Spatial light modulator

A spatial light modulator (SLM) is an object that imposes some form of spatially varying modulation on a beam of light. A simple example is an overhead projector transparency. Usually when the phrase SLM is used, it means that the transparency can be controlled by a computer. In the 1980s, large SLMs were placed on overhead projectors to project computer monitor contents to the screen. Since then more modern projectors have been developed where the SLM is built inside the projector. These are commonly used in meetings of all kinds for presentations. A spatial light modulator (SLM) is an object that imposes some form of spatially varying modulation on a beam of light. A simple example is an overhead projector transparency. Usually when the phrase SLM is used, it means that the transparency can be controlled by a computer. In the 1980s, large SLMs were placed on overhead projectors to project computer monitor contents to the screen. Since then more modern projectors have been developed where the SLM is built inside the projector. These are commonly used in meetings of all kinds for presentations. Usually, an SLM modulates the intensity of the light beam. However, it is also possible to produce devices that modulate the phase of the beam or both the intensity and the phase simultaneously. SLMs are used extensively in holographic data storage setups to encode information into a laser beam in exactly the same way as a transparency does for an overhead projector. They can also be used as part of a holographic display technology. SLMs have been used as a component in optical computing. They also often find application in holographic optical tweezers. Liquid crystal SLMs can help solve problems related to laser microparticle manipulation. In this case spiral beam parameters can be changed dynamically. As its name implies, the image on an electrically addressed spatial light modulator is created and changed electronically, as in most electronic displays. EASLMs usually receive input via a conventional interface such as VGA or DVI input. They are available at resolutions up to QXGA (2048 × 1536). Unlike ordinary displays, they are usually much smaller (having an active area of about 2 cm²) as they are not normally meant to be viewed directly. An example of an EASLM is the Digital Micromirror Device at the heart of DLP displays or LCoS Displays using ferroelectric liquid crystals (FLCoS) or nematic liquid crystals (Electrically Controlled Birefringence effect). The image on an optically addressed spatial light modulator, also known as a light valve, is created and changed by shining light encoded with an image on its front or back surface. A photosensor allows the OASLM to sense the brightness of each pixel and replicate the image using liquid crystals. As long as the OASLM is powered, the image is retained even after the light is extinguished. An electrical signal is used to clear the whole OASLM at once.