Research On Stress-induced Single Frequency And Single Polarization Fiber Laser

Single-frequency fiber laser with outstanding features of excellent coherence, line width and low noise, has aroused much attention of numerous scholars. Besides maintaining a good polarization state of laser output is increasingly important in some application areas such as fiber optic gyroscope, fiber sensing, nonlinear frequency conversion, coherent beam combination and so on. Therefore, single-frequency single-polarization fiber laser with high cost-effective is becoming the trend.This article focuses on polarization effects of fiber and fiber Bragg grating under the transverse force, and single-frequency single-polarization fiber laser using the effect is simulated by matlab and verified by experiment, specific research works are as follows:1. The basic structure of fiber laser is illustrated briefly with explaining necessary conditions for laser-produced and the working principle of optical lasers. Then, single-frequency and polarization characteristics of optical laser are synthetically introduced, including the theory of longitudinal mode selection, analyzing laser polarization by Jones matrix, the common methods to achieve single-frequency or single-polarization lasers, and their advantages and disadvantages.2. Fiber Bragg grating (FBG) as the key components used in fiber laser is studied in depth. Obtaining its working principle and classification, coupled-mode equations of FBG corresponding to the ideal state and the disturbance state are respectively reasoned, which are derived from the classical coupled-mode theory. At the same time, the optical characteristics of FBG are discussed to provide a theoretical basis for the analysis of grating under transverse force.3. According to single-mode fiber birefringence and elastic-optic effect, characteristics of single-mode fiber and FBG under uniform external transverse pressure are researched in both cases of the plane stress and plane strain. The simulation results have shown that optical fiber under uniform transverse loads exhibits high birefringence, and the FBG reflection spectrum is gradually divided to dual resonant peaks as the extrusion pressure increases. The proportional linear relationship of wavelength offset of two resonant peaks and refraction change of the corresponding polarization is illustrated.4. The method to induce unique polarization effects of fiber and FBG by applying appropriate external stress is proposed, which is used in the case of outputting stable single polarization laser.5. The ring cavity single-frequency single-polarization fiber laser system model is proposed, which uses saturable absorber and polarization effect of the FBG induced by added stress. And combined with the rate equation its spectral characteristics and stability of the extinction ratio are analyzed in detail. Moreover, the preliminary experimental verification on the ring cavity laser in a laboratory environment is done, observing dual-wavelength laser output through the spectrometer.