Fibre Optics

total internal reflection - critical angle - refraction

What it shows:
Light is transmitted by a bundle of optical fibres and/or a coiled length of plastic rod, regardless of the twists and turns in the path it must negotiate. Total internal reflection keeps the light confined.

How it works:
A HeNe laser is used as the source of light. The bundle of optical fibres consists of a very large (but unknown) number of individual glass fibres measuring 0.05 mm (0.002") in diameter. About 30 cm of the bundle is exposed at the end while the rest of the length is protected by a rubber sheath. The bundle of fibres can be looped and twisted or tied in a knot without impeding the passage of light.

The 1/2" (13 mm) diameter plastic rod has been heat formed into a spiral shaped coil. Its ends have been polished for good optical coupling. The plastic scatters enough of the laser light so that the whole coil appears to glow red, but the virtue of the scattering is that the path of the laser beam can actually be seen to repeatedly bounce off the surface of the rod (by total internal reflection) as it makes its way around the spiral and out the other end.

Setting it up:
The laser, fibre bundle, and plastic coil are all hand-held during the demonstration and need only to be set out on the bench.

Comments:
For increased visibility, the lecture hall lights should be lowered. Very nice visual effect. This demonstration is a good precursor to the bucket of light. For amusement, you can accompany it with a kitsch fibre-optic flower desk lamp (complete with built-in music box). 1   Rating **



1 model YS-335PM, Optical Fiber Flowers Lamp made by Yirng Shehng Co., Taiwan