Metalenses are essential components in terahertz imaging systems. However, without careful design, they show limited field of view and their practical applications are hindered. Here, a wide-angle metalens is proposed whose structure is optimized for focusing within the incident angles of ±25°. Simulation and experiment results show that the focusing efficiency, spot size, and modulation transfer function of this lens are not sensitive to the incident angle. More importantly, this wide-angle metalens follows the ideal Gaussian formula for the object-image relation, which ensures a wider field of view and better contrast in the imaging experiment.

We investigate the laser emission from a polymer–cholesteric liquid crystal superstructure with coexisting opposite chiralities fabricated by refilling a right-handed polymeric scaffold with a left-handed cholesteric liquid crystalline material. The superstructure exhibits two photonic band gaps corresponding to the right- and left-circularly polarized light. By adding a suitable dye, dual-wavelength lasing with orthogonal circular polarizations is realized in this single-layer structure. The wavelength of the left-circularly polarized laser emission is thermally tunable, while the wavelength of the right-circularly polarized emission is relatively stable. Due to its relative simplicity and tunability characteristics, our design might have broad application prospects in various fields of photonics and display technology.

The advance of topological photonics has heralded a revolution for manipulating light as well as for the development of novel photonic devices such as topological insulator lasers. Here, the robust topological interface state lasing in a polymer‐cholesteric liquid crystal superlattice at the visible regime is demonstrated. By use of the femtosecond‐laser direct‐writing and self‐assembling techniques, the micron‐sized superlattice is established with a controlled mini‐band structure and a topological interface defect, thereby achieving a low threshold for robust topological lasing at about 0.4 µJ (722 W·mm −2 ). Thanks to the chiral liquid crystal, not only is the circularly polarized lasing readily achieved, but the emission wavelength is thermally tuned. The results bring about the possibility to realize tunable, circularly polarized, compact, and integrated topological photonic devices at low cost, as well as to engineer an ideal platform for exploring topological physics that involves light–matter interaction in soft‐matter environments.

Two-color lasing emission from an asymmetric structure, consisting of two dye-doped cholesteric liquid crystal (DD-CLC) layers separated by a transparent interlayer, is demonstrated. The DD-CLC mixtures have different reflection bands with long-wavelength band edges located at the green and red wavelengths of the visible spectrum, respectively. For the laser action, the CLC hosts provide the feedback, and the fluorescent laser dyes represent the active medium. When the stacked structure is optically pumped above the threshold, two simultaneous laser lines separated by 123 nm are observed at the long-wavelength band edges of the DD-CLC mixtures. The influence of an electric field on lasing behavior is also analyzed and discussed in terms of the reflection spectrum and laser action. The results show a reversible tuning of the reflection band, accompanied by a modification of the lasing characteristics under the application of an external field. Above a specific threshold voltage, one of the emission lines is suppressed and the other is conserved. With a further increase in the voltage, both laser emissions are entirely inhibited. The investigated structure demonstrates a simple technique to obtain an electrically tunable multi-wavelength laser, which might pave the way for a new generation of organic laser sources.

Terahertz (THz) lenses have numerous applications in imaging and communication systems. Currently, the common THz lenses are still based on the traditional design of a circular convex lens. In this work, we present a method for the design of a 3D-printed multilevel THz lens, taking advantage of the benefits offered by 3D printing technology, including compact size, lightweight construction, and cost-effectiveness. The approach utilizes an inverse design methodology, employing optimization methods to promise accurate performance. To reduce simulation time, we employ the finite-difference time-domain method in cylindrical coordinates for near-field computation and couple it with the Rayleigh–Sommerfeld diffraction theory to address far-field calculations. This technology holds great potential for various applications in the field of THz imaging, sensing, and communications, offering a novel approach to the design and development of functional devices operating in the THz frequency range.

Low-threshold topological lasing at visible wavelengths and with circular polarizations is demonstrated theoretically, and experimentally in a femtosecond-laser-written micron-sized polymer-cholesteric liquid crystal composite structure by manipulating the topological mini-bands based on the Su-Schrieffer-Heeger model.

The advance of topological photonics has heralded a revolution for manipulating light as well as for the development of novel photonic devices such as topological insulator lasers. Here, we demonstrate topological lasing of circular polarization in a polymer-cholesteric liquid crystal (P-CLC) superlattice, tunable in the visible wavelength regime. By use of the femtosecond-laser direct-writing and self-assembling techniques, we establish the P-CLC superlattice with a controlled mini-band structure and a topological interface defect, thereby achieving a low threshold for robust topological lasing at about 0.4 uJ. Thanks to the chiral liquid crystal, not only the emission wavelength is thermally tuned, but the circularly polarized lasing is readily achieved. Our results bring about the possibility to realize compact and integrated topological photonic devices at low cost, as well as to engineer an ideal platform for exploring topological physics that involves light-matter interaction in soft-matter environments.

