Guided Media vs Unguided Media, and Advantages of Optical Fiber

Guided vs unguided media

Guided media (wired / bounded media) are physical conductors that confine the electromagnetic signal to a fixed path: twisted-pair wire (UTP/STP), coaxial cable and optical fibre. The signal travels only along the medium, so it can be measured, tapped only physically, and it does not radiate.

Unguided media (wireless / unbounded media) have no physical conductor; the signal is radiated through air or vacuum as electromagnetic waves and reaches any receiver within range by broadcasting: radio waves (AM/FM, Bluetooth, Wi-Fi), terrestrial microwave, satellite, infrared and laser.

Advantages of optical fibre over twisted-pair and coaxial cable

1. Very high bandwidth — a light carrier in the hundreds of THz range gives data rates of Gbps (10/40/100 Gbps per wavelength) over a single fibre; copper is limited to a few hundred MHz and much lower rates over distance.
2. Very low attenuation — typically about 0.2 dB/km at 1550 nm, against roughly 0.2 dB per 100 m for UTP. Repeaters/amplifiers are needed tens to hundreds of km apart instead of every kilometre or so.
3. Complete immunity to electromagnetic interference (EMI) and no electrical crosstalk — glass is a dielectric and carries no current, so it works safely beside motors, power lines and lift shafts where copper picks up noise.
4. Higher security and privacy — a fibre cannot be tapped by induction; attempting to bend it out causes a measurable power loss, so intrusion is detectable. Copper radiates signals that can be picked up remotely.
5. Much lower bit-error rate (of the order of $10^{-9}$ or better) and no ground-loop / lightning-induced currents.
6. Light weight and small diameter — far more channels per duct, important where conduit space is scarce.
7. Electrical isolation and safety — non-conducting, no sparking hazard in explosive atmospheres, and no risk of short circuits between networks.

Disadvantages (for completeness in the exam): higher cost of cable, transmitters (laser/LED) and detectors, and the fibre is fragile and difficult to splice or connect — it needs skilled installation.