On This Day in (Engineering) History
April 22, 1977 - Optical fibre used to carry live telephone traffic for the first time
A warm, sunny spring day in Long Beach, California. Someone is phoning the doctor, the insurance company or a relative from their apartment. Twenty-four hours ago, nothing would have been special about this call. Yesterday, the phone company funnelled calls through a copper coaxial cable. Today is different. Today, April 22, 1977 a fibre-optic telephone system has gone live, and it is not an experiment.
At its core
Fibre-optics involves the marriage of technologies to create a new, third technology. In simple terms, the idea is to put a beam of light down a tiny glass tube and send it over a distance.
The light doesn't leak from the tube because of what is called 'total internal reflection;' when light strikes a reflective surface at a low enough angle, it will bounce off that surface instead of going through it.
A fibre-optic cable has multiple layers. The core is the tube itself, is sheathed within a layer of glass cladding with a lower refractive index than the core, which reflects the light into the fibre tube. Another coating, plastic this time, surrounds the glass cladding. Surrounding that third layer are Kevlar strengthening fibres, which nestle within a protective outer coating.
Jagged edges
This could be a single or a multi-modal fibre; a single-modal cable has one core measuring between 5µm and 10µm in diameter, with a single laser light pointed directly down its centre. A multi-modal cable has a single core with a diameter between 50µm and 100µm. Here, light is fired from an angle low 
enough to reflect off the surface, winding through the tube in a snake-like pattern until it reaches the end.
There will be other light beams (sometimes of different colours) fed along the tube in a similar fashion, which means multiple communication streams can use one tiny tube.
These cables will be carried in bundles through pipes that run underground or under the sea.
Data is encoded into the light itself, provided by an LED or a laser diode. LEDs provide incoherent light, light with multiple, irregular peaks and troughs in its pattern, making the waves look like a scribble. This can be used over longer distances. This produces a more diffuse light, making it suitable for low-cost solutions and applications. Laser diodes provide
Above left Total internal reflection Source:Wikimedia Commons
a coherent light where the waves are regularly spaced, providing a sharp, well-defined light that is suited to anything requiring a high degree of accuracy. Laser diodes are better over shorter distances
Small starts…
After World War II, fibre optics saw great hard work and a furious pace of innovation on both sides of the Atlantic Ocean.
By the mid-1970s, the first fibre-optic communication networks were ready for field testing.
The first was for Dorset Police in the UK, during 1975. The Dorset Constabulary's radio antenna had been destroyed by a lightning strike, closing off communication with their Bournemouth-based eastern division. The police contacted the Home Office for help in finding a lightning-resistant replacement. As luck would have it, the head of the Home Office Police Scientific Development Branch had just the answer. Having worked at the Ministry of Defence, he knew fibre optics was what the police were looking for. By September 1975, the system designed and built by STC/STL was installed and working.
A few months later, in 1976, AT&T installed a fibre-optic system at a factory in Atlanta, Georgia. In early April of 1977, the company installed a fibre-optic system in Chicago, routed through the city's coal tunnels.
On April 22, 1977, the General Telephone and Electric company installed the world's first non-experimental commercial fibre-optic telephone network in Long Beach, California, with a speed of 6 Mbps.
In the two years since installing the fibre-optic system in Dorset, STL had demonstrated data transmission speeds of 1Gbit/s using a single-mode fibre, 8Mb/s in an HDB3 system (both 1975) and 140 Mb/s in the link between Hitchin and Stevenage (1977).
…big achievements
Fibre optics offer many advantages over traditional copper cabling. The light of the light and the purity of the fibre can help the fibres carry up to 1000 times the capacity of copper cables. Over long distances, a single-mode fibre can carry hundreds of calls with little to no electrical interference and signal degradation. It requires less space than copper and less maintenance than copper.
For example, the SEA-ME-WE-3 cable is 39,000km long. It uses two fibre pairs to carry 48 wavelengths of 10Gbit/s, sending data from the UK to Japan in 0.35 seconds.
While it is more expensive to produce than copper, it requires less space than copper and less maintenance, which reduces long-term costs. Because they are thinner than copper wire, the fibres can be bundled together in far greater volume, meaning more phone calls, television and internet services.
Above right Cross section of a fibre optic cable Source: Wikimedia Commons
Fibre optics can now send and receive data at the same speed, while latency ('lag') in phone and video calls is greatly reduced. These capabilities and the ability to deal with large volumes of data mean this technology is an ideal conduit for cloud computing services.
Now and then
The history of fibre-optic technology goes back much further than most would think, while its 20th Century progress has been furious. Nobody making the very first commercial call using a fibre-optic network would have realised how much work had gone into it - or could have guessed how far the technology would advance in the decades since.
What do you think?
How much further can we take fibre optics before it hits its maximum, beyond which it becomes necessary for a new communication technology?
By Stephen Phillips - IET Content Producer, with passions for history, engineering, tech and the sciences.