Study of gain flatness for multi-channel amplification in single stage EDFA for WDM applications

In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532-1,558 nm) in a single stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed gain flattening filter (GFF) is used in order to get the flat gain with gain variation +/- 0.5 dB for -20 dBm/ch input signal power (total input signal power is -8.0 dBm) at a fixed average inversion level which is maintained by proper selection of optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating of length 20 mm. Gain variations are studied by changing the total input signal levels from -8.0 dBm to -20.0 dBm and maintained within 20.0 +/- 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed +/- 0.5 dB gain-variation which is an important parameter in optical network system.