SOI optical waveguide-based refractive index sensor using a multi-slot subwavelength grating Mach–Zehnder interferometer

A compact and high-sensitivity Mach-Zehnder interferometer refractive index sensor is designed and fabricated on a standard 0.18 µm silicon-on-insulator process. The key is the design of a multi-slot subwavelength grating (MSGG) waveguide in the sensing arm, which synergistically combines the strong optical confinement of slot waveguides with the engineered dispersion of subwavelength gratings. By leveraging this MSSG structure, the device achieves a high experimental sensitivity of 462.4 nm/RIU for a sensing length of only 100 µm. The sensor's compatibility with standard, low-cost CMOS fabrication positions it as a promising and scalable solution for a variety of integrated optical sensing applications.