Passively mode-locked and Q-switched fiber laser utilizing a same tungsten oxide (WO3) film as absorbers

We demonstrate a passively mode-locked and a passively Q-switched erbium-doped fiber laser respectively by utilizing a same saturable absorber fabricated with tungsten trioxide (WO3). When the WO3 saturable absorber is employed to provide the pulse narrowing effect, Q-switched pulses were observed with a repetition rate of 44.11 kHz and a pulse width of 3.42 las. Moreover, the Q-switched laser could realize hybrid mode-locking after an in-line polarizer was inserted, which could introduce an additional pulse narrowing effect of nonlinear polarization rotation under a certain polarization state. The 3dB spectral bandwidth and the repetition rate of mode-locked pulses are about 7.5 nm and 22.51 MHz respectively. The pulse train is stable with a signal to noise ratio of 70 dB.