Based on a few-mode fiber Bragg grating as polarization-selective output coupler and topological insulators Bi2Te3 as the saturable absorber, we propose a passively Q-switched fiber laser with cylindrical vector beam output. Both radially and azimuthally polarized beams can be readily generated, and the output polarization can be switchable through tuning the polarization controllers inside the laser cavity. The laser operates at the wavelength of 1557.5 nm with a 3 dB linewidth of less than 0.04 nm. The repetition rate of the Q-switched laser can be tuned from 31.54 kHz to 49.40 kHz when the pump power increases from 103.5 mW to 139.5 mW.
We demonstrate a new method to detect the vortex beams carrying orbital angular momentum (OAM) by a sectorial screen. When the sectorial screen is illuminated with vortex beams, the far-field diffraction pattern can be used to define the modulus and sign of topological charges. The number of the petals denotes the number of topological charge. The direction of intensity pattern flip by 180° for a change in the sign of topological charge. The experimental results agree well with the simulated results.
We demonstrated an all fiber actively mode-locked laser emitting cylindrical vector beam. A few-mode fiber Bragg grating is adopted to achieve mode selecting and spectrum filtering. An offset splicing of single-mode fiber with fourmode fiber is utilized as a mode coupler in the laser cavity. A LiNbO3 Mach-Zehnder modulator is used to achieve active mode locking in the laser. The laser operates at 1547nm with 30 dB spectrum width of 0.3nm. The emitted modelocked pulses have a duration of 1ns and repetition of 12.06MHz. Both radially and azimuthally polarized beams have been obtained with very good modal symmetry by adjusting the polarization in the laser cavity.
Based on the few-mode fiber Bragg grating’s reflection characteristics, we propose and demonstrate a transverse modes switchable fiber laser fiber laser, fundamental mode and 1st higher order modes, and the states be switched by tuning the laser’s oscillating wavelength. The radial vector beam is also obtained by splitting the degenerated 1st higher order modes.