Extended L-band few-mode Er/Yb Co-doped fiber amplifier with a cladding-pumped pseudo-two-stage configuration

Spatial division multiplexing (SDM) is one of the most important technologies that may help to solve the future capacity crisis. However, to date, SDM optical amplification is still a challenge for its application. Herein, we numerically and experimentally demonstrated a few-mode Er/Yb co-doped fiber amplifier (FM-EYDFA) for extended L-band operation. A double cladding Er/Yb co-doped fiber was fabricated to expand the L-band bandwidth and a novel, to the best of our knowledge, cladding-pumped pseudo-two-stage amplification configuration was proposed to enhance the L-band gain. With an initial signal power of -16.8 dBm and an injected pump power of 8.8 W at 940 nm, the 20-dB gain range was covered to 1620 nm for two-mode groups of LP₀₁ and LP₁₁. Importantly, the average gain of 25 dB and average differential modal gain (DMG) of <1 dB were obtained in the wavelength range of 1570-1620 nm for all modes. Our results suggest that the cladding-pumped pseudo-two-stage amplifier based on Er/Yb co-doped fiber providing low DMG, and broad bandwidth has a great potential for increasing the future SDM capacity.