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Quantum dots target optical networks

15 Sep 2004

A Japanese team hopes its 10 Gbps quantum dot laser will be used in commercial applications by 2007.

Researchers from Fujitsu and the University of Tokyo in Japan claim to have developed the first 10 gigabits per second (Gbps) quantum dot (QD) laser. Emitting at 1.3 microns, the collaboration says no current adjustments are required to maintain both stable high-speed operation and average output power between 20°C and 70°C.

The team is now extending the temperature range for adjustment-free operation and is targeting practical commercial applications by 2007. "This breakthrough technology will pave the way for compact, low-cost and low power consumption optical transmitters targeting optical metro-access and high-speed optical LAN," says the team.

The key to the laser's stability is the structure of the active layer. It contains 10 layers of InAs quantum dots which are doped with a p-type impurity. A high-reflectivity coating was applied to the rear facet and the laser was mounted on a diamond heat-sink.

The QD laser was pitted against a quantum well (QW) laser with a 10 layer compressively strained InGaAsP active region. Testing both devices at 10 Gbps and over the range 20°C and 70°C, the team says the output power deviation of the QD laser was small and it maintained an extinction ratio of more than 7 dB. On the other hand, the QW device was sensitive to operating temperature and its output power deviated by -1.5 dB at 70°C.

"These performances, which are far superior to QW lasers, will open the way for low-cost transmitters and trigger the introduction of QD lasers to real optical networks," conclude the team.

This work was presented as a post-deadline paper at the European Conference on Optical Communication (ECOC) conference, held in Stockholm from September 5-9.

Author
Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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