Raman Gain Square‐Wave Noise‐Like Pulse Laser Pumped by a Random Fiber Laser.

Mode locking of a long‐cavity Raman fiber laser pumped by a low‐noise random fiber laser (RFL) is demonstrated experimentally, where tunable square‐wave noise‐like pulse (NLP) is generated through nonlinear polarization rotation technology. Pulse duration can be tuned from 26 to 134 ns by controlling the polarization state or pump power at a repetition rate of 93 kHz. A signal‐to‐noise ratio of 64 dB is obtained due to the low‐noise characteristic of RFL. In addition, up to 24th high‐order harmonic mode‐locked square‐wave NLP is observed, which has not been reported in mode‐locked Raman fiber lasers with large normal dispersion. This approach not only provides a good temporal stable pump source for mode locking of Raman fiber lasers, but also enriches the methods of laser pulse generation and regulation. [ABSTRACT FROM AUTHOR]