Q-switched and mode-locked laser based on aluminium zinc oxide deposited onto D-shape fiber as a saturable absorber

Abstract In contrast to the direct insertion of a saturable absorber (SA) to fiber laser cavity, the D-shape fiber coated with a SA material introduces more optical non-linearity and SA damage threshold is increased due to the evanescent field light-matter interaction. In this work, a D-shape fiber coated with aluminium-doped zinc oxide is used as a saturable absorber (SA). A Q-switched operation was obtained at 1559.6 nm. The pulsing was initiated at a low pump power of 25 mW and up to 198 mW, in which the pulses shortened from 6.67 µs to 2 µs and the repetition rate increased from 23.26 kHz to 83.9 kHz. The same technique was used to produce a nanosecond pulse mode-locked operation at 1564.8 nm, with pulse width and a repetition rate of 470 ns and 0.97 MHz, respectively. The laser produced a very stable Q-switching and mode-locking operations with a high signal to noise ratio of ∼ 65 dB.