Investigation On Polarization Characteristics Of Active Optical Filter Based On Stimulated Brillouin Scattering

Stimulated brillouin scattering(SBS) is an important nonlinear optical effect. It is often used as an active optical filter in optical fiber communication and sensing since its ultra-narrow gain bandwidth. This thesis focuses on the polarization properties of SBS based active optical filter(SBS-AOF); investigates the improvements of performance of a SBS-AOF based ultra-high resolution spectrum analyzer by manipulating the polarization. In addition, polarization mode dispersion(PMD) measurement is realized using the ultra-high resolution spectrometer. The main contents of this thesis are as follows:(1) Derive from the electric field vector differential equations which characterized the interaction mechanism of signal and pump light in SBS process, the polarization characteristics of the SBS effect in in random birefringence fiber are simulated and analyzed based on concatenated random wave-plate model. Results show that the SBS gain changes with signal polarization regularly, and let the polarization of signal go towards the one which get the maximum gain. The SBS gain is weakly related to the wavelength when signal and pump are injected into fiber with certain polarizations.(2) A method of improving the dynamic range of SBS-AOF based ultra-high resolution spectrometer using polarization pulling is investigated. The performance and validity of this method is studied. It is shown that the dynamic range can be promoted greatly when testing signal with high power and narrow spectra using this method. The dynamic range can be promoted by 8 d B by this method at a pump power of 8d Bm when measuring a-1d Bm signal which is modulated by 100 MHz sine wave.(3) The measurement method of PMD based on the antecedent spectrometer is studied. Six ultra-high resolution spectra are acquired under six specific pump polarization, taking advantage of the polarization properties of SBS-AOF, the corresponding stokes parameter are calculated. The PMD vector is then reckoned by a self-developed algorithm. The measurement of first order PMD of polarization maintaining fiber is realized.