Thermo-optically Tunable Wavelength Filter with Permanent Refractive Index Grating into Azo-Polymer Waveguide

摘要

Refractive index gratings into an azo-polymer waveguide were fabricated by irreversible photo-induced bleaching (photodecomposition) of the polymer. The waveguide grating was formed by exposure of an interference pattern from two laser beams. Coupling characteristics of the waveguide grating were investigated around the infrared wavelength region. The coupling efficiency of the grating was dependent on the polarization direction of the guiding beam. This phenomenon seems to result from the anisotropic refractive index change due to the photobleaching at the vertical plane of the film. Furthermore, we demonstrated a tunable wavelength filter with the refractive index gratings into the azo-polymer waveguide. This filter has a spatial tunability, i.e., wavelength tuning can be attained due to thermooptic refractive index change of the polymer. In the fabricated wavelength filter, the diffraction pass wavelength is tuned over 19 nm at around the 1.3 μm from 5℃ to 65℃.