Reflective 2D diffraction grating based on short pitch chiral liquid crystal

Thermotropic liquid crystals have recently become popular for use in optical components for augmented and virtual reality. Chiral liquid crystal (CLC), is of particular interest due to the formation of a photonic bandgap that allows for the creation of polarization-sensitive reflective optical components. Previous investigations have studied 2D diffraction gratings based on long-pitch (5 μm) CLC in combination with a 2D periodic alignment configuration. This yielded 2D diffraction patterns in transmission with the ability to switch between high and low voltage states with hysteresis. In the current study, short-pitch CLC (400 nm and 1 μm) is deposited between two substrates with perpendicularly rotating periodic photoalignment patterns, the shorter pitch resulting in a diffraction grating that produces a 2D diffraction pattern in reflection for wavelengths in the visible range. While a relatively high diffraction efficiency is achieved in the first diffraction order, additional diffraction orders with lower efficiency are present due to the complex CLC configuration in the bulk. •2D liquid crystal diffraction gratings have been fabricated using a photo-patterned alignment and chiral liquid crystal.•Periodicity in the helical structure of the chiral liquid crystal allows reflection in the visible wavelength range.•Two different states have been discovered in the bulk of the short pitch chiral liquid crystal based 2D diffraction gratings.•Neither diffraction pattern nor the diffraction efficiency depends on the structure in the bulk.•Around the mid-plane, transition layer exists, where in some regions along the diagonal director is close to the z-axis.