Performance study of mode-locked Er-doped fiber lasers based on nonlinear polarization rotation

Abstract Erbium-doped mode-locked fiber laser systems based on nonlinear polarization rotation (NPR) with different configurations are established. The mode-locking states under co-pumping and counter-pumping are achieved respectively through NPR, and the output spectra, input-output power curves, radio frequency (RF) spectra, and autocorrelation traces within the range of 1540–1600 nm are recorded. Meanwhile, in the case of co-pumping and shorter cavity, the mode-locking state is determined according to the angle of the three-paddle polarization controller (PC), and the analysis of the autocorrelation traces in the noise-like pulse (NLP) state is carried out. After the cavity length is shortened to 8.4 m, the transition between NLPs and soliton pulses is achieved through PC adjustment. Additionally, in the three-paddle PC (from the input to the output, the components are arranged sequentially as Paddle 1, Paddle 2, and Paddle 3) with co-pumping and 8.4 m cavity length, when two paddles are kept fixed and only one is rotated, different mode-locking states and output characteristics are achieved, and the autocorrelation traces of NLPs are obtained. By investigating the variation relationships of pedestal width and pedestal ratio R c with respect to the change of a certain paddle angle, a foundation has been laid for the research on the regulation of mode-locking states and autocorrelation characteristics.