Single-step creation of polarization gratings by scanning wave photopolymerization with unpolarized light

Abstract

Liquid crystalline materials with a cycloidal molecular orientation pattern are attractive for fabricating diffractive waveplates, diffracting incident light regardless of its polarization state into left- and/or right-circularly polarized light only in the +1st and/or −1st orders, applicable as next-generation optical devices. However, large-area high-speed processing of such molecular orientation is a challenge, since even state-of-the-art photoalignment methods require a precise spatial modulation of the polarization states of incident light, e.g., polarization holograms. Here, we propose and demonstrate that unpolarized light could easily generate cycloidal molecular orientation patterns over large areas in a single step merely by using our recently developed method of “scanning wave photopolymerization” with a simple optical setup. Importantly, the processing time for fabricating millimeter-scale films was significantly decreased to less than a few minutes. Detailed investigation revealed that the resultant film showed the desired diffraction behavior with a diffraction efficiency of 50%.