With the rapid development of artificial intelligence, it is of great significance to develop intelligent materials with fast response, high efficiency, and simple and easy processing. In recent years, researchers have been very interested in Near-Infrared (NIR) light-responsive intelligent liquid crystal nanocomposites. The marriage of NIR-absorbing nanomaterials with liquid crystals (LCs) can enable LC-based smart materials to respond to light stimuli in the NIR band, which holds promising applications in areas of wearable electronics, biomimetic machines, soft robotics and biomedical devices, etc. Herein, we provide a state-of-the-art account on the recent advancement in LC-based photonic crystals and smart actuators. LC-based photonic crystal is a composite of NIR-absorbing nanomaterials with chiral LCs such as cholesterics and blue phases, so that the photonic materials can respond in the NIR band to produce a structural color change; Nanostructured LC-actuator is a composite of NIR-absorbing nanomaterials with crosslinking liquid crystalline polymers, so that the smart liquid crystalline material can respond in the NIR band to enable a shape change or macroscopic locomotion. This review concludes with a perspective on the opportunities and challenges in the development of NIR light-responsive intelligent liquid crystal nanocomposites and their potential applications.

Twist-bend nematic phase is a chiral nematic phase with an inclined spiral structure possessing nanometer helical pitch. Due to its negative bend elastic constant, nano-scale pitch, and chiral structure formed by achiral molecules, it has attracted widespread attention from researchers all over the world. This article reviews the development of twist-bend nematics, focuses on the study of the characteristics, properties, molecular motion, and molecular groups of twist-bend nematics, and illustrates the effects of twist-bend nematics under external fields. The microstructure changes and the development of theoretical and simulation research on twist-bend nematic phase, and the application prospects and development trends of twist-bend nematic liquid crystal are discussed. The aim of this article is to provide readers with a comprehensive understanding of the related research of the special liquid crystal optical materials through the review of the materials characteristics, properties, applications and other aspects of twist-bend nematic liquid crystals, and thus stimulate the readers research inspiration on their phase structure, theoretical simulation, applications, etc. It is hoped that this paper can start a discussion and promote the research and development of this field to some extent.

Owing to the existing issues of poor thermal stability and narrow temperature interval in applications of organic liquid crystal materials, developing novel inorganic liquid crystal is an alternative strategy due to the virtues of electron-rich characteristics and high thermal stability of the well-developed inorganic nanomaterials. Starting from the summarization of the phase transition rules and the regulation mechanisms of liquid crystalline self-assembly, including Onsager theory, DLVO theory, and entropy effects on depletion attraction and steric repulsion, this review demonstrates recent progress in entropy-driven liquid crystalline self-assembly of the inorganic nanomaterials. Taking the ideal building block of gold nanorods as an example, the regulations of the advanced self-assembly methods and the interactions between the nanorods on the diverse assembly structures are discussed, and their potential applications in optoelectronic devices are illustrated. Finally, future developments are prospected aiming at the problems in preparing inorganic liquid crystal materials using the self-assembly technology.

The ferroelectric liquid crystal (FLC) which has the advantage of a fast response under a low electric field has become one of the most promising candidates of the next generation liquid crystal display (LCD) as well as photonic devices. Three electrooptic modes including surface stabilized FLC (SSFLC), deformed helix ferroelectric (DHF) mode, and electrically suppressed helix (ESH) mode are reviewed with the corresponding electrooptic effects like bi-and multi-stable switching, continuous modulation of grayscale or phase, and high contrast switching. Moreover, the photo-aligning technique is in high demand compared with the traditional rubbing method for FLC devices, since photo-aligning is a non-contact process, which avoids static charges, particles, and contacting damages. With the advantages of controllable anchoring energy, the photoalignment provides FLC samples with uniform alignment and high contrast ratio. The fast FLCs with a high resolution and high contrast can be applied in the next generation display including field sequential color FLC micro-displays as well as switchable 2D/3D televisions.

Blue phase liquid crystals possess several extraordinary optical properties, such as fast response time (sub-milliseconds), Bragg reflection in visible range, optical isotropic property. These properties make blue phase liquid crystals have a good application in electro-optical devices. Besides of displays, blue phase liquid crystals demonstrate series of new developments in polymer-stabilized blue phase film, crystal lattice structure, structural color and tunable application recently. These developments not only deepen cognitions in fabrication and basic structure of blue phase liquid crystals, and also broaden the applications of blue phase liquid crystals at the meantime. In this review, we discuss about the research developments of crystal lattice structure and structural color in blue phase liquid crystals in recent years. First, the fabrication and development of blue phase liquid crystals are introduced. Then, the recent developments of crystal lattice structure, including monodomain crystal, single crystal and structural color of blue phase liquid crystals are demonstrated. Last, the tunable crystal structure of blue phase liquid crystal, such as the effects of electric field and optical field on blue phase liquid crystals are shown.

