Abstract
A double-pass long-wavelength-band erbium-doped fiber amplifier (L-band EDFA), which can effectively suppress and completely exploit the backward amplified spontaneous emission (ASE), is presented in this paper. Our experimental results have shown that, compared to a conventional single-pass amplifier, the gain coefficient can be improved considerably from 1.5 dB/mW to 3.1 dB/mW with only a small increase in the noise level. The L-band EDFA can also reduce the pump power necessary to achieve a specified gain to about half, at the cost of a noise figure increase of 1.6 dB. The maximum gain improvement of 15.5 dB was observed at a signal wavelength of 1572 nm of while signal and pump powers were fixed at -30 dBm and 103 mW, respectively.