Dual-Parameter Fiber-Optics Relative Humidity and Displacement Sensor Based on the Topological Ring Structures

The dual-parameter sensors based on topological ring structure are proposed and experimentally demonstrated, which has obvious advantages in relative humidity (RH) and displacement measurement. The topological ring structures are composed of two separated optical microfiber couplers (OMCs) as independent sensing units. The two OMCs are connected by two 30 cm length single-mode fibers (SMFs). The first sensor is formed by introducing OMC into the loop resonator (LR). The second sensor is constructed by introducing OMC into the Sagnac interferometer (SI). The LR-OMC and SI-OMC structures are made by splicing the two ports of OMC with two ports on one side of the different central axis. The coupling coefficient and effective refractive index (ERI) of OMC vary with RH and displacement. The reason for the wavelength shift caused by RH is that water molecules trigger the change ERI of the OMC evanescent. Furthermore, the RH measurement is realized without any humidity-sensitive material. Here, we present a topological ring structure that can measure two parameters discretely, eliminating the problem of RH and displacement crosstalk. The LR-OMC structure and SI-OMC structure have different RH and displacement sensitivity. The proposed topology sensors could find applications in the multi-parameter RH and displacement sensing due to their simple fabrication and low cross-sensitivity.