixels were used, and the simulation took 15 min. with a Sun SPARCstation 2.

Wave-front control using liquid-crystal devices

We report on complete wave-front control with amplitude- and phase-modulation liquid-crystal devices (LCD's). A twisted nematic device is used for amplitude modulation, and an electrically controlled birefringent device is used for phase modulation. Because the LCD's are optically coupled with afocal optics and are driven by individual LCD driver circuits, the amplitude and the phase can be controlled two dimensionally and independently. Complex amplitude data are calculated, and on-axis computergenerated holograms are directly recorded. Furthermore, we discuss LCD performance requirements for high-quality reconstruction.

Optical correlator using very-large-scale integrated circuit/ferroelectric-liquid-crystal electrically addressed spatial light modulators

The use of 2-kHz 64 × 64 very-large-scale integrated circuit/ferroelectric-liquid-crystal electrically addressed spatial light modulators as the input and filter planes of a VanderLugt-type optical correlator is discussed. Liquid-crystal layer thickness variations that are present in the devices are analyzed, and the effects on correlator performance are investigated through computer simulations. Experimental results from the very-large-scale-integrated/ferroelectric-liquid-crystal optical-correlator system are presented and are consistent with the level of performance predicted by the simulations.

Effects and correction of magneto-optic spatial light modulator phase errors in an optical correlator

Here we study the optical phase errors introduced into an optical correlator by the input and filter plane magneto-optic spatial light modulators. We measure and characterize the magnitude of these phase errors, evaluate their effects on the correlation results, and present a means of correction by a design modification of the binary phase-only optical-filter function. The efficacy of the phase-correction technique is quantified and is found to restore the correlation characteristics to those obtained in the absence of errors, to a high degree. The phase errors of other correlator system elements are also discussed and treated in a similar fashion.