A novel and simple technique for gain flatness control is reported for gain
shifted, long wavelength band (L-band) erbium-doped fiber amplifiers (EDFA
s). Utilization of the backward traveling amplified spontaneous emission (A
SE) in the C-band is analyzed with respect to controlling the gain tilt obs
erved in the L-band when the total input power of the EDFA is changed. It i
s shown that a gain flatness of 0.6 dB/30 nm can be achieved over a dynamic
range greater than 10 dB by using the backward traveling ASE power in the
C-band as a monitor to adjust the copropagating pump power of the EDFA. The
proposed technique eliminates the need to extract the output signals from
the monitored ASE signal, demonstrating the suitability and simplicity of t
he proposed technique for wavelength division multiplexed applications.