Polarization state detection based on an active liquid crystal polarization grating

Existing polarization state measurement systems often have complex structures and reliance on passive components, which limits their application. Therefore, a polarization state detection method based on an active liquid crystal polarization grating (ALCPG) is proposed in this paper. First, an ALCPG was prepared using a wedged liquid crystal (LC) cell. Next, the diffraction characteristics of the ALCPG are employed to analyze the relationship between the order energy ratio ( ) and the polarization state of the measured light. Finally, the detection of both linearly and arbitrarily polarized laser beams is experimentally verified. The experimental results demonstrate that this proposed method can accurately detect the polarization state of light over a wide wavelength range. For linear polarization detection, the root mean square errors (RMSEs) of and under a red laser ( ) are 0.807% and 1.218%, respectively; under a green laser ( ), they are 1.695% and 1.712%, respectively. For arbitrary polarization detection, the RMSEs of the normalized Stokes parameters ( , , and ) under a red laser are 0.758%, 0.596%, and 1.657%, respectively; under a green laser, they are 0.369%, 0.804%, and 2.697%, respectively.