I don’t know the physics well enough, but here is some general information.

https://en.m.wikipedia.org/wiki/Photonic-crystal_fiber

https://www.rp-photonics.com/hollow_core_fibers.html

High Group Velocity, Low Latency Signal Transmission

The group velocity of guided light is usually close to the vacuum velocity of light. This implies substantially lower latency for signal transmission through hollow-core fibers.