Wide tunble in C + L band single-wavelength passively Q-switched fiber laser based on cascaded EDF and EYDF

In this paper, a Wide tunble in C + L band single-wavelength passively Q-switched fiber laser (PQFL) consisting of cascaded doped fiber segments and a tunable band-pass filter (TBF) is proposed. The TBF achieves precise tuning of the wavelength with a maximum tunable range of 45.04 nm (1529.08–1574.12 nm). When the fiber is non-completely pumped, erbium-doped fiber (EDF) and erbium-ytterbium co-doped fiber (EYDF) act as saturable absorbers (SA). It has different nonlinearities under different pump power combinations, producing passively Q-switched pulses with repetition frequencies from 8.23 kHz to 46.47 kHz and pulse widths reduced from 12.82 μs to 2.00 μs. In addition, the wavelength range of passively Q-switched is also changing from 11.55 nm to 31.04 nm. In the experiment, the change in the wavelength range of the passively Q-switched pulse was explained by analyzing the gain saturation absorption characteristics of the EDF and the EYDF. In the experiment, only four devices are used to achieve single-wavelength wide tuning and passively Q-switched, which is enough to prove the simplicity and compactness of the structure. The proposed FQFL has broad application prospects in the fields of distributed sensing systems and bio-medical imaging.