Optical Waveguide Films With Two-Layer Skirt-Type Core Structures for Beam Leakage/Scattering Reduction at Tapered Mirrors

Using the self-organized lightwave network (SOLNET) technique, we observed guided beam leakage and scattering at tapered mirrors of core end facets in optical waveguide Alms. The leakage/scattering are caused by the tunneling of guided beams into the cladding film and pattern imperfection of core edge corners. To reduce them, we proposed the two-layer skirt-type core structure, where a core has a layered structure of low-index (LI) part and high-index (HI) part. The LI part located between the HI part and the cladding film prevents guided beams from tunneling into the cladding film. The skirt-type shape of core end facets puts core edge corners away from the guided beam paths. The beam propagation method and the finite-difference time-domain method revealed that the leakage/scattering are reduced in the proposed core structure. Optical waveguide films with the two-layer skirt-type core structure were fabricated by the built-in mask method. Appropriate skirt lengths were found to be around core widths. Guided beams were confined into the HI part to reduce the tunneling into the cladding film.