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Project: Phase conjugated twin waves to unlock the potential of future spatial division multiplexed systems (TWave)

Acronym: TWave
Main Objective: Single-mode fiber (SMF) transport systems are rapidly approaching the Shannon´s limit,pointing to fiber capacities of no more than 100 Tbit/s, corresponding to filling the C and L EDFA bands at a spectral efficiency of 10 bit/s/Hz. This limit can be derived from an extension of the Shannon capacity limit to a nonlinear fiber channel, since the fiber Kerr nonlinearity leads to distortion when the signal power is increased to achieve sufficient Signal-to-Noise Ratio, the ultimate limit resulting from the interaction between amplified spontaneous emission and nonlinearity, which is not deterministic. This may still be not be enough to answer the capacity requirements in the near future which points to spectral efficiencies of 20bit/s/Hz over ~1500 km links, associated with the current growth in capacity of fiber-optic communication systems.
Over the last decades, the steady progress in optical transmission systems was enhanced by the exploitation of the several properties of electromagnetic waves, namely time, phase, frequency and polarization. Since 2010, the research community has generally agreed that optical transport systems will have to resort to the last remaining physical dimension (space) by employing spatial division multiplexing (SDM), which has the potential to substantially increase optical transport capacities. Although SDM was first proposed in 1979 (considering MCF) and 1982 (considering MMF), the current progress is occurring now due to a convergence of technological capabilities (fiber fabrication methods, mode control and analysis methods, coherent detection and digital compensation) and the mentioned emerging necessity.
The main challenge in SDM occurs due to crosstalk between pathways, which is typically small for MCF and high for MMF. For MCF the crosstalk depends on core number, spacing and arrangement, while for MMF the modes are prone to randomly couple during propagation, with different differential mode group delays (DMGD). This requires multiple-input multiple-output linear equalization techniques, similar to the signal processing techniques used for polarization de-multiplexing, which poses computational complexity concerns when considering equalization for long haul mode division multiplexed (MDM) systems. However, similarly to SMF based modern telecommunication systems, the nonlinear penalties in MDM systems will eventually become the ultimate limiting factor.
In this project we propose to explore the concept of phase conjugated twin waves (PCTW) in SDM optical systems, which has recently been proved to cancel out signal-to-signal nonlinear interactions in single-mode fibers by coherently superimposing of a pair of phase-conjugated twin waves, as a means to overcome the nonlinear impairments arising in mode division multiplexed systems, in a practical and sustainable way, paving the way for optical transmission capacities beyond next-generation systems.
Reference: EXPL/EEI-TEL/1748/2013
Funding: FCT/COMPETE/FEDER
Start Date: 01-03-2014
End Date: 01-03-2015
Team: Mário José Neves de Lima, Antonio Luis Jesus Teixeira, Giorgia Parca, Paulo Miguel Nepomuceno Pereira Monteiro
Groups: Optical Communications Systems – Av
Partners: Instituto de Engenharia de Sistemas e Computadores do Porto (INESC Porto/FE/UP) - INESC TEC
Local Coordinator: Mário José Neves de Lima
Links: Internal Page
Associated Publications