Electronics Design


Fig. 1. Fibre cable being installed underneath the streets of Manhattan.


Photo courtesy of Shuli Hallak


Could dark fibre define how our future internet is powered? Louise Smyth reports on the latest research into the potential of this new approach to communications.


Out of the darkness D 34 www.engineerlive.com


espite its somewhat mysterious name, dark fibre is simply optical fibre that was installed during fibre-


optic communications projects but not put to use at that time (i.e. it’s not ‘lit’ with data). Dark fibre can be accessed at the optical data level, rather than the electrical data level used in conventional communications networks. Access at this level means users can experiment with novel communication techniques, including high-order optical modulation or what’s known as quantum communication.


There are two key reasons why there’s such a vast amount of a potentially valuable resource lying dormant.


One is that it costs a lot of money in terms of labour, time and resources for telecoms firms to lay any kind of optical fibre networks, so they have traditionally laid


far more than they intended to use for any one project to cover themselves as demand for fibre increases in the future.


Secondly, the telephone companies creating these networks each wanted to get a commercial lead on their competitors by offering a network with sufficient capacity to take all existing and forecast future traffic for the entire region served. After all, with the rise of the internet, this traffic was not anticipated to do anything but increase greatly.


What happened parallel to this was the advent of what’s called wavelength-division multiplexing, which reduced the demand for fibre by increasing the capacity that could be placed on a single fibre by a factor of as much as 100.


Consequently, the price of data traffic collapsed – which opened up the ability for other, non-telecoms organisations to get a piece of the


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