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Liquid crystal on silicon (LCOS) is a reflective microdisplay technology that is based on a silicon backplate. It is a combination of digital light processing (DLP) and liquid crystal display (LCD) projection technologies as it is reflective, but instead of using mirrors as in DLP, it uses liquid crystals that are applied on a reflective silicon backplate. Light is reflected off the backplate, while the liquid crystals open and close to modulate it.
LCOS microdisplay is constructed with a liquid crystal layer sandwiched between a thin-film transistor (TFT) and a silicon semiconductor with a reflective coating, hence the name. Like in DLP technology, light passing through a polarizing layer is reflected, but in the case of LCOS, it uses a reflective semiconductor instead of mirrors, while the liquid crystals act as gates that control the amount of light that passes and reaches the reflective surface, modulating the light and creating the image. As with LCD technology, LCOS modulates light in the RGB channel, so there are still three separate subpixels of red, green and blue.
Parts of an LCOS microdisplay starting from the top:
LCOS offers the following advantages: