Laser video projector

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A laser video projector takes a video signal and modulates a laser beam in order to project a raster-based image. laser light shows use a vector-based system of rendering a pattern so are not appropriate for video projection. 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.

1 Assembly
- 1.1 Modulating the Laser Signal
- 1.2 Horizontal and Vertical Refresh
2 Applications
3 Concepts
4 See also

[edit] Assembly

[edit] Modulating the Laser Signal

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.

[edit] 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.

[edit] Applications

In general, laser projectors (LP) use a laser as light source.

There are several realisations of LPs. E.g. the technology of the german company JENOPTIK LDT GmbH (http://www.jenoptik-laserdisplay.de/cps/rde/xchg/ldt/) is based on the principle of a flying light spot writing the image directly on a screen.
A LP of this type consists of three main components: A laser source uses the video signal to provide modulated light being composed of 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.
These LPs and laser projection systems are used at the professional market for flight simulators, planetariums as well as for virtual reality applications.
Due to these LP’s special features it is possible to project images or data on any kind of projection surface in an outstanding quality regarding sharpness, colour space and contrast (on – off contrast typical 50,000:1 and higher).
In comparison to conventional projectors the JENOPTIK LP provides a lower luminous flux – output, but due to the extremely high picture contrast the subjective brightness impression of the human eye is higher. That’s why the brightness is high enough for applications as mentioned above. The principle of a directly writing light beam on a screen has a lot of advantages, that do not appear in conventional projection technologies. So no lenses are required to reach a limitless depth of sharpness. Attaching lenses at the output is anyway possible and provides the possibility to enlarge or reduce the picture size at a given projection distance. Another outstanding advantage of this principle, together with the usage of the acoustooptic effect, is the presentability of the lowest grey levels. This property is preferably used in both civil and military flight simulators to allow realistic night flight missions.