L-band extended EDFA co-pumped by backward ASE

We employ the backward amplified spontaneous emission (ASE) co-pump technique in L-band extended erbium-doped fiber amplifier (LE-EDFA) for the first time. The gain is improved by $5.1 \sim 16.7$ dB in the wavelength range of $1570 \sim 1620$ nm when the pump power is 450 mW. A two-stage LE-EDFA co-pumped by backward ASE is then demonstrated with a 20dB gain bandwidth covering $1570 \sim 1610$ nm and the noise figure of less than 6 dB.