Micro-Bending Effect on the Field and Energy of Weakly Guiding Optical Fiber with a Gradient Profile in Single-Mode Regime

Introduction. Optical fibers are widely used for high-bandwidth transmitting communication signals over long distances. The key feature enabling this performance is signal low attenuation, that is signals experience minimal power loss propagating along the optical fiber. One of the factors influencing power loss during information transmission is the fiber bending. Bending can increase the signal transmission power loss of an optical fiber because of both macrobending and microbending. Studying the dependence of signal power losses when bending on waveguide parameters makes it possible to control the signal power losses of an optical fiber during information transmission. Aim of the Study. The study ia aimed at evaluating the effect of microbending on the field and energy of a weakly guiding optical fiber with a gradient refractive index profile in a single-mode regime. Materials and Methods. From the equations for the fields of straight and curved sections of weakly guiding fiber for an arbitrary gradient profile of the refractive index with the help of the subsequent solution of inhomogeneous Helmholtz equations by the Green’s function method, there were obtained expressions for relative energy: the ratio of the field energy of the fiber curved section to the field energy of the fiber straight section (in the first approximation for a single-mode regime). Results. The obtained expression for the relative energy depends on two parameters: the waveguide parameter and the ratio of the optical fiber radius to the radius of curvature. For the quadratic case of a power-law profile, as the closest to the actually used one, numerical calculations were used to construct the dependences of the relative energy on the parameter characterizing the bending for different values of the waveguide parameter. Discussion and Conclusion. It has been shown that in the case of microbending, the longer the wavelength or the smaller the fiber radius, the lower the losses. The results obtained can be used in calculating optical fiber profiles designed to operate in a bent state and eliminate expensive experimental modeling of light guides and in designing waveguides to solve specific applications, in particular, to increase energy efficiency, reliability and performance of the measuring instruments.