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Japanese team claims optical breakthrough

Scientists from Fujitsu and the Tokyo University have developed a laser that is capable of maintaining a stable output over a wide temperature range at speeds and frequencies.

The device could enable the creation of optical networking equipment that is smaller, cheaper and consumes less power than current devices, the research team said.

The laser was developed by a team led by Yasuhiko Arakawa, director of the Nanoelectronics Collaborative Research Center at the University of Tokyo, and is based on quantum dots.

Current lasers suffer output fluctuations as the operating temperature changes. As the temperature changes from 20ºC to 70ºC the output power can drop by about a quarter, according to data provided by Arakawa and Fujitsu.

To provide the kind of stable output required by applications such as optical networking, systems must be built to adjust the power of the laser to keep the output constant as the temperature changes or keep the laser at a constant temperature so the input power can remain the same. Both of these solutions mean extra cost, extra power consumption and extra bulk.

"If the laser is inherently temperature stable, then it is much better," said Arakawa.

The laser announced by Arakawa's team uses quantum dot technology. Quantum dot lasers are capable of maintaining a stable output over a temperature range of several tens of degrees Celsius but until now have not been demonstrated working at the kind of speeds and frequencies demanded for commercial optical communications work.

That has now changed with Arakawa's announcement that his team maintained a stable output from a quantum dot laser over a temperature range of 20ºC to 50ºC while working at 10gbps at the 1.3 micron wavelength, which is one of the two major standard wavelengths used in current optical communications systems, he said in an interview. Getting a quantum dot laser to work at that speed and frequency is a first, Arakawa said.

Looking ahead, Arakawa said he wants to increase the temperature range over which stable output is maintained. At present the laser exhibits a minimal change in output between 50ºC and 70ºC and Arakawa said it is "not so difficult" to expand the temperature range.

The team's goal is to have a product ready for commercialisation by 2007 that can be used in telecommunications equipment and is one quarter the size of current lasers, works at a lower power and is one third the cost.

Martyn Williams writes for IDG News Service

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