Dual-peak Brillouin Gain Property In Optical Fibers And Its Applications

The dual-peak Brillouin gain mechanism in optical fibers is one of thehot topics in researches of nonlinear fiber optics in recent years. Supported bythe project of Natural Science Foundation of China “Abnormal Brillouinscattering effect in photonic crystal fibers and its application in fiber lasergyroscope without lock-in effect”, this dissertation studies the realization ofdual-peak/multi-peak Brillouin gain spectra (BGS) in fibers and theirapplications experimentally and theoretically.Utilizing the hybrid fiber ring as a dual-peak gain medium, bi-directionaldual-wavelength multi-mode lasing of Brillouin fiber laser (BFL) based on anunbalanced Mach-Zehnder interferometer (UMZI) hybrid fiber ring cavity isexperimentally realized. Its effect as a gyroscope is demonstrated. The scalefactor is measured as1.0305kHz/(deg/s), which agrees well with the result oftheoretical analysis. The rotating direction of the cavity can be clearlydistinguished through the direction of frequency shift. The lock-in effect isnot observed in the experiment.The single-mode lasing of bi-directional dual-wavelength BFL based onthe hybrid fiber ring cavity with one fiber coupler is experimentally realized.The condition of pump oscillation enhancement and bi-directionalsingle-mode lasing of this cavity are analyzed theoretically. Utilizing thefeedback loop technique, a stable uni-directional single-mode lasing of thisBFL is realized under uni-directional pump and a bi-directionaldual-wavelength single-mode lasing is realized under bi-directional pump.The Brillouin frequency shifts of the two lasing modes are10.57GHz and10.51GHz, respectively, with3dB linewidths of lasing modes being~150Hz.The crucial problems influencing the stability of bi-directionaldual-wavelength single-mode lasing are discussed.According to the influence of doping on the acoustical characteristics of silica material, a novel fiber structure is proposed to achievedual-peak/multi-peak Brillouin gain by acoustical mode coupling. Theinfluences of structural and material parameters of fiber on the mode couplingproperties are analyzed theoretically. A specific fiber design with multi-peakBGS is given and its responses on temperature and tensile strain are analyzed.The theoretical analysis shows that the accuracies of discriminativemeasurement of temperature and strain by this fiber are about1.4℃and33με, respectively, which indicates a potential in the application of distributedBrillouin temperature and strain sensing.