Tilt Angle Detection Based on Edge-Core Parallel Gratings Fabricated by Femtosecond Laser Point-by-Point Method

A compact directional tilt sensor based on edge-core parallel gratings (ECPGs) is demonstrated. By using the femtoseconds laser point-by-point (PbP) writing method, the ECPGs are inscribed near the core-cladding boundary of a single-mode fiber (SMF) to enhance its grating reflectivity’s sensitivity to fiber curvature. The grating sensor is incorporated into a hinge-like mechanical structure to translate the tilt angle into fiber curvature, enabling tilt angle detection based on the changes in the reflection spectrum intensity. An effective signal demodulation approach based on the intensity difference between the reflections from the two ECPGs ( $\Delta I_{A} - \Delta I_{B}$ ) is employed to mitigate the influence of fiber bending loss, producing a monotonic signal response with tilt angle. The signal indicator $\Delta I_{A} - \Delta I_{B}$ demonstrates a linear sensitivity of 0.148 dB/° with an $R^{2}$ value of 0.997 within a tilt angle range of ±80°. The characterization test indicates low-temperature sensitivity ( $\sim$ $4\times 10^{-4}$ dB/°), high consistency, and excellent durability, as demonstrated by its robust performance during cyclic tilt measurements (MAE =0.045°). These characteristics highlight the significant potential of this sensor for various applications.