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.
2-way comms uses 2 fibers, or 2 frequency bands on same fiber.
Sender - LED (low-spec)
converts electrical signal to light pulses.
Receiver - Photodiode
detector generates electrical pulse when light falls on it.
- Fiber-Optic Chronology
- Fiber optic laid on ocean floor.
Atlantic cable laid 1988.
- Compare with Telegraph Chronology.
- Fiber optic dominates Internet and telephone
(except for wireless satellite links
and wireless land links).
- Fiber optic also used for LANs.
- Less easy in the home - hard to replace
millions of new local loops.
cable TV (no install)
and wireless broadband
(easier install than fiber)
still competing strongly.
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
promise even faster fiber-optic communication
(no need to convert to/from electrical signals).
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
- Fiber higher bandwidth.
- Fiber needs less amplification/repeating.
Fiber needs repeaters every 50 km.
Copper every 5 km.
- Fiber less affected by electromagnetic interference.
But on downside, easily damaged if bent.
- Fiber thinner and lighter: Makes big difference to telephone company
with thousands of cables.
- For new routes, fiber cheaper to install.
- Massive installed base of copper.
- Fiber more expensive, but clearly the future of all cables of more than a few metres