Ultraviolet transparent silicon oxynitride waveguides for biochemical microsystems

Abstract

The UV wavelength region is of great interest in absorption spectroscopy, which is employed for chemical analysis, since many organic compounds absorb in only this region. Germanium-doped silica, which is often preferred as the waveguide core material in optical devices for telecommunication, cannot accommodate guidance below 400 nm, owing to the presence of UV-absorbing centers. We show that silicon oxynitride $\left({\mathrm{SiO}}_x{\mathrm{N}}_y\right)$ waveguides exhibit very good UV performance. The propagation loss for $24‐\mu \mathrm{m}$-wide ${\mathrm{SiO}}_x{\mathrm{N}}_y$ waveguides was found to be $\sim 1.0 \mathrm{dB}/\mathrm{cm}$ in the wavelength range 220–550 nm. The applicability of these waveguides was demonstrated in a biochemical microsystem consisting of multimode buried-channel ${\mathrm{SiO}}_x{\mathrm{N}}_y$ waveguides that were monolithically integrated with microfluidic channels. Absorption measurements of a $\beta$-blocking agent, propranolol, at 212–215 nm were performed. The detection limit was reached at a concentration of $13 \mu \mathrm{M}$, with an optical path length of $500 \mu \mathrm{m}$ (signal/noise ratio, 2).