Researchers from France, Japan and the US have demonstrated wideband optical transmission in fibres with more 15 modes for the first time, achieving a record data rate over 1 petabit/s for the first time.
The researchers from fibre cable supplier Prysimian in France, led by Pierre Sillard, worked with the Network System Research Institute of the National Institute of Information and Communications Technology (NICT) in Japan and Nokia Bell Labs in the US to combine highly spectral efficient wideband optical transmission with an optical fibre guiding 15 fibre modes that had a cladding diameter in agreement with the current industry standard of 0.125 mm.
This was enabled by mode multiplexers and an optical fibre that supported wideband transmission of more than 80 nm over a distance of 23 km. The study at the European ECOC conference highlights the large potential of single-core multi-mode fibres for high capacity transmission using fibre manufacturing processes similar to those used in the production of standard multi-mode fibres.
Compared to multi-core optical fibres, multi-mode fibres can support a higher spatial-signal-density and are easier to manufacture. However, using multi-mode fibres for high capacity space-division multiplexed transmission requires the use of computationally intensive digital signal processing. These requirements increase with the number of transmission modes with a challenge in supporting large number of fibre modes.
At NICT, a transmission experiment was designed and carried out that utilized the transmission fibre made by Prysmian and mode multiplexers developed by Bell Labs. A wideband transceiver subsystem was developed at NICT to transmit and receive several hundred highly spectral efficient WDM channels of high signal quality.
The mode multiplexers were based on a multi-plane light conversion process where the light of 15 input fibres was reflected multiple times on a phase plate to match the modes of the transmission fibre. The transmission fibre was 23 km long and had a graded-index design.
The key is that this is an industry-standard fibre with a cladding diameter of 0.125 mm and a coating diameter of 0.245 mm.
Increasing the number of modes in a multi-mode fibre transmission system increases the computational complexity of the required MIMO digital signal processing. However, the transmission fibre had a small modal delay, simplifying the MIMO complexity and maintained this low modal delay over a large optical bandwidth.
As a result, the team could demonstrate the transmission of 382 wavelength channels, each modulated with 64-QAM signals. This enabled the first transmission over 1Pbit/s, increasing the current record demonstration by a factor of 2.5.
The team is how looking at extending the distance of large-capacity multi-mode transmission and integrating it with multi-core technology to establish the foundation of future optical transmission technology with large capacity.
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