Research On The Mixed Optical Fiber Sagnac Loop With Built-in PMF

With the development of technology of high precision optical sensing technology of optical communication and fiber optical gyroscope, the polarization state of output light requires high stability, the characteristics of polarization maintaining fiber(PMF) are that the attenuation rate of its two state of polarization equals each other and their phase constants varys greatly, thus the polarization state of PMF is more stable than ordinary optical fiber, the study of parameters of the polarization maintaining fiber, in some extent,gives a certain guidance of real manufacturing of PMF.There have been a variety of approaches for the measurement of parameters of polarization maintaining fiber. This thesis presents two ways to measure the birefringence of PMF based on same principal of sagnac loop with built-in PMF, we use Jones matrix method to analysis the theory of the measurement setup. In addition,we use sagnac loop because there are some advantages of Sagnac interferometer, such as high extinction ratio, loss insensitive and independence of input polarization. By establishing the relationship between the modal birefringence and the output interference spectrum, we get the measurement purpose we need, what’s more,the transmission is simulated in MATLAB to get a direct comprehension. The main contents of this paper are summarized as follows:First of all, the basic principle of polarization maintaining fiber and the applications of Sagnac loop are outlined. The latter can be widely used because it’s thermal independent and hardly affected by the polarization state of incident beamSecondly, the theory of the mixed fiber Sagnac loop with built-in high birefringence fiber are analyzed in detail, we discusse their characteristics when they are regarded as filters. The sagnac loop with built-in one PMF and two PMF are both investigated by the simulation software MATLAB. so different simulation reflection and transmission spectras are obtained with different conditions.Thirdly, to make a proper improvement of these two above sagnac interferometer, two methods are proposed to measure the modal birefringence of high birefringence fiber and low birefringence fiber respectively. Through the MATLAB numerical simulation of its transmission spectrum, the second approach of measuring low birefringence fiber is emphasized.In this way,even in the context of the unclear parameters of the reference fiber 1 cases,we still could measure the modal birefringence of the fiber under tested(FUT), it will give some guidance in actual experiment of measuring the parameter of PMF.