Bi-doped fiber amplifiers in the E + S band with a high gain per unit length

We present a bismuth (Bi)-doped fiber amplifier (BDFA) operating in the 1400–1480 nm range using 35 m of Bi-doped germanosilicate fiber. A maximum gain of 23 dB for an input signal of −23dBm at 1440 nm has been achieved, which, to the best of our knowledge, is the highest gain per unit length of 0.66 dB/m reported for a BDFA. The 3 dB bandwidth is measured to be 40 nm (1415–1455 nm), and the gain coefficient is 0.2 dB/mW. A further temperature dependence study of BDFA across the temperature range of −60°C to 80°C also showed a negligible effect of temperature on the E + S band BDFA gain.