The PHASORS project (“Phase Sensitive Amplifier Systems and Optical Regenerators and Their Applications”) secured nearly €3 million in funding under the European Union’s Seventh Framework Programme (FP7) Information and Communication Technologies (ICT) program. The system was presented in the journal Nature Photonics.

Data transmission over optical networks is limited by phase noise from optical amplifiers and crosstalk, induced by the interaction of the signal with the signals of many others simultaneously circulating through the network.

Phase noise consists of rapid, short-term, random fluctuations in the phase of a signal that affect the quality of the transmitted information and result in data transmission errors. Crosstalk refers to any signal that unintentionally affects another signal. The partners in the PHASORS project, under the auspices of the Optical Research Centre at the University of Southampton, have taken a significant step towards eliminating this interference.

Traditionally, optical data has been transmitted as a sequence of bits encoded in the amplitude of the light beam—a system that was simple and practical, but inefficient in its use of bandwidth. This wasn't a problem in the past, given the enormous data-carrying capacity of an optical fiber. But the continued growth of the internet, and in particular the introduction of high-bandwidth video applications such as YouTube, has led to increased demands for more efficient data signal formats, especially formats that encode data in the phase rather than the amplitude of an optical signal.

The PHASORS consortium developed the first practical phase-sensitive amplifier and regenerator for high-bit-rate binary phase-encoded signals. This device, unlike others developed in the past, eliminates phase noise directly without the need for conversion to an electronic signal, which inevitably slows down the achievable speed. The device takes a noisy input data signal and restores its quality by reducing the buildup of phase noise and also reducing amplitude noise simultaneously.

“This result is an important first step towards the practical application of all-optical signal processing of phase-coded signals, which are being commercially exploited due to the improved data-carrying capacity relative to the amplitude of conventional coding schemes,” said PHASORS project leader and Optical Research Centre professor David Richardson.

“Our regenerator can clean noise from incoming data signals and should enable systems with greater endurance and physical capacity. Achieving this result, a key objective of the PHASORS project, has required significant advances in optical fiber and semiconductor laser technology across the consortium.”

Commenting on the impact of the device, Professor Richardson said: “We believe this device and the associated component technology will have important applications across a wide range of disciplines beyond telecommunications, including optical sensing, metrology, as well as many basic testing and measurement applications in science and engineering.”

Key contributions to PHASORS, which began in 2008 and is scheduled to end in 2011, are being made by institutes across the EU, nominated by the Optical Research Centre at the University of Southampton (ORC), Chalmers University of Technology (Sweden), the Tyndall National Institute at University College Cork (Ireland), and the National and Kapodistrian University of Athens (Greece). Expertise is provided by Onefive (Switzerland), Eblana Photonics (Ireland), and the Danish fiber optics specialist OFS.