Dr. Mark Humphrys

School of Computing. Dublin City University.

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My big idea: Ancient Brain


CA216      CA249      CA318

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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

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On the Internet since 1987.