Optical waveguide films with two-layer skirt-type core end facets for beam leakage reduction at 45° mirrors

Abstract

Three-dimensional optical wiring, consisting of stacked optical waveguide films with 45 o mirrors, is a backbone for integrated optical interconnects and solar energy conversion systems. By using the self-organized lightwave network (SOLNET) technique, we observed leakage/scattering of guided light beams at 45 o mirrors of core end facets in optical waveguide films. When 405-nm write beams were introduced into the optical waveguide having a photo-refractive material layer on the back, three excess lines of SOLNET, which may be caused by the guided beam tunneling into the cladding film and by the refraction at core end facet corners, were grown from the 45 o mirror, in addition to a vertical waveguide of SOLNET formed by reflected beams. To reduce the leakage/scattering, we proposed the two-layer skirttype cores with low-index (LI) part and high-index (HI) part. The LI part located between the HI part and the cladding film prevents the guided beams from tunneling into the film. The skirt-type core end facets put the corners away from the beam path. These effects were confirmed by simulations using the beam propagation method and the finite difference time domain method. Optical waveguide films with the proposed structure were fabricated by the built-in mask method.