The acrylic rod used in previous experiments carries light from one end to the other, but it doesn't really do a very good job. To transmit light long distances, commercial optical fibers must be composed of ultrapure transparent materials.
For example, some commercial optical fiber material is so pure that the light lost when traveling through a one-kilometer (5/8 of a mile) length is more than 90 percent of the light which entered the fiber.
In the illustration to the right is a basic optical fiber, with concentric layers of core and cladding. The fiber you will use in
this experiment contains a central "light carrying" core and a very thin (10 µm/.0004 inches) cladding layer to trap the light inside. (The cladding is also transparent. You probably won't be able to distinguish it from the core.)