Fig. 1. (a) AFM image and (b) Raman spectra of BP nanosheets. (c) Side profile and (d) saturable absorption of BP-PVA film.

Fig. 2. (a) Reflection spectrum of the TMFBG. (b) Setup of BP Q-switched cylindrical vector laser. LD, laser diode; WDM, wavelength division multiplexer; EDF, erbium-doped fiber; OC, output coupler; SMFBG, single-mode fiber Bragg grating; MC, mode converter; SA, saturable absorber; TMFBG, two-mode fiber Bragg grating; PC, polarization controller; CCD, charge coupled device; SMF, single-mode fiber.

Fig. 3. Spatial intensity distributions of Q-switched (a) RPB and (b) APB, and their corresponding evolution with the rotation of the linear polarizer. (c) Optical spectra and (d) pulse trains of typical Q-switched APB and RPB at the pump power of 79.85 mW.

Fig. 4. (a) Repetition rate and pulse duration versus pump power. (b) Evolution of output power of RPB/APB from TMFBG and coupler with pump power (the linear fitting results are denoted by black lines).