Dr. Mark Humphrys

School of Computing. Dublin City University.

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Fiber optic

2.2.4 Fiber optics

Pulses of light sent down ultra-thin (as thin as a human hair or less), ultra-transparent fiber of glass, with total internal reflection (no loss in light as it bounces off side).
Pulse=1, Absence of light=0.
Electrical signal - to - light pulses - to electrical signal.
1-way system. 2-way comms uses 2 fibers, or 2 frequency bands on same fiber.

  1. Sender - LED (low-spec) or Laser (high-spec) converts electrical signal to light pulses.
  2. Receiver - Photodiode detector generates electrical pulse when light falls on it.


Fiber optic theoretical transmission limit 50 T bps.
100 G bps has been achieved in test in practice.
50 G bps for 100 km has been achieved in practice.
40 G bps in someone's home

Seems like computation speed will hit physical limits before communication speed does.
In future? - Computation is slow. Communication is fast. Redesign all systems to minimise computation, no matter how much bandwidth it wastes.

Comparison of fiber optic and copper

ancientbrain.com      w2mind.org      humphrysfamilytree.com

On the Internet since 1987.

Wikipedia: Sometimes I link to Wikipedia. I have written something In defence of Wikipedia. It is often a useful starting point but you cannot trust it. Linking to it is like linking to a Google search. A starting point, not a destination. I automatically highlight in red all links to Wikipedia and Google search and other possibly-unreliable user-generated content.