The circular polarizer is composed of a linear polarizer and a quarter-wave plate, which is made of a special birefringent material.
The optical properties of the birefringence are when the light will have two different directions of refraction. And the wave plate itself according to its own material has the so-called optical axis, when a linearly polarized light into his vibration will be broken down into two directions of vibration: one is the direction of the optical axis, known as the fast axis, The other is the direction perpendicular to the optical axis, called the slow axis.
When the linearly polarized light and the optical axis of the quarter-wave plate are parallel or vertical (the angle is 0 degrees or 90 degrees), the amplitude of the other direction is zero and the original linearly polarized light is maintained.
It is not broken down into two directions. And when the angle between the linearly polarized light and the optical axis is 45 degrees, the amplitude of the two directions is equal and the so-called circularly polarized light is formed; but if it is other angles, the amplitude of the two directions is different , And become elliptical polarized light. So in fact, circular polarization and linear polarization can be regarded as a special case of elliptical polarization.
In addition to the wave of light will be divided into two directions of vibration, vibration in these two directions because of the different thickness of the wave plate, there are different phase difference; and in the circular polarizer on the quarter of the wave plate.
That is, will produce a quarter of the phase difference. But also because of this quarter of the phase difference, so in the fast axis and slow axis of the two directions of the wave synthesis, it will produce a vibration direction will rotate the wave.