Vernier Effect-Based Fabry–Perot Interferometer Sensing Structure for Vector Curvature Measurement

A hybrid structured fiber sensor based on a cascaded Fabry–Perot interferometer (cFPI) is proposed for vector curvature sensing. The structure is fabricated by self-assembly of cFPI, air-cavity Fabry–Perot interferometer (acFPI), and single-mode fiber (SMF). Since the sensing fiber in the triangularly distributed sensing structure always deviates from the neutral plane, the sensing structure can realize vector curvature sensing. The elastic-optical effect of the photosensitive adhesive contributes to the enhancement of the curvature sensitivity of the cFPI. When light is incident from side A of asymmetric cFPI, a Vernier effect is produced in the spectrum amplifying the curvature sensitivity from 2.017 to 21.022 nm/m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>. A fiber Bragg grating (FBG) is cascaded with an acFPI to exclude temperature crosstalk. The two FPIs for cascading to form the Vernier effect are simultaneously used for curvature sensing, which facilitates the miniaturization of the sensing structure. The sensing structure has the advantages of high sensitivity, miniaturization, and flexible fabrication, which is beneficial to the application of sensing structures in artificial intelligence and biomedicine.