Liquid‐Crystal‐Mediated Geometric Phase: From Transmissive to Broadband Reflective Planar Optics

Abstract

Planar optical elements that can manipulate the multidimensional physical parameters of light efficiently and compactly are highly sought after in modern optics and nanophotonics. In recent years, the geometric phase, induced by the photonic spin–orbit interaction, has attracted extensive attention for planar optics due to its powerful beam shaping capability. The geometric phase can usually be generated via inhomogeneous anisotropic materials, among which liquid crystals (LCs) have been a focus. Their pronounced optical properties and controllable and stimuli‐responsive self‐assembly behavior introduce new possibilities for LCs beyond traditional panel displays. Recent advances in LC‐mediated geometric phase planar optics are briefly reviewed. First, several recently developed photopatterning techniques are presented, enabling the accurate fabrication of complicated LC microstructures. Subsequently, nematic LC‐based transmissive planar optical elements and chiral LC‐based broadband reflective elements are reviewed systematically. Versatile functionalities are revealed, from conventional beam steering and focusing, to advanced structuring. Combining the geometric phase with structured LC materials offers a satisfactory platform for planar optics with desired functionalities and drastically extends exceptional applications of ordered soft matter. Some prospects on this rapidly advancing field are also provided.

A practical guide to versatile photoalignment of azobenzenes

“…Brilliant Yellow is popular for photoalignment in a variety of recent efforts research in optics [6] and soft robotics [27]. To utilise its full potential in terms of alignment quality, it is essential to know the optimal parameters.…”

“…This process is best-suited for uniaxial alignment, in which all mesogens are aligned in one direction. However, novel applications in the fields of light modulation [6] and soft robotics [7] require alignment patterns that vary spatially, i. e. the alignment direction is not uniaxial but follows a specific pattern. To enable this, finer techniques to microstructure the command layer through photo-lithography, soft lithography and maskless lithography have been demonstrated [8][9][10].…”

Enlarging the Eyebox of Maxwellian Displays with a Customized Liquid Crystal Dammann Grating

“…To create the patterned binary phase, the LCs are aligned in either 0 • or 90 • with the desired alignment pattern created from a spatial light modulator (SLM), and the LC polymer film serves as a patterned half-wave plate. For incident left-handed circularly polarized light, its polarization is flipped to right-handed upon transmitting through such a wave plate and a geometric phase term is added [20]. Most previous Dammann grating designs have focused on achieving perfect binary gratings.…”

Broadband Multichannel Optical Vortex Generators via Patterned Double-Layer Reverse-Twist Liquid Crystal Polymer

“…Meanwhile, for right-circularly polarized light, the opposite phase modulation is carried out. The above design could be easily realized in an LC system where the optical axis orientation could be directly encoded with azimuthal angle control of LC directors [22]. As shown in Figure 1b, photoalignment agents indicated in yellow are utilized to perform the alignment, and the adjacent LC directors marked in orange follow the local guidance and further spread this order to the bulky LC.…”