Optical correlator using ferroelectric liquid crystal spatial light

Abstract

An optical correlator uses ferroelectric liquid crystal spatial light modulators (FLC-SLM's) in both the reference and filter planes. The SLM's include an electrically addressable memory to store images in the form a two-dimensional array of reflective pixels beneath the FLC layer. The SLM's selectively rotate the polarization of the light reflected by each pixel in accordance with the stored image. In particular, a laser produces a polarized beam that is directed through a first polarizing beamsplitter and onto the reference SLM. This beamsplitter blocks unmodulated light reflected by the reference SLM and transmits modulated light through a set of Fourier tranform lenses. The resulting beam is directed through a second polarizing beam splitter onto a filter SLM that has been programmed with the complex conjugate of the Fourier transform of a desired target image. Unmodulated light reflected from the filter SLM is blocked by the second polarizing beamsplitter and modulated light is reflected by the second polarizing beamsplitter through a set of inverse Fourier transform lenses. A CCD camera detects any correlation peak produced by the inverse Fourier transform lenses. A computer system downloads images to the SLM's and analyzes the correlation peaks detected by the camera. A half-wave plate can be included between both sets of SLM's and polarizing beamsplitters to allow manual adjustment of the polarization of the incident beam entering the SLM.