Optical fibres are thin, flexible strands of transparent material used to ‘pipe’ light signals around a network, transmitting all kinds of data including Internet traffic and phone calls. These fibres can allow faster data transfer than conventional electrical cables and can transmit signals for tens of kilometres without any amplification.
A single fibre has a thin glass or plastic core with an outer cladding of optical material that constantly reflects light back into the fibre to confine it, a process called total internal reflection. An outer plastic coating protects the fibre from moisture and damage. Typically, hundreds or thousands of fibres are bundled together in cables with an outer jacket.
Single-mode cables transmit one wavelength of light through cores thinner than a human hair, while multimode cables have wider cores that can transmit several different wavelengths. Light signals travel through them at around 200,000 km/s [450 million mph], allowing phone conversations to anywhere in the world without an annoying delay or echo on the line.