Fiber optic

2.2.4 Fiber optics

Fiber-optic
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 Chronology
• Fiber optic laid on ocean floor. Atlantic cable laid 1988.

• Compare with Telegraph Chronology.

• Fiber optic dominates Internet and telephone backbone now (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. Phone and cable TV (no install) and wireless broadband (easier install than fiber) still competing strongly.

Speeds

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

• Theoretical All-optical computers 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 is fiber.