Method for preparing polarization volume holographic grating capable of achieving different diffraction efficiencies, and polarization volume holographic grating

A method for preparing a polarization volume holographic grating capable of achieving different diffraction efficiencies, comprising:

• step 1:
• coating a top surface of a substrate medium with a photo-alignment layer;
• step 2:
• covering a top surface of the photo-alignment layer with a mask, and performing interference exposure using two orthogonal circularly-polarized beams;
• step 3:
• removing the mask after completion of the exposure, and then coating the top surface of the photo-alignment layer with a layer of liquid crystal solution of a preset concentration, wherein the liquid crystal solution is used for preparing a grating medium layer and is 100 nm to 10 μm in thickness;
• step 4:
• placing the substrate medium covered with the liquid crystal solution into a nitrogen environment, and curing the liquid crystal solution under ultraviolet (UV) irradiation to obtain a liquid crystal film;
• step 5:
• removing a disordered liquid crystal film in a non-grating region on the substrate medium using a laser cleaning device, so as to obtain a polarization volume grating (PVG);
• and
• step 6:
• covering a surface of the PVG with a graded-UV-transmittance filter, and exposing the grating through the filter to UV light to obtain PVG regions in which a grating medium thickness is uniform and diffraction efficiencies vary continuously and increase progressively.