typical index of refraction in fiber is of order 1.5. Over 1000 km, that's nearly 2 ms compared to n=1. Of course HF doesn't propagate "straight" so a direct c

typical index of refraction in fiber is of order 1.5. Over 1000 km, that's nearly 2 ms compared to n=1. Of course HF doesn't propagate "straight" so a direct comparison is not straightforward.