Sample Problem 1: Speed and Frequency
of Light Leaving an Optical Fiber
Light moving from an optical fiber to air changes wavelength
from 452nm to 633nm.
- What is the index of refraction of the fiber?
- What is the speed of light in the fiber?
- What is the frequency of the light in the fiber?
- What is the frequency of the light in air?
- Since we do not have five digits of accuracy in this problem, we can assume
that the wavelength of light in air, air = 633 nm is
the wavelength of the light in vacuum 0.
The index of refraction inside the fiber is 1.40.
- From the definition of n, we have
The speed of light inside the fiber is 2.14 x 108m/s.
- The frequency in the fiber can be found from the speed and the wavelength
in the fiber:
- The frequency of light does not change as the light moves between two different
media, so the frequency in air is the same as the frequency in the fiber:
4.74 x 1014Hz. You can double-check this result by calculating
the frequency from the speed of light and wavelength in air:
Copyright © 1999 Rensselaer Polytechnic Institute and DJ Wagner. All Rights Reserved.