Dye-doped band-edge cholesteric liquid crystal (CLC) microlaser has been one of the focus of academic researches ever because of intrinsic properties, such as low threshold and mirrorless. As a novel three-dimensional omnidirectional microlaser, CLC emulsion droplets with complex microstructures exhibit appealing characteristics, such as miniaturization, integration and wavelength tunabilities, etc., arousing broad interests in the research field of liquid crystals (LCs) for non-display applications. The complex spherical core-shell microstructure results in the generation of a variety of laser modes such as distributed feedback (DFB) mode, whispering gallery (WG) mode and Fabry-Pérot(FP). The rapid development of glass-capillary microfluidic technique makes it possible to produce monodispersed CLC droplets with controllable sizes, providing conditions that are necessary for the fabrication of multiple emulsions with complex microstructures. In this review, the glass-capillary microfluidic technique is briefly introduced for the production of monodispersed LC emulsions. And the recent studies on the laser behavior in both the single-emulsion CLC droplets and multiple-emulsion CLC core-shell microstructures are presented and well discussed.

In order to achieve a natural and comfortable augmented reality display, it is necessary to solve the accommodation-vergence conflict problem in the conventional augmented reality displays. Multi-plane display realizes 3D display by constructing 2D slice pictures in space. Since each slice picture is displayed at a different depth, it can accurately display the depth information and effectively alleviate the accommodation-vergence conflict problem. This paper mainly introduces multi-plane augmented reality displays based on liquid crystal scattering devices, including normal-mode polymer stabilized liquid crystal (PSLC), reverse-mode PSLC and polymer stabilized cholesteric liquid crystal. The response time of the PSLC can reach 0.65 ms, and the response time of the polymer stabilized cholesteric liquid crystal is also within 3 ms, so multi-plane augmented reality displays can be realized based on time multiplexing method. Finally, the difficulties and future trends of multi-plane augmented reality displays based on liquid crystal scattering films are discussed.

As a newly emerging advanced two-dimensional material, the discovery and in-depth research of graphene have a huge impact on many fields such as semiconductors, energy harvesting, and biological sciences, etc. This review systematically highlights the current research status of graphene oxide liquid crystal (GO-LC), applying to transmissive and reflective-mode liquid crystal display. In particular, an extremely large Kerr coefficient of graphene oxide liquid crystal contributes to fabricate low power, quick response, and easy switching of electro-optic devices. By applying horizontal fields, the structural color can be written and erased accordingly. These results elucidate that graphene oxide liquid crystal has great potential in the electrical-optical device and provides a new possibility for two-dimension liquid crystal materials in actual applications.

Lens with tunable focal length play an important roles in imaging, sensing and detection. In this paper, by studying the polarization characteristics of liquid crystal polarization lenses (LCPL), a zoom system that realizes multi-point zoom through a combination of multiple LCPL is designed. LCPL is an optical element that utilizes a specific spatial arrangement of liquid crystal molecular directors (Optical anisotropy axes) to produce a specific geometric phase difference to control wavefront. For left/right circularly polarized light, LCPL is equivalent to a positive/negative lens. By using the polarization characteristics of LCPL and the electro-optic characteristics of liquid crystal, a liquid crystal polarization zoom lens system consisting of a common positive lens, a liquid crystal wave plate and two LCPLs is designed. The system can achieve zooming of 7 focal lengths under circularly polarized incident light. At the same time, by optimizing the parameters of the LCPLs (such as focal length, spacing, etc.), the system can achieve effects such as equal interval zoom. The experimental results show that under the 633 nm circularly polarized light, the liquid crystal polarization zoom lens combining system (composed of a self-made LCPL) successfully realizes zooming of 7 focal lengths, and the zooming distance meets the expected requirements essentially. This experiment fully verified the feasibility of multi-point zoom in LCPLs system.

Liquid crystal microlens arrays, as one of the basic optical elements, have the advantages of tunable focal length, compact structure, low power consumption and good stability. They have a wide range of applications in the field of micro-/nano-optics. After nearly 40-year development, the research on liquid crystal microlens arrays has become gradually matured. Liquid crystal microlens arrays with different structures and applications have emerged rapidly. Here, this review article briefly summarizes the three working principles of liquid crystal microlens arrays, and describes the recent research progress separately. The review focuses on the manufacturing process, structural characteristics and working principle of liquid crystal microlens. Particularly, liquid crystal microlens arrays based on refraction and diffraction principles are respectively discussed, involving microlens structures, liquid crystal alignment techniques, as well as their applications. Finally, the key issues and future development trends of liquid crystal microlens arrays are summarized.

Liquid crystal, with a broadband external field induced tunability, has obvious application advantages in the terahertz band. It is expected to realize efficient and active terahertz wavefront modulation. This article briefly summarizes some of the recent researches carried out by the group of liquid crystal and micro/nano optics of Nanjing University and other research teams in the field of liquid crystal based terahertz wavefront modulators. There are mainly two types, including pure liquid crystal based modulators and liquid crystal integrated metadevices. The characteristics of the dynamic tunability, diversified functions and potential application prospects of these devices are systematically described. The development trend of the combination of liquid crystal and terahertz technology is also discussed.