Abstract
A planarized optical fibre designed for two-dimensional bend monitoring and external refractive index sensing is presented. The approach uses two single-mode waveguides each containing a set of spectrally multiplexed Bragg gratings. To achieve sensitivity to bending and external refractive index, the cladding material of the fibre is partially removed through physical machining. This acts to offset the neutral axis, increasing bend sensitivity, and exposes the evanescent field of the guided mode, permitting external refractive index monitoring. Through collective monitoring of the Bragg grating array, real time, multiparameter sensing is attainable, allowing new capability for intelligent monitoring.
Highlights
Design Concept and FabricationFlat fiber is fabricated using modified chemical vapour deposition (MCVD) and fiber drawing
A planarized optical fibre designed for 2-dimensional bend monitoring and external refractive index sensing is presented
Multiparameter bend monitoring has been demonstrated in flexible planar optical platforms, notably silica [5], [6], polymer [7], chalcogenide [8]–[10] and silicon [11]
Summary
Flat fiber is fabricated using modified chemical vapour deposition (MCVD) and fiber drawing. The strain observed in the core layer of flat fibre is dependent upon the bending moments applied and relative position from the neutral axis. For bending moments about the x-axis, Mx, the neutral axis overlaps with the core layer, illustrated in Figure 2 (b). The partial removal of cladding material on one side of the flat fibre acts to offset the neutral axis, as shown in Figure 2 (c), meaning strain induced bending for the Mx can be observed. To theoretically corroborate the optical response, the strain induced in flat fibre was modelled through finite element analysis (FEA) (Comsol Multiphysics, Solid Mechanics). This considered all three orthogonal linear strain components [5]
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