Fabrication of optical vortex array by fixing standing wave mediated periodic defects in nematic liquid crystals via photopolymerization

Optical vortex beams have attracted significant research interest owing to their potential for application in optical communication and imaging. In this study, we demonstrated devices with electrically switchable topological defects as well as those with permanent topological defects using reactive mesogen (RM) and vertically aligned LC cells. A defect array was created via standing wave-mediated periodic LC orientation control by applying pulse train waves. At a low RM concentration (0.6 wt%), polymerisation induced a pretilt angle, and the periodic LC alignment was memorised with a topological defect array. Thus, the memorised defect structure reappeared upon applying a direct current field or standard square electric fields. In contrast, at a high RM concentration (3 wt.%), a permanent defect array device was realised. Thus, depending on the RM concentration, various types of defect arrays were selectively created. The devices developed in this study can be used for various potential applications, such as in digital data transfer and imaging systems.