A miniaturized tip Fabry-Perot interferometer (tip-FPI) is proposed for high-temperature sensing. It is simply fabricated for the first time by splicing a short length of microfiber (MF) to the cleaved end of a standard single mode fiber (SMF) with precise control of the relative cross section position. Such a MF acts as a Fabry-Perot (FP) cavity and serves as a tip sensor. A change in temperature modifies the length and refractive index of the FP cavity, and then a corresponding change in the reflected interference spectrum can be observed. High temperatures of up to 1000 °C are measured in the experiments, and a high sensitivity of 13.6 pm/°C is achieved. This compact sensor, with tip diameter and length both of tens of microns, is suitable for localized detection, especially in harsh environments.

Circular dichroism (CD) is required in the applications of biological detection, analytical chemistry, etc. Here, we numerically demonstrated large-range switchable CD by controlling the phase change of Ge₂Sb₂Te₅ (GST) in a zigzag array. At the amorphous state of GST (a-GST), the strong and dual-waveband CD effects are realized via the selective excitations of electric, magnetic, and toroidal resonances. With the transition from a-GST to crystalline state GST, CD strengths are tailored dynamically in large ranges. In detail, the CD magnitudes change by about 0.93 and the modulation depths exceed 94% at dual wavebands. The strong CD effects and large-range switch capability in the GST-based metasurfaces will boost the development of active chiroptical devices.

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.

An in-fiber Mach-Zehnder interferometer (MZI) with a micro-cavity (MC) exploited for strain and temperature simultaneous measurement. The research is carried out experimentally and simulatively. The MC fabricated by splicing a hollow quartz tube between two single-mode fibers serves as a light splitter for the two arms of MZI beams and a Fabry-Pérot interferometer (FPI) component at the same time. Thus both functions of the MZI and FPI were implemented in a single sensor. With aid of the different response of the MZI and FPI to the strain and temperature, this device can achieve a simultaneous measurement and the strain/temperature cross-sensitivity issue has been alleviated. Such a composite interference structure, possess the characteristics of easy making, high performance-price ratio provides a promising approach to implement strain and high-temperature simultaneous measurement.

A multifunctional metasurface capable of dynamic control for polarization selectivity and absorption is proposed by controlling the phase of Ge₂Sb₂Te₅ (GST) in the near-infrared region. At amorphous state of GST (a-GST), the proposed GST strip array realized polarization selectivity in transmission-reflection integrated modes. The high-efficiency asymmetric transmission (AT = 0.92) and asymmetric reflection (AR = -0.82) are both obtained by selectively exciting Mie multipole resonances. With the transition from a-GST to crystalline (c-GST) state, the giant polarization selectivity almost disappeared, and the absorptions climb from < 0.1 to > 0.9. The maximum modulation depth reaches 94%. The mechanism of the dynamic switching between polarization selectivity and absorption is quantitively analyzed via multipole expansion. The GST based metasurfaces simultaneously possess excellent switchable capability for AT, AR, and absorption without refabricating structures, which is promising to the applications for next generation optical devices.

High-Q chiral quasi-bound states in the continuum (q-BICs) have great prospects for applications in detectors, modulators, switches, etc. Here, we demonstrate the chiral q-BIC with near-unity and switchable circular dichroism (CD) in a photosensitive silicon metasurface. By breaking the out-of-plane symmetry of the windmill-shaped structure, the high-Q q-BIC and near-unity CD are simultaneously realized. Interestingly, CD keeps the near-unity values as the asymmetry parameter varies, which is an important merit for chiroptical devices. The CD could be dynamically switched from 0.98 to 0.04 by optically pumping photosensitive silicon. Besides, an extrinsic chiral q-BIC is demonstrated and switched by optically pumping photosensitive silicon. The intrinsic and extrinsic chirality are both obtained by exciting electric quadrupole (EQ) resonance, which are verified by quantitative multipole decompositions and electric field distribution analysis.