Cascaded-resonator architecture with tunable Fano interference for high-sensitivity optical gyroscopes

In high-performance photonic sensors driven by resonators, the Lorentz response of the system often limits the ultimate sensitivity, its inherent amplitude-phase coupling limits the improvement of the phase slope. In this paper, we propose a compact architecture based on dual-cavity cascade, which uses dual-path coherent interference to reshape the Lorentz line shape into a tunable Fano resonance. This structure breaks the circumferential constraint of the single cavity trajectory on the complex plane, geometrically decouples the amplitude and phase, yielding a 7.7-fold enhancement in the phase slope. In addition, this interference mechanism not only enhances phase sensitivity, but also contributes to the suppression of backscattered noise and thermal drift through destructive interference and common-mode suppression. As a proof of concept, we applied this architecture to a resonant integrated optical gyroscope (RIOG) model. Numerical evaluations demonstrate that the system achieves a bias instability of 0.012°/h, representing an order-of-magnitude improvement over single-resonator design. This work provides a highly robust and sensitive blueprint for next-generation integrated interferometric sensors.