21 July 1998 Mode-selective/filtering microbend sensor structure for use in distributed and quasi-distributed sensor systems
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This paper describes a novel optical fiber microbend sensor architecture which may be utilized in distributed and quasi distributed measurement. The actual sensor element is graded index multimode fiber coupled to the measurand field through the usual microbend inducing structures. However, the feed to the sensing section is through a single mode fiber spliced to the multimode 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 single mode within multimode fiber propagates with minimal mode coupling with source to receiver losses of typically 0.5 dB for short sensor ranging to approximately 0.3dB per each additional kilometer of sensing fiber. The sensitivity of this structure to microbend induced losses has been thoroughly characterized. Typically the optical power loss for a given microbend structure and force is about three to six times higher in this architecture than for conventional fully mode filled microbend sensor. Further since the microbend operates only on the lowest order mode of the sensor fiber operation of the sensors does not depend on initial modal distribution in sensing fiber. The structure is also almost totally insensitive to the macrobend induced losses and allows a variety of novel designs in microbend inducing structures. Additionally, the use of spatial mode filters allows effective control over concatenation effects that are common in microbend sensors.
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Denis Donlagic, Denis Donlagic, Brian Culshaw, Brian Culshaw, } "Mode-selective/filtering microbend sensor structure for use in distributed and quasi-distributed sensor systems", Proc. SPIE 3330, Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (21 July 1998); doi: 10.1117/12.316972; https://doi.org/10.1117/12.316972

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