Laser video projector

A laser video projector takes a video signal and modulates a laser beam in order to project a raster-based image. The systems work either by scanning the entire picture a dot at a time and modulating the laser directly at high frequency, much like the electron beams in a CRT, or by optically spreading and then modulating the laser and scanning a line at a time, the line itself being modulated in much the same way as in a DLP. When well implemented this technology produces the broadest color gamut available in practical display equipment today, derived from the fact that lasers produce truly monochromatic primaries.

Assembly

Laser signal modulation

The video signal is introduced to the laser beam by an acousto-optic modulator (AOM) that uses a photorefractive crystal to separate the beam at distinct diffraction angles. The beam must enter the crystal at the specific Bragg angle of that AOM crystal. A piezoelectric element transforms the video signal into vibrations in the crystal to create a diffraction grating.

The first order diffraction signal is used and the other beams discarded.

Horizontal and vertical refresh

A rapidly rotating polygonal mirror gives the laser beam the horizontal refresh modulation. It reflects off of a curved mirror onto a galvanometer-mounted mirror which provides the vertical refresh. Another way is to optically spread the beam and modulate each entire line at once, much like in a DLP, reducing the peak power needed in the laser and keeping power consumption constant.

Applications

In general, laser projectors use a laser as light source.

There are several realisations of laser projectors; one example being based on the principle of a flying light spot writing the image directly on a screen. A laser projector of this type consists of three main components: a laser source uses the video signal to provide modulated light composed of the three sharp spectral colours red, green and blue. A flexible fibre optical waveguide transports this light to a relatively small projection head that deflects the beam according the pixel clock and emits it onto a screen at an arbitrary distance. Such laser projectors are used for flight simulators, planetariums as well as in virtual reality applications.

Due to the special features of laser projectors it is possible to project images or data on any kind of projection surface. Typically sharpness, colour space and contrast are higher than that of other projection technologies (on – off contrast is typically 50,000:1 and higher). In comparison to conventional projectors laser projectors provide a lower luminous flux output, but because of the extremely high contrast, the brightness appears greater.

Concepts

*Acousto-optic effect
*piezoelectric
*photorefractive effect
*Bragg diffraction

ee also

*Digital projector
*LCD projector
*Laser light show
* [http://www.colorvision-lasers.com Colorvisions] , a company that makes these type of projectors