Novel technique promises to speed up time from lab to product development for optical fibre transmission systems
Date: 30 November, 2015
As part of a BBC R&D EPSRC Industrial CASE award within the UNLOC project, researchers at UCL have experimentally verified an elegant new approach to testing the transmission characteristics of long-haul fibre optic links which carry 99% of global digital traffic. The new technique replaces a complex transmitter system which consists of multiple lasers and modulators with a single broadband source, greatly reducing the cost and time needed to experimentally verify the potential of innovative research ideas before they can be commercially adopted.
Since their first commercial deployment in mid 1970s, communications systems using optical fibre cables as the main medium of data transmission have steadily become the underlying infrastructure facilitating the modern digital revolution. This has fundamentally changed not only the way we run today’s global economy, but it is also defining new ways of human interaction and connection to each other. The recent surge in human and machine generated data collectively referred to as Big Data, cloud services and growing demand for live streaming of HD video are just some of the drives of technological innovations that constantly push the limits of optical communication system to accommodate the incessant growth in data volumes and hunger for more bandwidth.
In the last few decades, scientists and engineers have devised clever ways to manipulate various characteristics of light like amplitude, frequency and polarisation to fit ever more information within an optical fibre. But before any of these new techniques reaches the stage of commercial deployment, it needs to be extensively tested in laboratory and field experiments. While experimental investigation of modern complex communications systems is imperative for commercial deployments, it is slowly becoming too complex and expensive for R&D experiments. This usually results in prolonged laboratory testing phase before a new technology can advance to product development and commercial deployment. To address this, researchers from the UNLOC project, funded by EPSRC to unlock the capacity of future optical communications have demonstrated a novel technique to measure the performance of optical fibre transmission systems which significantly reduces the complexity of the experimental set-up involved using equipment at a fraction of the cost of conventional lab testbeds currently used by the ICT industry.
Focus on simplicity
Information from different sources is often encoded in and carried by light of different frequencies. Each of these form a channel and many channels are carried by a single optical fibre to their destination. Therefore, to evaluate the performance of a fibre link, a series of lasers each tuned to a different frequency (corresponding to a channel), and a set of modulators (devices used to encode the information onto the light carriers) are required to replicate a real transmission scenario. Ideally, communications experts are interested to investigate how transmission systems operate over a wide optical bandwidth in the presence of many, potentially interfering channels, which requires a large number of lasers and modulators to be set up for experiments. In the proposed technique, this large system of lasers and modulators is replaced by a single fibre amplifier with no input, which serves as a noise source. It turns out that this noise source responds in similar ways as a band of channels carrying actual signals to the nonlinear distortions introduced within optical fibres. This nonlinear behaviour is the main source of corruption of transmitted signals and data loss, and methods to transmit large amounts of data while minimising such distortions is the main focus of intensive research world-wide.
The team proved that their input signal behaves statistically in the same way as a collection of real signals and for commonly used modulation formats like QPSK and 16QAM, the proposed technique can be used to characterise system performance in fibre links longer than few hundred kilometres. Subsequent system experiment confirmed this suggesting that in the future this approach can form the basis of next-generation, high-speed optical transmitters. “We hope that our work can ultimately enable and speed up the commercial development of next-generation wideband optical communications systems by reducing the complexity of laboratory facilities needed to investigate techniques to maximise optical fibre capacity.” - said Polina Bayvel, professor in Optical Fibre Communications at UCL and director of the UNLOC project.
The research has been accepted for publication in Optics Letters and will appear in their December 15 issue under the title “High Spectral Density Transmission Emulation Using ASE Noise as a Substitute for Nyquist-Spaced Channels”.
UNLOC is a 5 year project funded with £4.8 million by the EPSRC to explore theoretically and experimentally the current limits of optical fibre communications technology having a holistic, system-based approach, and device the next generation technologies that can expand the capacity of global fibre infrastructure such that it continues to meet the exponentially growing demands for faster and reliable transfer of massive amounts of data across networks of varying sizes and extent. The project is led by researchers at the Optical Networks Group in UCL and Aston Institute of Photonic Technologies in Aston University, and is supported by multiple industry partners among which are leaders in the commercial telecommunications arena like BT, Ciena, Google, Huawei. Orange Labs, Deutsche Telekom and more.
About the EPSRC Industrial CASE award
This research was conducted as part of a PhD studentship within the UNLOC project funded by the EPSRC Industrial CASE award with BBC R&D. The Industrial Cooperative Awards in Science & Technology (CASE) is a scheme under the EPSRC which grants funding to businesses who establish a mutually beneficial research collaboration with an academic partner of their choice. The funding supports a PhD student who is jointly supervised by an academic and industry advisor throughout his PhD studies. CASE’s main goal is to provide a stimulating framework for research training through access to distinctive but complementary environments.
Research-related inquiries: Polina Bayvel
Professor in Optical Fibre Communications & UNLOC Director
EE Department, UCL
Media related inquiries: Iva Kostadinova
UNLOC Communications Manager EE Department, UCL