spatial light modulator
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A spatial light modulator (SLM) is an object that imposes some form of spatially varying
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
on a beam of light. A simple example is an
overhead projector An overhead projector (often abbreviated to OHP), like a film or slide projector, uses light to project an enlarged image on a screen, allowing the view of a small document or picture to be shared with a large audience. In the overhead projec ...
transparency. Usually when the term SLM is used, it means that the transparency can be controlled by a
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
. In the 1980s, large SLMs were placed on overhead projectors to project computer monitor contents to the screen. Since then, more modern
projectors A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer types ...
have been developed where the SLM is built inside the projector. These are commonly used in meetings of all kinds for presentations. Usually, a SLM modulates the intensity of the light beam. However, it is also possible to produce devices that modulate the
phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...
of the beam or both the intensity and the phase simultaneously. SLMs are used extensively in
holographic data storage Holographic data storage is a potential technology in the area of high-capacity data storage. While magnetic and optical data storage devices rely on individual bits being stored as distinct magnetic or optical changes on the surface of the recor ...
setups to encode information into a laser beam similarly to way 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 Optical computing or photonic computing uses light waves produced by lasers or incoherent sources for data processing, data storage or data communication for computing. For decades, photons have shown promise to enable a higher bandwidth than the ...
. 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. SLMs primarily marketed for image projection, displays devices, and
maskless lithography Maskless lithography (MPL) is a photomask-less photolithography-like technology used to project or focal-spot write the image pattern onto a chemical resist-coated substrate (e.g. wafer) by means of UV radiation or electron beam. In microlithograp ...
.


Electrically-addressed spatial light modulator (EASLM)

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 The graphics display resolution is the width and height dimension of an electronic visual display device, measured in pixels. This information is used for electronic devices such as a computer monitor. Certain combinations of width and height ar ...
(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 The digital micromirror device, or DMD, is the microoptoelectromechanical system (MOEMS) that is the core of the trademarked DLP projection technology from Texas Instruments (TI). Texas Instrument's DMD was created by solid-state physicist and ...
at the heart of DLP displays or
LCoS Liquid crystal on silicon (LCoS or LCOS) is a miniaturized reflective active-matrix liquid-crystal display or "microdisplay" using a liquid crystal layer on top of a silicon backplane. It is also referred to as a spatial light modulator. LCoS was ...
Displays using
ferroelectric Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the ad ...
liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. The ...
( FLCoS) or nematic liquid crystals (Electrically Controlled Birefringence effect).


Optically-addressed spatial light modulator (OASLM)

The image on an optically addressed spatial light modulator, also known as a
light valve A light valve (LV) is a device for varying the quantity of light, from a source, which reaches a target. Examples of targets are computer screen surfaces, or a wall screen in the case of a light projector. There are two basic principles of achievin ...
, 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. They are often used as the second stage of a very-high-resolution display, such as one for a computer-generated holographic display. In a process called active tiling, images displayed on an EASLM are sequentially transferred to different parts on an OASLM, before the whole image on the OASLM is presented to the viewer. As EASLMs can run as fast as 2500 frames per second, it is possible to tile around 100 copies of the image on the EASLM onto an OASLM while still displaying full-motion video on the OASLM. This potentially gives images with resolutions of above 100 megapixels.


Application in ultrafast pulse measuring and shaping

Multiphoton intrapulse interference phase scan Multiphoton intrapulse interference phase scan (MIIPS) is a method used in ultrashort laser technology that simultaneously measures (phase characterization), and compensates (phase correction) femtosecond laser pulses using an adaptive pulse shape ...
(MIIPS) is a technique based on the computer-controlled phase scan of a linear-array spatial light modulator. Through the phase scan to an ultrashort pulse, MIIPS can not only characterize but also manipulate the ultrashort pulse to get the needed pulse shape at target spot (such as transform-limited pulse for optimized peak power, and other specific pulse shapes). This technique features with full calibration and control of the ultrashort pulse, with no moving parts, and simple optical setup. Linear array SLMs that use nematic liquid crystal elements are available that can modulate amplitude, phase, or both simultaneously.


See also

* Active filters in femtosecond pulse shaping


References

*Larry J. Hornbeck ( TI), ''Digital Light Processing for High-Brightness, High-Resolution Applications'', 21st century Archive

*Coomber, Stuart D.; Cameron, Colin D.; Hughes, Jonathon R.; Sheerin, David T.; Slinger, Christopher W.; Smith, Mark A.; Stanley, Maurice ( QinetiQ), "Optically addressed spatial light modulators for replaying computer-generated holograms", ''Proc.
SPIE SPIE (formerly the Society of Photographic Instrumentation Engineers, later the Society of Photo-Optical Instrumentation Engineers) is an international not-for-profit professional society for optics and photonics technology, founded in 1955. It ...
'' Vol. '4457', p. 9-19 (2001) *''Liquid Crystal Optically Addressed Spatial Light Modulator''

*Slinger, C.; Cameron, C.; Stanley, M.
"Computer-Generated Holography as a Generic Display Technology"
''IEEE Computer'', Volume 38, Issue 8, Aug. 2005, pp 46–53 {{Reflist


External links


9781510613010/10.1117/3.2281295?SSO=1 How to Shape Light with Spatial Light Modulators

SLM ToolBox
A free Windows application for controlling phase-only spatial light modulators.
Phase calibration of a Spatial Light Modulator
Optical components Display technology Optical devices