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

• 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.