1 May 2014 On the design of few-mode Er-doped fiber amplifiers for space-division multiplexing optical communications systems
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Long-haul optical communications links based on space-division multiplexing use space as the final degree of multiplexing freedom, possibly exploring the modal orthogonality in a few-mode fiber (FMF). However, if conventional EDFAs are used, each mode will experience a different value of optical gain, on account of distinct field profile configurations. This lack of gain equalization imposes difficulties for mode demultiplexing and may impair the system performance. The FMF-EDFA designer should define Er doping and/or refractive index profiles, as well as the pumping configuration, to provide the best possible mode equalization of optical gain and noise figure. In the case of the FMFEDFA, the problem is involved because each mode contributes with its own set of coupled differential equations. To use this approach to carry out a rigorous optimization procedure is not feasible and typical FMF-EDFAs designs proposed in the literature are empirical. A novel optimization method is proposed here. The definition of a figure of merit related to the equalization of the pump-mode signal overlap integral significantly reduces computation time, allowing the implementation of a multiobjective optimization approach. The results obtained were validated against the solution provided by the full set of rate and propagation equations and we conducted a FMF-EDFA optimization case study. Our double-ring Er doping profile design requires a single 350 mW LP11,p pump to provide a mean gain of 21.6 dB, within 0.6 dB of equalization for each of the four modes considered.
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A. Herbster, A. Herbster, M. A. Romero, M. A. Romero, "On the design of few-mode Er-doped fiber amplifiers for space-division multiplexing optical communications systems", Proc. SPIE 9131, Optical Modelling and Design III, 91310Y (1 May 2014); doi: 10.1117/12.2052038; https://doi.org/10.1117/12.2052038

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