Refractive index profiles and propagation losses in bent laser fibers

Abstract

A better understanding of stress effects that affect the bending losses in active and passive optical fibers allows us to improve fiber system designs and helps to optimize refractive index profiles in high power, large mode area laser fibers. Bending an optical fiber affects the light in a fiber core by two different phenomena. First, the curved shape of the waveguide changes the light propagation. The second phenomenon is the refractive index change caused by the mechanical stress in a bent optical fiber. The refractive index changes due to bending stresses are estimated by the elasto-optic and stress optic models. The light propagation in a curved waveguide can be modelled applying the electromagnetic wave theory together with the conformally transformed refractive index profiles that include the stress effects. The modelled refractive index profiles that include the bending stress induced index changes are compared to the refractive index profiles that were measured from actual bent optical fibers. We tested if this comparison would allow us to estimate C2 values in stress optic model. Measured bend loss values are compared to the bend loss values simulated with the modelled refractive index profiles.