Surface-Initiated Polymerization Technique for Stabilizing Tilt Angles in the Fabrication of Twisted Nematic Liquid Crystal Gratings/Fresnel Zone Plates

A method for the fabrication of low-scattering liquid crystal (LC) photonic devices, including a Fresnel zone plate (FZP) and grating, was proposed. The core of this method lies in doping the alignment layer with a photoinitiator, followed by the generation of polymer brushes via surface-initiated polymerization (SIP) technology. This technology effectively fixes the tilt angle of LC molecules under saturation voltage, resulting in the formation of a stable structure characterized by the alternating distribution of twisted nematic and vertically aligned regions within the twist nematic (TN) type of LC cells. Compared with conventional methods that rely on polymer networks to stabilize the tilt angles of LC molecules, this approach significantly mitigates scattering caused by refractive index mismatches between the polymer network and the LC material. Owing to its low scattering property, the fabricated binary FZP achieved a diffraction efficiency as high as 35.3%, and the haze is only 8.6%. The fabricated amplitude grating has a contrast ratio as high as 625 and a haze of only 14.1%. The proposed method enables the rapid and efficient production of low-scattering LC devices, demonstrating great application potential in photonic device fabrication.