Advantages of fibre over metalled wire

An optical fibre carries information as light through glass, while a metallic wire (twisted pair or coaxial cable) carries it as electric current. Because of this, fibre has many advantages.

1. Very large bandwidth: optical carrier frequencies are about $10^{14}$ Hz, so a fibre can carry Tb/s with WDM. Copper is limited to MHz–GHz.
2. Low attenuation: about 0.2 dB/km at 1550 nm, so repeaters can be 100 km or more apart. Coaxial cable needs repeaters every few km.
3. Immunity to electromagnetic interference: glass is a dielectric, so motors, power lines and lightning do not induce noise. Useful in factories and along power lines.
4. No crosstalk: light does not leak from one fibre to another in the same cable.
5. Electrical isolation: no ground loops, sparks or shock hazard; safe in explosive or high-voltage areas.
6. Security: the fibre does not radiate, so it is hard to tap without being detected.
7. Small size and light weight: a fibre cable is much thinner and lighter than a copper cable of the same capacity, so it is easier to install in ducts.
8. Low cost raw material: silica (sand) is plentiful, while copper is costly.
9. Long life and corrosion resistance: glass does not corrode in moist or chemical environments.
10. Flexibility of upgrade: higher bit rates and more wavelengths can be added by changing end equipment only.