Solid-state lasers project laser television signals

The rapid development of solid-state lasers has led to laser-based television sets becoming a reality. A laser TV system was demonstrated recently at the IFA (Internationale Funkausstellung) fair in Berlin, Germany, to an enthusiastic audience. Availability of professional laser TV systems is planned for next year, with consumer sets appearing in living rooms by the year 2002. The market for these systems is projected to be DM 100 billion ($57 billion) by 2010.

The appeal of laser TV is based on several factors. Most obvious is the brilliance of the colors—which is significantly better than that of conventional TV—but the size and flexibility of the screen is also intriguing, because sharp images can be projected onto various surfaces, even curved ones. All current TV standards—such as PAL, NTSC, SECAM, VGA or HDTV—can be handled by the system.

The company driving development of laser TV, Laser Display Technology (LDT; Gera, Thuringia, Germany), is a 50-50 joint venture between auto manufacturer Daimler Benz AG and Schneider Rundfunkwerke AG, a manufacturer of radio sets and multimedia equipment. The first license for the system will be issued by LDT to Schneider, although licensing is open to other manufacturers.

The system is based on projection of spots of the three primary colors—red, green, and blue (RGB)—in a sequence determined by the video signal. Continuous-wave (CW) lasers emitting at 635, 532, and 447 nm are electro-optically modulated and synchronized to the x-y operation of the scanner unit (see Fig. 1). Currently the horizontal sweep of the scan is created by a 25-face polygon mirror rotating at 1300 rpm. Vertical beam movement is driven by a galvanometer scanner.

For projection of the image there are several options. Most straightforward is direct beam projection, which can be extended to large screens in the far field via a telephoto lens. Projection distances up to 40 m are currently possible. Variable optics enable the image size to be altered in the ratio of 1:3 for a fixed projection distance.

For multimedia events and for home video, projection onto a screen seems the most likely configuration because the image size can be adjusted to fit the viewing area. For home video the size of the projector is expected to be similar to that of a current video cassette recorder (VCR). It could, for example, be installed on a book shelf and the screen could be simply the opposite wall.

The revolution in size that makes the system a reality came about because of solid-state lasers. Only two years ago ion lasers were being used—requiring about 80 kW of electrical power and water cooling. With solid-state lasers the power requirement has been reduced to about 1 kW for production of three colors—each 4 to 5 W—from a diode-pumped solid-state integrated device. A less-powerful version of the system uses three separate solid-state lasers providing about 1 W of output power (RGB).

These specifications will be further improved in the near future. In fact, laser wavelengths currently used already fill a much wider segment of the color triangle than existing TVs, meaning that the color rendition of laser TV far exceeds that of conventional systems. Professional applications of the system are expected to dominate well before laser TV gets into the home—multimedia events, seminars, education, flight simulation, and advertising could all benefit.

About 20 German research institutes are involved in the development of laser TV, which is funded by the federal Ministry BMBF (Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie; Bonn). Germany pioneered much of the early development of existing television, including the introduction of the PAL system 30 years ago, which led to the growth of a prosperous industry. The country`s market share, however, was continuously lost to producers in the Far East. For that reason, the laser TV project has gained national importance and is seen as an opportunity to regain national leadership.