Figure 2
Thermal sensitivity (TCD) of various types of fibres. (a) In standard fibre the TCD is dominated by the thermo-optic coefficient of the glass material in the fibre core through which the light propagates. (b) This is eliminated in HCF (e.g., HC-PBGFs) in which light propagates through air, making thermally-induced fibre elongation the dominant effect that determines the TCD. (c) In engineered HC-PBGF, changes in the waveguide properties (e.g., a larger fraction of the guided mode is inside the central hollow fibre core as the fibre is heated up and the transverse fibre structure expands) can be set to have a contribution to the TCD that has the opposite sign and equal magnitude contribution to the fibre elongation, making HC-PBGF thermally insensitive. ng: group index; ΔL: change of length; HC-PBGF: Hollow Core Photonics Bandgap Fiber; SMF: single-mode fiber.
