What is Optical Fiber - Definition, Principle, Work, Advantages, FAQs

What is Optical Fibre?

An optical fibre is a thin, flexible strand of glass or plastic that carries light signals from one place to another. It works on the principle of total internal reflection, where light bounces inside the fibre without escaping, even when the fibre bends.

Optical fibres are used to transmit data, images, and messages at very high speed over long distances.

Principle of Optical Fibre

The working principle of an optical fibre is based on Total Internal Reflection (TIR).

When light travels from a denser medium (core) to a rarer medium (cladding) at an angle greater than the critical angle, it is completely reflected back into the core instead of passing out. This repeated reflection allows light to travel through the fibre, even if it bends.

Types of optical fibre

The following is the classification based on the refractive index:

1. Step Index Fibers have a single uniform index of refraction and are made up of a core and cladding.
2. Graded Index Fibers: As the radial distance from the fibre axis rises, the refractive index of the optical fibre falls.

The following is a categorization based on the materials used:

1. Plastic Optical Fibers: For light transmission, polymethylmethacrylate is employed as the core material.
2. Glass Fibers: It is made up of ultra-fine glass fibres.

The following is a classification based on the mode of light propagation:

1. Single-Mode Fibers: These fibres are used to transmit signals over vast distances.
2. Multimode Fibers: These fibres are used to transmit signals across short distances.

The core's refractive index and mode of propagation are used to create four different types of optic fibres:

1. Single-mode fibres with a step-index
2. Single-mode fibres with a graded-index
3. Multimode fibres step-index
4. Multimode fibres with a graded-index

Construction of Optical Fibre

An optical fibre is made up of three main parts:
1. Core:

• The inner glass or plastic part through which the light travels.
• It has a high refractive index to keep the light inside.

2. Cladding:

• A covering layer around the core made of glass or plastic with a lower refractive index.
• It helps in total internal reflection, preventing light from escaping.

3. Protective Coating (or Jacket):

• The outer layer made of plastic.
• Protects the fibre from moisture, damage, and bending.

Work of Optical Fibre

Total internal reflection is used to operate the optical fibre. Light beams can transport a large quantity of data, but they travel in straight lines, which is an issue. So, unless we have a long straight wire with no bends, making use of this advantage will be time-consuming. Optical wires, on the other hand, bend all light rays inwards (using TIR). Light rays travel indefinitely, bouncing off the walls of optical fibres and transmitting data end to end. Although light signals degrade with time depending on the purity of the material employed, the loss is substantially lower than with metal cables.

A Fiber Optic Relay System is made up of the following components:

1. The Transmitter generates light signals and encodes them for transmission.
2. The Optical Fiber is the medium used to transfer light pulses (signal).
3. The Optical Receiver - This device receives and decodes sent light pulses (signals) to make them usable.
4. An optical regenerator is required for long-distance data transmission.

Also Read:

• NCERT solutions for Class 12 Physics Chapter 9 Ray Optics and Optical Instruments
• NCERT Exemplar Class 12 Physics Solutions Chapter 9 Ray Optics and Optical Instruments
• NCERT notes Class 12 Physics Chapter 9 Ray Optics and Optical Instruments

Advantages of Optical Fibre

1. Cost-effective and economical
2. Non-flammable and thin
3. Power usage is reduced.
4. Signal degradation is reduced.
5. Lightweight and flexible

Also check-

• NCERT Exemplar Class 11th Physics Solutions
• NCERT Exemplar Class 12th Physics Solutions
• NCERT Exemplar Solutions for All Subjects

NCERT Physics Notes:

• NCERT Notes Class 11th Physics
• NCERT Notes Class 12th Physics
• NCERT Notes For All Subjects