Number study on the coupling loss of the photonic crystal fiber

The coupling loss between photonic crystal fiber(PCF),single mode fiber(SMF),and other PCF with different structure is an urgent problem to be solved today.The local orthogonal functions model of PCF was applied to theoretical analysis of the coupling loss between PCF,SMF and PCF with different structures.The relation between coupling loss and the structural parameter of PCF and mode wavelength was obtained,and the optimal structural parameter was given.The result shows that(1) the main factor that affects the coupling loss between PCF and SMF is the hole space Λ of PCF.When the hole space is fixed to a certain value and the mode radii of PCF and SMF are the same,the coupling loss reaches its minimum value,i.e.,any deviation from this value will increase the coupling loss;(2) The coupling loss between PCFs is determined by the difference of their hole spaces.As the mode radius depends on mode wavelength,the coupling loss will also be in its minimum value when wavelength keeps constant and the mode radii of PCF and SMF are the same.Therefore,the factors should be comprehensively considered in the design process of PCF.