Photonics Spectra - September 2009

year to more than three million in 2013.

Sanju Khatri, principal analyst for sig-nage/projection at iSuppli, said tiny displays have been a major obstacle, preventing smart phones and small laptops from becoming primary platforms for computing and Internet access.

“The growth potential for embedded pico projectors will be limited during the next few years due to challenges in areas including power consumption, size and manufacturing,” she said. “As these issues are resolved, pico projectors will appear in many more mobile electronics devices.”

That might make microprojectors the hot accessory, possibly as soon as this Christmas. The upside: You could soon project bigger versions of the photos or videos from mobile devices onto virtually any surface without having to download them first. The downside: There may be no escaping a slide show of Uncle Phil’s two weeks in Branson, Mo.

Self-contained pico projectors now are about the size of a garage-door opener, but the trend is to embed them into portable things, such as a cell phone, an MP3 player or a digital camera.

Pico projectors with laser light sources are expected on the market sometime this year as consumers demand smaller devices. Diode manufacturers have been busy building diodes that lase at shorter and shorter wavelengths because the shorter the wavelength, the less power they use and the brighter the image is to the human eye.

“We are still planning to begin initial shipments of SHOWWX later this summer,” said Matt Nichols, director of communications for the Redmond, Wash.-based Microvision. SHOWWX is a handheld pico projector driven by the laser-based PicoP display engine. (For more information on projection technology, see “Microdisplays: Coming Soon to an Eye Near You?” September 2008, p. 68, and, in this issue, “Flat Screens Go Deep – and More,” p. 56.)

Seeing red

High-power red laser diodes emitting at 660 nm are standard in devices such as recordable DVD players, but that wavelength appears relatively dark to the human eye, making the diodes ill-suited for compact projectors equipped with RGB lasers.

Mitsubishi Electric said it solved that problem with its new red series – diodes that emit at 638 nm – which provide the

A green laser emits from an oscillator. Courtesy of Sumitomo Electric Industries Ltd.

brightness needed for pico projectors.

The company introduced the red diodes at Laser World of Photonics in Munich in June, saying they appear much brighter than 660 nm or even the commonly used 645-nm diodes at the same output power.

Blue (450 to 480 nm) diodes showed up about 15 years ago and are used now in Blu-ray disc players. In January at Photonics West 2009, Osram Opto Semiconductors GmbH of Regensburg, Germany, announced a blue laser with a wavelength of 450 nm and an output of 50 mW that it said is the smallest in its class.

It ain’t easy beamin’ green

One hurdle that laser makers have had to overcome is with the green wavelength, which stretches from 520 to 570 nm, with 532 considered optimal for displays.

Green lasers have been achieved through frequency conversion of infrared lasers but have been unable to directly emit green light. Recently, engineers have been inching closer to pure green emitters by producing wavelengths in the blue-green spectrum.

In February, researchers at Rohm Co. Ltd. in Kyoto, Japan, said they had pushed a gallium nitride (GaN) diode to the longest recorded wavelength yet produced, 499.8 nm, but said their technique is not suitable for mass production. Later that month, Osram Opto Semiconductors Inc., whose North American headquarters is in

Shown is
Microvision’s
pico projector, the SHOWWX.
Courtesy of Microvision Inc.

Pocket Projectors

Sunnyvale, Calif., published a paper in Applied Physics Letters describing an electrically pumped 500-nm-emitting diode based on its blue technology. In May, in an Applied Physics Express paper, Nichia Corp. of Tokushima, Japan, said it had created a 515-nm device. (At press time, Osram Opto announced it achieved a direct-emitting green indium GaN laser at 515 nm.)

Then in July, Sumitomo Electric Industries Ltd. of Osaka, Japan, announced that it had created the first direct-emitting green laser at 531 nm. The company said it overcame a problem with GaN semiconductors (used commercially for blue LEDs), in which the material’s luminance efficiency rapidly declines as the wavelength increases, by developing a GaN crystal that inhibits the efficiency drop. The result was room-temperature pulse operation of a laser diode emitting in the pure-green region at 531 nm. Sumitomo has applied for 60 patents on the technology.

Spectralus Corp. of Santa Clara, Calif., is reporting this month at the Eurodisplay 2009 conference on its developments in green laser efficiency. In June, it announced a milestone in shrinking green lasers: an eight-pin butterfly package for its 100-mW green laser. It also said that the lasers demonstrated 30 percent optical-to-optical (808- into 532-nm wavelength) conversion efficiency levels.

The company said in a statement that it is preparing a mass-production package tailored for pico and embedded projectors for the fourth quarter of 2009.

Microvision signed a supply deal with Corning Inc. of Rochester, N. Y., in May for its G-1000 synthetic green lasers and an agreement with Osram Opto for its blue and green lasers, to ensure an ample supply of diodes as it prepares to begin commercial production of the SHOWWX.