Quantum dot lasers poised for mass production

20 Mar 2008

QD Laser has firm orders for its quantum-dot Fabry-Perot lasers and by the end of this year should become the first company to make such devices on a volume production scale.

Michael Usami of QD Laser said that the company expects to be mass-producing quantum-dot Fabry-Perot (FP) lasers before the year is out, with a subsequent six-month ramp to reach full production volumes. The first products will be FP lasers emitting at 1310 nm. Distributed feedback lasers are set to follow.

A joint venture between Japanese telecom giant Fujitsu and Mitsui Ventures that specializes in quantum-dot optoelectronics, QD Laser has firm orders from customers in Japan and is currently providing engineering samples and testing mass production.

The critical advantage of the InAs quantum-dot nanostructures used in these lasers is that they render the devices almost completely insensitive to changes in temperature over a very wide range, from –40 to 100°C according to the company.

At high temperatures, conventional FP lasers require much higher drive currents to generate useful power than they do when either cooled or running at room temperature. The switch-on current required to stimulate lasing is also much higher.

Other advantages of the technology, which makes the lasers behave more like individual atoms than bulk materials, include improved efficiency and a smaller package size. All of this is possible because at these atomic scales it is the size of the dot, rather than its material make-up, that controls physical behaviour.

The new lasers feature anywhere between five and 12 layers of InAs quantum dots, each one measuring around 20 x 20 x 5 nm. "We have the highest dot density growth in the world," Usami said. "It is about 60 billion [dots] per square centimetre for mass production."

Controlling the size of the self-assembling quantum dots during the epitaxial growth stage is one of the key problems that QD Laser's engineers have overcome and which, until now, has hindered the scale-up to mass production and restricted the commercial viability of quantum-dot devices.

At QD Laser, layers of InAs islands are deposited between a stack of intermediate layers of GaAs, with careful control of the growth recipe and temperature.

In collaboration with the Arakawa group at the University of Tokyo, the company has introduced antimony into the epitaxial process to increase the dot density to record levels, which delivers additional gain in the lasers. In the past couple of years, they have been able to improve control over the laser's polarization and wavelength.

Growth of the InAs dots on InP substrates to make longer-wavelength components is also progressing well, and future products will be aimed at longer-reach communications.

The company is also working on polarization-insensitive semiconductor optical amplifiers (SOAs) for use in the metropolitan and access levels of fibre-optic networks.