12 June 2000 Novel macrobend sensor structure based on selective launch of the fundamental mode in graded index multimode fiber
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Novel optical fiber sensor architecture has been developed. The actual element of the sensor is highly curved multimode fiber. However, the feed to the multimode fiber is through a single mode fiber to ensure that only the lowest order spatial mode is launched. Similarly the receiver is also coupled to the sensing element through a single mode fiber. The fundamental mode within graded index multimode fiber proves to be very insensitive to macrobends, if bend radius is larger than certain critical value. If bend radius is reduced below critical value the loss increases very rapidly and this allows for construction of relatively sensitive macrobend fiber optic sensor. In this paper we describe a quantitative theoretical model and a corresponding experimental investigation of the proposed structure. A proposal for simple and practical sensor design based on the proposed structure is presented. It is consisted of a miniature fiber optic coil that is deformed proportionally to the measured environmental parameter. We practically demonstrated sensitivities in the range of ΔI/Δx=130%/N and ΔI/ΔF= 1.1%/μm. Even higher sensitivities are possible by proper mechanical construction of the sensor element. The proposed structure can configured in variety of different distributed and quasi-distributed architectures and is suitable for embedding into the composite materials.
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Denis Donlagic, Brian Culshaw, "Novel macrobend sensor structure based on selective launch of the fundamental mode in graded index multimode fiber", Proc. SPIE 3986, Smart Structures and Materials 2000: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (12 June 2000); doi: 10.1117/12.388122; https://doi.org/10.1117/12.388122


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