Total Internal Reflection is a special case of reflection which happens when the it goes beyond the critical angle. Total Internal Reflection has many uses in our modern world, one of which is in optical fibers. An optical fiber has two layers: a core made of a material of with a high refractive index, and a second, outer layer with lower refractive index. The light waves carried by an optical fiber are reflected off of the boundary between these two substances, as shown in the diagram of a cross-section of a fiber below. Optical fibers are used in a many different aspects in our modern world. In communication they are used for carrying signals precisely, and at the speed of light. This is much, much faster than the speed of electrons, and therefore faster than electric signals. In medicine, optical fibers are used by operating doctors to view inaccessible places, such as the inside of a lung. Optical fibers are helpful in that they allow the transmission of light to or from places not usually possible. Because they are fibers, they can be bent, allowing light to be bent easily and precisely around many corners, with out the use of more clumsy devices such as mirrors.