Highly sensitive fiber optic temperature sensor based on a Solc-Sagnac interferometer with the harmonic Vernier effect.

Abstract

We propose and demonstrate a novel fiber optic temperature sensor (FOTS), to our knowledge, that simultaneously achieves both high sensitivity and rapid response. The FOTS is based on a compact Solc-Sagnac interferometer that incorporates thin polarization-maintaining fibers (TPMFs). Splicing two TPMFs of different lengths at a certain angle could achieve the Vernier effect to enhance sensitivity. The low thermal capacity of TPMF could significantly enhance the dynamic response of a harmonic Vernier effect-based FOTS. Theoretical and simulation analyses demonstrate that a distinct normal Vernier effect is generated when two TPMFs of nearly equal length are fused at a 45° splicing angle between their fast axes. The different-order harmonic Vernier effect is realized by configuring the length of one TPMF to be an additional detuning factor plus an integer multiple of the other TPMF length, and the inner-envelope fitting technique is also proposed. The impact of different-order harmonics (i) and the detuning factor (ΔL₀) on sensitivity is investigated. The experiments demonstrate that the temperature sensitivity is directly proportional to the harmonic order (i) and inversely proportional to the detuning factor (ΔL₀). When the FOTS realized the second-order Vernier effect, it achieved a temperature sensitivity of 27.12 nm/°C. The FOTS features high sensitivity, simple structure, ease of manufacturing, rapid response, low hysteresis effect, and excellent stability. It holds significant potential for engineering applications requiring real-time temperature monitoring and precise temperature control.