What's the minimum network latency for a 1000 km connection using optic fibers?

A typical index of refraction for optical fiber is 1.62, therefore the speed of light in a fiber is approximately 3e8 m/s / 1.62 = 1.85e8 m/s. Therefore it would take at least 1000000 m /1.85e8 m/s = 0.0054 s to travel that distance. Note that this value doesn't cover the extra distance traveled by the light from bouncing side to side.

Ignacio Vazquez-Abrams

Posted 2011-05-28T19:21:39.247

Reputation: 100 516

1I expect more than this theoretical 5.4 ns/m, isn't there any source that says what actual latencies are? – Jader Dias – 2011-05-28T19:35:39.503

And fiber cables aren't laid in straight lines neither. – Jader Dias – 2011-05-28T19:37:12.110

4@Jader, lol, first you ask for "minimum network latency" and then you complain they aren't realistic enough? You must be confused. – akappa – 2011-05-28T21:19:30.220

1@akappa I'm not confused. I'm asking the the "minimum network latency", not the "minimum latency through an ideal-but-yet-not-manufactured-medium" – Jader Dias – 2011-05-28T21:21:44.680

The fact that "fiber cables aren't laid in straight lines" has nothing to do with fiber technology. As for the actual speed of light in the medium, the informations you can find in the linked wikipedia article is more than adequate. – akappa – 2011-05-28T21:34:09.870

@akappa but not adequate enough to figure out the speed taking the internal reflections in account – Jader Dias – 2011-05-29T00:41:39.990

@Jader Dias: those are taken into account by the refractive index. – akappa – 2011-05-29T00:55:49.843

@akappa No they're not. Light speed is slower inside glass regardless of reflections. The existence reflections just mean that the light isn't following a straight path, even if the cable is straight. If I knew the average reflection angle for an optical fiber then I could calculate the average speed of a light beam inside it. – Jader Dias – 2011-05-29T01:04:53.737

From http://en.wikipedia.org/wiki/Refractive_index : The refractive index or index of refraction of a substance is a measure of the speed of light in that substance. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium.

– akappa – 2011-05-29T01:12:41.987

@Jader Dias: also take a look at that: http://en.wikipedia.org/wiki/Snell%27s_law , hope this clears your confusion

– akappa – 2011-05-29T01:14:25.463

@akappa I thought in pointing the same articles to you. I hope you read them. Where the hell did you get the idea that the refractive index take in account the internal reflections? – Jader Dias – 2011-05-29T17:41:50.730

@Jader Dias is right on that last point - the refractive index is a property of bulk material and can't take reflections into account. The actual delay factor due to these reflections depends on the angle of light rays entering the fiber. The maximum angle is determined by the NA of the fiber. Note that for thin (single-mode, less than 10 lambda diameter) fibers it doesn't even make sense to think about light rays bouncing around in the fiber... see http://en.wikipedia.org/wiki/Optical_fiber#Single-mode_fiber

– Jonas Heidelberg – 2011-05-29T18:00:08.943

What's the minimum network latency for a 1000 km connection using optic fibers?

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