Research On Fused Biconical Tapering Of The Polarization Maintaining Optical Fiber Based On Viscoelastic Model

Polarization-maintaining fiber coupler which is one of the key components of the coherent communication, is widely used in many fields such as hydrophone, fiber optic gyroscope and military interferometric sensor etc. Polarization-maintaining fiber couplers are mainly produced by fused biconical tapering(FBT), and the FBT process parameters have a significant impact on the the polarization maintaining fiber couplers manufacturing. Most performance studies of the Polarization maintaining fiber couplers are from the perspective of optical principle in the ideal state, which ignore the impact of process parameters on the coupler rheological forming in the manufacturing process. Therefore, in this paper, the FBT process and the process parameters were studied from the perspective of rheoforming. Finally the appropriate process parameters is determined, which is instructive to manufacture low-loss polarization maintaining fiber coupler.Firstly, through the analysis and compared to viscoelastic mechanical model, Generalized Maxwell model is determined to describe the rheological behavior of the FBT of the polarization maintaining fiber. The constitutive equation of the fiber was obtained based on the Boltzmann superposition principle under isothermal conditions, to obtain Prony series form of fiber relaxation modulus, and temperature superposition principle is adopted to get variable temperature relaxation modulus. The numerical integral form of the optical fiber fused cone constitutive equation was obtained by the incremental finite element method.Secondly, the fused biconical tapering simulation was conducted by the finite element analysis. In order to obtain the parameters of the polarization-maintaining fiber viscoelastic model, the high temperature creep experiments were carried out and the material mechanics performance curve was obtained. The viscoelastic parameters of optical fiber can be acquired based on the relaxation modulus curve fitting with the curve fitting functions of ABAQUS. The high voltage arc temperature distribution was measured by the thermal infrared imager, which served as the boundary conditions of the fused taper thermal analysis. The geometric model of the fiber taper was established. The boundary conditions and contact conditions were set., and the loads were applied. The fused biconical tapering was simulated using sequential coupling thermal stress analysis method, and the rheological shape of the fiber was obtained. Meanwhile the influence on the polarization maintaining optical fiber stress-strain and tapering shape of process parameters, such as melting temperature, stretching speed, stretching force, was analyzed, which provides guidance to select subsequent technological parameters of FBT experiments.Finally, FBT experiments of the single polarization maintaining fiber was conducted on the micro operations experiment platform. Based on the simulated analysis, the fused biconical tapering was conducted in conditions with different stretching force and stretching speed. After completing the experiments, the influence of the process parameters on the rheological shapes and surface morphology of the fiber was observed under the scanning electron microscopy(SEM). Finally, the optical power on line was detected to determine the appropriate process parameters. When the fused polarization-maintaining optical fiber tapering experiment was conducted under the stretching force of 200 mgf, stretching speed of 80μm/s, stretching length 4000μm, the excess loss is 0.65 d B,which can be used to guide polarization maintaining fiber coupler manufacturing.