Tech Explained: Fibre Optics

Fibre optics provide a very fast, efficient way to send telephone and internet signals. How does it work?

Fibre optic cables have been used to provide telephone and internet connectivity for decades. The first fibre-optic telephone cable was laid between Long Beach and Artesia, California, in 1977. In 1988, the first transatlantic fibre-optic telephone cable was laid between the United States, France and the UK.

Fibre optics provide a very fast, efficient way to send telephone and internet signals. Yet, there are still many places that are not connected in this way. So, how do fibre optics work, and what are some of the challenges to their use?

How fibre optic cables work

Fibre optics use light to send information via cables. A fibre-optic cable is made up of many, very-thin strands of glass or plastic. Each strand has less than a tenth of the thickness of a human hair. The inside of the cable acts like a mirror and light travels down the cable by bouncing off the inside walls. The cable is then wrapped in a material with a lower refractive index, which prevents the light from leaking out.

To send a message, a transmitter changes the light into binary code (where ‘on’ and ‘off’ stand for 0s and 1s). Lasers and LEDs are both used to transmit the light signals. As the light travels, there is some signal loss, so optical generators are placed along the cable at intervals to boost the signal. The generators use lasers to amplify the signal as it travels. At the other end of the cable, an optical receiver takes the incoming digital light signals, decodes them and sends the result to the computer, television or telephone.

Uses for fibre optics

Fibre optics are not confined to long distance communications – they are also used in medicine. Gastroscopes use thick optic fibres, which allow doctors to see inside a patient’s stomach. At one end is an eyepiece and a light source. The light travels down the fibre and reflects off the stomach walls into a lens at the bottom of the cable, giving the physician a view of the inside of the stomach. There is also an industrial version of a gastroscope, called a fibrescope, which is used to examine inaccessible parts of machinery and buildings.

Another recent medical development is called “lab on a fibre.” This uses very thin fibre-optic cables, with built-in sensors that are inserted into a patient’s body. Light is sent through them using a laser. By measuring the way the light changes as it moves through the body, doctors can measure temperature, blood pressure, cell pH, and levels of medication in the bloodstream.

Fibre optic cables are also commonly used to connect computer networks together, due to the cables’ high capacity, security and reliability. Businesses either set up their own fibre networks or buy space on a private fibre network. It is also possible to buy unused fibre optic capacity, called dark fibre, from another private network.

Advantages of fibre optics

Fibre optic cables have several advantages over traditional copper cables. One is that they have less attenuation (loss of signal), meaning that information can travel further before it needs amplifying, which saves money. There is no electromagnetic interference with fibre optics, so signal quality is better and fibre optics can carry more data than copper cables. Since they don’t carry electrical signals, fibre optics don’t give off electromagnetic radiation that can be detected, and so offer protection against “jamming” through electromagnetic interference.

The future of fibre

The optical generators used to boost fibre optic signals need to be placed every 50-60 miles along the cable. These generators can be costly to build and maintain, which is why it can be expensive to bring fibre into a new area. Gaining the right of way to install the cables, along with digging trenches and laying the cable, adds to the cost. But the benefits of fibre optics mean that there is also a growing demand for it.

For example, San Francisco is installing a citywide fibre initiative. To support increased international demand for Internet connectivity, the Pacific Light Cable Network is laying an undersea cable between Los Angeles and Hong Kong. The new cable will have a record-breaking 144 TB of capacity. However, some businesses are also looking toward wireless solutions, which offer scalability without the risk of physical disruption. It is likely too early to tell if fibre optics will be the last word in connectivity.