Wideband Optical Communication Systems Using Phase-Sensitive/Insensitive Fibre Optical Parametric Amplifiers

As communication services applications continue to grow in number (e.g. Twitter, YouTube, Facebook, etc.) and in bandwidth (e.g. HDTV, 3D,...), all parts of the communication systems carrying this traffic must be able to operate at higher and higher speeds. This ever-growing capacity demand can only be handled by continually upgrading the capacity of all parts of the network, including long-haul links between major cities, as well as the 'last mile' distribution networks ending at or near the customer premises.
As part of this upgrading of the physical layer of optical communication systems, there is increasing pressure to provide more optical bandwidth to accommodate more individual wavelength carriers in high-capacity wavelength-division multiplexed (WDM) systems. The current type of optical amplifiers, namely Erbium-doped fibre amplifiers (EDFAs) were introduced in the early 1990s, but have a fixed bandwidth of the order of 35 nm, covering the so-called C-band (1530-1565 nm). This bandwidth is being rapidly exhausted, and so there is a need for introducing novel optical amplifiers with substantially larger bandwidth.
In addition, there is also a trend toward using high-spectral efficiency modulation formats (e.g. quadrature amplitude modulation, or QAM). However, such formats require high optical signal to noise ratios (OSNRs).

We propose to investigate the suitability of fibre optical parametric amplifiers (OPAs) to amplify WDM optical communication signals in wideband optical communication systems. We will investigate both phase-insensitive OPAs (PIAs) and phase-sensitive OPAs (PSAs).The latter are particularly attractive because of their potential for noiseless amplification, which cannot be achieved with EDFAs or phase-insensitive OPAs.

The project will consist of three phases with the following objectives:
Phase I (12 months). We will first demonstrate phase-insensitive OPAs (PIAs) with an optical bandwidth matching that of EDFAs. These will be tested in a recirculating loop, with a fully-populated WDM signal spectrum, simulating propagation in a long-haul system. Only the signals will be used; the idlers will be discarded after each OPA. It is expected that the reach of the system will be several thousand kilometres. Different modulation formats will be tested, with baud rates up to 43.7 Gb/s. Aggregate throughput will reach several terabits per second.
Phase II (12 months). We will then use signals and idlers in an alternating manner in the recirculating loop. This will allow us to exploit the wavelength conversion/phase conjugation aspects of OPAs to combat dispersion as well as some nonlinear effects. Testing will be done with a wider fully populated CWDM spectrum, at a higher aggregate rate.
Phase III (12 months). We will use phase-sensitive OPAs (PSAs), which have the potential for lossless amplification, leading to an increase in system reach. We will investigate the suitability of propagation along principal states of polarization, in order to maintain the states of polarization of signals, idlers, and pump, necessary for optimum PSA operation.

If the project is successful, it will demonstrate that fibre OPAs are indeed a potential contender for providing optical amplification over wavelength ranges exceeding that of EDFAs, and in a nearly noiseless manner, which is compatible with use in either long-haul or distribution optical communication networks. Hence they could in principle provide the next generation of optical amplifiers for future high-capacity optical networks.

Commercial impact
If the project progresses as intended, we will demonstrate the first practical optical communication systems based on fibre OPAs. This development would have a considerable impact on the optical communication industry. (This is of course why Oclaro has joined us as an industrial partner.) Clearly there would be a need for companies to invest in research, development and manufacture of fibre OPAs. As a result, there would be a significant economic impact associated with this evolution. Since this technology is being developed in the UK, there would be opportunities for UK companies to play a major role in its commercialization, with support from Swansea University. (See attached support letter from Oclaro.)
The amount of know-how required to design, build and operate fibre OPAs is considerably higher than for EDFAs. Consequently there will be substantial barriers to entry for companies wishing to exploit this technology. Optical communication systems are expensive, and upgrading key components such as optical amplifiers in all systems worldwide will eventually represent a very significant capital outlay. It will take a long time for these amplifiers to become a low-cost commodity, and this will provide a window of opportunity for high-technology companies to obtain a good return on investments in this area.
We will protect our IP by applying for patents on key aspects of the technology. The patents will be taken in developed countries, in which possible OPA manufacturers are likely to be found, namely Europe, USA, Japan.

Societal impact
In addition to the possibility of having a significant economic impact, fibre OPAs will also have an indirect societal impact. This is because the increase in communication bandwidth made possible by their use will facilitate the introduction of more communication services, and/or of higher-bandwidth services. For example they could facilitate the widespread deployment of HDTV, 3D TV, streaming high-definition video communication between individuals, high-resolution telemedicine, remote monitoring of the elderly etc. All of these new services will improve means of doing business remotely, and enhance the realism of various forms of entertainment. Overall, this bandwidth expansion could lead to a significant improvement of the way all segments of society communicate, and more generally to an improvement of the quality of life in developed as well as developing countries.

Knowledge impact
In addition to the preceding economical and societal benefits, the successful development of fibre OPAs for optical communication should also act as a catalyst for increased activity in this field in engineering and scientific circles. Once other groups realize that fibre OPAs are indeed a strong contender for providing the next generation of amplifiers for optical communications, we fully expect that this will trigger many new ideas in the minds of clever researchers to keep improving the technology, and keep making it more efficient and cost effective.
While we intend to protect our own ideas as described above, we will also welcome the participation of others in this process, as additional improvements can only speed up the advent of this technology, thereby hastening the adoption pace, and consequently leveraging our own work.
To that effect, we intend to actively participate in a lively exchange of ideas. The results of the proposed research will thus be disseminated in the usual ways, through conferences and journal publications.

Skills and training impact
Personnel working on this project would include a senior research associate, and two research assistants. Upon completion of the project the latter would be well-trained in this subject, and would therefore be attractive candidates for companies interested in exploring and/or developing this technology for commercial exploitation.Previous RA working for the PI has is now working for Oclaro.