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What Is a Spatial Light Modulator?

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  • Written By: Andrew Kirmayer
  • Edited By: Shereen Skola
  • Last Modified Date: 22 October 2014
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A spatial light modulator (SLM) uses the input of an electrical or optical signal to alter light and create an image as fast as multiple times per millisecond. This can be found in many different variations and is used in a wide range of optical devices, including an overhead projector, television, or other video and graphics display. One- and two-dimensional types are available, both featuring pixels, the basic elements of any picture displayed on a screen. The many varieties of spatial light modulator can perform electrical or optical functions individually or combine them in one modulator.

Liquid crystal is often the medium used by a spatial light modulator, while a control circuit processes data into the pixel array for each frame of an image. The two-dimensional types are used in video projectors, but an SLM can also be used in many different applications. One kind, known as a Variable Electro-Optic Mirror is suited for optical systems such as beamsplitters, shutters, and mirrors. It can be utilized in highly reflective systems and manufactured on such small scales that the modulators can be integrated into windows that can lighten and darken. Micromirror devices can be built into individual chips used in scientific equipment like high-power lasers.

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Depending on the application, an SLM can work with wavelengths including near infrared. Ultraviolet and short-, mid-, or long-wave infrared wavelengths can be used to modify a specific wavelength in the light spectrum as well. A spatial light modulator is sometimes used in an effort to control the direction of laser beams, to correct the deviation of light waves, and for processing and analyzing images. It can also alter the amplitude or the phase of the light, or both if the combination of functions best suits the application.

The spatial light modulator can provide such precise control of light that engineers are considering its use in optical computing and holographic data storage. Light can be modified down to the individual pixel. The modulator and the liquid crystal element can be built on a single silicone chip for placement on circuit board components for computer video cards. Images can be transferred at very high speeds across digital video interfaces as the SLM processes dense pixel data and allows for a very high resolution display for the user. Phase rates can be as fast as less than a millisecond, so high-speed and high-quality video is made possible for all types of computers and mobile devices.

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allenJo
Post 3

@SkyWhisperer - That’s certainly one application. I am interested in how it can be used to control laser beams.

I think that the military is working on space based, strategic missile defense systems (the so-called “Star Wars” shield), and I know that lasers are a big part of that initiative.

Regardless of what you think about the SDI program, there’s no doubt that being able to use a spatial light modulator to calibrate the lasers will result in greater accuracy.

SkyWhisperer
Post 2

@nony - I didn’t realize that such simple technology as a transparency on an overhead projector was considered a spatial light modulator.

However, it helps that the article uses that as an example, because it clarifies what the technology actually does. I imagine that in addition to holographic data storage it would most certainly be used to create holographic images themselves.

Imagine having something like a wallet photo or something that could be projected into a holographic image, using such a portable device! I think it would bring a lot of your most cherished memories to life.

nony
Post 1

I am very fascinated by the prospect of holographic data storage. I believe that we will be able to store much more information on modulated light than we can currently store on physical or even flash memory drives.

I am looking forward to its use in video technology. Video remains as one of the most demanding forms of data storage. I do some work in video editing and a single second of video can occupy 30 frames per second or more of digital images.

Each frame takes up a lot of space on your hard drive and that’s why video is so slow over the Internet or on mobile devices. However, if it can be “projected” using a spatial light modulator device, it will approach real time in my opinion, regardless of where the video is actually stored.

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