Nematic Liquid Crystal-Embedded Optical Fiber Cryogenic Temperature Sensor Amplified by Vernier Effect

Accurate cryogenic temperature sensing is critical for superconductivity, space technology, and low-temperature biomedicine. We present a high-sensitivity fiber-optic cryogenic temperature sensor based on Vernier effect amplified cascaded Sagnac interferometers (CSIs). The sensing arm incorporates a nematic liquid crystal (NLC)-embedded Sagnac interferometer (SI), while the reference arm uses a polarization-maintaining fiber (PMF)-based SI with a slightly detuned free spectral range (FSR), generating the Vernier effect for sensitivity enhancement. A fiber Bragg grating (FBG) with monotonic linear cryogenic response is integrated into the sensing loop to provide wavelength markers for coarse temperature estimation and FSR period identification, overcoming spectral aliasing and extending the measurement range. Experiments show an average sensitivity of 14.43 nm/K over 260–210 K, a 6.36-fold improvement over a single SI. These results validate NLCs as effective cryogenic thermometric materials and demonstrate the sensor's potential for applications such as short term biobanking of temperature-sensitive biomaterials and low temperature mechanical testing in industrial environments.