Tunable Hybrid Antiresonance and Mach–Zehnder Interferometer Based on Silica Capillary for Dual-Parameter Sensing

An all-silica-based sensor comprising a section of capillary fiber spliced between two singlemode fibers (SMFs) is proposed for the simultaneous measurement of strain and temperature. By intentionally introducing a controlled transversal offset at one of the fusion splice points, core and cladding modes are simultaneously excited in the capillary, enabling the coexistence of two distinct guiding mechanisms within the sensor. The resulting spectral response exhibits two superimposed modulations associated with antiresonance (AR) guidance and a Mach–Zehnder interferometer (MZI). A comprehensive numerical model is developed to describe the interaction between the two mechanisms as a function of the offset. The model is experimentally validated through characterization of the spectral response for increasing offsets, confirming the coexistence and evolution of the AR and MZI components through free spectral range and visibility analysis. The two interference components allow for independent tracking of their wavelength shifts, enabling simultaneous strain and temperature measurements with estimated resolutions of 11.9 με and 0.45 °C, respectively. Owing to the single-element, one-step fabrication process, and the entirely silica-based configuration, the proposed sensor offers a compact and cost-effective solution for localized multiparameter monitoring.