High sensitivity visible light refractive index sensor based on high order mode Si3N4 photonic crystal nanobeam cavity.

We design and demonstrate a suspended high sensitivity silicon nitride (Si3N4) photonic crystal (PhC) nanobeam cavity sensor. By utilizing the higher order mode, the optical field distribution in the analytes increases dramatically and the light matter interaction between the optical mode and the analytes has been enhanced. A high sensitivity of 321 nm/refractive index unit (nm/RIU) has been experimentally achieved at the wavelength ~700 nm which is the highest value reported so far for a resonator based sensor at such a short wavelength.