QD Laser (Tokyo, Japan) announced yesterday that they have developed the first green laser using quantum dot technology. It is aimed at mobile picoprojection applications. Samples of the new laser will be available in December, with mass production in 2010.

Chris Chinnock
Senior Analyst and Editor
for Insight Media

Quantum dot lasers are the next generation structure. Current generation lasers use quantum wells that confine the electrons in two directions. Quantum dots confine electrons in three directions and literally look like dots on a wafer surface (see graphic).

What are the key advantages? There are several including improved efficiency, much better consistency of light output over a wider temperature range, low operating voltages and high modulation rates. Here is what QD Laser is saying about their new device:
· Stable operation up to 60C without a cooler
· Modulation rates up to 500MHz
· 2VDC operation
· 532nm output (100-200mW power level, with frequency doubling)
· Tiny TO-56 package (5.6mm diameter)

These specs are impressive. In an email dialog with QD Laser’s VP Sales & Marketing, Michael Usami, we learned a few more interesting details. For example, the low operating voltage and wide temperature range are great for battery powered CE devices that need to operate in a demanding environment. Blue and (eventually) green direct emitting lasers based on GaN require 4-6 volts (compared to their 2 volts) and wall plug efficiency is said to be about 10%, less than the 21% efficiency reported by Nichia on their current 500mW blue lasers. Modulation up to 500MHz means these lasers can be used in scanned MEMS picoprojectors or in flood-illuminated LCOS or DLP designs. And the device is compact. (see photo).

The device architecture consists of a quantum dot laser fabricated with GaAs material to lase at 1064nm by including a distributed feedback structure (grating) that helps set the wavelength. This output is coupled to a frequency doubling crystal, typically composed of periodically poled Lithium Niobate material (PPLN). This creates a laser output at 532nm (see graphic).

In a picoprojector, this green laser would normally be combined with a red and blue laser to create a full color image. One advantage of laser picoprojectors is the ability to get an always-in-focus image on any surface shape, along with good colorimetry and high efficiency. But lasers have speckle. There is no de-speckling technology included in this laser, so it is up to the system integrators to implement a solution as they see fit.

As for cost, Usami was a bit elusive, but noted that a 2-inch GaN wafer for blue lasers can cost $5K to $10K per wafer. QD Laser uses 3-inch GaAs wafers, which cost $200/wafer, so the basic laser costs will be much lower (The 1064nm laser uses the same wafers used for red lasers for DVDs and CD-ROMs, so they are produced in very high volumes). However, QD Laser must also add the PPLN and assemble, which is more likely to dominate the costs. However, multiple suppliers of PPLN exist, so as volume creeps up, he expects pricing to moderate.

QD Laser was founded in April 2006 with capital from Fujitsu Limited and Mitsui Ventures. The company developed this new device in cooperation with the University of Tokyo (Professor Yasuhiko Arakawa) and Fujitsu Laboratories. Fujitsu has already commercialized quantum dot lasers for use in telecom applications. -Chris Chinnock