Fig. 5: Process flowchart of cascade liquid crystal Pancharatnam-Berry lens fabrication.

a For the single Pancharatnam-Berry lens fabrication, photoalignment films are spin-coated on two pieces of ITO glass, and framing adhesive is applied to the photoalignment film of one of the pieces. The photoalignment film surfaces on the two pieces of glass are then aligned and pressed together to form a cavity. A laser is used to expose the photoalignment layer. Finally, liquid crystals are injected and the cavity is completely sealed. The remaining PB lenses follow this procedure, except that the exposure must be aligned with the first exposure. b Photoalignment exposure path. After the greyscale pattern is loaded into the spatial light modulator (SLM), the laser passes through a beam expander and a polarizer, then irradiates the square aperture, the light field is imaged onto the SLM via lens 1 and lens 2. The image field is modulated by the SLM and quarter wave plate (QWP), and then imaged onto the surface of the sample again by lens 3 and 4. The charge coupled device (CCD) receives the reflected light from the sample to observe the exposure process, two beam splitting (BS) prisms are used to change the direction of the light path.