---
title: "Optical fiber and its advantages"
subject: "Basic Electronics Engineering"
chapter: 5
key: "semester_2/basic_electronics_engineering:optical-fiber-advantages"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/optical-fiber-advantages
site: BCT Engineering
---

# Optical fiber and its advantages

Basic Electronics Engineering · Chapter 5: Communication System

- Asked in: 2073 Bhadra, 1+3 marks; 2073 Magh, 2+2 marks; 2071 Bhadra, 2+3 marks; 2068 Bhadra, 1+3 marks; 2075 Baisakh, 2+4 marks (asked 5 times)
- Video: [Optical fiber cables, how do they work? | ICT #3](https://www.youtube.com/watch?v=jZOg39v73c4) — Sabin Civil Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/optical-fiber-advantages
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-5

## Question

What is optical fiber? Explain its working principle and advantages of optical fiber communication over traditional (copper/coaxial cable) communication systems.

## Short answer

An optical fiber is a thin glass or plastic strand that guides light by total internal reflection due to a higher-index core surrounded by a lower-index cladding. Advantages over copper include much higher bandwidth, lower attenuation, immunity to electromagnetic interference, better security, smaller size, and abundant raw material.

## Answer

An **optical fiber** is a thin, flexible strand of very pure glass or plastic that guides light along its length. It is used to carry information as light pulses.

#### Structure

```text
  +-----------------------------------+
  |  Jacket (protective coating)      |
  |  +-----------------------------+  |
  |  |  Cladding (n2)              |  |
  |  |  +-----------------------+  |  |
  |  |  |  Core (n1 > n2)       |  |  |
  |  |  +-----------------------+  |  |
  |  +-----------------------------+  |
  +-----------------------------------+
```

#### Working principle: total internal reflection

The core has a refractive index n1 higher than the cladding index n2. Light that strikes the core-cladding boundary at an angle (measured from the normal) greater than the critical angle θc = sin⁻¹(n2/n1) is totally reflected back into the core. It zigzags along the core without leaving it, even when the fiber is bent.

```text
  ray  \  /\  /\  /\  /
 ------>\/  \/  \/  \/ ----> out
```

In a system, an LED or laser converts the electrical signal to light, the fiber carries it, and a photodiode at the far end converts it back.

#### Advantages over copper or coaxial cable

- Very large bandwidth and high data rate (Gbps to Tbps).
- Very low attenuation, so fewer repeaters are needed over long distances.
- Immune to electromagnetic interference and crosstalk, because it carries light.
- Better security: it is difficult to tap without detection.
- Small size and light weight; thin cables carry many channels.
- No spark or fire risk (no electrical current), so it is safe in hazardous areas.
- The raw material (silica) is abundant, so it is cheap per unit bandwidth.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How do the refractive indices of core and cladding compare?
   A. n1 < n2
   B. n1 = n2
   C. n1 (core) > n2 (cladding)
   D. Index does not matter
   Answer: C. Higher core index is needed for total internal reflection. (Key point: Fiber structure)

2. What guides light in an optical fiber?
   A. Total internal reflection at the core-cladding boundary
   B. Refraction into the cladding
   C. Absorption by the jacket
   D. Electrical conduction
   Answer: A. Light striking at more than the critical angle is totally reflected. (Key point: Working principle)

3. What is the critical angle?
   A. θc = sin⁻¹(n1/n2)
   B. θc = cos⁻¹(n2/n1)
   C. θc = sin⁻¹(n2/n1)
   D. θc = tan⁻¹(n1 n2)
   Answer: C. The critical angle depends on the index ratio n2/n1. (Key point: Critical angle)

4. Why is fiber immune to EMI and crosstalk?
   A. It carries light, not electrical current
   B. It is thicker than copper
   C. It uses higher voltage
   D. It has a metal shield
   Answer: A. Light is not affected by electromagnetic fields. (Key point: Advantages)

## Related in Basic Electronics Engineering

- [Communication system; optical fiber merits](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Adefine-comm-optical-merits) — Basic Electronics Engineering, chapter 5
- [Optical fiber advantages and labelled diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aoptical-fiber-adv-diagram) — Basic Electronics Engineering, chapter 5
- [Role of antenna; optical fiber pros and cons](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aantenna-role-optical) — Basic Electronics Engineering, chapter 5
- [Optical fiber advantages and disadvantages](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aoptical-fiber-adv-disadv) — Basic Electronics Engineering, chapter 5
- [Wired and wireless communication systems](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Awired-wireless-systems) — Basic Electronics Engineering, chapter 5, asked 2×
- [MOSFET construction and working principle](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Amosfet-construction-working) — Basic Electronics Engineering, chapter 3, asked 2×

## Related in other subjects

- [Coaxial cable vs optical fiber](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acoax-vs-fiber) — Data Communication, chapter 4
- [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×
- [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×
- [Fiber optic vs copper cable](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Afiber-vs-copper-applications) — Telecommunications, chapter 2