Page 591 - Introduction to Information Optics

576 10. Sensing with Optics

8=0 0<8<f

8=71 TC<8<

37C
<6<2n

Fig. 10.4. Illustrations of allowed polarization states.

Obviously, there are only three independent components due to the relation
s
So = si + $2 + i- The beauty of the Stokes vector is that all the components
of the vector can be measured in a relatively easy way. Figure 10.5 shows an
experimental setup used to measure the Stokes vector, which includes a
photodetector sensitive to the wavelength of interest, a linear polarizer,, and a
quarter-wave plate. Assume that the polarizer transmission axis is oriented at
an angle 9 relative to the x axis, while the fast axis of the wave plate is along
x. Six light beam intensities (/j,/ 2 ,... ,/ 6 ) are measured under different
conditions:

1. / s is measured with the polarizer aligned in the x direction without a
quarter-wave plate.
2. J 2 is measured with the polarizer aligned in the y direction without a
quarter-wave plate.
3. 7 3 is measured with the polarizer aligned in 45° relative to the x direction
without a quarter-wave plate.