Refractive index sensor of Mach–Zehnder interferometer based on thermo-optic effect of SOI waveguide

We propose a Mach–Zehnder interferometry (MZI) refractive index sensor based on thermo-optic effect of silicon-on-insulator (SOI) waveguide to detect refractive index of liquid. By modulating silicon temperature the phased shift induced by the sample index change is compensated to ensure the output power is unchanged. The phase-matching conditions for a valid refractive index sensor are discussed to direct the design for lengths of sensing and heating areas. Meanwhile the sensitivity and resolution of the refractive index sensor are also analyzed. The proposed thermo-optic compensation method shows noticeable advantages compared with refractive index sensor by directly detecting the output power. Based on these discussions, a refractive index sensor with a compact size of 2 mm × 1.5 mm can be realized with a sensitivity of 48,000K/RIU and a resolution of 2 × 10−6 can be realized.