Adaptive feedback control for intelligent phase noise suppression in a figure-9 fiber laser.

Phase noise characteristics of ultrafast fiber lasers are critical to practical applications, such as high-resolution photonics sampling. Herein, we investigated the impact of pump power and linear phase shift difference of counter-propagating light in the nonlinear amplifying loop mirror on phase noise suppression in a figure-9 fiber laser. Based on these results, we proposed a method for intelligent suppression of phase noise through real-time feedback control. By adaptively controlling the linear phase shift difference and pump power, the phase noise can be effectively suppressed in the high offset frequency region even in variable environments. In particular, a reduction of ∼21.40% of integrated timing jitter in the offset frequency region from 10 kHz to 1 MHz was achieved. Our approach was proved to be effective and automatic to obtain ultrafast lasers with low phase noise and may also facilitate the related applications.