All-Fiber High Efficiency Wavelength-Tunable Mode-Locked Cylindrical Vector Beam Laser

A wavelength-tunable mode-locked cylindrical vector beam (CVB) fiber laser with a dumbbell-shaped structure was proposed and demonstrated experimentally. A homemade broadband long-period fiber grating (LPFG) and a high-birefringence Sagnac fiber loop work as mode converter and comb filter respectively. The mode-locking mechanism is based on the nonlinear polarization rotation (NPR) effect. The central wavelength can be tuned from 1023.257 nm to 1046.123 nm with mode-locked operating state. The laser has a high slope efficiency of 15.75% with the mode-locking threshold value of 232.5 mW at the central wavelength of 1041.361 nm. The mode-locked CVB pulses have a repetition rate of 7.06 MHz with the duration of 107 picoseconds. Radially and azimuthally polarized beams can be obtained by eliminating the degeneracy of LP
₁₁
mode, with the purity of 94.86%. This CVB laser with controllable operating wavelength may have potential applications in mode division multiplexed (MDM) systems, optical manipulation, and electron acceleration.