This study presents an extrinsic Fabry–Perot interferometric (EFPI) fiber-optic strain sensor with a very short cavity. The sensor consists of two vertically cut standard single-mode fibers (SMFs) and a glass capillary with a length of several centimeters. The two SMFs penetrate into the glass capillary and are fixed at its two ends with the use of ultraviolet (UV) curable adhesives. Based on the use of the lengthy glass capillary sensitive element, the strain sensitivity can be greatly enhanced. Experiments showed that the microcavity EPFI strain sensor with initial cavity lengths of 20 μm, 30 μm, and 40 μm, and a capillary length of 40 mm, can yield respective cavity length–strain sensitivities of 15.928 nm/με, 25.281 nm/με, and 40.178 nm/με, while its linearity was very close to unity for strain measurements spanning a range in excess of 3500 με. Furthermore, the strain–temperature cross-sensitivity was extremely low.

The aspect ratio of nanostructures determines the mechanical sensitivities and responses, such as hydrodynamic and oscillating flow detection. Nanopillar arrays with ultrahigh aspect ratio were fabricated using deep reactive-ion etching (DRIE) based on the optimized parameters in this study. Wafer-scale nanopatterning was achieved using dislocation lithography with normal photolithography machine instead of e-beam or EUVL. The wafer-scale Cr masks with 300, 500, and 700 nm line arrays were successfully patterned on silicon, providing etching mask for the fabrication of nanopillar arrays with a high aspect ratio. The important limitation of undercut during DRIE was solved by modifying the process parameters and using double masks composed of photoresist and Cr. Finally, the aspect ratio of the silicon nanopillar array reached 120 with smooth surface and vertical sidewalls. The methodology can provide a general approach for fabricating complex 3D periodic nanostructures that can be applied to various fields of multifunctional detection applications to increase detection probability and sensitivity.