Tunable and Low Noise Gain-Clamped Double-Pass L-Band Erbium-Doped Fiber Amplifier

A highly efficient, low-noise and tunable gain-clamped L-band erbium-doped fiber amplifier is demonstrated using a Fabry-Perot laser in a double-pass system. The broad-band fiber Bragg grating (FBG) operating in the L-band region is used to retro pass the test signal to the system for enhanced gain. Gain clamping is achieved by incorporating a narrow-band FBG operating at the C-band wavelength in conjunction with an optical circulator to generate a Fabry-Perot laser, which can be tuned by a variable optical attenuator (VOA). The gain is clamped at 19.0 dB for all input signal powers from -40 to -12 dBm with a gain variation of less than 0.2 dB at a VOA setting of 0 dB. The clamped gain can be controlled between 19.0 and 21.4 dB by varying cavity loss setting. The corresponding noise figures obtained are below 4.8 dB within the dynamic input power range. The low noise figure is achieved due to the incorporation of a short forward-pumped erbium-doped fiber in front of a double-pass amplifier.