Design And Permormance Analysis Of High Birefringence Fiber And Polarization Dependent Splitter

Traditional optical fibers have been developed and researched for more than half a century,so lots of their characteristics have reached the theoretical peak.In the current information age,people want to receive more information and the optical communication network based on traditional optical fibers cannot satisfy people's needs.As a kind of special optical fibers,photonic crystal fibers?PCF?have plenty of excellent optical characteristics,because of their special and flexible structure.In particular,PCF with high birefringence characteristic can be made into polarization-maintaining fibers for long distance transmission or be used as components of polarization beam splitters.This master thesis,which is based on optical waveguide theory and modes coupling theory,uses finite element method to simulation and analyze PCF's polarization characteristic,coupling characteristic and bandwidth.The main research results are as follows:1.This master thesis analyzes the impacts of adding elliptical holes or germanium at the core area on birefringence characteristic.On this basis,a novel octagonal-structure PCF is proposed.Parameter optimization and numerical results show that its birefringence can reach 1.25×10^-2 in the communication window 1550 nm.Its confinement loss coefficient keeps stable between 10^-9 and10^-8.The nonlinear coefficients of two polarization states are 35.84 km^-1·W^-1 and 34.09 km^-1·W^-1 at the wavelength of 1550 nm.What's more,this PCF can realize single-mode transmission at specific wavelength.2.This master thesis analyzes the impacts of different cladding structures on coupling characteristic of dual-core PCF.It indicates that the difference between x direction coupling length and y direction coupling length will be more and more obvious due to compressed cladding structure.Meanwhile,the article researches the relationship between Surface Plasmon Polariton?SPP?modes of graphene and core modes of PCF.Then a novel polarization beam splitter based on compressed-structure dual-core PCF is designed.The research results show that DC-PCF even mode birefringence and odd mode birefringence are 2.22×10^-3 and 1.05×10^-3 respectively.In addition,the 664?m-long splitter can achieve an extinction ratio?ER?of-72.4 d B at the wavelength of 1550 nm.Its bandwidth is 75 nm,covering C bands when ER is less than-20 d B.3.Based on finite element method and modes coupling theory,a broadband polarization beam splitter is designed.This master thesis analyzes influence of fiber structural parameters on coupling characteristics.Numerical results indicate that the 4.038 mm-long splitter can achieve an extinction ratio?ER?of-72.7 d B at the wavelength of 1550 nm.When ER is less than-20 d B,the bandwidth is618 nm as well as the range of the wavelength is 1040-1658 nm.When structural parameters are changed by±1%,the performance of this broadband polarization beam splitter is also excel ent.