AT CHALMERS UNIVERSITY of Technology in Gothenburg, Sweden, researchers have successfully demonstrated an optical amplifier that can amplify light with extremely low noise. This breakthrough allows optical-fiber signals to reach and be detected across greater distances from 1000 to 4000 km. Clearly, this capability could result in increased capacity for data communications. For example, the use of such new amplifiers could lead to better traffic on the Internet as well as improved laser radar technology. It also may further applications that require the detection of very weak levels of light, such as free-space communication.

In addition to improving their speed and capacity, optical amplifiers have to maintain a high signal-to-noise ratio for the signal being transmitted. By using a phase-sensitive, fiber-optic parametric amplifier (PSA), the researchers at Chalmers have reduced the noise figure to 1 dB. According to the university, that is the lowest noise reported in any amplifier with reasonably large signal gain. In contrast, the noise figure in traditional erbium-doped fiber amplifiers is 3 dB at best.

This optical amplifier was implemented via a practical approach, which should make it attractive to numerous applicationsthe most prominent of them being high-capacity optical-communications systems. The researchers leveraged the fact that the refractive index of glass is not constant, as it depends on the light intensity in the fiber. The new amplifier shows experimentally to have 1 dB noise level with a theoretical minimum of 0 dB. In other words, no noise is being added in the amplification process.

According to Professor Peter Andrekson (see photo), this amplifier is compatible with any modulation format used with traditional laser transmitters. It can therefore be very broadband, making it compatible with many lasers at different wavelengths. The next step for the researchers will be to investigate the use of the amplifier in practical applications. This research is funded by the European project PHASORS and the Swedish Research Council (VR). Participating partners in the EU project include the University of Southampton, University College Cork, the University of Athens, Eblana, OFS, OneFive Photonics, and EXFO Sweden AB.