Titanium dioxide waveguide with an embedded grating coupler

Optical transport in planar waveguide structures is of great importance for spectroscopic chemical and biological sensing applications. We have fabricated a TiO2-polymer planar waveguide with an embedded grating coupler. The grating coupler consists of a low index layer of SiO2 on a Si(100) substrate. The SiO2 layer has a grating pattern reactive ion etched into the surface. On top of this surface is a high index TiO2 waveguide. The TiO2 film is generated from a spin-coated polymer solution, OptiNDEX (TM) EXP04054 from Brewer Science. The TiO2 film has low optical absorption, a high refractive index, and good thermal and UV stability. It is possible to make up to a 420nm film in a single coating operation. To form the TiO2 film the polymer solution is spin-coated onto a wafer and the wafer is baked at 300 degrees C for 10 minutes. Scanning electron microscopy and focused ion beam cross-sections verified that the TiO2 conformally fills the groves of the grating. We made electrodynamic calculations based on the indices of the materials for our waveguiding structure and the wavelength of the incident light for single-mode wave guiding. These calculations gave a projected TiO2 thickness for our waveguides. Experimental results show that the waveguide structures that we fabricated were in close agreement with these predictions.