A passively Q-switched random fiber laser with cascaded doped fiber segments and random phase-shift Bragg grating

In this paper, stable pulse train generated from an all-optical passively Q-switched random fiber laser (RFL) with cascaded doped fiber segments and random phase-shift Bragg grating is demonstrated for the first time. A 25 mm random phase-shifted fiber Bragg grating (RPS-FBG) is used to provide random feedback. Two cascaded doped fiber segments, Erbium-doped fiber (EDF) and Erbium-Ytterbium co-doped fiber (EYDF), are used as saturable absorber when the fibers are incompletely pumped. The characteristics of the RFL under different power of two pump lasers are investigated. The doped fiber has different nonlinearities under different pump power combinations, which results in passively Q-switched pulse with repetition rate from 5.1 kHz to 29.3 kHz. The RFL not only has low-threshold but also exhibits stable random pulse with repetition rate and pulse width controlled by the combination of two pump powers.