Dual Sagnac interferometers for sensitivity-enhanced temperature sensing based on amplitude comparison function

A sensitivity-enhanced optical fiber temperature sensor based on dual Sagnac interferometers is proposed and experimentally demonstrated. In the proposed system, Sagnac interferometers are constructed by embedding different lengths of polarization-maintaining fibers into single-mode fibers, resulting in two Sagnac interferometers (SIs) with distinct transmission characteristics. As the temperature changes, the transmission spectra of the SIs shifts, resulting in changes in the output power of the system. To enhance the sensitivity to temperature, an amplitude comparison function is employed based on the power ratio of two outputs of the SIs. A temperature variation experiment based on the temperature-controlled chamber has been carried out for verification, validating the ability to detect slight temperature variations. Furthermore, the sensor based on the dual-SIs configuration effectively resolves the dead zone issue inherent in the single-SI configuration, achieving up to a 32.3-fold enhancement in sensitivity. Compared to conventional methods, the proposed temperature sensor has a simpler configuration and does not rely on complex instruments such as an optical spectrum analyzer, offering low-cost sensors with enhanced sensitivity for precision temperature measurements.