Needle in a Haystack: Brillouin photonic processing for carrier recovery in optical communications

The project aims to apply Brillouin processing to the development of an innovative self-tracking optical filter for isolating optical carriers for coherent receivers in future ultrahigh bit-rate optical communication systems. By recovering a needle-like optical carrier with great precision from a drifting sea of wide-band noise and data channels, the project expects to minimise the effect of optical carrier distortions on the data-carrying signals. The project should advance knowledge in optical signal processing and communications technologies, with outcomes that increase the data-carrying capacity of optical networks. Future telecommunication networks should benefit through improved transmission rates and extended fibre links.

This opportunity will be close once a suitable candidate has been found - if you are interested, please apply ASAP.

Optical fibre communication systems provide the backbone for the internet and our connected society. Next-generation applications – self-driving cars, smart cities, and the internet of things – will grow our demand for higher data capacities by 30–40% per year. This growth is currently met by complex modulation techniques that use the amplitude and phase of the optical field to encode multiple information bits on each pulse of light sent. Such increased spectral efficiency improves overall capacity without upgrading existing fibre infrastructure but requires extremely stable optical carriers (undistorted laser light) and advanced digital signal processing (DSP) for signal recovery. Extending this approach to terabit-per-second channel rates and beyond to support future growth is set to push current techniques beyond their feasible range, resulting in distortions and errors that limit capacity. Now is the time for a disruptive photonic technology in coherent communications.

An elegant method that relaxes the requirements on coherent communications is to use photonic approaches to optically recover the carrier and its distortions at the receiver, rather than through advanced DSP. The recovered carrier can then be used as a reference for optical self-homodyne reception, allowing terabit-per-second channels to be accurately received in systems even with significant optical carrier distortions. This optical approach to carrier recovery has not been possible for ultra-high bit-rate channels because of a lack of suitable carrier extraction technology.

The aim of the project is to develop and demonstrate a novel optical filtering scheme that precisely recovers, with high fidelity, a needle-like transmitted optical carrier from a drifting sea of wideband noise and data channels, allowing efficient self-homodyne reception to support channels at terabit-per-second rates and beyond in optical communication systems. This transformative photonic approach will cancel the effects of optical carrier distortions on the data-carrying signal in short-distance systems, where cost-effective lasers cause distorted optical carriers, and in long-distance systems, where ‘nonlinear’ cross-talk through transmission causes distortions.

Our specific approach to the problem of optical carrier recovery will build on our recent successful demonstrations of narrowband amplification and spectral purification of frequency comb lines for coherent optical communications at modest channel rates [4-6]. We will create an ultra-high-resolution photonic optical filter that self-tracks the frequency of the optical carrier, allowing for carrier extraction and recovery of the carrier at the receiver.

The key innovation is to exploit the intrinsic narrowband nature of stimulated Brillouin scattering (SBS) to create a flexibly defined photonic optical filter optimised for optical carrier recovery. The filter will function like an amplifier that boosts\ only the brightest colour, to recover the desired optical carrier with high fidelity.

Our specific aims are to:

1. Develop new design rules for SBS filters to control their properties in terms of phase, amplitude, polarisation, and noise, so that they can be tailored to meet the requirements of high-capacity coherent fibre optical communications.

2. Optimise SBS as a tool for optical carrier recovery by enhancing self-tracking with novel injection-locking and depolarisation techniques. We will design and construct a new class of optical filter with a unique combination of ultra-high spectral resolution, flexible filter shaping, and polarisation independence.

3. Implement the scheme in a fully self-referenced high-capacity optical communication system. We will verify\ suppression of optical carrier distortions in both short- and long-distance links and will demonstrate enhanced capacity and reach in optical fibre communications.

Keywords: Optical Communications, Photonics, Optical Signal Processing, Integrate Photonics, Nonlinear Optics, Communications Technologies