Quantum-dot laser shows broadband capability

16 Jun 2006

Ioffe Institute spin-out NL Nanosemiconductor has developed a ten-layer quantum-dot laser that can operate over a 25 nm wavelength range while retaining singlemode operation.

Quantum-dot (QD) laser specialist NL Nanosemiconductor has come up with a novel structure that delivers singlemode operation over a 25 nm-wide range of wavelengths.

The company says that the broadband laser chip will enable cost-effective integration of silicon photonics such as arrayed waveguides and light modulators with active components based on indium phosphide and other compound semiconductors. Based in Dortmund, Germany, NL Nanosemiconductor has recently completed its Series B funding round to raise €5 m ($6.3 million), and has opened an office in San Jose, California.

As well as having potential applications in optical communications, the broadband source could be used in place of superluminescent LEDs for the medical imaging technique known as optical coherence tomography, where the higher power of the laser should lead to higher-quality images.

"We managed to develop a way to get a laser to lase with a very wide emission spectrum, which is of course the opposite of the fundamental nature of lasing - a very narrow spectrum," said company COO Alexey Kovsh.

To create the broadband emission, Kovsh and colleagues designed a special epitaxial structure featuring ten layers of quantum dots on a 3-inch GaAs substrate. "Each layer was grown under a different regime to make the gain spectrum broader," he explained.

Although this sounds like a very complex process, Kovsh says that the laser is compatible with a manufacturing environment. While the maximum output power achieved in continuous-wave mode so far is 400 mW, emission of 150 mW over a wavelength range of 20 nm has been shown to be reproducible, Kovsh told Compoundsemiconductor.net.

In the longer term, Kovsh believes that the QD lasers under development could find widespread use in both optical interconnects and optical clock systems for high-performance computing applications. Acknowledging that such applications are unlikely to take off before 2010, Kovsh admits that the company is looking for shorter-term market opportunities.

Large manufacturing volumes are not yet required, but Kovsh says that the quantum-dot process is at a level of maturity where the laser could be switched into mass production if necessary.

Some improvements are still needed, however. For instance, the laser currently operates at up to 80 deg C in a stable fashion. But operation at 100 deg C will be required for final implementation in an uncooled system.

Kovsh says that the NL Nanosemiconductor team is working to optimize chip dimensions, the number of QD lasers, and careful adjustment of each of those layers to improve performance and further extend the laser's emission band.