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Fiber based flexure sensor utilizing the sensitivity of evanescent coupling

: Nelsen, Bryan; Rudek, Florian; Taudt, Christopher; Baselt, Tobias; Hartmann, Peter

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Erstellt am: 5.1.2018

Witzigmann, Bernd (Hrsg.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Physics and Simulation of Optoelectronic Devices XXV : 30 January-2 February 2017, San Francisco, California
Bellingham, WA: SPIE, 2017 (Proceedings of SPIE 10098)
ISBN: 978-151060637-1
Paper 100981C, 9 S.
Conference "Physics and Simulation of Optoelectronic Devices" <25, 2017, San Francisco/Calif.>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IWS ()
coupled mode theory; evanescent coupling; fiber optic; flexure sensor; Hilbert space; rayleigh backscattering; simulated long wavelength

Sensing in harsh environments, such as in high magnetic fields like those found within MRI machines or in high-voltage conditions like those found within power transformers lends itself well for the use of fiber optic sensors. Where conventional electronic sensors fail for obvious reasons, specially designed fiber optic sensors can fill in these gaps. The aim of this research was to investigate the feasibility and technical parameters necessary to design a flexure sensor based on evanescent coupling between the modes of a two- (or more) core fiber. The design parameters are discussed and the sensitivity of the sensor is shown to be tunable by modifying variables which the coupling constant is sensitive to. The physical model used to simulate this system is derived from an effective index change due to a combination of strain and an effective path difference which is induced by bending the fiber. The result of this model is a coupled-mode equation that can be systematically solved using an eigenvector approach to mode coupling. With proper fiber drawing techniques, this model predicts measurement sensitivities of curvature down to km-1. Furthermore, this technique can be extended based on simulated long-wavelength measurements to make predictions about where along the length of the fiber the flexing took place. This system has the potential to be used as a competing system for Rayleigh backscattering based flexure measurements.