Web sites with webbed feet

© 2000 Craig Williamson
Entry to Young Science Writer 2000

Have you ever wondered how web pages from around the world find their way to our computers?  They do not travel via satellites as might seem sensible.  In fact, neither do most international telephone calls that we make.  Instead, the web sites and the phone calls swim to our homes.  That’s right, they travel through the harsh conditions of the world’s oceans, and do not even once need to surface for air.

They reach us through cables laid on seabeds around the world, connecting countries and collectively providing the majority of our long distance communications.  One particularly busy route is the Atlantic Ocean, with around 20 cables between the USA and Europe.  Each such cable is typically around 4000 miles in length, and consists of a polythene, copper and steel casing which protects the glass optical fibres that actually transmit the information.  The cables are usually not much thicker than the larger end of a pool cue, and yet they can withstand the incredible pressures that the ocean exerts on them.

Ian Fletcher is the head of undersea cable research at BT laboratories, and takes these matters in his stride.  “The strength of these cables has to be pretty amazing when you consider that a football at the bottom of the Atlantic would be squashed to the size of a grape,” he comments.  To take these cables to the ocean floor, special fleets of cable ships are used to navigate the oceans and lay over a precise, predetermined route.  The enormous lengths of cable are coiled in the heart of the ship, and then slowly lowered over the stern to the seabed, which can be several miles down.  There are more unexpected tests once they are on the ocean floor.  “In shallower water,” Fletcher explains, “there can be the problem of fishing boats accidentally catching the cables, and it has also been known for sharks to have a nibble.” 

The optical fibres within the strong casing are fine strands of glass, no thicker than a human hair, that are specially designed to allow light to travel through them over long distances.  Light entering a fibre will travel along its length by bouncing off the inner walls until it reaches the end.  Information is transmitted as a stream of flashing light through the fibre, provided by a precision laser in this case.  The on-off sequences of light are used in a similar way to Morse code to make readable web pages or audible voices, once decoded.

In a fairly recent development, researchers have made it possible to transmit several of these light signals on the same fibre at the same time.  This is achieved by simply using different colours of light that do not interfere with each other.  So whereas each fibre could only carry one signal at a time in the past, in principle they can now carry several hundred.  One of the latest cables to be designed, connecting the UK and the USA, will use 16 different colours on each of 8 optical fibres in the same cable.  The capacity of such a system is truly phenomenal.  “The new transatlantic cable will be able to carry the equivalent of almost 8 million phone calls at any one time,” says Fletcher.  “If that is put into data terms, you could send around a quarter of a million books in just one second.”

Fletcher’s team looks into a range of issues with these underwater systems, always looking for the new technologies that will transmit more information, over longer distances, and at a reduced cost.  This is a real necessity, as the demand for international communications is anticipated to increase significantly over the coming years.  Cables in the ocean are expected to meet this demand, as they work out many times cheaper overall than satellite systems.  “And besides,” adds Fletcher, “cables work much better than satellites underwater.”

So the next time you are on the Internet and access a web page that has travelled from a foreign country, spare a thought for its incredible underwater journey.  It may have swum for thousands of miles, narrowly avoided capture by fishermen, and almost been eaten by sharks.  Perhaps the least you could do is to have a soft warm towel waiting for it.