 xuanlunhuang20
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Sorry for the unclear expression. For example, I set the phase difference between two sources to be 0 degree, the vector sum is a linearly polarized light, right? Then I simulate without the waveplate structure, I can get a polarization plot of the linearly polarized light. Next, I set the phase difference to be 90 degree, it is a circularly polarized light. After passing through the quarter waveplate, this “90 degree” phase difference should be eliminated and the circularly polarized light can be converted back to the linearly polarized light. Hence, I am expecting that if I use a circularly polarized light to pass through the waveplate, the direction of output polarization plot should be the same as that of the linearly polarized light. However, it’s not the case for the situation “theta=15 and phi=45”.

In “some other tests“, I wanted to verify my expecting and used three cases to test. It seems that in these three cases, the output polarization plot of the waveplate is the same as that of the original linear polarized light which is simulated without the waveplate.

For case (1), I first got the polarization plot of a linearly polarized light, which was simulated without the structure. Next I enabled the waveplate structure and used the same linearly polarized light to simulate. Because the vector sum of this linearly polarized light is along the y direction of the meta atom, it will not be transformed to a circularly polarized light. So the output polarization is the same as that of the original source which is simulated without the structure. This accords with intuition.

For case (2), I got the polarization plot of a linearly polarized light first. Next I changed the phase between two sources to be 90 deg to create a circularly polarized light. Because the vector sum of E field is 45 deg to the y direction, the waveplate should work. Therefore, after passing through the waveplate, this circularly polarized light was converted back to the original linearly polarized light. The output polarization plot is similar to the original linearly polarized light, this is also what I expect.

For case (3), similar to case (2), the vector sum of E field is also 45 deg to the y direction. Therefore, after passing through the waveplate, the circularly polarized light can be converted back to the original linearly polarized light. The output polarization plot is also similar to the original linearly polarized light.

However, for the case “theta=15 and phi=45”, the polarization plot of the linearly polarized light without the structure is in 45 degrees while the circularly polarized light is transformed to vertical direction after passing through the waveplate. I know the function of the quarter waveplate is correct, I just wonder why the case “theta=15 and phi=45” is different from the others. 