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Fast 850nm VCSEL Could Revolutionise Data Communications

Researchers hope their development will see the power consumption of a complete optical link, between circuits in a computer (including drive electronics and receiver) will be no more than 100 fJ/bit.

Researchers at Chalmers have shown that a surface emitting laser, a cheaper and more energy-efficient type of laser for fibre optics than conventional lasers, can deliver error-free data at a record speed of 40 Gbit/s.

The break-through could lead to faster Internet traffic, computers and mobile phones.

Today's commercial lasers can send up to 10 Gb of data per second (Gbit/s) through optical fibres. This applies to both conventional lasers and to surface emitting lasers. Researchers at Chalmers University of Technology have managed to increase the speed of the surface emitting laser four times, and see potential for further capacity increase.

 



Up to 100 000 lasers can be fabricated and tested before we cut the wafer into chips, says Anders Larsson. PHOTO: J-O Yxell

 

This research will create great opportunities, not only for different types of local networks and supercomputers, but also for consumer electronics. By using multiple (parallel) channels computer cables with a total capacity of several hundred Gbit/s can be constructed.

“The market for this technology is gigantic. In the huge data centres that handle the Internet there are today over one hundred million surface emitting lasers. That figure is expected to increase a hundredfold," says Anders Larsson, who has developed the high speed laser together with his research group in optoelectronics.

Unlike a conventional laser the light from a surface emitting laser is emitted from the surface of the laser chip (not from the edge), like in an LED. The gain is the ability to not only fabricate, but also test, the lasers on the wafer (a 75 mm wide substrate of semiconductor material of industrial type) before it is cut into individual chips for assembly.

The lasers work directly where they sit on the wafer. Conventional lasers work only after partition. The ability to test up to 100 000 lasers on a wafer reduces the cost of production to one tenth compared with conventional lasers.

The laser volume is smaller. It requires less power without losing speed. The energy and power consumption is a tenth of what a conventional laser requires at 40 Gbit/s  – only a few hundred fJ/bit.  If Anders Larsson and co-workers succeed in their development he expects that the power consumption of a complete optical link, between eg circuits in a computer (including drive electronics and receiver) will be no more than 100 fJ/bit.

“The laser's unique design makes it cheap to produce, while it transmits data at high rates with low power consumption," Larsson sums up.

The combination is unique, and opens up to a large-scale transition from electrical cables to optical cables in computers, and to side equipment, as a substitute for USB cables, for instance. Electric wires can handle up to a few Gbit/s. One can easily imagine dramatic performance gains in mobile phones and other electronics ahead. Most imminent are applications in supercomputers and the type of large data centres run by Google, eBay and Amazon.

“Here we are heading for a power catastrophe. The data centres represent a few percents of America's entire electricity consumption," continues Larsson.

The next step for the Chalmers researchers is to modify the design and refine the ways to control the laser, to increase speed and reduce power consumption even further.

“We strive to meet market demands ten years from now," says Larsson, who estimates that we by 2020 will need energy-efficient cables that can handle 100 Gbit/s per channel.

The research is performed at the Chalmers research centre FORCE. It is funded by Swedish Foundation for Strategic Research, SSF, and by the EU through the project VISIT. Participating companies in the European project are IQE Europe (UK), VI Systems (Germany) and Intel (Ireland). Informal partners in the project are Tyco Electronics and Ericsson (both Sweden). The findings are published in Electronics Letters from IEEE Explore.

Further details of this research are described in the paper “40 Gbit/s error-free operation of oxide-confined 850 nm VCSEL" by P. Westbergh et al, Electron. Lett, 2010, vol. 46, no. 14, pp. 1014-1016.
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