High frequency traders do NOT want to be limited by the speed of light in a fiber - due to its refractive index (1.5 for ZBLAN according to Wikipedia) this is o

High frequency traders do NOT want to be limited by the speed of light in a fiber - due to its refractive index (1.5 for ZBLAN according to Wikipedia) this is only 66% of the speed of a radio signal. Over 10km this amounts to an 11 microseconds difference - already significant for HFT. This is why they have been leveling hills to carve a (mostly, with minimal amount of repeater towers) line of sight path between NYC and Chicago, gaining 3ms (1), or set up a line of sight laser link between NYSE and NASDAQ to eke out a handful of microseconds (2), or set up multiple links across the English channel to reduce latency between London, Amsterdam and Frankfurt (3). 1. https://www.nytimes.com/2014/04/14/opinion/krugman-three-expensive-milliseconds.html https://www.nytimes.com/2014/04/14/opinion/krugman-three-exp... 2. https://www.extremetech.com/extreme/176551-new-laser-network-between-nyse-and-nasdaq-will-allow-high-frequency-traders-to-make-even-more-money https://www.extremetech.com/extreme/176551-new-laser-network... 3. https://sniperinmahwah.wordpress.com/2016/01/26/hft-in-the-banana-land/ https://sniperinmahwah.wordpress.com/2016/01/26/hft-in-the-b...