RIGOROUS ANALYSIS OF FORM BIREFRINGENCE OF WEAKLY FUSED FIBEROPTIC COUPLERS

Based on a rigorous vectorial formulation, the surface integral equati on method is used to solve the vectorial mode patterns and the couplin g characteristics of weakly fi;sed fiberoptic couplers, Form birefring ence versus aspect ratio of the coupler cross-section for different no rmalized frequencies V are calculated, A dramatic feature-that there i s a local maximum of form birefringence for the weakly fused couplers with large V-values-is found,The dependence of the aspect ratio at whi ch the coupler is isotropic on the V-value is also presented, The fuse d coupler with large V-value is isotropic as the aspect ratio is close to 1.8, but its polarization effect is still significant when the asp ect ratio is 2.0.