What is fiber optics, how it works and why it is faster than copper cables

A hair-thin cable with a core inside fiber Of glass: thanks to its properties, the optic fiber carries information in the form of signals bright through small glassy or macromolecular filaments. This feature makes fiber connections more efficient performers of the traditional copper cable, allowing us to travel through the depths of the internet at large speed. But how is it made? And what types are there?

What is optical fiber

With the term optic fiber usually indicated is that cable made of fiberglass or plastic polymers, with a diameter of 125 thousandths of a millimetre, inside which light signals travel, thanks to which it is possible to transport digital information. Using this technology to transceive data in thick cables such as a hair and the construction characteristics of the fiber make it possible to transport information at high speed: this technology is in fact used above all to improve the performance of data transmission for electronic devices connected to the Internet.

In the world of communications digitalthe information is transferred in the form of bit that is, in sequences of 0 and 1. The choice of as each of these symbols must be represented is a function of the channel of transmission and technology engaged. In optical fiber this process occurs using light pulses, so a 1 will correspond to the sending of a light signal of a certain intensity while a 0 could correspond to a signal of lesser or no intensity. Inside the optical fiber, taking advantage of the optical properties – in particular the reflection – the light signals sent by the transmitter propagate in a succession of rebounds from one end of the cable to the other.

The light signal sent by the transmitter propagates inside the fiber cable, reflecting inside it. Credits: fastweb.it

How a fiber optic cable is made and how it works

Let's imagine cutting a fiber optic cable: what we would see would be a set of concentric materials of various nature. There are 5 main elements:

  • The core, glassy core of the hollow;
  • The cludding, literally “cloak” that wraps the core;
  • The buffer;
  • a filament of reinforcement (usually aramid fiber or any other material capable of increasing the resistance and flexibility of the filament);
  • a jacket, i.e. an external sheath.
Section of a fiber optic cable. Credits: unidata.it


The core, is usually made of glass fibers (silicon dioxide) or polymeric materials. It constitutes the innermost layer of the fiber optic cable, and it is in this layer that the propagation of light pulses occurs. Whatever the material with which it is made, it is important that the core is very pure: the presence of every minimum imperfection in fact, it could get in the way – and then to compromise irremediably – the transmission of light within it, resulting in degradation of the transmitted signal e loss of data.


The core is then wrapped in another no less important layer: the cludding. Its function is fundamental since, surrounding the core, it prevents the light from being able to disperse on the outside. Cludding is a kind of “mirror” which reflects light rays, guiding them through the core.


The buffer in turn surrounds the fundamental components of the cable: core and clutter; it provides the most fragile components of the cable protection And flexibilitygiving the cable greater resistance.

Diagram of the propagation of light signals by successive reflections.


Usually buffer, cladding and core are wrapped in a fiber layer aramid, an extremely light but very resistant material, also known as Kevlar. To get an idea, this is the material also used for i jackets bulletproof. Its use in the structure of fiber optic cables serves to increase their tensile strength once buried inside them trenches i.e. excavations within the land or roads.


Finally there is an external sheath, the jacket. It surrounds the entire cable avoiding abrasive effects and protecting it from chemical and/or atmospheric agents. They are generally made of PVC or other plastic material: the colored cable orange that we see lying inside the excavations in our streets.

Because fiber optics are faster than copper cables

Compared to traditional copper cables, the typical “telephone twisted pairs” so to speak, optical fiber offers performance decidedly superior… but why? First of all, the principle with which signals are transmitted within the two types of cable changes: in the copper cable the information is sent in the form of signals in voltage. More values high of voltage correspond to a 1 while values ​​more low to one 0. In optical fiber, however, 1 and 0 are coded respectively with the presence or absence of a light signal. This is the key to understanding why fiber performs well: the electrical signals transmitted in the copper conductor are subject to physical phenomena such as inductances and resistances which “limit” the passage of information within the cable. Furthermore, external electromagnetic interference can have important repercussions on transmitted signals. Light signals, on the other hand, are not affected by these phenomena.

Furthermore, given that there is no interference in the propagation of signals via optical fibre, it is possible to cover greater distances with a greater bandwidth – in other words, for the same distance, the amount of information that can be sent increases.

What are the types of fiber optics

Depending on the uses for which it is intended and, in relation to the ways in which the light rays propagate in the optical fibre, we distinguish two categories:

  1. the optical fiber multimodal;
  2. the optical fiber single-mode.

Multimodal is the most commonly used and less expensive: inside it propagate light signals sent by “less sophisticated” and simpler emitters such as, for example, led. In contrast, single-mode fibers require specific transmitters lasercapable of generating light pulses that propagate in line straight inside the cable. For this reason, single-mode fibers have a core diameter minor compared to multimodal ones and find application in dorsals of communication oceanic, long cable runs where very large quantities of high-speed signals must travel.

Construction differences between singlemode and multimode fiber. Credits: it.opticomfiber.com