We report a new, to our knowledge, technique for encoding amplitude information onto a phase-only filter with a single liquid-crystal spatial light modulator. In our approach we spatially modulate 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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In this paper we provide evidence of the temporal fluctuations of the phase modulation property of a liquid crystal on silicon (LCoS) display, and we analyze its effect when the device is used for displaying a diffractive optical element. We use a commercial twisted nematic LCoS display configured to produce a phase-only modulation, and we provide time resolved measurements of the diffraction efficiency that show rapid fluctuations of the phase modulation, in the millisecond order. We analyze how these fluctuations have to be considered in two typical methods for the characterization of the phase modulation: two beam interference and diffraction from a binary grating. We finally provide experimental results on the use of this device for displaying a computer generated hologram. A reduction of the modulation diffraction efficiency results from the phase modulation fluctuation.

We derive theoretical expressions for the eigenvalues and the eigenvectors for a twisted-nematic liquid-crystal display (LCD) as a function of the twist angle and the birefringence by use of the Jones-matrix formalism. These polarization eigenvectors are of particular interest for phase-only transmission because they propagate unchanged through the display. We find that the eigenvectors are elliptically polarized and that the ellipticity changes as a function of the birefringence of the LCD (which is proportional to the external voltage applied to the display). We can define an average eigenvector over a desired range for the applied voltage. We show, using Jones matrices, how this average eigenvector can be generated using a quarter-wave plate and a linear polarizer having appropriate orientation angles. Using this average eigenvector, we show that superior phase-only operation can be obtained over a given operating range for the LCD compared with other approaches.

Both radially polarized and azimuthally polarized beams can be decomposed into linear combinations of circularly polarized vortex beams having opposite vortex charges. We show experimental evidence for this decomposition using a specially designed vortex sensing diffraction grating that generates multiple vortex patterns having different senses of circularly polarization in the different diffracted orders. When this grating is illuminated with a radially or azimuthally polarized beam, the grating separates the components into different diffracted orders. Experimental results are shown.

We demonstrate a specially designed vortex sensing diffraction grating that generates multiple vortex patterns in the different diffracted orders. When this grating is illuminated with a separate vortex beam, the sign and order of the topological charge of the incident beam can be easily detected. Experimental results are shown for a variety of vortex beams including fractional values of the topological charge, and where both the diffraction grating and incident vortex illumination beam are generated by two different liquid crystal displays (LCDs). The programmability offered by the LCDs offers extremely convenient flexibility.