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Total Internal Reflection

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Light Pipes

Light Pipes

Credit: Tobias Brixen
Source: http://www.flickr.com/photos/brixendk/4349817216/
License: CC BY-NC 3.0

Made of a flexible glass or plastic, optical fibers are waveguides that transmit light over long distances with little to no loss of color intensity.

Amazing But True

  • The optical fiber consists of two parts: an inner core and a surrounding layer with a lower index of refraction. This difference in the refractive indexes allows any pulses of light that are sent down the waveguide to stay within the inner core. The process of total internal reflection allows the light to be transmitted down a cylindrical waveguide . 

Credit: Rosham Nikam
Source: http://www.flickr.com/photos/31916678@N07/4753800195/
License: CC BY-NC 3.0

Optic Fibers function as a guide for electronic information [Figure2]

 

  • Total internal reflection is the process in which light that is traveling in a medium hits a boundary at such an angle that the light is completely reflected. Looking at Snell's law, it is easy to see under what conditions and at what angles this would happen:

n_1 \sin \theta_2 & = n_2 \sin \theta_2 \\\theta_1 & = \sin^{-1} \left(\frac{n_2}{n_1}\right)

  • Therefore, total internal reflection will occur when light is incident on the boundary of a second medium with a lower index of refraction and the incident angle is greater than the critical angle.

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Using the information provided above, answer the following questions.

  1. What is the purpose of having an inner and outer core in the optical fiber?
  2. If light is traveling from a medium with an index of refraction equal to 1.33 into air, at what minimum angle would total internal reflection be seen?
  3. How do the impurities in the material an optical fiber is made out of affect how much information is lost?

Image Attributions

  1. [1]^ Credit: Tobias Brixen; Source: http://www.flickr.com/photos/brixendk/4349817216/; License: CC BY-NC 3.0
  2. [2]^ Credit: Rosham Nikam; Source: http://www.flickr.com/photos/31916678@N07/4753800195/; License: CC BY-NC 3.0

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