--- title: "Fiber optic vs copper cable" subject: "Telecommunications" chapter: 2 key: "semester_8/telecommunications:fiber-vs-copper-applications" source: https://www.bctengineer.com/q/semester_8/telecommunications/fiber-vs-copper-applications site: BCT Engineering --- # Fiber optic vs copper cable Telecommunications · Chapter 2: Transmission Media - Asked in: 2070 Chaitra, 4+3 marks - Video: [Fibre (Fiber) vs Copper as Fast As Possible](https://www.youtube.com/watch?v=_Bw2NFBDxR8) — Techquickie - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/fiber-vs-copper-applications - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-2 ## Question Describe briefly the advantages of fiber optic cable over the copper cable. Advise suitable application of both the media. ## Short answer Fibre offers huge bandwidth, very low attenuation (0.2 dB/km at 1550 nm), immunity to EMI, no crosstalk, security, small size and electrical safety. Use fibre for backbone, submarine, FTTH, base-station backhaul, OPGW and high-EMI links. Use twisted pair for subscriber loops, DSL and short LANs, and coax for antenna feeders, cable TV and CCTV. ## Answer **Optical fibre** carries information as light pulses through a glass core by total internal reflection, while **copper cable** (twisted pair, coaxial) carries electrical signals. Fibre is now the main medium for backbone networks. #### Advantages of fibre over copper 1. **Huge bandwidth** – tens of GHz·km per fibre and terabit capacity with WDM, compared with a few hundred MHz on copper. 2. **Low attenuation** – about 0.2 dB/km at 1550 nm, so repeater spacing of 80–100 km or more; copper needs repeaters every 1–2 km at high bit rates. 3. **Immunity to EMI/RFI** – glass is non-conducting, so no electrical interference, lightning surge or ground-loop problems; can run beside power lines (e.g. OPGW on HV towers). 4. **No crosstalk** – light does not leak into neighbouring fibres. 5. **Security** – very hard to tap without detection; no radiation. 6. **Small size and weight** – a thin cable holds many fibres; easier to install in ducts. 7. **Electrical isolation and safety** – no sparks; usable in hazardous areas. 8. **Raw material** – silica is abundant; no copper theft value. 9. **Long life** – no corrosion. Limitations: higher cost of terminal equipment (lasers, photodetectors), difficult splicing, fragile, and cannot carry power to remote equipment. #### Suitable applications | Medium | Suitable applications | |---|---| | Optical fibre | Inter-exchange trunks and national backbone (e.g. optical fibre along highways in Nepal), submarine and international cables, mobile base-station backhaul, FTTH internet, data-centre and LAN backbones, OPGW on power lines, links in high-EMI areas | | Twisted pair copper | Subscriber telephone loops, DSL, Ethernet LAN up to 100 m, intercoms, low-speed control and alarm circuits | | Coaxial copper | Antenna feeders, cable TV distribution, short high-frequency links between equipment, CCTV | In short, fibre is used where distance, capacity or interference is the main issue, and copper where the distance is short, the data rate modest, power feeding is needed, or low cost of terminal equipment matters. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why does fibre need far fewer repeaters than copper at high bit rates? A. Its attenuation is very low (about 0.2 dB/km at 1550 nm) B. It carries electrical power to the repeaters C. It uses thicker conductors D. It has higher crosstalk that boosts the signal Answer: A. Fibre loss is about 0.2 dB/km, allowing 80-100 km spacing, while copper needs repeaters every 1-2 km at high rates. (Key point: Low attenuation) 2. Why can an optical fibre be run beside high-voltage power lines without picking up noise? A. It is shielded by a braided metal screen B. Glass is non-conducting, so there is no EMI, RFI or lightning surge pickup C. It uses balanced twisted wires D. It operates at very low frequency Answer: B. The glass core and light signal are not affected by electromagnetic fields, so no electrical interference occurs. (Key point: Immunity to interference) 3. Which is a genuine limitation of fibre compared with copper? A. It suffers from more crosstalk B. It has lower bandwidth C. It cannot carry power to remote equipment D. It corrodes quickly Answer: C. Fibre cannot feed power, and it also needs costly terminals and difficult splicing; copper can power remote equipment. (Key point: Fibre limitations) 4. Which choice of medium for an application is correct according to the answer? A. Fibre for subscriber telephone loops, copper for submarine cables B. Coaxial for national backbone, fibre for intercoms C. Twisted pair for international submarine links, fibre for alarms D. Fibre for backbone and backhaul, twisted pair for subscriber loops and short LAN up to 100 m Answer: D. Fibre suits long distance, high capacity or high-EMI links; copper suits short distance, modest rate, power feeding or low terminal cost. (Key point: Choosing the medium) ## Related in Telecommunications - [Optical fiber advantages and wireless media](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aoptical-fiber-wireless-media) — Telecommunications, chapter 2 - [Wired vs wireless media; four-wire and hybrid](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Awired-wireless-four-wire-hybrid) — Telecommunications, chapter 2, asked 2× - [Guided vs unguided media; 2-wire to 4-wire](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aguided-unguided-two-four-wire) — Telecommunications, chapter 2, asked 2× ## Related in other subjects - [Advantages of optical fiber over copper](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aoptical-fiber-advantages) — Instrumentation II, chapter 5, asked 3× - [Coaxial cable vs optical fiber](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acoax-vs-fiber) — Data Communication, chapter 4 - [Compare twisted pair, coaxial, fiber](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Acompare-twisted-coax-fiber) — Computer Networks and Security, chapter 2 - [Optical fiber advantages over coax and twisted pair](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afiber-advantages) — Data Communication, chapter 4, asked 3×