Research On Random Fiber Laser Based On Brillouin Effect

Random fiber laser is a new type of fiber laser,which has broad prospects in the fields of optical fiber communication,optical fiber sensing and industrial processing.In the thesis,by adopting the dual-end-pumped hybrid-cavity,we have demonstrated a dualwavelength Brillouin random fiber laser(DW-BRFL)and a multi-wavelength Brillouin random fiber laser(MW-BRFL)based on the stimulated Brillouin scattering(SBS)and the Rayleigh scattering(RS)in fibers.The main contents of this thesis are as follows:1.Firstly,the pump formula of dual-end-pumped linear cavity is established based on the gain characteristics of doped fibers.Then,the models of narrow linewidth lasers and random lasers are established and optimized numerically.The influences of doped ion concentration and doped fiber length on the laser characteristics are studied.The laser output characteristics such as threshold,output power and slope efficiency are numerically investigated by choosing different doping concentrations and fiber length as the pump power changes.The optimum length of the erbium-doped fiber(EDF)used in this narrow linewidth laser is 1 m.The principle of using fiber Bragg grating Fabry-Perot(FBG-F-P)as the laser cavity mirror to obtain narrow linewidth laser output is also analyzed.2.The physical model of the interaction between the pump light and the Stokes light in the dual-wavelength random fiber laser is established and simulated theoretically.A narrow linewidth DW-BRFL system based on SBS is constructed.The linear cavity of the system consists of a 1-m-long high concentration EDF and a pair of FBG-F-P cavities with a central wavelength of 1550 nm and a reflectivity of 80%.A 10-km-long singlemode fiber(SMF)is used as the gain medium of random cavity to realize Brillouin random lasers.Two narrow linewidth lasers at 1549.612 nm and 1549.70 nm are obtained from the same port under two 976 nm laser diodes bidirectional pumping.Their thresholds are 30 mW and 40 mW,and the measured linewidths are ~586.2 Hz and ~578.2 Hz,respectively.It not only has very narrow linewidth,but also has high stationarity.In 2 hours,(35)RMS(28)0.1226%,the maximum difference of wave peaks in 1 hour is only 0.5312 dB.3.A novel structure of narrow linewidth MW-BRFL is designed.The laser adopts a hybrid cavity structure consisting of a linear cavity and a semi-open random cavity,which combines a random fiber laser with a Brillouin laser.The principle of laser generation is analyzed,and the power coupling equation is established according to the structure of MW-BRFL.Then the MW-BRFL experimental system is constructed.The stable fifthorder and sixth-order Stokes laser outputs are obtained by using 10-km-long and 20-kmlong SMFs as SBS gain media,respectively.The wavelength spacing is 0.088 nm.By adding a fiber ring mirror at the output of MW-BRFL,the output stability can be improved.An ultra-high optical signal-to-noise ratio of more than 50 dB and an optimal peak power difference of 0.143 dB can be obtained when using the 20-km-long SMF as the SBS gain medium.