Measurement of the effective refractive index of silicon-on-insulator waveguide using Mach–Zehnder interferometers

We propose and demonstrate an accurate method of measuring the effective refractive index of silicon-on-insulator waveguides. By conducting the combined analysis to the troughs’ wavelength in spectra of Mach–Zehnder interferometers on chip. The wavelength-dependent and temperature-dependent effective refractive index of the fabricated waveguides are measured experimentally, and obtained the thermo-optic coefficient of silicon-on-insulator waveguides is about 2×10⁻⁴ /℃ in the 1550 nm communication band. The maximum measurement error for effective and group refractive index respectively are 1.5×10⁻⁵ and 1.5×10⁻³ obtained by numerical simulation. And an improved method for taking value of the free spectral range was discussed to obtain a more accurate group refractive index. It proves a fast and lost-cost measurement way to evaluate key optical parameters of waveguide, which can indicate the quality of fabrication process and optimize photonic components.