Abstract
A liquid-filled D-shaped fiber (DF) cavity serving as an in-fiber Mach–Zehnder interferometer (MZI) has been proposed and experimentally demonstrated for temperature sensing with ultrahigh sensitivity. The miniature MZI is constructed by splicing a segment of DF between two single-mode fibers (SMFs) to form a microcavity (MC) for filling and replacement of various refractive index (RI) liquids. By adjusting the effective RI difference between the DF and MC (the two interference arms), experimental and calculated results indicate that the interference spectra show different degrees of temperature dependence. As the effective RI of the liquid-filled MC approaches that of the DF, temperature sensitivity up to −84.72 nm/°C with a linear correlation coefficient of 0.9953 has been experimentally achieved for a device with the MC length of 456 μm, filled with liquid RI of 1.482. Apart from ultrahigh sensitivity, the proposed MCMZI device possesses additional advantages of its miniature size and simple configuration; these features make it promising and competitive in various temperature sensing applications, such as consumer electronics, biological treatments, and medical diagnosis.
Highlights
Owing to their lightweight, compact size, high sensitivity, and fast response, optical fiber-based sensors for temperature measurement have been extensively studied and applied in scientific research and different industrial areas [1]
We propose and demonstrate a simple, miniature, and ultrasensitive temperature sensor based on a liquid-filled in-fiber Mach–Zehnder interferometer (MZI)
These two portions of light propagate through the MC and the residual core layer of the D-shaped fiber (DF) respectively, and experience difference optical paths; their spectral interference occurs at the rear combiner joint
Summary
Owing to their lightweight, compact size, high sensitivity, and fast response, optical fiber-based sensors for temperature measurement have been extensively studied and applied in scientific research and different industrial areas [1]. Compared with traditional electric sensors, fiber optic sensors offer the distinguished features of immunity to electromagnetic interference, capability of distributed remote measurement, and durability against harsh environments such as high temperature and high pressure [2,3] Based on these advantages, much more efforts have been made. Most of in-fiber MZI sensors utilize some mode-field-mismatched structures, such as micro-air-holes [15], and waist-enlarged fiber bitapers [16], to excite different cladding modes which are intended to interfere with the core mode Both cladding modes and core mode participate in the interference propagate in silica, they have similar mode effective refractive indicies (RI), which results in a sensing area of up to a few centimeters long, in order to accumulate enough phase difference [15]. The thermal expansion and thermo-optic coefficients (TOCs) of silica-based optical fibers are small, which limits the sensitivities of the reported
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