Long-wavelength EDFA gain enhancement through 1550 nm band signal injection

An experiment on gain enhancement in the long band (L-band) is demonstrated. Gain at the L-band is relatively inefficient because the operating wavelengths are far from the peak emission band of erbium ions. Gain enhancement for the L-band is achieved by using a signal from the conventional band (C-band). The efficiency of gain enhancement is strongly determined by the absorption coefficient of the C-band signal. Gain enhancement as high as 5.3 dB is obtained at - 15 dBm of 1535 nm injected signal. Maximum gain enhancement for other injected signal wavelengths can be optimised by varying their power. Noise figure penalty is measured to be less than 1.0 dB at its optimised power. Furthermore, there is no penalty on the noise figure for injected signals longer than 1545 nm.