A Spatial Light Modulator (SLM) is a device that modulates light according to a fixed spatial pixel pattern. It consists of an array of electrostatic parallel plate actuators that are directly coupled with square mirror pixels by mechanical attachment posts. SLM plays a vital role in several projection and display areas where light is controlled on a pixel-by-pixel basis in order to achieve optimum system quality and performance. SLMs are primarily used to control incident light in amplitude-only, phase-only or in combination. The general idea of such devices is to modulate a constant source optical signal as a function of a modulating signal that may be optical, mechanical or electrical. The mechanical tilt of the electrostatic parallel plate actuator (integrated with mirror) takes place as a result of the electric field imposed by the potential differences between the addressable electrodes. The imposed electric field is derived from the modulating signal. The device can be fabricated using a three-layer, polysilicon, surface micromachining process. These silicon based tiltable mirrors have the potential to modulate the spatial and temporal features of constant source optical wavefronts, and have wider applications in imaging, beam-forming, and optical communication systems. SLMs are very fast, compact and reliable devices with excellent optical qualities.
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