Total Internal Reflection
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Dispersion
Light can also disperse. The index of refraction depends on the wavelength. We don’t have the capability of sending a perfectly monochromatic light into an optical fiber, therefore there will be some dispersion of light. This also has implications for optical fibers. We must pick materials for optical fibers that do not absorb in the near IR, the popular wavelength for telecommunications. In general terms as the index of refraction increases the wavelength decreases. For example, n for blue light is larger than n for red light. A blue photon has an energy of about 3 eV, vs 1.5 eV on the red side of the spectrum.
Dispersion is defined as
<math>\frac {Dn(d)}{d\lambda}\,\!</math>
If you send white light into a material the material will respond differently to each wavelength of light. Therefore the angle of deflection will be slightly different for each color. This explains how a prism makes a rainbow. White lighte passes from air into the glass and becomes decomposed into each color.