Agradecimentos: We thank F.M. Smolka, and Cristiano M. de B. Cordeiro, for the assistance with the heat-and-pulling stations, and C.P. Guerra for the assistance with some optical measurements. This research had the following funding: Author S.C. was supported under researchship CNPq-DTI grant 381532/2021-6, and FUNTTEL financial grant # 01.16.0053.01 FINEP/MCTI-Brazilian Ministry of Science, Communications, and Innovations. Author C.R.B was supported under CNPq-PCI grant number 300616/2022-8. G.N.M.-S. would like to thank the support of the INCT FOTONICOM/CNPq/FAPESP Ver menos

Abstract: An in-line digital optical sensor was proposed. It was built from a tapered depressed-cladding single-mode fiber and modeled as a coaxial Mach-Zehnder interferometer. The principle of operation of the optical digital sensor is based on the computation of the number of optical power transfer turning points (PTTP) from the transmission data of the component. Biconic tapers with high values of PTTP, high spectral resolution, high extinction ratio, and low insertion loss were modeled, fabricated, and characterized. As a proof of concept, an in-line digital strain sensor was fabricated and characterized. It presents a free spectral range of 1.3 nm, and produced 96 PTTP, at ?0 = 1.55 µm, under stretch of ?L = 707 µm, therefore producing a digital resolution of 7.4 µm/PTTP. The sensor also produced a quasi-symmetric response to stretch and compression Ver menos