Super-resolution liquid-crystal photoalignment based on polarization-induced molecular reorientation and sub-spot...

We propose and experimentally demonstrate a super-resolution liquid-crystal photoalignment (SPLCP) method based on polarization-induced molecular reorientation and sub-spot mechanical displacement. The molecular orientation angles of photoalignment material SD1 can be reversibly reoriented by ultraviolet (UV) exposure with different linear polarization states, from which the liquid crystal (LC) molecules coated on the SD1 layer are oriented along the long-axis of the SD1 molecules. By combining precise mechanical scanning with sub-spot displacement and UV exposure cycles with tunable linear polarization states, the photoalignment resolution of SD1 layer with a feature size of sub-diffraction limit is achieved, from which a super-resolution planar LC element can be fabricated solely through UV exposure and coating. Therefore, light can be arbitrarily manipulated by the LC element with a designed orientation angle pattern of molecules corresponding to Pancharatnam-Berry phase. A UV pulsed laser with a wavelength of 355 nm, an objective lens with numerical aperture (NA) of 0.8 and a translation stage with sub-spot displacement of 0.2 µm are implemented to construct the exposure system. The minimum linewidth of the fabricated LC element by the proposed SPLCP method achieves 0.2 µm, which is ∼ 0.74 times that of the diffraction limit. Furthermore, a polarization volume grating (PVG) with an aperture of 1 cm, a thickness of 3.9 µm and a period of 1.6 µm is fabricated, in which the first-order diffraction efficiency achieves 93.7% compared with the theoretical efficiency of 100% at the working wavelength of 532 nm. The proposed SPLCP method provides an idea for super-resolution, high-speed and large-scale fabrication of planar and functional optical elements without complicated coating and etching preparation.