Study Of Fiber Optic Directional Coupler Based On Weak Coupling Theory

With the development of optical fiber communication technology,various kinds of optical fiber communication system have been constantly developed.Directional coupler is a directional transmission passive device,which is widely used in the fields of measurement,communication,transmission and radar.The directional coupler has different coupling principle according to the variety of transmission line and the design structure.The directional coupler is a key device in fiber optic communication system.The optical fiber directional coupler is a directional coupler whose transmission line is optical fiber and coupling mode is parallel.In this paper,the 2×2 optical fiber directional coupler is taken as the research object,the related knowledge of the directional coupler is preliminarily understood,and the transmission mode of fiber optic and weak conductance coupling theory are discussed in detail.In this paper,the simulation model of 2×2 optical fiber directional coupler is established,and the effects of cross sectional area,relative length of fiber and core space on coupling efficiency are discussed by means of R-soft software.The simulation results are accord with the theoretical analysis.And then,the coupling between the core fundamental mode and the cotransmission cladding mode in LPFG is discussed from the coupling mode equation.With the help of R-soft software,the effects of the effective refractive index and grating period on the coupling efficiency are discussed respectively.After continuous simulation test,the same result as the design is achieved.The main contents of this paper are as follows:1.Based on the theory of optical fiber mode,the electromagnetic field mode in optical fiber is studied,and then the mode cutoff condition and single mode transmission condition are studied.2.The irregular waveguide is regarded as a result of the perturbation of geometry or refractive index in a normal waveguide with close structure.Furthermore,the mode coupling mechanism of the directional coupler composed of two parallel optical fibers is analyzed.3.Based on the simulation software R-soft,the effects of cross-sectional area,relative length and distance of directional coupler waveguide on the coupling efficiency were studied,and the simulation results were analyzed.4.Based on the simulation software R-soft,the coupling between the core fundamental mode and the coaxial cladding mode in LPFG is studied,and the effects of effective refractive index and grating period on the coupling efficiency are discussed.