PMC

(a) Hodograph plane for a fictitious flow generated by a symmetrical completely wettable fibre shown in b. (b) A semi-infinite strip with solid boundaries ABCA in the W-plane corresponds to the meniscus on a circular fibre. When the fibre is not circular, the boundary BC deforms in a dotted line BC.

Model fibre cross-sectional geometries. (a) Solid circle, (b) uncollapsed circular tube and (c) fully collapsed ribbon.

Optomechanical time-domain reflectometry spectra. Measured normalized nonlinear coefficients γ⁽⁷⁾(Ω) at specific fibre locations (blue circular signs) are shown alongside fitted Lorentzian line-shapes (red solid traces). The nonlinear coefficients are normalized so that is the same for all measurements. A standard, single-mode fibre was under test. a A 100 m-long, uncoated fibre section in air, 2.5 km from the input end. b Same fibre section immersed in ethanol. c Same fibre section immersed in deionized water. d A 100 m-long fibre section with standard dual-layer acrylate coating, 2.2 km from the input end. The four curves may be distinguished based on their linewidths. The full-widths at half-maximum of the optomechanical spectra in the four panels are 1.1 MHz, 2.8 MHz, 4.5 MHz and 5.5 MHz, respectively

Comparison of the spectral distributions of the effective modal scattering areas for the 2.8 µm diameter suspended-core fibre investigated here (green curve) and a circular silica taper embedded in water with a diameter of 3.62 µm (purple curve). The dashed and solid lines refer to air or water as analyte medium, respectively. It is assumed that the particle is located 1 nm above the glass surface as indicated by the red dots in the sketches.