Microprojectors spur development of green lasers

Caren B. Les, caren.les@photonics.com

Picoprojectors will drive the green laser market – expected to reach about $500 million in revenue by 2016, up from an estimated $20 million in 2011 – with more than 45 million devices, according to a market analysis by Yole Développement sarl.

The emerging microprojector technology has applications in mobile phones, digital cameras, media players, personal digital assistants, head-mounted or head-up displays, laptop computers and other portable devices, enabling users to project the smaller image from their device onto a wall or other surface so that it may be easily viewed or shared in a larger format. The technology – stand-alone or embedded – requires delivery of a high-quality image and may allow the projection of movies, video games or even touch-screen menus.

In the microprojector market, lasers would be the ideal light-emitting device because of their ability to deliver highly saturated colors in the widest possible gamut, according to Yole’s report, Green Laser Market for Projection Devices. Published in April 2010, it comprises a market analysis of direct- and indirect-emitting semiconductor green laser diodes in projection applications. Lasers offer focus-free operation and are expected to deliver improved wall-plug efficiency, which will affect the power consumption for battery operation, the company said.

There are three vastly different technologies battling for the heart of the picoprojector: liquid-crystal-on-silicon microdisplays, digital light processing devices and scanning mirror systems (also called laser beam-steering systems), according to an article in the May 2010 issue of IEEE Spectrum titled March of the Pico Projectors by Jacques Lincoln, global product manager for automotive displays at Microvision Inc. in Redmond, Wash. He wrote that the imagery of the scanning mirror systems is extremely sharp, has the highest contrast of the three technologies and potentially could be produced in the smallest package.

Red, green and blue lasers are required for the laser-based microprojector. The report from Yole notes that the light-engine module, including the light engine and the scanning device, is expected at a target price of $40 to $70, depending upon the application, implying a laser price target of $10 per color. Neither blue nor green lasers currently meet these price requirements, the report states.

Green lasers have niche applications in industry, medicine, defense and biomedical instrumentation, all of which can work with existing solid-state lasers or the more recent combinations of semiconductor lasers with nonlinear crystals, according to Yole. The company said that three green laser semiconductor-based technologies are frequency-doubled diode-pumped solid-state lasers, second-harmonic generation of semiconductor edge- and surface-emitting lasers, and direct-emission laser diodes. It indicated that the technology will undergo development from second-harmonic generation to direct-emission sources.

Green laser developments

Various companies have been developing green laser technology for applications in microprojection; e.g., a green laser employing quantum dot semiconductor crystals was developed by QD Laser Inc. of Tokyo in collaboration with Yasuhiko Arakawa of the University of Tokyo’s Institute for Nano Quantum Information Electronics. QD Laser said in a September 2009 press release that the compact laser, which operates with low power consumption, is optimal for use in projectors that can be mounted on mobile phones or laptop computers.

The company said that it produced the green laser by applying distributed feedback laser technology to create a quantum dot semiconductor crystal laser operating at 1064 nm. The photon stream is then filtered through a nonlinear crystal via second-harmonic generation, forming photons with a 532-nm wavelength, half the original. The green laser can be housed in a generic TO-56 package operating from a 2-VDC supply.

Michael Usami, vice president of sales and marketing, said that the company is sampling the green laser by targeting mass production by the end of the year. He added that the green laser is suitable for any mobile projection system – especially for flying spot-type scanning systems, which require high-speed modulations – or for applications that require high beam quality.

“If green lasers can be mass-produced with reasonable pricing and enough manufacturing capacity, red-green-blue small-projection engines would be realized and would enable the creation of brand new applications. We would like to contribute them,” Usami said.

As announced in an August 2009 press release, Osram Opto Semiconductors GmbH of Regensburg, Germany, achieved a direct-emitting green InGaN laser with 50 mW in its laboratory. Suitable for mobile laser projection, the diode emits a true green, defined by the spectral range of 515 to 535 nm.

Direct green InGaN-based laser emission with CW output of 50 mW is a milestone for mobile laser projection technology. Courtesy of Osram Opto Semiconductors.

The release also stated that, compared with semiconductor lasers that operate with frequency doubling based on current technology, direct emitting green lasers are more compact and easier to control, offer greater temperature stability and have higher modulation capability. The main advantages of a direct-emitting InGaN laser are a smaller form factor (similar to blue laser diodes), high modulation capabilities and long-term price potential (similar to the blue laser), it said.

Osram noted that the main challenges lie in the fact that the direct green laser must be competitive with its second-harmonic green laser. For example, mobile laser projection systems need single-mode operation, 50 mW of output power at 515 to 525 nm (this requires low threshold and good slope efficiency), comparable wall plug efficiency and sufficiently long lifetimes.

In a report titled Progress of blue and green InGaN laser diodes by Stephan Lutgen et al in the Proceedings of SPIE, Vol. 7616, Feb. 8, 2010, laser operation at 516 nm with more than 50 mW of output power in CW operation is described in combination with a wall plug efficiency of 2.7 percent.

In another report, True green InGaN laser diodes by Lutgen et al, published in physica status solidi (a) online in May 2010, research is presented on true-green InGaN ridge waveguide laser diodes at 520 nm on c-plane GaN substrates in pulse operation at room temperature.

Using an LED light source, it is necessary to refocus the projector each time the distance between the projector and screen changes. With laser light sources, refocusing is unnecessary, regardless of the distance. The Yole report indicated that, in 2009, the first LED-based picoprojectors were available commercially, but, perhaps because of their poor brightness and relatively high price, no more than 300,000 units were sold. However, LEDs and high-brightness LEDs are serious competitors to laser-based systems because some picoprojectors have already been announced with brightness up to 30 lm, Yole said.

Applications forecasts

Yole predicts that 10 to 20 percent of stand-alone projectors will be laser-based by 2011, and that the ratio could grow to 50 to 75 percent by 2016. It forecasts that laser-based projection systems gradually will enter the cell phone market, especially if direct-emission green lasers contribute to the small size requirement. LED technology is expected to dominate until at least 2016, however.

A boom in media players equipped with projection functionality is expected by 2012. Second-harmonic-generation green lasers are likely to dominate in this market initially while waiting for direct-emission technology to become compatible in price and performance, Yole said.