Researchers at Chalmers have demonstrated an optical amplifier which can amplify light with extremely low noise. The breakthrough enables a reach increase for optical fiber signals from e.g. 1000 km to 4000 km, paving way for increasing the capacity of data communications. The new amplifier could lead to better Internet traffic and laser radar technology, and promote any applications where detection of very weak levels of light is essential, such as free-space communication.
Today´s flow of information demands increasing capacity. Optical amplifiers are crucial enablers of data communication, with the mission to increase data signals without first converting them to electrical signals. Not only the speed and capacity require improvements, but it has become increasingly important to maintain a high signal-to-noise ratio of the signal being transmitted.
The researchers at Chalmers University of Technology 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. 1 dB 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," says Professor Peter Andrekson, who has developed the low-noise amplifier together with his research group in fiber optics.
The group has taken advantage of the fact that the refractive index of glass is not constant, but dependent on light intensity in the fiber. The new amplifier shows experimentally to have 1 dB noise level, with a theoretical minimum of 0 dB, i.e. no noise being added in the amplification process. The next step for the Chalmers researchers are towards 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," says Peter Andrekson.
The research is performed at Chalmers University of Technology. It is funded by the European project PHASORS and the Swedish Research Council (VR). Participating partners in the EU project includes University of Southampton, University College Cork, University of Athens, Eblana, OFS, OneFive Photonics and EXFO Sweden AB. The results were published in Nature Photonics.
- Z. Tong, C. Lundström, P. A. Andrekson, C. J. McKinstrie, M. Karlsson, D. J. Blessing, E. Tipsuwannakul, B. J. Puttnam, H. Toda, L. Grüner-Nielsen. Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.79
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