Generation of Bright–Dark Pulse Pairs in the Er-Doped Mode-Locked Fiber Laser Based on Doped Fiber Saturable Absorber

Abstract

This study reports two new types of passive mode-locked Er-doped fiber lasers (EDFLs) based on a segment of doping fiber saturable absorber (DFSA) with Yb-doped fiber (YDF) and Er-doped fiber (EDF). By employing YDF-SA, a bright pulse sequence with the fundamental repetition rate of 17.86 MHz is obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, second-harmonic pulses, and three-wavelength pulse sequence, are obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in two polarization directions is verified. Furthermore, using EDF-SA, dark pulses and dark–bright pulses are obtained. A comparison of the two experiments reveals that YDF-SA effectively reduces the mode-locked threshold as well as improves the average output power. Compared with bright pulses, dark pulses have numerous advantages in resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL proposed can be widely used in long-distance transmission, precision measurement, and other fields.

Keywords: passive mode-locked, DFSA, bright pulse, dark pulse, EDFL