Integrated Si Sagnac Interferometer With Rayleigh Back Wave

ABSTRACT

We estimate the phase sensitivity of the proposed Sagnac interferometer with a single input beam coupled to a micro‐ring waveguide, where the backward wave arises from Rayleigh scattering inside the ring resonator. Interference causes resonance splitting in the optical spectra observed at the through or drop ports. Estimating the sensitivity of these spectral features to the phase difference between counter‐propagating waves requires developing and adjusting a model to experimental spectra, then introducing a phase shift and detecting changes. Here is presented a comprehensive experimental and theoretical study of resonance splitting statistics in silicon micro‐ring resonators to match the model. We systematically measure distributions of three key splitting parameters—peak separation, height asymmetry, and width asymmetry—as functions of waveguide geometry (width, gap) and sidewall roughness. We develop a refined matrix formalism model that self‐consistently predicts resonance splitting statistics, fits all types of resonance splitting, including asymmetric ones, and extracts critical resonator parameters (coupling coefficients, losses, backscattering) from transmission and reflection spectra. The sensitivity of the asymmetry in the split peaks’ height to the phase difference is estimated at 0.12–0.14 % per 10 ⁻⁴   rad. Our model shows excellent agreement with experiment, offering a robust framework for microresonator‐based rotational interferometry.