Recent Advances in Photoalignment Liquid Crystal Polarization Gratings and Their Applications

Recent Development of Tunable Optical Devices Based on Liquid

Liquid opens up a new stage of device tunability and gradually replaced solid-state devices and mechanical tuning. It optimizes the control method and improves the dynamic range of many optical devices, exhibiting several attractive features, such as rapid prototyping, miniaturization, easy integration and low power consumption. The advantage makes optical devices widely used in imaging, optical control, telecommunications, autopilot and lab-on-a-chip. Here, we review the tunable liquid devices, including isotropic liquid and anisotropic liquid crystal devices. Due to the unique characteristics of the two types of liquids, the tuning principles and tuning methods are distinguished and demonstrated in detail firstly and then some recent progress in this field, covering the adaptive lens, beam controller, beam filter, bending waveguide, iris, resonator and display devices. Finally, the limitations and future perspectives of the current liquid devices are discussed.

Catenary optics: a perspective of applications and challenges

Catenary optics is an emerging direction of subwavelength optics, which is indispensable in describing the electric fields and dispersion property of coupled metallic subwavelength structures, and designing broadband high-efficiency geometric-phase metasurfaces. It involves catenary optical fields and catenary structures, in which both ordinary and equal-length catenary functions play important roles. In recent years, catenary optics has realized a variety of exotic phenomena and optical applications, including broadband photonic spin-Hall effect, super-resolution lithography, broadband absorbers, and extreme-angle imaging. Here, we discuss developments of catenary optics, including a brief history, physical concept and properties, applications, and future perspectives.

Photosensitive Alignment: Advanced Electronic Paper-Based Devices

In this review we describe the reversible photoalignment effect imposed on the director in nematic liquid crystals that provides an approach for fabrication of advanced optically addressed devices. Several new concepts have been developed to render photosensitive materials during the past decade. Functional soft azo dye compounds exhibiting distinct functionalities in response to polarized light are highly desirable for fabrication of optically rewritable electronic paper. An optically rewritable element base using simple and inexpensive materials can potentially enable the development of novel environmentally friendly, paper-like gadgets with improved functionality over regular electronic paper. We argue that an optically rewritable technique is relevant for some applications, where conventional paper might be irrelevant. In particular, we have tested and discussed several techniques of color and 3D image formation. This strategy for fabrication of novel devices offers versatile methods for visualization. We also show that the intensity modulation of the irradiation light has a potential to generate improved grayscale visualization. This principle is based on the statistical distribution control of photosensitive azo dye molecules, driven by the incident polarized light. Additionally, we discuss the functional characteristics of the developed prototypes.

Fabrication of Polarization Grating on N-Benzylideneaniline Polymer Liquid Crystal and Control of Diffraction Beam

Photoresponsive photoalignable liquid crystalline polymers composed of phenyl benzoate terminated with N-benzylideneaniline were evaluated. These polymers are capable of axis-selective photoreaction, photoinduced orientation, and surface relief grating formation. Polarization holography using an He-Cd laser beam at a wavelength of 325 nm demonstrated the formation of a surface relief grating with a molecularly oriented structure based on periodic light-induced reorientation and molecular motion. Electrical switching of diffracted light using an electric field response of twisted-nematic cell containing a low-molecular-weight liquid crystal in combination was also demonstrated.

A Review of Two-Dimensional Liquid Crystal Polarization Gratings

In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal manipulation stimulates the development of multibeam optical devices. Therefore, the development of two-dimensional (2D) PGs is in demand. This review summarizes the research progress of 2D PGs. Different designs and fabrication methods are summarized, including assembling two 1D polarization patterns, a 2D holographic lithography by polarization interference and a micro-pixelated electric field stimulated 2D liquid crystal (LC) structure. Both experiments and analyses are included. The design strategy, diffraction property, merits and demerits are discussed and summarized for the different methods.