A novel use of liquid-crystal television (LCTV) is described. It is shown that, if the phase nonuniformity of the LCTV is corrected by a liquid gate, then a simple computer-generated hologram can be written and coherently reconstructed.It is well known that spatial light modulators (SLM's) are essential for real-time optical information processing. For that reason, much research has been devoted to them, and many types of SLM have been developed. 1Most of the existing SLM's are either forbiddingly expensive or still in the research and development stages. Recently an extremely inexpensive liquidcrystal television (LCTV) was investigated in relation to its use in optical data processing. 2 -1 0 One advantage of the LCTV is that it can be addressed either electronically or optically. However, because of the thickness variations over the aperture of the screen of the devices, its usefulness for coherent optical processing is limited.We have examined the thickness nonuniformities of the LCTV screen in a Mach-Zehnder interferometer.We have successfully corrected the nonuniformities by submerging the screen in a liquid gate and have demonstrated the feasibility of using this device to write and reconstruct a computer-generated hologram. The results are briefly reported below.The operating principle of the LCTV has been described. When no electric field is applied, the plane of polarization for linearly polarized light is rotated through 90 deg by the twisted liquid-crystal molecules, and no light is transmitted through the second polarizer. However, with an electric field applied, the twist and tilt of the liquid-crystal molecules are altered, resulting in transmission of a controllable and variable fraction of light. The input signal to the LCTV can be from a TV receiver, a computer, or a TV camera.A Mach-Zehnder interferometer was set up to analyze the optical quality of the LCTV screen. A 6.4-cm 2 (1-in.2 ) region of the LCTV screen was illuminated by a collimated He-Ne laser beam. The results are shown in Fig. 1(a). It can be seen that more than five fringes are produced, indicating thickness nonuniformities of the LCTV screen amounting to about 0.046 gm per pixel. It has been found that the phase nonuniformity is due mainly to the poor quality of the polarizer sheets. Because of the nonuniformity, Fraunhofer diffraction patterns show fuzziness in the various orders. 3We investigated two ways of removing the phase distortions. The first was to correct the phase variation by a phase-conjugation method. We used a 10-mW He-Ne laser to produce a holographic filter of the LCTV screen and addressed it with a phase-conjugated beam projected through a holographic plate. Unfortunately, the beam reconstructed through the LCTV was too weak to be observed visually because of the low diffraction efficiency of the hologram and the low power of the laser.

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A novel use of a liquid-crystal television (LCTC) is described. It is shown that, if the phase non-uniformity of the LCTV is corrected by a liquid gate, then a simple computer-generated hologram can be written and coherently reconstructed.

We describe the principle of the recognition and tracking of several objects that are moving at different directions in the same plane. This can be accomplished via a multifocus hololens and the liquid crystal TV spatial light modulator.2 A videotape demonstrating the experimental results is presented.