Abstract

Phase-only/binary-phase-only filters have been shown to give sharp correlation peaks in optical correlations. However, these filters transmit all the incoming light, including noise, to the correlation plane so that, theoretically speaking, under additive white noise corruption the signal-to-noise ratio is zero for these filters.¹ The optimal phase-only/binary-phase-only filters recently studied^1,2 incorporate the use of a supporting binary amplitude function that masks out certain regions of the filter and consequently increases the SNR ratio. While an optimal binary-phase-only filter can be implemented with a polarization modulation device (e.g., ternary filters displayed on a MOD²), simultaneous modulation of continuous phase and binary amplitude has not been shown. In this paper, we propose to use a twisted nematic liquid crystal SLM to implement a phase/amplitude filter. Continuous phase modulation can be achieved by modulating the LC below optical threshold. Besides, a pixel can be turned off (zero transmittance) by applying full voltage across the pixel and by placing an analyzer behind the modulator. This architecture can also be used to display binary-amplitude continuous-phase holograms, which generate better quality images.

© 1992 Optical Society of America