Spectralus claims green-laser breakthrough

14 Jul 2009

A Silicon Valley company has developed a highly efficient green-laser microchip for use in mobile projectors.

Spectralus, a US start-up firm that until recently has been operating in stealth mode, is now ready to announce a monolithic microchip laser that can deliver up to 200 mW power at green wavelengths. The company believes that its highly efficient laser source will fill the "green gap" that has so far hindered the development of laser-based pico-projectors.

"Market developments in the last several months have essentially validated the pico-projector story and we are starting to feel a lot of interest in our green-laser technology," Andrei Shchegrov, Spectralus' vice-president for product development, told optics.org. "High efficiency and cost-effective design are key to the success of laser sources [in these devices], and we are now demonstrating that we have a winning platform on both aspects."

The Spectralus device generates laser output at 532 nm by second harmonic generation (SHG), in which infrared light is frequency-doubled to green wavelengths. SHG has long been recognized as a promising approach for generating high-power green output, but companies seeking to commercialize the technology have struggled to create efficient, low-cost devices with a small enough form factor for use in mobile devices.

Spectralus' approach is to create a monolithic laser chip that combines a Nd:YVO₄ gain medium with an engineered nonlinear crystal for frequency doubling. And it's this proprietary crystal that makes the difference: it is made from periodically poled magnesium-oxide-doped lithium niobate (PPMgOLN), which has been shown to achieve the most efficient SHG from infrared to visible wavelengths.

"The laser cavity is monolithic and alignment-free, so the whole concept is similar to the laser pointer that delivers a brighter green beam with much higher efficiency and with perfectly linear polarization," commented Shchegrov.

Current Spectralus devices achieve an optical-to-optical conversion efficiency of up to 30% and a peak output power of 200 mW. They also offer a wall-plug efficiency of more than 10% at ambient temperatures between 10 and 50 °C, meeting one of the key performance metrics for battery-operated projectors.

Spectralus is now shipping engineering samples to customers in the consumer electronics business. These demonstrator versions are housed in a mini-butterfly package, which is too costly for use in pico-projectors, but the company is now working to integrate the laser source into a smaller and lower-cost package.

"We are not done yet," said Shchegrov. "We are currently developing a mass-production package design that will be less than 0.4 cm³ in volume and less than 4 mm in height."

Spectralus plans to report on the details and performance of its new package at Eurodisplay 2009, which will be held 14–17 September in Rome, Italy. The first units are expected to ship to customers before the end of the year.