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.
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