Random phase-shift Bragg grating-based random fiber laser with a half-open cavity

A random fiber laser based on a 25 mm long random phase-shift fiber Bragg grating with a half-open cavity is experimentally demonstrated in this paper. The random phase-shift grating is fabricated in single-mode fiber with the beam-scanning method. The random feedback and light localization are achieved by introducing 20 phase shifts with random amplitudes along the grating length. Different couplers and different directions are adopted to investigate the output characteristics under multiple conditions. The stable single-wavelength laser operation with the pump threshold of only 25 mW is realized using a 980 nm pump laser. The optical signal-to-noise ratio up to 67 dB and the 3 dB bandwidth of 17.7 pm are obtained at the pump power of 350 mW. It is found that the emitted wavelength varies linearly with the surrounding refractive index within a certain range by immersing the grating in different concentrations of NaCl solutions, which provides a potential method for lasing wavelength tuning and refractive index detection.