Abstract
This paper proposes an ultra-high sensitivity temperature sensor based on the dual-stage Vernier effect, systematically establishes the theoretical framework, and provides comprehensive experimental validation. Conventional Vernier-based optical sensors often suffer from signal demodulation complexities and computational errors induced by mathematical envelope fitting. To overcome this, we designed a cascaded architecture comprising a modified second-order Solc-Sagnac interferometer (SSI) and a standard Sagnac interferometer (SI). By strategically introducing a 90° orthogonal splice between the fast axes of two polarization-maintaining fibers (PMFs) within the SSI, the high-frequency fine spectrum is physically canceled, yielding a pure envelope spectrum. This configuration achieves an initial sensitivity amplification while fundamentally eliminating the need for algorithmic envelope tracking. Furthermore, by cascading an SI with a meticulously matched free spectral range (FSR), a secondary spectral amplification is excited. Theoretical analysis and experimental results consistently indicate that the proposed system delivers an ultra-high temperature sensitivity of −74.28 nm/°C. Benefiting from its compact sensing unit (0.3 m), exceptional reversibility, and an ultra-low detection limit of 0.0013 °C, the proposed sensor offers a robust and elegant solution for highly demanding structural health monitoring and industrial metrology.