A high-temperature sensor based on a Mach–Zehnder interferometer (MZI) in a conventional single-mode optical fiber is proposed and fabricated by concatenating two microcavities separated by a middle section. A femtosecond laser is used to fabricate a microhole on the center of a fiber end. Then a micro-air-cavity is formed by splicing the microholed fiber end with a normal fiber end. The interferometer is applied for high-temperature sensing, in the range of $500–1200°\mathrm{C}$, with a sensitivity of $109\mathrm{pm}/°\mathrm{C}$ that, to the best of our knowledge, is highest in silica fiber temperature sensors. Also, the interferometer is insensitive to external refractive index (RI), which is desirable for temperature sensors.

In this study, graphene-based supercapacitors with optical transparency and mechanical flexibility have been achieved using a combination of poly(vinyl alcohol)/phosphoric acid gel electrolyte and graphene electrodes. An optical transmittance of ∼67% in a wavelength range of 500-800 nm and a 92.4% remnant capacitance under a bending angle of 80° have been achieved for the supercapacitors. The decrease in capacitance under bending is ascribed to the buckling of the graphene electrode in compression. The supercapacitors with high optical transparency, electrochemical stability, and mechanical flexibility hold promises for transparent and flexible electronics.

A taper-based Mach–Zehnder interferometer (MZI) embedded in a thinned optical fiber is demonstrated as a highly sensitive refractive index (RI) sensor. A RI sensitivity of $2210.84\mathrm{nm}/\mathrm{RIU}$ (refractive index unit) is obtained at the external RI of 1.40, which is ten times higher than that of normal taper- and long-period fiber grating (LPFG)-based sensors. The sensitivity can be further improved by decreasing the diameter of the thinned fiber and increasing the interferometer length of the MZI. The proposed MZIs have lower temperature sensitivities compared with normal fiber sensors, which is a desirable merit for RI sensors to reduce the cross sensitivity caused by thermal drift.