New light gives rapid data transmission

17 Jun 2002

An LED that spontaneously emits 1.4mW of red light (650 nanometers) with a small signal modulation bandwidth of 200 MHz, could offer an efficient, reasonably priced alternative to laser diodes for short-haul communications (less than about 100 meters). This bandwidth would correspond to a data transfer rate of 250 Mbits/s.

Researchers at the Optoelectronics Research Centre (ORC) at Tampere University of Technology in Finland have demonstrated this speed with resonance-cavity light-emitting diodes (RC-LEDs), a light source that produces very intense light from quantum wells located in a microcavity.

RC-LEDs are expected to find applications with the new polymethyl methacrylate polymer optical fibers for local networks. These fibers have a data transmission window at a wavelength of about 650 nanometers and RC-LEDs can easily be attached to the fibers at reasonable cost.

In an RC-LED, electrons move between semiconductor layers, which are only nanometers thick, and drop into 'quantum wells' to release photons. When the quantum well is between two parallel mirrors at a distance of a wavelength from each other, the light is only emitted perpendicular to the mirrors. This is different from a conventional LED, which radiates light in all directions. The light signal in an RC-LED also switches on and off very rapidly, giving a high modulation frequency.

Markus Pessa, the director of ORC, says that the RC-LED technology is now mature enough for applications. "ORC is currently assessing the commercial potential of RC-LEDs in collaboration with Nordic Epitaxy Inc of Finland, which manufactures epitaxial semiconductor wafers mainly for telecoms applications. Nordic Epitaxy uses the same growth method as ORC, so the technology transfer from the research environment to industry is quite straightforward."

The latest results from ORC are due to be published in the journal Photon Technology Letters. The research was part of the Nanotechnology Research Programme organized by Tekes (the National Technology Agency), the Academy of Finland, and the European Union funded SMILED Project.

SH