WCA March 2010

Why fibre optics ? The question produces two immediate answers: (1) fibre optic cables allow for faster and clearer transmission of signals; and, (2) fibre optic cables can span greater distances, with all that that implies for more efficient connectivity. by Dorothy Fabian A fuller response might make reference to the greater durability of fibre optic cables, their stronger resistance to tension, their lower price. No need to ask: faster, clearer, greater than what? Stronger, cheaper than what? The implicit comparison is with copper cable, about which enthusiasts of optical fibre tend to be dismissive. They assert that copper wires are delicate and difficult to maintain; that the sole superiority, if any, of copper cable lies in its ease of termination; that, in any case, copper is in chronically short or at least uncertain supply. Copper, say the fibre people, is a retrograde and wrong-headed choice for advanced telecom purposes. The benefits of fibre optic cable are incontrovertible. More robust than copper wire to signal degradation, low-loss optical fibre allows for longer intervals between amplifiers and repeaters. Together with the fact that no further propulsive power is needed once the signal has been sent, this means a lower power requirement over-all. Fibre cables laid in parallel are not susceptible to crosstalk. Because optical fibres are thinner and lighter-weight than copper wire, cable of the same diameter will accommodate more of them than if it were filled with copper wiring. And fibre is famously indifferent to the company it keeps, permitting installation of opportunity such as alongside rail beds and utility and power lines. As to capacity, many optical networks can send 1 terabit/second (Tbit/s) of information. The theoretical maximum for optical fibres is 350Tbit/s. Advanced copper DSL (digital subscriber line) systems can send 50 megabits/second (Mbit/s) of information. The theoretical maximum for copper cables is 1 gigabit/second (Gbit/s). Last, but scarcely least: in typical (long) lengths, optical fibre costs much less than equivalent measures of copper wire. For one thing, here, as in many other sectors, possession is still nine points of the law; and most telecom networks now in operation were built on metal wiring, mainly copper. Installing fibre optics into a network is an expensive proposition. At a very conservative estimate, it will cost a phone company $1,000 per subscriber for an FTTP (fibre-to-the-premises) installation. Short-distance (box-to-box, even chip-to-chip) and relatively low-bandwidth applications do exist; in fact they are not uncommon. For these, electrical transmission (ie via copper) is preferred. Copper offers greater ease in the operation of transducers in linear mode; and, for custom-designed cables, the red metal’s dual capability in electrical and signal conductance is a considerable plus. Even the most confirmed proponent of fibre will likely concede that it is more difficult and expensive to splice than copper wire. And, at high optical strengths, fibre can be vulnerable to destructive fusion if the light should meet with even a minute imperfection. Fibre fuse detection circuity at the transmitter is an effective preventive device, but an additional expense. Finally, as to the cost of materials, in smaller quantities copper is priced lower than fibre; as are transmitters and receivers for copper-based systems. Why, then, if fibre is manifestly superior, does King Copper retain its prestige in the telecom industry?

Optical fibre and copper are central to the development of the global telecommunications industry. Both are indispensable; their respective contributions to telecom infrastructure —incalculable.

Is one superior to the other?

Once upon a time, when asked for the distinction between the Major and the Minor Prophets, an unprepared but resourceful student answered, “Far be it from me to draw any comparison between these wonderful men.”

Photo credit: bigstockphoto.com Photographer: ‘fotko’ (Frank Podgoršek)

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Wire & Cable ASIA – March/April 2010