Total Internal Reflection and Optical Fiber

Total reflection and critical angle

When light enters from a medium with a large refractive index to a medium with small refractive index, the incident light does not pass through the boundary surface but is reflected at all.


When light enters a medium with a high refractive index from a medium with a low refractive index, the refraction angle becomes larger than the incident angle. At this time, as the incident angle increases, the refraction angle also increases. The angle of incidence when the angle of refraction is 90 ° is called the “critical angle”.

By utilizing the total reflection phenomenon of light, the direction of light can be freely changed.

Optical fiber and optical communication

The optical fiber is made up of thin glass thread. Light can not go out and is passed through without loss through total internal reflection.


1. It is transmitted to far without loss.
2. When used with a telephone line, you can send thousands of simultaneous call signals with one lines. Thickness is smaller than copper wire, and the price is much cheaper.
3. You can see the places where cameras are difficult to see. (Inside the engine, inside the human body)
4. It is not affected by ambient magnetic field or electric field. The noise is small.

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