light - total internal reflection

Total internal reflection
Light can be trapped and transmitted through glass fibers. Such fibers are called optical fibers and are used widely in high speed communication channels. Communication takes place at the speed of light as light travels through the optical fiber. Light can be totally internally reflected if it enters a glass fiber at an angle greater than the critical angle. The critical angle is the angle that the light starts to be internally reflected within the glass fiber.
	When a ray of light reaches the critical angle of the particular fiber it is travelling through it is refracted along the surface of the fiber or prism. At angles less than the critical angle the light ray is refracted and partially internally reflected, as shown inthe animation below.
The animation on the right shows a ray of red light passing through a glass prism. As the angle at which it enters the glass prism increases and gets beyond the critical angle the light is totally internally reflected. The light beam is trapped withing the fiber and is transmitted along the length of the fiber. Click to see a 120Kb video of low grade optical fibers. As you look at the clear fibers no signs of light in the fiber can be detected. Only at the ends of the fibers is light visible. Explain this phenomenon.