Study Of Polarization Dependence Of Stimulated Brillouin Scattering Effect And Its Applications

The highly selective gain spectra associated with stimulated Brillouin scattering(SBS),together with its narrow linewidth and low-threshold power,are found to be attractive for fiber laser,distributed fiber sensor,optical filter and numerous other applications.In this paper,the theory of polarization dependence of SBS effect is studied,which is applied to the suppression of polarization fading for the Brillouin optical time domain analysis(BOTDA)system and the measurement of state of polarization(SOP).The main contents and achievements of this dissertation are threefold:(1)Following the principle of physical process of SBS effect,the evolution of pump power and pump SOP,as well as the evolution of Stokes power and Stokes SOP under the double action of fiber random birefringence and SBS effect are analyzed theoretically.Then the variation of the gain of Stokes with pump SOP and Stokes SOP is given.(2)A technique for suppression of polarization fading,based on delayed orthogonal pump is proposed.By using a device with Mach-Zehnder structure,the conversion of single pump pulse to delayed orthogonal pump pulse pair is realized.Then the fluctuation of Brillouin gain trace caused by polarization fading is suppressed by adding and averaging the Brillouin gain traces corresponding to the two pulses.The results show that the fluctuation of Brillouin gain trace is reduced by about 88% using this technique.In addition,the technique has the characteristics of simple structure and good stability.(3)A SOP measuring method,based on polarization dependent narrowband filtering is proposed.By scanning the wavelength of pump that stimulates SBS effect,the signal spectrum with high resolution of ?0.1 pm is obtained.Then,through measuring the signal spectra under six specific polarization states of pump,the Stokes vectors of each wavelength component of signal are retrieved.The results show that a mean error that is 0.018 is achieved for the wavelength-resolved SOP measurement of a 40-Gb/s nonreturn-to-zero differential quadrature phase-shift keying(NRZ-DQPSK)signal.