What is dark fibre and how is it used?

Cloud computing, edge computing, and the Internet of Things (IoT) are increasing the need for connectivity and consequently, there is a growing number of organisations investigating the use of dark fibre as an alternative to commercial Internet services. 

The term ‘dark fibre’ which is also known as unlit fibre or black fibre refers to fibre optic cables that have been laid in the ground but is not being used. Since the cost of installing cables is high, companies bury more cabling than needed and thus less than half of the actual cables underground are being used, leaving the rest available for companies to lease. 

Dark fibre is thus pre-existing underground infrastructure that does not yet have the hardware or software that enable it to run services. Companies anticipating the need for growth in the future and considering the difficulty of physically digging to install cables were building fibre footprints and laid far more fibre than they needed thus creating a surplus of infrastructure. Dark fibre offers the following advantages:


A benefit of dark fibre is the potential speed since an organisation leasing dark fibre does not have to contend with the traffic of a lot of different points before arriving at its destination. With dark fibre, organisations can get a straight line from point A to point B, which improves performance. Dark fibre thus showcases remarkable ability when it comes to speed. Since when selecting dark fibre, enterprises can ensure they are getting the most direct, and therefore most efficient, path from end-to-end. 

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An important benefit is the fact that dark fibre can provide physical redundancy for existing systems. Because providers may rely on the same physical infrastructure, dark fibre provides an alternative in the event of a disaster due to a construction accident or burst water main. 

Scalability and flexibility

Dark fibre can be broken down into a multitude of wavelengths through a process called wavelength-division multiplexing (DWDM). DWDM enables the transmission of multiple data streams along different light wavelengths which means that businesses can adjust their need to what they lease. Smaller companies could be leasing a single wavelength, while larger companies can lease an entire fibre strand. Dark fibre can also easily accommodate the rapidly-scaling needs of today’s businesses.

Although dark fibre may be regarded as only suitable for service providers, it leased more commonly these days than many businesses would assume. Dark fibre can meet a wide variety of business needs such as effectively future-proofing businesses and empowering them to meet the growing needs of their end-users. 

Dark fibre repurposed as seismic sensors

Findings of a recent research study indicate that dark fibre can serve as regional seismic activity monitors and detect earthquakes thousands of kilometres away, according to new research. 

A research team used a relatively new technique called distributed acoustic sensing, or DAS, to measure how seismic waves affect the underground cables. “The neat thing about the technique is that you can use it to measure seismic waveforms at a very large number of locations on an existing fibre. When applied to existing dark-fibre networks, DAS gives the same data at a lower cost than a comparable number of above-ground seismic stations”.” Jonathan Ajo-Franklin, lead author quoted by Eos. 

Disadvantages of using dark fibre

Although there are advantages to running a dark fibre optic network, there are also disadvantages. The primary disadvantages are the loss of time and money that it takes to set up the infrastructure.

Availability is an important issue because not every town has dark fibre capabilities and before companies invest, they should determine if there is dark fibre available.

Regular maintenance and repairs can be an inconvenience since not all technicians will have a solid grasp on how to remedy every dark fibre situation they may encounter. Significant or major repairs may mean incurring tremendous expense. 

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