Passively Q-switched mode-locking Er-doped fiber laser with tunable wavelength and pulsating soliton

A passively Q-switched mode-locking erbium-doped fiber laser with tunable wavelength and pulsating soliton is demonstrated. The polarization-maintaining erbium-doped fiber, working as the gain medium, combines with nonlinear polarization rotation to form a Lyot filter in the cavity. A tapered fiber is placed between two polarization controllers to cause a significant insertion loss in the optical path, which makes it easy to generate Q-switched mode-locking (QML) pulses. The wavelength tunable QML laser is implemented simply and easily, and the tunable wavelength ranged from 1528.05 nm to 1569.55 nm, as large as 41.5 nm. In addition, a new type of QML pulse involving pulsating soliton has been discovered in the laser, which was called Q-switched harmonic mode-locking pulsating soliton (QHML-PS). We find that the harmonic order and repetition frequency increases with the rising of the pump power. Our work has tremendous significance for expanding the research and application of emerging QML fiber lasers.