Resonant Couplings in U-Shaped Fibers for Biosensing

Abstract

U-shaped tight curvatures in optical fibers lead to resonant couplings between the fundamental and higher order modes that are sensible to different parameters, such as strain or temperature, for example. The optical response of the sensor consists on the shift of the resonant wavelength of the coupling. In the case of singlemode fibers, the coupling involves a so-called "cladding mode" and, due to its evanescent field, the curved region will be sensible to changes in the external medium, as well. In this paper, we present the fabrication and characterization of a robust, easy-to-make, U-shaped fiber sensor based on singlemode telecom fiber and its application for biosensing. The resonant nature of the sensing mechanism presents the advantage of large dynamic ranges for RI variations without the ambiguity of other techniques such as interferometry. We studied the performance of the U-shaped fiber sensor for different bending radii, to optimize its sensitivity and detection limit at 1550 nm operation wavelength, as well as the effect of temperature on its response. The shift of the resonant wavelength was measured in detail as a function of the external RI within the range [1.33-1,37]; the detection limit was established in (3.71±0.03)×10 -5 RIU. Furthermore, the device was successfully tested as a proof of concept biosensor, using a system model antigen-antibody (BSA-aBSA.)

Dielectric Waveguide-Based Sensors with Enhanced Evanescent Field: Unveiling the Dynamic Interaction with the Ambient Medium for Biosensing and Gas-Sensing Applications—A Review

“…The diverse applications of these sensors encompass fields such as biomedical research, environmental monitoring, and industrial processes. By exploiting the evanescent field, these photonic sensors provide a robust foundation for advancing sensing technologies, offering innovative solutions with broad implications for scientific research and practical applications [25][26][27][28][29]. This review systematically delves into the nuanced concept of the evanescent field ratio in Section 2, elucidating its critical role in the development of highly sensitive photonic devices.…”

Fiber optic refractive index sensor based on U-Tapered structure

“…Different types of fiber optic RI sensors have been studied and developed, such as surface plasmon resonance [2] , fiber grating [3] , Fabry-Perot interference [4] , Mach-Zehnder interference (MZI) [5] and other types. Among them, Mach-Zehnder interferometers have been developed with different structural types of fiber optic Mach-Zehnder interferometric sensors, such as tapered [6] , U-shape [7] , and heterocore structures [8] , due to the flexibility of designing them in fiber optic structures.…”