Optical Fibre Communication: Working Principle, Construction, Advantages & Applications

Introduction

Fiber-optic communication is a method of transmitting data from one point to another by sending infrared light pulses through an optical fibre. Light acts as a carrier wave and can be modulated to carry information. Optical fibre is preferred over electrical cabling for long-distance transmission, high bandwidth requirements, and immunity to electromagnetic interference. Voice, video, and telemetry data can be transmitted over local networks or long distances using this technology.

Most telecommunications companies rely on optical fibre to transmit telephone signals, internet data, and cable television content. Using fibre-optic communication, Bell Labs researchers once achieved a record bandwidth-distance product of over 100 petabit-kilometres per second.

Working Principle

The refractive index is a key parameter in understanding fiber optics. It is defined as:

n = c / v

Where:
c = speed of light in free space (3 × 10⁸ m/s)
v = speed of light in a dielectric material

When light travels between materials with different refractive indices, it bends at their interface. This behavior is governed by Snell’s Law:

n₂ sin φ₂ = n₁ sin φ₁

Where φ₁ is the angle of incidence, φ₂ is the angle of refraction, and n₁ and n₂ are the refractive indices.

Total internal reflection occurs when the incident angle exceeds a certain critical angle. At this point, the refracted angle becomes 90°, and the light is reflected entirely within the denser medium. This principle is the foundation of optical fibre communication.

Construction of Optical Fibre

An optical fibre is a low-loss cylindrical dielectric waveguide. It is flexible and made of high-quality plastic or glass, with a diameter between 0.25 mm and 0.5 mm. A typical fibre cable consists of four main parts:

1. Core

The core is a cylindrical region through which light travels. It is made of plastic or glass and surrounded by cladding. Light stays inside the core due to internal reflection. The core diameter varies depending on the application.

2. Cladding

The cladding surrounds the core and has a lower refractive index. Its purpose is to reflect light back into the core, enabling total internal reflection.

3. Buffer

The buffer layer protects the fibre from physical damage. Multiple fibre strands are grouped together and shielded by the outer jacket.

4. Jacket

The jacket is the outer protective layer. Jacket colours indicate cable types—yellow for single-mode fibre and orange for multimode fibre.

How Optical Fibre Communication Works?

Fibre-optic communication involves transmitting a signal as light, converting electrical signals to optical signals at the transmitter end and reversing the process at the receiver end.

Transmitter Side

• If the input is analogue, it is first converted into digital pulses using a coder.
• Digital signals are sent directly to a light source (LED or laser diode) that converts them into light waves.

Optical Fibre Cable

The light waves travel through the optical fibre from the source to the destination using total internal reflection.

Receiver Side

• A photodetector (photocell) receives the light pulses.
• The received light is converted back into electrical signals.
• The signal is amplified and decoded depending on whether the output needs to be digital or analogue.

This entire process—transmitting electrical signals as light through optical fibre—is known as Optical Fibre Communication.

Advantages

• Cost-effective and economical
• Thin, lightweight, and non-flammable
• Low power consumption
• Reduced signal degradation
• Highly flexible and easy to install