Laser video projector

A laser video projector is a video projector that 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 cathode ray tube, 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 with Digital Light Processing (DLP). When well implemented this technology produces the broadest color gamut available in practical display equipment today, because 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.^{[citation needed]}

Applications

There are several realizations of laser projectors, one example being based on the principle of a flying light spot writing the image directly onto 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 colors — red, green, and blue — which a flexible, fiber-optic waveguide then transports to a relatively small projection head. The projection head deflects the beam according the pixel clock and emits it onto a screen at an arbitrary distance. Such laser projection techniques are used in handheld projectors, planetariums, and for flight simulators and other virtual reality applications.

Due to the special features of laser projectors, such as a high depth of field, it is possible to project images or data onto any kind of projection surface, even non-flat. Typically, the sharpness, color space, and contrast ratio are higher than those of other projection technologies. For example, the on-off contrast of a laser projector is typically 50,000:1 and higher, while modern DLP and LCD projectors range from 1000:1 to 40,000:1. In comparison to conventional projectors, laser projectors provide a lower luminous flux output, but because of the extremely high contrast the brightness actually appears to be greater.

Concepts

• Acousto-optic effect
• Bragg diffraction

Manufacturers of projectors

• LDT Laser Display Technology GmbH — High-end laser projectors with double amount of colors and high contrast of 50.000:1 for simulation, planetaria and virtual reality applications
• Evans and Sutherland — 2000 and 8000 Lumen projectors for large screen high resolution (8K) applications
• Microvision ShowWX — 15 Lumen handheld mobile projector and OEM component
• Light Blue Optics — 4 Lumen projector (Colorado Springs, Colorado office closed as of 2011-09-01)

See also

• Digital projector
• LCD projector
• Laser light show