المدربA hollow-core fibre guides light in a core of air (or vacuum), held by a microstructure of thin glass membranes around it, so that light travels at nearly instead of at .
firm.fibreroute: as inverted from its quoted latency, with optical dispersion compensation, in hollow-core fibre on the same path, and in standard fibre along the geodesic. Equipment times, the DCF length and the hollow-core index are the model’s assumptions. Data: fig_fibre.py, nw_fibre.variants().