RSS Feeds

Email a Friend Printer Friendly

RC-LEDs - Super-fast light sources suitable for data transfer

February 25, 2000

Resonance-cavity light-emitting diodes (RC-LEDs) are a new type of light source which produces very intense light from quantum wells located in a microcavity. As light sources, RC-LEDs are classified as something between laser diodes and conventional light-emitting diodes (LEDs). The advantages of RC-LEDs compared with conventional LEDs include a higher brightness, improved spectral purity, improved beam directionality, and higher speed of modulation.

This research carried out at the Optoelectronics Research Centre at Tampere University of Technology is an excellent example of potential applications in the nanotechnology field. The research was a part of the Nanotechnology Research Programme organised by Tekes, the National Technology Agency, and the Academy of Finland.

Suitable for plastic optical fibre communications
The most promising application of RC-LEDs is the potential for using them for data transfer communication in optical fibres, as the components can be easily attached to various fibre materials at a reasonable cost.
"Europe seems to be one step ahead of the USA and Japan in some special applications in the field of optoelectronics, such as fast RC-LEDs", says Professor Markus Pessa from Tampere University of Technology. "The industry most interested in our work recently has been the European car industry. They are voluntarily accepting these lightweight, elegant plastic optic-fibre-based communication systems instead of traditional copper cables."
Professor Pessa explains that the car industry is, however, expecting slightly better test results. "The car has to work under extreme conditions, both in the Sahara at +85 C and in Vladivostok at -50 C. The bandwidth of our RC-LEDs is perfectly adequate for them, but the temperature variations cause excessive changes in output. The wavelength stability with respect to temperature variations must still be improved" says Pessa.

How does the RC-LED work?
In RC-LEDs electricity puts the electrons in motion between thin semiconductor layers, which are only millionths of a millimetre thick. The moving electrons drop into a quantum well, generating a photon i.e. the light signal. The RC-LED components are prepared in layers of a few atoms at a time by semiconductor reactors the size of a room.
In a conventional LED the light radiates in all directions. However, when there is a quantum well in a microcavity between two parallel mirrors at a distance of a wavelength from each other, the light is emitted only perpendicular to the mirrors. The light signal switches on and off extremely rapidly, although not as fast as in lasers. This means that the components have a high modulation frequency.

The research group at Tampere University of Technology recently achieved a frequency of 200 MHz at the wavelength of red light (650 nm); i.e. light is flashing 200 million times a second. This is probably the fastest speed ever reached in the red part of the spectrum by a spontaneous light emitter. In plastic optical fibre systems this bandwidth would offer a data transfer rate of 250 Mb/s; this is one reason why RC-LEDs, which are relatively cheap to produce, are expected to find applications in local networks.

More information: Professor Markus Pessa, Tampere University of Technology,
e-mail: Markus.Pessa@orc.tut.fi, Tel. 358 50 675 70, Fax 358 3 365 3400
http://www.orc.tut.fi/index03.html
http://www.tekes.fi/eng/news/



Tekes, the Finnish Funding Agency for Technology and Innovation