Applications of optical fibres
1. Why Fibre Wins
Fibre offers huge bandwidth (~THz), low loss (0.2 dB/km), light weight, immunity to EMI, security (hard to tap), and dielectric safety vs copper (MHz, loss ~dB/100 m, EMI, heavy). Replaced copper for long-haul.
2. Major Applications (exam list — 6 with one-line each)
| Field | Use | Why Fibre |
|---|---|---|
| Telecommunications | Long-haul backbone, metro, FTTH, internet | 1550 nm low loss, DWDM (many per fibre, Tbps); 100 km repeater spacing vs copper 1 km |
| Data links / LAN | Datacentre, 10–400G Ethernet, HDMI | High bandwidth, low crosstalk |
| Sensing | Fibre optic sensors (next topic) | EMI immunity, remote; bridges, pipelines, oil wells |
| Medical | Endoscope, laser surgery delivery, OCT imaging | Flexible, biocompatible, guides visible/IR + images via fibre bundle |
| Illumination / Decor | Fibre lamps, signage | Flexible light pipes |
| Military/Aerospace | Gyroscope (Sagnac), secure comms, fly-by-light | Light, EMI immune, secure |
| Power + sensing combo | Power-over-fibre (rare) | — |
3. Telecom Note (quantitative)
Single SMF with DWDM: 80- × 100 Gbps =8 Tbps per fibre; lab demo >100 Tbps. Copper coax ~1 GHz·km. Fibre loss allows transoceanic 10,000 km with EDFAs every 80 km.
4. Worked Illustration
FTTH: OLT → splitter → ONT at home via SMF 1550 nm downstream, 1310 upstream, PON (passive optical network) shares fibre via TDM.
Endoscope: coherent bundle of 10k fibres transmits image pixel-by-pixel from lens at tip to eyepiece.
Ocean cable: 6 fibre pairs × 80 waves × 100 Gbps =48 Tbps across Atlantic.
5. Exam Points
- List applications with one-line advantage — 5-7 marks, very frequent (telecom is compulsory).
- Compare fibre vs copper (bandwidth, loss, EMI) — 5 marks, frequent.
- Mention DWDM and FTTH — 3 marks.
- Medical endoscope — 3 marks.