Japanese team claims optical breakthrough

Scientists from Fujitsu and The University of Tokyo have developed a laser that is capable of maintaining a stable output over a wide temperature range at speeds and frequencies useful for optical communications, the research team said Friday. The device could enable the creation of optical networking equipment that is smaller, cheaper and consumes less power than current devices, the leader of the research team said.

Scientists from Fujitsu and The University of Tokyo have developed a laser that is capable of maintaining a stable output over a wide temperature range at speeds and frequencies useful for optical communications, the research team said Friday. The device could enable the creation of optical networking equipment that is smaller, cheaper and consumes less power than current devices, the leader of 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.

Details of the technology were presented as a post-deadline paper at the European Conference and Exhibition on Optical Communication 2004 that took place in Stockholm from Sept. 5 to 9.

Current lasers suffer output fluctuations as the operating temperature changes: As the temperature changes from 20 degrees Celsius to 70 degrees Celsius 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 haven’t 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 20 degrees Celsius to 50 degrees Celsius while working at 10G bit/sec 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 50 degrees Celsius and 70 degrees Celsius and Arakawa said it is “not so difficult” to expand the temperature range.

The team’s goal is to have a product ready for commercialization 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.

This isn’t the first time this year Arakawa’s team announced progress in quantum dot research. In July as part of another research project being conducted with Fujitsu, Arakawa’s team said they reliably generated and detected single photons using a quantum dot photon emitter. Such generation of single photons is vital for quantum cryptography systems.

There are other potential uses for quantum dot devices, said Arakawa.

These include new types of ultra-dense memory chip where data is encoded onto a handful of electrons or biotechnology and sensing applications. However at present the two applications closest to being realized are the two he is researching, quantum cryptography and optical communications, he said.