Abstract

The large electro-optical coefficient of barium titanate yields strong two-beam coupling. Here we describe a nonlinear photorefractive technique to reduce noise in a signal that is embedded in additive speckle noise. This approach implements an adaptive Wiener filter, which improves the contrast ratio by a factor of eight for a binary input signal with peaks equal to the noise peak. This technique relies on thresholding the Fourier transform of the noisy signal. The Fourier transform of the signal is a diffraction pattern of high intensity relative to the noise, and two-beam coupling is used to reduce the weaker-intensity noise Fourier transform. Our experimental results shows that it is possible to enhance features that are smaller than the grain size of the noise. The mechanism of enhancement depends on the initial signal-to-noise ratio and the specific geometry of the signal. We have also used the same technique for reducing multiplicative artifact noise and defects in images.

© 1990 Optical Society of America