Birefringence Of Single-mode Fiber Stress And Interferometric Fiber Optic Sensor Device

One of the most important parameters about high birefringence fibers is the beat length. Because of its shortness and periodicity, measuring beat length is a critical one. Here we propose a highly accurate method which relies on electromagnetic modulation technique.We have measured several high birefringence fibers, the resolution of the beat length is beter than 0.01mm, the rotation state of the fiber has no influences on final measuring results.Bending-induced birefringence in single-mode fibers is one of the most important factors to degrade the polarization state of light wave. Bending-induced transverse stress distribution in single-mode fibers had been researched, the theoretical results match experimental data very well.The experiment results of fiber Fabry Perot interferometer with fineness more than 100 at center wavelength 0.63μm and throughput of 40— 50 percent have been achieved. The relations of fineness N and peak transmission τ to coupling loss β and mirror reflecticity R are discussed here. A 1.1m length of fiber made from a standard step-index deppressed-cladding fiber with 4μm diameter core was prepared with polished ends . The tilt angle of the fiber end can be insured better than 0.2°A new method for count-detection of optical Fabry-Perot interferometer had been developed in this paper.The frequency of the incident light is modulated with variation about 20KHz, the signals from entering or lagging edge of pulse are different in phase and the direction of the change can be indentified .