<title>Grating couplers in tapered waveguides for integrated optical sensing</title>

Abstract

Design considerations and experimental results are presented for the fabrication and characterization of grating couplers in gradient effective index waveguides used for realizing miniature integrated optical sensor modules. Hard dielectric substrates such as glass and fused silica have been structured by photolithographic techniques, while hot embossing has been used for the grating fabrication in plastic substrates. The gradient effective index waveguides were produced by shadow mask evaporation techniques in one single deposition step in a rotating substrate holder arrangement. Optical diffraction measurements, atomic force microscopy, and a newly developed method based on performing spatially resolved grating coupler resonance angle measurements are shown to be valuable tools for the characterization of the waveguides and the grating couplers. The experimental results indicate that the deposition of high-index waveguiding films such as Ta<SUB>2</SUB>O<SUB>5</SUB> and TiO<SUB>2</SUB> on previously structured substrates is a viable technique for the cost-effective fabrication of integrated optical sensor chips.