Optical Fibre

This thin, almost hair-like plastic fibre is an optical fibre. Optical fibres like this are used as a medium to transmit light from one end to the other. They can be used for sending data down communications cables, with higher bandwidth (faster data rate) over long distances, and less data loss and interference compared to electrical cables. Alternatively, optical fibres like this can also be used for carrying light into confined spaces, or transmitting images out of confined spaces. For example, optical fibres have been embedded in concrete architectural wall panels as a way of (decoratively) allowing natural light into a building, and fibre optics are used to transmit images from inside the body in medical imaging of internal organs using endoscopes.

 

Polymer optical fibres are usually made from a polymethyl methacrylate (PMMA, acrylic) core, surrounded by a cladding made from fluorinated polymer. The cladding material must be of lower refractive index than the core – in other words, light must travel slower through the core material than the cladding. The fibre relies on the phenomenon of total internal reflection; if light travelling through the core reaches the interface between the core and cladding, it is reflected back into the fibre, rather than escaping, thanks to the difference in refractive index of the two layers. Total internal reflection was first recognised scientifically in the 19th century: not in a solid fibre but in a curved fountain of falling water. 

 

Optical fibres for long-distance communications would typically be made of glass, rather than plastic, but plastic fibres beat glass on robustness and price. Plastic optical fibres like this are usually used for low speed, short-distance networks, for example in the home and in cars. They are manufactured by the extrusion of molten plastic through a thin nozzle called a spinneret.