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Osram gives laser projectors the green light

The firm's direct emitting green laser diodes are ideal for miniature projectors for mobile devices like smartphones and cameras
Osram Opto Semiconductors is now offering its first direct green diode lasers.

The company's two compact laser diodes have an optical output of 30 and 50 milliwatts (mW) and a high beam quality.

Osram believes they represent a milestone in the development of miniature projectors for mobile devices such as smartphones and cameras. Projection units for laser shows, point lasers and line lasers will also benefit from the new technology.

Direct green diode lasers are a big step towards powerful pico projectors. Hopefully it will mean that the laborious way of producing green light by doubling the frequency of infrared lasers will no longer  be needed.

What’s more, the new technology is claimed to enable high colour rendering and excellent contrast  but this is a work still in progress.

Direct green emitting PL 520 laser diode

The wavelength of the new PL 520 laser diode of 515-530nm produces precisely the right green for projection applications. Its optical output is 50mW and its efficiency is typically 5 to 6 percent at present.

The PL515 offers an output of 30mW in a wavelength range of 510 to 530nm. With a package diameter of just 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,” says Stephan Haneder, Marketing Manager for Consumer Lasers at Osram Opto Semiconductors.

The lasers have a high beam quality with a 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 in this case. Both laser diodes operate in single mode, which means they emit only a single transverse oscillation mode.

Direct emitting lasers can be easier to modulate than other lasers, such as frequency-doubled infrared lasers. This is an important property for MEMS-based projectors in which the colour 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. Osram says the image is always sharp, even on curved surfaces.

Osram believes 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. 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 metres, 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.

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