Getting your fiber to go straight (in the great circle sense) from point A to point B can be quite challenging given the presence of mountains, water, and peopl

Getting your fiber to go straight (in the great circle sense) from point A to point B can be quite challenging given the presence of mountains, water, and people or countries that control the land in the way. For what it’s worth, hollow core fiber is available now, although at least the one vendor I found is very very expensive. I haven’t found an entirely clear answer as to the group velocity in hollow core fiber (it’s not in the data sheets), but it ought to be pretty fast. (The group velocity in vacuum-filled waveguide is not the speed of light in a vacuum — it’s slower.)