Optical fiber: working principle, composition and application

In today’s high-tech world, optical fiber has become an integral part of the telecommunications infrastructure. Due to its unique properties, it provides high-speed data transmission over huge distances. But what is optical fiber, what does it consist of and how does it work? Let’s take a closer look at these issues.

What is optical fiber?

An optical fiber is a thin, flexible strand of glass or transparent plastic designed to carry light. Unlike traditional copper cables that carry electrical signals, optical fibers use light pulses to transmit information. The diameter of such a fiber is comparable to the thickness of a human hair — from 8 to 125 micrometers.

The main advantage of optical fiber is its ability to transmit huge amounts of data over long distances with minimal loss. The speed of information transmission in fiber optic lines can reach several terabits per second, which is thousands of times higher than the capabilities of copper conductors..

The first experiments with the transmission of light through glass threads began in the 1840s, but fiber optics did not find practical application until the second half of the 20th century. Today, optical fibers form the basis of the global Internet, connecting continents with submarine cables and providing stable high-speed communication around the world.

What is fiber optic made of?

The structure of an optical fiber is multilayered and thought out to the smallest detail. Each component performs its important function in ensuring the efficient transmission of light signals. Let’s consider the main components of an optical fiber:

1. Core

The core is the central part of the optical fiber, through which light is directly transmitted. It is made of high-purity quartz glass (silicon dioxide SiO₂) with the addition of dopants, such as germanium oxide (GeO₂), which increase the refractive index of the material. The core diameter can range from 8-10 μm in single-mode fibers to 50-62.5 μm in multimode fibers.

The purity of the core material is critically important – even minor impurities can significantly reduce the transparency of the glass and increase signal attenuation. Modern technologies allow achieving fantastic material purity – up to 99.9999%.

2. Cladding

Around the core is an optical cladding, also made of silicon dioxide, but with a lower refractive index than the core. The standard cladding diameter is 125 microns. The main task of the cladding is to create conditions for total internal reflection of light so that it does not go beyond the core and propagates inside the fiber.

The difference in refractive indices between the core and cladding is a key parameter that determines the angle of total internal reflection and, as a result, the conditions for light propagation in the fiber.

3. Primary Coating

A primary protective coating of acrylate or other polymer is applied over the optical cladding. Its diameter is usually 250 microns. This coating protects the fragile glass from mechanical damage and moisture, and also increases the flexibility of the fiber.

4. Secondary Coating

For additional protection, a secondary coating can be applied over the primary coating, increasing the diameter to 900 microns. It provides additional mechanical strength and protection against external influences.

5. Buffer coating

As part of an optical cable, the fiber is usually placed in a buffer coating of dense plastic, which provides additional protection and ease of installation.

6. Power elements and outer shell

For use in various conditions, optical fibers are combined into a cable that contains strength elements made of aramid threads or steel wire to protect against tensile loads, as well as an outer sheath made of polyethylene, polyvinyl chloride or other polymers, which provides protection against mechanical damage and environmental influences.

How does fiber optic work?

The principle of operation of optical fiber is based on the physical phenomenon of total internal reflection of light. When light passes from a medium with a higher refractive index to a medium with a lower index at an angle greater than the critical angle, it is completely reflected from the interface of the media without loss of energy.

Physical principle

In an optical fiber, the core has a higher refractive index than the cladding surrounding it. This causes a light beam, introduced into the core at a certain angle, to reflect many times from the core-cladding interface, remaining inside the core and propagating along the fiber for long distances.

Data transfer

To transmit information over optical fibers, light sources such as lasers or LEDs are used to convert electrical signals into light pulses. These pulses are modulated according to the data being transmitted and introduced into the optical fiber.

On the receiving side, a photodetector converts the light pulses back into electrical signals, which are then processed by electronic devices.

Types of optical fibers

1. Single-mode fiber has a very thin core (about 8-10 microns) and is designed to propagate only one mode (path) of the light beam. This allows signals to be transmitted over long distances (up to 100 km without amplification) with minimal distortion. Such fibers are used in trunk communication lines and submarine cables.
2. Multimode fiber has a wider core (50-62.5 microns), which allows multiple modes of light to propagate simultaneously. This simplifies the connection and reduces the requirements for light sources, but limits the transmission distance (usually up to 2 km) due to modal dispersion. Such fibers are used in local area networks and inside buildings.

Application of fiber optics

The application areas of optical fiber are constantly expanding. Here are the main areas of its use:

1. Telecommunications is the primary application of fiber optics. Optical communication lines form the basis of the Internet, telephony, and television, providing high-speed data transmission between cities and continents.
2. Local Area Networks – Fiber optic cables are used to create high-speed local area networks within buildings and campuses.
3. Medicine – fiber optic systems are used in endoscopy for visualization of internal organs, in laser surgery, and for delivering light to hard-to-reach areas of the body.
4. Industry – fiber optics are used to create sensors for temperature, pressure, deformation, and other parameters in conditions of strong electromagnetic interference.
5. Military equipment – in communication, navigation, and weapons control systems.
6. Art and design – for creating decorative lighting and light installations.

Advantages and disadvantages of fiber optics

Advantages:

• High throughput — up to several terabits per second
• Low signal attenuation – possibility of transmission over long distances
• Immunity to electromagnetic interference
• Electrical insulation – no risk of short circuit
• Light weight and size compared to copper cables of similar capacity
• High level of information protection — difficulty of unauthorized access
• Durability — service life up to 25-30 years

Disadvantages:

• The fragility of fiberglass – requires careful handling during installation
• The complexity of fiber connection – the need for special equipment and qualified personnel
• High cost of equipment for working with fiber optics
• Difficulty of repair in field conditions

Fiber optics is a revolutionary technology that has changed the way information is transmitted in the modern world. Due to its structure and unique properties, it provides unprecedented speed and reliability of communication.

Understanding what fiber optics are, what they are made of, and how they work allows us to appreciate the scale of the technological breakthrough they represent. As manufacturing technologies improve and costs decrease, fiber optic systems are becoming increasingly affordable, opening up new possibilities for communications and data transmission.

Today, optical fiber is not just a technological solution, but the foundation of the modern digital era, ensuring the rapid development of the information society and global interaction of people around the world.