A comparative perspective on Differential Modal Gain reduction techniques for optimized few mode EDFA systems

Abstract

Different designed Modal Gain Equalized Few Mode-Erbium Doped Fiber Amplifier (FM-EDFA) systems are evaluated and compared in this paper. These systems include Two Mode (2M-EDFA), Four Mode (4 M-EDFA) and Six Mode (6 M-EDFA). Comparison between designed FM-EDFA systems indicated that with increase in signal modes, an appropriate pump combination is more effective in reduction of both Differential Modal Gain (DMG) and Amplified Spontaneous Emission (ASE) ratio as compared to modification of erbium ion profile. For higher order modes, the pump combination must include at least two modes with matching radial or azimuthal index. DMG in Modified Erbium Doped Profile (MEDP) system shows more sensitivity to length, concentration and wavelength for higher order modes. Mode Specific Pump Combination (MSPC) system being independent of erbium ion profile is observed to be completely immune to upconversion quenching process as far as DMG is concerned. The Power Conversion Efficiency (PCE) is observed to decrease from 19.28 % in 2M-EDFA system to 5.3 % in 6 M-EDFA system as higher number of modes result in increase in effective utilization of pump power. All FM-EDFA systems show comparable pre-amplification performance for each individual mode up to data rates of 15 Gb/s.