Optical fibres are narrow tubes of glass fibres with a plastic coating that carry light from one end to the other. The light bounces off the walls of the fibre and can even bounce around corners. The properties of optical fibres make them useful for a wide range of applications including:
Medical - to transmit pictures of organs and arteries
Industrial - to transmit pictures of the inside of complex machinery
Communications - to transmit data over long distances without transmission loss
Light rays use total internal reflection to travel along the fibres. In order for this to be achieved, the light ray must hit the walls of the fibre at a minimum angle of 82°, which is the critical angle for light travelling from glass to plastic. Since the fibres are very narrow, this is usually not a problem.