That's interesting, I remember reading last year about advances in hollow fibers that said they were better than glass for a single frequency.

I followed the reference and it leads to a paper from 2013;

>Hollow-core fibers (HCFs) are a revolution in light guidance with enormous potential. They promise lower loss than any other waveguide, but have not yet achieved this potential because of a tradeoff between loss and single-moded operation.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-21-5-62...

I haven't yet found the reference to the fiber I was reading about, though I do know it was still in the lab.

edit - it might be this stuff - http://optics.org/news/6/6/20

edit2 - https://www.novuslight.com/hollow-core-fiber-breakthrough_N8...