How Fibre Optic

Cables Work

Reading Time: 5 minutes
Fibre broadband is everything we’ve shouted about before and more. Ultrafast, super-reliable and ultimately the next step in digital infrastructure.

But what is fibre broadband?

Fibre Optic Cables

A fibre broadband network is made up of fibre optic cables. These fibre optic cables are what go into the ground when you see roadworks taking place in your area and what serve your home with internet.

How do they Work?

The main differential factor with fibre optic cables from existing copper cables is that they use light as their data transmission method.

Where copper would use electrical signals that get weaker the further they travelled, light signals are able to travel much further, much quicker and ensure similar speed is provided to everyone connected on the line – no matter the distance between their home and the cabinet.

But how can light transmit data?

Well, digital devices think of information in binary code – 1’s and 0’s. These are called bits.

When data is requested, these bits are transferred one at a time along a physical transmission. In the case of copper cables, an electric charge carries the information from one end of the cable to the other.

When an electric charge is present, a 1 is transmitted; when an electric charge is not present, a 0 is transmitted.

When you turn the current on and off rapidly (millions of times a second), the 1’s and 0’s (bits) travel along the cable.

With fibre optic cables, the exact same process happens in terms of 1’s and 0’s. But instead of using electric charges, they use light.

There is an LED light at one end of the cable and when light is present a 1 is recorded and when light is absent a 0 is recorded.

Because the sheer speed of light is so fast, the data can be transmitted a lot quicker along the cables from the servers to your devices.

What are they made of?

Well, a fibre optic cable has many components to it: the core, the cladding, the Kevlar, the jacket/sheathing, the boot of the cable, the connector and the ferrule.

diagram of fibre optic cable

The Core

The core is a strand of extraordinarily thin glass that is about the same size a strand of hair. It is placed at the centre of the cable and is where the light pulses transmit through the cable.

The Cladding

Surrounding the core, is a layer of cladding. This encapsulates the core and helps the light pulses reflect back into the core and aid with data transmission.

Both the cladding and the core together is what is generally considered as the fibre cable.

The Kevlar

The Kevlar’s purpose is to protect the cable from damage when it is being blown through the ducts (blowing cable means threading it through the ducts underground).

It is heat resistant, lightweight and synthetic that delivers an extreme amount of super-strength to protect the fibre optic core and cladding.

The Jacket/Sheathing

The outside, rubber sealing of the cable is known as the jacket/sheathing.

It usually made from PVC (a type of rubber-like plastic) or what is called ‘riser’. Alternatively, it could be made of plenum which is similar, but isn’t as flammable nor toxin emitting within its smoke.

diagram of fibre optic cable boot

The Boot of the Cable

The boot of the cable’s role is to bridge the fibre cables to the connector. Due to the flexibility of the fibre optic cable, the boot will stabilise these cables allowing for greater rates of data transmission.

The Connector

The connector is the piece at the end of the entire cable that plugs into the equipment. A tab is the most common use of locking mechanism on the cable, and when it comes to installing or removing cables, the connector is what you plug in and pull out of the equipment.

The Ferrule

The Ferrule contains the end of the fibre in it and is used to help with alignment with the interconnection with other fibre cables and transceivers.

It is often made from ceramics, plastics or stainless-steel.

How is a Successful Connection Measured?

When it comes to ensuring the cable operates correctly, we must complete some testing to ensure that the light can travel through the entire length of the network.

Copper networks (FTTC) lose a lot of power throughout the line. The further the data has to travel, the slower the speeds get.

As the light source travels along the fibre, its power level decreases. Also known as ‘optical loss’, it is measured in Decibels (dB).

When we test for optical loss, we have found the most accurate way to do this is by using an OLTS  (Optical Loss Test Set) and inputting a known level of light into one end of the cable.

By measuring the light level at the other end of the cable, you can then see how much optical loss has occurred.

This helps tell us if the optical loss is significant, if there are any potential breaks within the cable or if any maintenance is required to help improve the amount of light retained in the cable.

This testing must be completed for each cable to ensure that every connection has the capability of transmitting the data into your home.

How is fibre broadband installed?

We have an entire post going into the details of how fibre is brought in from the network In your area into your home.

On an overview level, it is usually a 5-step process.

Step 1: Your ISP will be in touch to confirm an installation date with you and inform our engineers of the agreed time.

Step 2: On installation day, we call you to let you know that we are on route and you are given a 4 hour time slot for the installation to be carried out.

Step 3: We will install a Customer Splice Point (CSP) to the outside of your home.

Step 4: A fibre cable is then threaded through from the CSP, through your wall into the Optical Network Terminal (ONT) which will be inside your home. This ONT will be the device that connects your router to the internet.

Step 5: Our engineer will carry out a remote configuration test and once this is confirmed, the installation will be complete.

Can you get fibre broadband in your area?

The answer is; it depends.

If you live within an area that is currently building an FTTP (Fibre to the Premise) network, then your chances are quite high that you will be able to access FTTP broadband.

However, if there are currently no plans for a provider to come to your area to serve the town with FTTP networks, then you could be waiting a few years – it is completely dependent on when a network builder will come to your area and implement fibre optic cables.

To see if we are building in your area, you can use our postcode checker on the website. If you are keen on having a full fibre connection to your home or even to learn more information, fill out our contact form.

Additionally, we will email the day your home is ready to receive our ultrafast network.

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Fibre Heroes are swooping in to save underserved market towns across the country, by providing ultrafast fibre broadband to 500,000 homes and businesses by 2025.

Fibre Heroes is part of Full Fibre Limited. Prices shown are indicative of ISP pricing and subject to change.

Terms and Conditions


This information does not constitute an offer by Full Fibre Limited (“Full Fibre”) which is available to you to accept (or transfer or sell). Instead, Full Fibre is putting in place a network which would enable those ISPs which sign up to using that network to offer their own customers prices in the ranges illustrated. These prices (which would include free standard installation and VAT) are indicative only and whether they will be available to you depends on the following factors:-

  • Has your ISP signed up to using Full Fibre’s network?
  • Is your ISP offering these prices? Which prices are offered to end-users ultimately depend on the ISP concerned and Full Fibre does not control this decision or impose prices.
  • Has the Full Fibre network gone live in your area?
  • Are there any technical or other issues affecting your access to the Full Fibre network?
  • Would you be a new fibre connection with the ISP? The indicative prices are not aimed at an ISP’s existing customers.

Full Fibre also reserves the right to amend these price illustrations (and its website generally) at any time.”