Grating coupler fabricated in photoresist for optical coupling into thin planar waveguides

In this article practical realisation of grating coupler fabricated in photoresist, integrated with the optical planar waveguides made of different materials and technologies, is presented. Particularly the silica-titania thin fiIm (SiO₂:TiO₂), prepared by sol-gel technology, were employed for coupling a laser light into optical waveguide experiment. Diffraction grating, which is a base for grating coupler device, with 640 nm period was made in positive photoresist Shipley SPR 700, using holographic setup with operating wavelength of 355 nm from pulsed Nd-YAG laser. The gratings were checked with a 632.8 nm He-Ne laser beam; waveguide mode excitation was observed, both as a guided light streak and the series of M-lines. M-link spectrum indicated that three TE modes were excited in the composite waveguide, The method was also successfully applied to S₃N₄ and TiO₂ thin films obtained by magnetron sputtering process. The concept of investigation of planar 2-D photonic crystal is described also.