Direct green diode lasers are an important step toward powerful pico projectors. It means that the old laborious way of producing green light by doubling the frequency of infrared laser is no longer needed. What’s more, the new technology enables high color rendering and excellent contrast to be achieved. The wavelength of the new PL 520 laser diode of 515-530 nm produces precisely the right green for projection applications. Its optical output is 50 mW and its efficiency is typically 5-6 % at present. The PL 515 offers an output of 30 mW in a wavelength range of 510 to 530 nm. With a package diameter of only 3.8 mm the laser diodes enable the dimensions of projection units to be reduced considerably. “The commercial breakthrough for compact laser projectors is closer than ever before”, said Stephan Haneder, Marketing Manager for Consumer Lasers at Osram Opto Semiconductors.”
Single mode lasers with high beam quality
The lasers have a very high beam quality – in other words an extremely narrow beam that spreads out only slightly thanks to its small divergence angle. In the case of pico projectors, which project the laser light with a MEMS mirror (micro-electromechanical system) without any other optics, the size of the light point determines the image resolution. The beam quality is particularly important here. Both laser diodes operate in single mode, which means they emit only a single transverse oscillation mode.
Direct emitting lasers can be better modulated than other laser types, such as frequency-doubled infrared lasers. This is an important property for MEMS-based projectors in which the color components per pixel result from the emission time of the laser diode. There is also no need to adjust the focus of the projection image. The image is always sharp, even on curved surfaces.
Laser shows, point lasers and line lasers
The single mode lasers open up new possibilities as light sources for laser shows. Their high beam quality enables extremely fine structures to be displayed even over large distances. The projectors also benefit from the high thermal stability and small size of the lasers.
Green diode lasers are also ideal as point or line lasers for measuring distances for example. The human eye is most sensitive in the green spectrum so they offer another important advantage over red laser light. For the same laser output, and therefore the same laser safety class, green light is perceived more easily by the eye than the red light that is usually used. This means that distance meters, such as those used by builders, can be used over larger distances.
By launching one of the first direct emitting green laser diodes Osram Opto Semiconductors is underlining its leading position in lasers based on indium gallium nitride. The green laser is the result of years of intensive development work in Regensburg. It has been developed as part of the MOLAS project sponsored by the German Ministry for Education and Research and involving technologies for ultra-compact and mobile laser projection systems. In 2010, researchers at the company received the Karl-Heinz-Beckurts Award for development work on the green laser.