Cyclops opening-up fiber for real-time fluorescence sensing

Compared with traditional fluorescence-based microstructured fibre sensors using filled structure, the opening-up microstructured fibres have shown many advantages for real-time sensing. The design and theoretical study about Cyclops opening-up microstructured fibre is present in this paper. In Cyclops fibre, a large asymmetry hole is placed in fibre cladding. A tri-hole design is adopted for fibre core to enlarge the evanescent field interactions with measured material. This structure is compatible with the traditional stack-draw processing. To make the opening-up structure, chemical etching (with acid) or polishing machining could be used for the asymmetry hole. The opening depth and shape of large asymmetry hole is important for real-time sensing response in Cyclops opening-up fibre. The relationship between marching depth in cladding and fluid concentration distribution at different time in evanescent field near fibre core is analyzed numerically based on incompressible Navier-Stokes equations and finite element method (FEM). The results show that the concentration distribution in evanescent field adjacent to fibre core can reach the true value out of cladding below ten seconds by design cladding structure appropriately. The field distribution of fundamental mode and some cladding mode of Cyclops fibre without tri-hole core and with different tri-hole are presented in this paper too. Cyclops fibre show good characters in these aspects compared with wagon wheel (WW) opening-up fibre. In order to evaluate the performance of sensing based on Cyclops opening-up fibres we adopted the modal power fraction (PF) within the sensing region and the effective modal area (Aeff) and the fluorescence capture fraction (FCF). The results show the Cyclops opening-up fibre is a competitive candidate for real-time fluorescence sensing.