Folks already know that the speed limit in the Universe is the Speed of Light … nothing is faster. However, many will be surprised to know that light travels slower in an optical fiber than it does in free space! Due to light-matter interaction, the speed of light, which is about 300 million m/s in free-space is ‘only’ 200 million m/s in glass. But in a world that prizes getting the latest information fast, this fundamental additional latency can sometimes be limiting for many applications. This was dramatized best in the Selma Hayek movie the “Humming-Bird Project”, where she builds a set of line-of-sight microwave links to eliminate milliseconds worth of latency between the Chicago and New York bourses.
In this paper Comcast introduces Hollow Core Fibers and the cutting-edge work being done to reduce this fundamental latency and enhance capacity all at the same time. New fiber technology creates a fiber guiding mechanism that has a core that is hollow and consequently allows light to travel in the hollow of the fiber as-if in free space, but along the fiber path!
We describe a system which is a hybrid of hollow core fibers and standard single-mode fibers. Keeping in view that Comcast operates core and access networks this system has amplified and unamplified bidirectional Coherent systems of 400G and 100G wavelengths along with direct detect systems of 40G, 25G and 10G wavelengths all simultaneously on a single strand of fiber, in what we believe to be the first such system in the world.
In addition to describing our test system and initial results, we also analyze some of the benefits in addition to latency reduction that are related to reduced optical non-linearities and other effects and the wider spectrum and the consequent Capacity enhancements possible. Practical deployment strategy of fibers is essential at Comcast, the ability to use a portfolio of fibers for some of the emerging low latency market while also driving fiber technology deeper into the network is of the essence of our approach towards the industry initiative of 10G.