In the present investigation, we have undertaken photoluminescence, UV-Vis absorbance, transmission and polarised light microscopy of the composites of a cholesteric liquid crystal (CLC) doped with quantum dots (QDs). The locally formed QDs clusters may distort the CLC's helix to induce an imperfect planar texture and cause broadening of CLC's photonic band gap. This broadening is accompanied by a change of the wavelength positions of the central and both the long and short band-edges of the photonic band gap as the concentration of the doped QDs increases. A remarkable enhancement in the photoluminescence intensity of CLC materials is observed by doping with QDs. A decrement in the FWHM parameter also supports this increased photoluminescence intensity. The UV absorbance increases for the QDs dispersed CLC material and is followed by a slight red shift when compared to the pure CLC. The optical band gap obtained by the Tauc plot method suggests that the observed optical band gap narrows after the dispersion of QDs into the CLC. The outcome of these investigations proves that the dispersion of QDs in CLC is beneficial and may be useful in liquid crystal displays and other opto-electronic devices, which require less band gap materials.

We propose a new kind of reconfigurable topological valley photonic crystal (TVPC), and a novel topological waveguide can be formed by constructing a domain wall between two TVPCs with opposite valley-Chern indices. The topological waveguide mode in the composite TVPC has large group refractive index. A topologically protected coupled waveguide cavity system is then designed by introducing a hexagonal ring cavity at the center of the straight domain wall of a combined TVPC, in which a narrow plasmon induced transparency window rises at 3.8848 GHz with a Q-factor of 1387 and a maximum group refractive index as high as 186. We propose a notch filter with a resonant frequency of 3.8852 GHz and a very high Q-factor of 10224. By changing the refractive index of liquid crystals via an external voltage applied between two parallel metal plates, the filter can be switched between band-pass and band-stop based on the reconfigurable topological interface state.

Liquid crystals (LCs) have been one of the hot topics in physics, chemistry and material science for decades. Nematic liquid crystals (NLCs) are composed of molecules tending to align in a preferred direction and thus have orientational order. Hence, NLCs possess electromagnetic and optical properties similar to crystals, and play an important role in applications ranging from display to light field regulation, etc. LCs usually contain defects and therein exhibit special optical textures. In order to study these defects, a prevailing method is to build proper theoretical models for the LCs. In this review article, several static models of LCs and their applicable conditions are reviewed. The variation of free energy caused by anchoring energy under the interface effect is also analyzed in detail. Moreover, this article introduces the recent advances of the most widely used Landau-de Gennes Q-tensor model in case of elastic constant L -> 0 and low temperature limit. Finally, the progress of these theoretical models in practical applications is also discussed.

By taking a cholesteric liquid crystal (CLC) as an example and treating it as a multilayer stack of birefringent plates, we use a transfer matrix method to analyze light propagation in a common chiral medium in consideration of interlayer reflection and transmission. Based on the transfer matrix, the electric field distribution can be expressed in the form of linearly as well as circularly polarized components, so as to discuss the change of the polarization state of light in the transmission process. The transfer matrix of the same medium with different chirality can be converted by only changing the rotation matrix in the calculation process. Electric field distributions, band structure, transmission, and reflection spectra are calculated when circularly polarized light is incident normally on CLCs or on composite periodic structures of left- and right-handed CLCs. The results obtained by using this transfer matrix method are in good agreement with those obtained by the method based on solving the eigenvalues of Maxwell's equations. Finally, the transfer matrix method is used to calculate the dynamic transmission properties of CLCs under external magnetic field, which is of great significance for the research of noncontact controllable optical devices. The presented computational method saves computing time and can be used for constructing new photonic microstructures with different chiral media.

In this paper, a heterogeneous Au-Ag nanostructure consisting of a rod and concentric square ring-disk is pro-posed to generate intense plasmonic Fano resonances. And the Fano resonance in plasmonic nanostructures is produced by the coupling between broad bright mode and narrow dark mode, causing a Fano dip in the scattering spectrum. One of the main characteristic of the Fano dip is the line width which can be reduced to 0.0135 eV in this nanostructure, and the local electric field enhancement factor can reach 64, which enables its promising applications in biosensing, detecting and surface-enhanced Raman scattering.