Do you know how the total internal reflection works? The light cannot leave water. In the same manner light can be sent in a cable.
The cable is made of glass and is very similar to the electric one. But it differs a little bit inside and on the surface. Light cannot leave the cable because of the differences in the refraction indexes ( they are greater in the cable that on its edges) and travels till the edge of the cable.
The fibre-optic cables are used in telecommunication to send information. If the cable is made of fibre it can be made into a lamp or a colourful sweeper.
The optical fibre cable is a thin cable which consists of a glass or plastic core which is surrounded by a cladding layer with the refractive index lower (n2) than the refractive index of the core (n1).It employs the effect of multiple internal reflection of a beam of light transmitted along the cable, as it happens in case of a light ray reflected on the boundary between water and air., see the penguins toy before...
The beams of light may propagate in the optical fibre cable in a form of waves. More than one type of wave (modes) can propagate inside the light-guide. But only those which enter "enough" parallel can be transmitted to the end. The so-called numerical aperture NA determines the divergence angle for the entering wave:
In a single-mode cable, it can propagate only one type of wave.
The number of modes can reach 1000 in so called multi-mode cables. 1000 telephone calls can be transmitted along such a cable at the same time.