We report a new, to our knowledge, technique for encoding amphtude information onto a phase-only filter with a single liquid-crystal spatial light modulator. In our approach we spatially moduiate the phase that is encoded onto the filter and, consequently, spatially modify the diffraction efficiency of the filter. Light that is not diffracted into the first order is sent into the zero order, effectively allowing for amplitude modulation of either the first-order or the zero-order diffracted light. This technique has several applications in both optical pattern recognition and image processing, including amplitude modulation and inverse filters. Experimental results are included for the new technique.
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