Research On Dispeision And Sensing Characteristic Of Polarization-Maintaining Few-Mode Fiber

Polarization-maintaining few-mode fibers(PM-FMFs),as a new type of fiber,have many excellent characteristics of both single-mode polarization-maintaining fibers(PM-SMFs)and few-mode fibers(FMFs),which have great prospects in the field of optical fiber communication and sensing.Effective characteristic measurement methods are needed for the development of PM-FMFs.In this paper,modal dispersion characteristic measurement methods for PM-FMFs including beat-length and differential mode group delay(DMGD)are investigated and the sensing characteristics of PM-FMFs is explored.The paper will focus on the following aspects:1.The basic theory of PM-FMFs is introduced.The number of modes supported by FMF and the mode field distribution of each mode are discussed.The common methods of mode excitation and conversion and mode(de)multiplexing are summarized.Two scenarios of mode coupling in optical fibers are introduced.The coupling model of mode transmission in fibers is established by using linear coupling matrix.The basic structure and characteristics of PM-FMF are introduced.2.The method for measuring beat-length of PM-FMF is proposed.The basic principles of mode-by-mode and simultaneous beat-length measurement of fiber are analyzed.The performance and details of each part of the experimental setup are analyzed.The experimental results are given and the data are processed.3.The principle of temperature and stress sensor based on PM-FMF is analyzed,and the error estimation formulas of temperature and stress measurement are summarized.The sensing experiments were carried out on a 3-mode panda-type PM-FMF.A temperature and strain simulation model based on PM-FMF is established by using the finite element analysis software COMSOL.A optimization scheme of fiber to reduce temperature and stress sensing errors was proposed.The stress-applying rods of PM-FMF were optimized to reduce temperature and stress sensing errors.4.The basic principle of DMGD measurement based on Spatially and Spectrally Resolved Imaging(S~2)method for PM-FMFs is introduced.The instruments used in DMGD measurement system based on S~2 method are introduced in detail.The DMGD among modes in a 31 meter elliptical-core PM-FMF is measured experimentally.