Thursday, May 20, 2010

Fujitsu and University of Tokyo Develop 25 Gbps Quantum Dot Laser

Fujitsu Laboratories and the University of Tokyo have developed the first quantum dot laser capable of 25 Gbps transmission. Researchers believe the technology can be scaled to 100 Gbps and above.

Quantum dot lasers are semiconductor lasers which employ quantum dots - nanometer-sized semiconductor particles as an active material for lasing. The researchers cite several advantages over other types of semiconductor lasers, such as being less sensitive to temperature fluctuations, while offering tremendous advances over previous semiconductor lasers in terms of lower power consumption, greater transmission distances, and faster speeds.

Quantum well lasers, which have conventionally been used as optical sources for data communications, have a problem of dramatic increases in power consumption attributable to increased driving current when temperatures rise. The quantum dot laser developed by Fujitsu Laboratories and the University of Tokyo uses 3-dimensional (3D) semiconductor nanostructures to produce quantum effects, thus giving it excellent characteristics, including stable operation over a range of temperatures and low power consumption. However, the quantum dot laser had been limited to handling data transfer speeds up to 10 Gbps.

In order to increase the speed of quantum dot lasers, it was necessary to increase the laser's optical gain, which in turn required an increase in the number of underlying quantum dots. New quantum dot fabrication technology was developed and applied. Layers of quantum dots with a higher density than conventionally employed were then stacked, thereby doubling the laser's operation speed and enabling a significant improvement over previous technologies. The result was a quantum dot laser capable of high-speed operations at 25 Gbps.

Fujitsu and Fujitsu Laboratories have developed this technology in an industrial-academic collaboration with Professor Yasuhiko Arakawa's laboratory of the University of Tokyo. Part of this research belongs to a project contracted to the Photonics Electronics Technology Research Association (PETRA) by the New Energy and Industrial Technology Development Organization (NEDO), while part of the research was carried out under Japan's Ministry of Education, Culture, Sports, Science and Technology's Special Coordination Funds for Promoting Science and Technology.


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