A second-order approximation coupling model of fused biconical tapered fiber coupler

The paper presents a mathematical model of the fused tapered fiber coupling theory, which considers the practical position of fibers in the coupling region. Based on the theory of regular optical waveguide, attention is concentrated on the second-order approximations of the propagation constant and coupling coefficient. Experimental studies of fiber coupler are investigated in detail by fabricating couplers. It is shown that the experimental data agree with the theoretical analysis with regard to the coupling ratio.