Distributed Temperature Measurement Utilizing Optical Carrier-Based Microwave Interferometry

Optical carrier-based microwave interferometry (OCMI) has been widely considered and studied due to its unique advantages in combining the strengths of optics and microwaves. This article theoretically and experimentally investigates the OCMI-based distributed measurement of temperature. The distributed temperature measurement is demonstrated experimentally using a single-mode fiber (SMF) with cascading weak optical reflectors inscribed along the fiber core, where any two reflectors are paired to define an intrinsic Fabry-Perot interferometer (IFPI). Spatially continuous distributed temperature demodulation is achieved by reconstructing the microwave interferogram of the IFPIs consisting of two adjacent reflectors. IFPIs with different cavity lengths consisting of two non-adjacent reflectors are also demodulated to study the temperature sensitivity at different spatial resolutions. Experimental results show that the IFPIs along the sensing fiber have a linear response to the temperature, especially the IFPI with the 30 cm cavity length exhibits a better linear response, reversibility, and stability in the temperature range of 35 °C-75 °C. Comparing with the experimental and theoretical values, this article further theoretically investigates the effect of fiber coating layer on the temperature sensitivity of the sensing system, taking into account the physical and geometric properties of the fiber outer coating layer. In addition, a dual-path distributed temperature measurement based on spatial division multiplexing is demonstrated, validating the excellent multiplexing ability and application potential of the OCMI-based multipath distributed measurement.