Optical Amplifier Breaks Low-Noise Record

An optical amplifier that can amplify light with extremely low noise has been demonstrated at Chalmers University of Technology. The new amplifier enables a reach increase for optical fiber signals from, for example, 1000 to 4000 km. This could lead to better Internet traffic and laser radar technology and could promote applications where detection of very weak levels of light is essential, such as free-space communication.

Because of the demand for increased data capacity, optical amplifiers are crucial enablers of communication. Their mission is to increase data signals without first converting them to electrical signals. Not only is it necessary to increase speed and capacity, but it also has become increasingly important to maintain a high signal-to-noise ratio during transmission.

The researchers at the university have, by using a so-called phase-sensitive fiber optic parametric amplifier (PSA), reduced the noise figure to 1 dB. In traditional erbium-doped fiber amplifiers, the noise figure is 3 dB at best, resulting in loss of signal integrity. One decibel is the lowest noise ever reported in any kind of amplifier with reasonably large signal gain. This represents a breakthrough also because it is implemented in a practical way, making it potentially very attractive in various applications – most notably in high-capacity optical communication systems.

“This is the ultimate optical amplifier. It enables connecting cities, countries and continents more efficiently by placing the amplification hubs at much greater intervals. The signal can also be modulated more effectively. In addition, the amplifier is compatible with any modulation format, with traditional laser transmitters and can be very broadband, making it compatible with many lasers at different wavelengths,” said Peter Andrekson, a professor at Chalmers who, together with his fiber optics research group, has developed the low-noise amplifier.

The group has taken advantage of the fact that the refractive index of glass is not constant but instead dependent on light intensity in the fiber. The new amplifier has been shown experimentally to have a 1-dB noise level, with a theoretical minimum of 0 dB -- that is, no added noise during the amplification process. The next step for the Chalmers researchers is to work on applications.

“The entire optical telecom industry is our market, but the technology is generic and scalable to other wavelengths like visible or infrared light, which makes it attractive in areas such as measurements, spectroscopy, laser radar technology and any applications where detection of very weak levels of light is essential,” said Andrekson.

The research is funded by the European project PHASORS and the Swedish Research Council. Participating partners in the EU project include the University of Southampton, University College Cork, University of Athens, Eblana, OFS, OneFive Photonics and EXFO Sweden AB. The results were published in Nature Photonics.

For more information, visit: www.chalmers.se