Gain clamping in double-pass L-band EDFA using a ring resonator

A gain-clamped long-wavelength-band erbium-doped fiber amplifier (L-band EDFA) based on a ring-laser cavity is demonstrated using two C/L-band wavelength-selective couplers. This new design provides improved gain characteristics and high tuneability. The gain is clamped at 11.5 dB with a gain variation of less than 0.1 dB from an input-signal power of -40 to -6 dBm by setting the variable attenua tion setting (VOA) at 8 dB, Also, the clamped-gain level can he controlled to he in the range from 4.7 to 21.3 dB by varying the VOA settings from 0 to 24 dB. However, the proposed gain-clamped amplifier suffers from noise-figure degradation, as compared to the open-ring amplifier, due to the intense ring-laser light, which counter-propagates through the EDF.