Wavelength switchable erbium-doped random fiber laser based on cascaded fiber Bragg gratings fabricated by femtosecond laser processing technology.

• This study used femtosecond laser processing technology to fabricate cascaded fiber Bragg gratings. • This study proposd an erbium-doped random fiber laser based on long-distance single mode fiber. • Random laser wavelength switching was achieved by changing the polarization state of the light in the system. This study proposed a wavelength switching system for the linear cavity erbium-doped random fiber laser (RFL) based on cascaded fiber Bragg gratings (FBGs). High reflection cascaded FBGs was fabricated by point-by-point inscription method based on femtosecond laser processing technology. The erbium-doped fiber (EDF) was used to provide effective gain for the laser system, the backward Rayleigh scattering (RS) in the long distance passive single-mode fiber (SMF) was used to provide random distributed feedback for the system, and the single-RS was changed into double-RS by the full reflection mirror to improve the feedback intensity. Combined with the frequency selection function of cascaded FBGs, the polarization state of the light in the system was changed by adjusting the polarization controller (PC) to achieve wavelength switching. The designed laser system achieved a low threshold power of 37 mW. When the pumping power was 57 mW, the output wavelength was 1549.6 nm and 1550.0 nm single-wavelength laser channel, respectively. The laser stability was observed within 50 min, and the maximum wavelength fluctuation was 0.01 nm and 0.09 nm with the maximum power fluctuation being 0.30 dB and 1.44 dB respectively. The dual-wavelength laser generation was obtained by adjusting the PC, the wavelength fluctuation was less than 0.07 nm and the power fluctuation was less than 1.01 dB. With the increase of input power, the fitting linear determination coefficient of output power was 0.979 and the correlation coefficient was 0.990. The wavelength switchable RFL proposed in this paper is uncomplicated in structure, switchable, and has excellent wavelength and power stability, which is of great significance in the fields of laser sensing, laser communication and diffuse spot imaging. [ABSTRACT FROM AUTHOR]