Experimental demonstration of highly sensitive optical sensor based on grating-assisted light coupling between strip and slot waveguides

An optical sensor based on grating-assisted light coupling between a strip waveguide and a slot waveguide is demonstrated (the sensor was proposed and analyzed in [Opt. Express21, 5897-5909 (2013)]. The wavelength at which the light is strongly coupled between two waveguides is used to the measure the external medium's refractive index. The sensor was fabricated with silicon nitride waveguides and obvious grating induced band-rejection and band-pass characteristics were observed. The measured sensitivity of the fabricated sensor was -756.1 nm/RIU. Furthermore, by covering the strip waveguide with the silicon dioxide cladding, the sensitivity was measured to be as large as -1970 nm/RIU, which was 2.6 times enhanced. The experimental results agreed well with the calculated sensitivity values.