A zero-cross detection algorithm was proposed for the cavity-length interrogation of fiber-optic Fabry–Perot (FP) sensors. The method can avoid the inaccuracy of peak determination in the conventional peak-to-peak method for the cavity-length interrogation of fiber-optic FP sensors caused by the slow variation of the spectral power density in peak neighboring regions. Both simulations and experiments were carried out to investigate the feasibility and performance of the zero-cross detection algorithm. Fiber-optic FP sensors with cavity lengths in the range of 150–1000 μm were successfully interrogated with a maximum error of 0.083 μm.

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.

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