Air Blown Fibre

What is air blown fibre?

Air blown fibre is the technique of installing fibre optic cabling using compressed air. Pre-installed microducts, or conduits, are injected with compressed air, propelling the fibre cables along the microducts at high speed, allowing for faster installation and longer distances than traditional fibre cabling. Since air blown fibre is blown into place, rather than pulled, tensile stress is removed from the fibre which eliminates potential damage to cables during hauling, reduces the need for splicing and helps improve system performance.

Air blown fibre microducts can be reused to expand or replace networks by simply blowing out the existing cabling and blowing in new ones. This ease of future upgrade, and simplified maintenance and repairs, helps lower overall network costs, making air blown fibre a popular choice for new network installations.

What are the advantages of air blown fibre?

Air blown fibre has a number of advantages over traditional fibre optic installations.

• Allows for incremental installation of cables
• Reduction of splice points
• Reduction of installation time
• Simplified network design
• Higher reliability and performance
• Overall reduction in initial deployment costs and greatly reduced costs for upgrades and overlay builds

Compared to traditional fibre optic installations, air blown fibre allows for faster and cheaper upgrades to existing networks. As the needs and requirements of businesses change over time, often their bandwidth requirements expand. Once the backbone of microducts of air blown fibre has been installed, with spare ducts designed into the network, it makes the addition of more fibres a simple matter of blowing a new cable into the already installed duct, with an associated very low cost for deployment. Should all the ducts be occupied then existing fibre can be either blown out or retained, before new fibre is blown in. This allows flexibility for incremental installation of fibre whilst reducing installation time and cost.

Due to its space saving installation compared to traditional fibre, network technology can be upgraded without any disruptions, at a lower cost and much faster, giving businesses much more flexibility in their network setups. Air blown fibre requires fewer connection points, which greatly reduces splicing points, helping lower attenuation and simplifying the overall network design.

How does air blown fibre compare to other network types?

Whilst the fibre in an air blown installation is the same as any other, it is the installation technique that differs to traditional fibre networks. Traditional fibre optic cable is installed like other cabling, by using a winch to pull the cables through microducts. Each time the fibre rounds a corner, the pulling forces increase. This pulling force can be reduced with lubricant, however the final installed cable typically is under extreme pulling forces.

In contrast, air blown fibre is installed by blowing the fibre down the microducts, rather than pulling. The injection of compressed air at a high flow rate uses drag forces to float and propel the cabling, acting as a type of “air lubrication” as it reduces the friction between the cable jacket and the microduct wall.

Due to the speeds at which the cabling travels down the ducts, which can be up to 150m per minute using air blown installation, much longer installation distances can be reached compared to traditional winched fibre. Since the forces on the fibre cables are lower, there is less impact from bends and undulations in the microducts, and without the requirement of a winch, installation equipment is only required at one end of the microduct. This overall reduction in equipment and manpower reduces costs considerably compared to traditional fibre optic cabling installations.

Using the air blown method, it is possible to cover lengths of 3.5km in a single blast, and spliceless connections of up to 12km can been covered by combining several pieces of air blowing equipment. With this method of installation, it is feasible to lay 12km of cable in a single day with a modest installation team.

What is the history of air blown fibre?

Also known internationally as cable jetting, or jetted fiber, the technique of installing cabling using compressed air has existed since the 1980s, and was first developed by British Telecom. Later in the same decade, the Dutch telecommunications company KPN, working with Swiss cabling company Plumettaz, expanded the techniques and developed the first air blown equipment, which included simultaneously “pushing” the cable in to the microduct as the air is injected.

Through the 1990s, methods were developed to install multiple smaller bundles of microducts into a larger duct during one installation. This method is known as bundle blowing, or multi-ducting, and allowed each duct to hold a cable. It also allowed installation of small microducts into already occupied ducts. Since the most expensive part of fibre installation is the civil works, re-using occupied microducts without the need to re-dig to lay extra ducting, could help drastically reduce costs of future network upgrades.