Fig. 1. All-fiber FM-EDFA based on IWDMs. (a) FM-IWDM. (b) All-fiber FM-EDFA configuration.

Fig. 2. Experimental results for the IWDM-based FM-EDFA. (a) The input signal spectrum, (b) the variations of the modal gain and the DMG with the forward LP₀₁-mode pump power, and (c) the output spectrum at the pump power of 940 mW.

Fig. 3. Cascade FM-EDFA system for long-haul transmission of MDM signals.

Fig. 4. Experimental test setup for the equivalent spectrum method.

Fig. 5. Performance for the cascade FM-EDFA system. (a) Amplified powers and the overall DMG. (b) Output OSNRs and ASE noise power.

Fig. 6. Simulation on cascade FM-EDFA systems. (a) Recirculating loop model. (b) Comparison of the simulation and experimental results.

Fig. 7. Optimization of the FMF length in the recirculating loop. (a) The system output powers and overall DMG for 10-stage FM-EDFA system. (b) The max stage number of the overall DMG permitted in the limit of 2 dB.

Fig. 8. Curves of the modal gain and the DMG in the C-band.