We report algorithms and laboratory practices that tell the full complex behavior of an SLM over its entire face, pixel by pixel, and put the information into a form that is useful to our filter optimization code. We add a quadrature component to the interferometry and image each pixel of the SLM. We analyze the fringes not at one value of drive and in an across-pixels dimension, but instead at each pixel in the drive dimension. We describe details of the method and given examples of spatially-variant filter SLM behavior. We provide examples of performance degradation when the filter's spatial variance has not been accommodated.
We report experimental laboratory results using filters that optimize the Rayleigh quotient [Richard D. Juday, 'Generalized Rayleigh quotient approach to filter optimization,' JOSA-A 15(4), 777-790 (April 1998)] for discriminating between two similar objects. That quotient is the ratio of the correlation responses to two differing objects. In distinction from previous optical processing methods it includes the phase of both objects -- not the phase of only the 'accept' object -- in the computation of the filter. In distinction from digital methods it is explicitly constrained to optically realizable filter values throughout the optimization process.
We describe the optical correlator subsystem of a hybrid vision system. The optical correlator has a Kopin SLM at the input plane and a fast analog nematic Boulder Nonlinear Systems SLM at the filter plane. Filters are computed to provide identification and pose estimation for various objects. Spatial non-uniformities in the filter SLM are particularly bothersome from an operational standpoint. Methods of measuring and accommodating for the non- uniformities are described. Correlation filters produce an initially coarse identification, and later filters are intended to refine the coarse estimate of the pose of the observed object. Certain image preprocessing operations and their results are discussed; these include the cross- correlation that result when a Laplacian of Gaussian image is used as input to the system whose filter has been computed for a Sobel edge-extracted version of the reference image.
KEYWORDS: Spatial light modulators, Interference (communication), Liquids, Signal to noise ratio, Signal processing, Modulation, Clouds, Process modeling, Electronic filtering, Digital filtering
A measure is proposed for the utility of a spatial light modulator, as relates to using the SLM in a realistic optical correlator. In this paper, the metric of utility is particularized to the birefringent liquid crystal SLM.
In order to implement computer generated holograms (CGHs) and correlation plane filters (CPFs) on an LCTV SLM, the pixel-level complex-amplitude properties of the modulator must be accurately known. These properties must then be incorporated into algorithms for achieving the pixel-level control via a frame grabber (FG) and NTSC video signal. Within this investigation we present techniques for measuring the properties of FG-to-video-to-LCTV system, and then develop an algorithm to allow pixel-level control of the LCTV.
KEYWORDS: Signal processing, Analog electronics, Electro optics, Space operations, Electronics, Chemical elements, Dispersion, Data processing, Optical signal processing, Computing systems
Within this paper we discuss the precision of a fixed-point discrete numeric vector-matrix processor. The concept of precision relates to the quantity of numerically exact information in the processor's calculated result. This analysis is based on a signal space formulation which allows for the determination of precision from the uncertainty in the output signal space. Characteristics of the ideal signal space are explored and then the implications of simple nonideal temporal and spatial effects are considered. The resulting precision limitations are discussed in terms of numerical roundoff and significance errors.
A simple complex-amplitude model is developed and used to establish the behavior of amplitude an polarization state noise. A simple experiment based upon this model shows that the dominate source of noise in a twisted nematic liquid crystal cell results from polarization state fluctuations. A Stokes polarimeter is described and then used to measure the polarization state dynamics of a commercially available liquid crystal modulator.
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