A Partial Double-Pass S-Band Erbium-Doped Fibre Amplifier

An efficient and low noise short wavelength band erbium-doped fibre amplifier (S-band EDFA) is proposed and demonstrated using double-pass configuration. This amplifier provides a gain of 1500nm signal as high as 26.9dB, which is 9.6dB higher than the two-stage single-pass amplifier. The corresponding noise figure obtained is 7.5dB, which is of the same level as in the single-pass amplifier and more than 2dB lower than the previously reported double-pass amplifier IEICE Electron. Express 2 (2005) 182. The gain enhancement is due to the double pass-propagation of the test signal in the second stage, which increases the effective erbium-doped fibre (EDF) length. The low noise is attributed to the optical circulator between EDFs, which prevents the backward amplified spontaneous emission from propagating into the input part of the amplifier. The proposed amplifier is expected to play an important role in the development of a practical S-band EDFA.