total internal reflection is the basic principle of the working of optical fibres.

an optical fibre is very thin fibre made of glass or plastic fire having radius about a micrometer. A  bunch of such thin fibres form a light pipe.

some of its uses are :

1)all organs of the body are not visible to the naked eye and it can be seen through optical fibres by inserting into the mouth.light is sent down through the one set of the fibres in illuminates the inside of the stomach.and can be seen on the computer screen.

2)2000 telephone signals ,approximately mixed with light waves ,may be transmitted through a optical fibre.