The transmission of data through optical networks is currently limited by so-called 'phase noise' from optical amplifiers and 'cross talk' induced by the interaction of the signal with the many other signals simultaneously circulating through the network.
Phase noise is the rapid, short-term, random fluctuations in the phase of a signal which affects the quality of the information sent and results in data transmission errors. Cross talk refers to any signal unintentionally affecting another signal. The PHASORS partners, under the tutelage of the University of Southampton's Optoelectronics Research Centre (ORC), however, have taken a major step towards eliminating this interference.
Traditionally optical data has been sent as a sequence of bits that were coded 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 fibre. But the continued growth of the Internet and, in particular, the introduction of bandwidth-hungry video applications such as YouTube, has led to increasing calls for more efficient data signalling formats, notably schemes that code data in the phase rather than amplitude of an optical beam.
The PHASORS consortium developed the first practical phase sensitive amplifier and phase regenerator for high-speed binary phase encoded signals. This device, unlike others developed in the past, eliminates the phase noise directly without the need for conversion to an electronic signal, which would inevitably slow the speeds achievable. The device takes an incoming noisy data signal and restores its quality by reducing the build up of phase noise and also any amplitude noise at the same time.
'This result is an important first step towards the practical implementation of all-optical signal processing of phase encoded signals, which are now being exploited commercially due to their improved data carrying capacity relative to conventional amplitude coding schemes,' said PHASORS project leader and ORC's Professor David Richardson.
'Our regenerator can clean noise from incoming data signals and should allow for systems of extended physical length and capacity. In order to achieve this result, a major goal of the PHASORS project, has required significant advances in both optical fibre and semiconductor laser technology across the consortium.'
Commenting on the device's impact, Professor Richardson said: 'We believe this device and associated component technology will have significant applications across a range of disciplines beyond telecommunications including optical sensing, metrology, as well as many other basic test 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 from across the EU, namely the ORC, Chalmers University of Technology (Sweden), the Tyndall National Institute at University College Cork (Ireland), and the National and Kapodestrian University of Athens (Greece). Industry know-how stems from Onefive (Switzerland), Eblana Photonics (Ireland) and the Danish fibre optic specialists OFS.
Source: Cordis news release
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Citation: Slavik, R., et al. (2010) All-optical phase and amplitude regenerator for next-generation telecommunications systems. Nature Photonics, published online 5 September. DOI: 10.1038/nphoton.2010.203.