Wavelength Dependence of Optimum Core-to-Cladding Ratio for Power Efficient Cladding-Pumped Coupled Multi-Core EDFA

This paper proposes cross-sectional design guidelines suitable for a power efficient cladding-pumped coupled multi-core erbium-doped fiber amplifier (MC-EDFA). Numerical calculations revealed that the optimal core-to-cladding ratio (R_cc) of the MC-EDFA for achieving a high power conversion efficiency (PCE) differs depending on the operational bandwidth (C- or L-band): specifically, the PCE in the C-band amplifier improves as R_cc increases, whereas that in the L-band amplifier maximizes at a specific R_cc value. We experimentally verified our calculation results using an R_cc-optimized 12-core EDFA and found we could achieve a more than 5% PCE for L-band operation. Finally, we investigated the effect of the number of cores and core radius on the PCE and confirmed a similar R_cc dependence for an MC-EDFA with an arbitrary number of cores.