Passive noise suppression in Yb-doped fiber amplifier based on nonlinear amplifying loop mirror

We investigated the frequency-dependent transfer function of amplitude noise in an all-polarization-maintaining Yb-doped fiber amplifier based on nonlinear amplifying loop mirror (NALM). We generated artificially designed amplitude noise in laser by adding weak sinusoidal modulation into the seed pulses and pump. After transmitting through the NALM-based amplifier, we obtained the amplitude-frequency and phase-frequency responses of the amplitude noise at different gains. Systematic measurements indicate that pump power optimization in the NALM-based amplifier suppresses the amplitude noises from the signal pulses and amplification pump, achieving suppression ratios exceeding 12.7 and 23.0 dB, respectively, with a simultaneous signal amplification ratio reaching 10.0 dB. Moreover, the output noise characteristics confirm that the NALM-based amplifier exhibits broadband amplitude noise and phase noise suppression. Clarifying the mechanism and bandwidth of this amplifier is necessary for low-noise laser generation because it provides insight into the nonlinear laser dynamics of broadband passive noise suppression and signal amplification.