With their helical structure, cholesteric liquid crystals figure prominently in liquid crystal science. The selective reflection of light is their flagship property, and they offer a myriad of ...applications as advanced optical materials with multiscale properties. The cholesteric structure is also a ubiquitous design in the animal and plant kingdoms. This book contains eight contributions on fundamental investigations about defects, textures and structures of cholesteric materials, and experimental studies aimed at applications such as temperature sensors, head-up displays for improving automobile driving safety, or smart windows.
Structural colorful cholesterics show impressive susceptibility to external stimulation, leading to applications in electro/mechano‐chromic devices. However, out‐of‐plane actuation of structural ...colorful actuators based on cholesterics and the integration with other stimulation remains underdeveloped. Herein, colorful actuators and motile humidity sensors are developed using humidity‐responsive cholesteric liquid crystal networks (CLCNs) and magnetic composites. The developed colorful actuator can exhibit synergistic out‐of‐plane shape morphing and color change in response to humidity, with CLCNs as colorful artificial muscles. Through the integration with magnetic control, the motile sensor can be navigated to open and confined spaces with the aid of friction to detect local relative humidity. The integration of multi‐stimulation actuation of cholesteric magnetic actuators will expand the research frontier of structural colorful actuators and motile sensors for confined spaces.
Humidity‐sensitive cholesteric liquid crystal network polymers combined with magnetic composite are developed into colorful actuators and motile sensors, which can be controlled and actuated using humidity and magnetic field. The actuators show synergistic color change and shape morphing while the motile sensors can locomote in open and confined spaces under magnetic actuation.
Abstract Integer winding disclinations are unstable in a nematic and are removed by an ‘escape into the third dimension’, resulting in a non-singular texture. This process is frustrated in a ...cholesteric material due to the requirement of maintaining a uniform handedness and instead results in the formation of strings of point defects, as well as complex three-dimensional solitons such as heliknotons that consist of linked dislocations. We give a complete description of this frustration using methods of contact topology. Furthermore, we describe how this frustration can be exploited to stabilise regions of the material where the handedness differs from the preferred handedness. These ‘twist solitons’ are stable in numerical simulation and are a new form of topological defect in cholesteric materials that have not previously been studied.
Metasurfaces are flat arrays of nanostructures that allow exquisite control of phase and amplitude of incident light. Although metasurfaces offer new active element for both fundamental science and ...applications, the challenge still remains to overcome their low information capacity and passive nature. Here, by integrating an inverse‐designed‐metasurface with oblique helicoidal cholesteric liquid crystal (ChOH), simultaneous spatial and spectral tunable metasurfaces with a high information capacity for dynamic hyperspectral holography, are demonstrated. The inverse design facilitates a single‐phase map encoding of ten independent holographic images at different wavelengths. ChOH provides precise spectral modulation with narrow bandwidth and wide tunable regime in response to programmed stimuli, thus enabling dynamic switching of the multicolor holography. The results provide simple and generalizable principles for the rational design of interactive metasurfaces that will find numerous applications, including security platform.
A dynamic hyperspectral holography is experimentally demonstrated by combining the inverse‐designed‐metasurface and the oblique helicoidal cholesteric liquid crystal. The inverse design enables high information capacity of the multicolor holography and the oblique helicoidal cholesteric liquid crystal provides precise and tunable spectral modulation. As a proof of concept, the optical secret‐sharing platform is demonstrated.
Orthogonal manipulation of multi‐dimensional parameters of light is urgently desired in high‐speed processing and reliable transmission of massive information. In article number 2201088, Zhi‐Gang ...Zheng, Yan‐Qing Lu, Wei Hu and co‐workers present a heliconical cholesterics‐based spatial phase modulator with electrically customizable working frequency. The device simultaneously manipulates the spatial phase and wavelength/frequency of light via photoaligning the initial orientation of the liquid crystal and electrically varying the pitch of the heliconical superstructure, respectively. It supplies a platform for multidimensional planar optics that may upgrade existing optical informatics.
Using tools and concepts from contact topology we show that non-vanishing twist implies conservation of the layer structure in cholesteric liquid crystals. This leads to a number of additional ...topological invariants for cholesteric configurations, such as layer numbers, that are not captured by traditional descriptions, characterises the nature and size of the chiral energy barriers between metastable configurations, and gives a geometric characterisation of cholesteric dynamics in any context, including active systems, those in confined geometries or under the influence of an external field.
Smart windows are crucial to dynamic control over light transmission to fulfill various demands in energy saving, privacy, and information display; however, most present technologies still perform a ...single function (often tint or haze adjustment) and require continuous electricity for operation. In this study, novel self‐assembled ionic liquid crystals (ILCs) doped with negative cholesteric liquid crystals (CLCs) to offer electrically switchable and stable scattering‐mode light modulators are presented. The novel smectic A phase based on the ILCs exhibits high solubility in the adopted nematics, enhancing the LC device's performance in several ways, including improved homogeneity, stable alignment quality, prolonged stability, and simplified fabrication. The LC device can potentially offer a dynamically rapid switching function between stable transparent (imperfect fingerprint textures) states and stable scattering (focal conic textures with small domains) states by using external stimuli and highly maintained multistable states for prolonged periods, even when the external stimuli are removed. The LC device also offers polarization‐independent scattering and transparent‐mode LC light modulators, low operating voltage, excellent contrast, and broad viewing angles. Its versatility and outstanding field‐off stability make it ideal for various applications such as smart lighting, building climate control, energy‐saving displays, and augmented reality (AR) glasses.
Explore the groundbreaking study on self‐assembled ionic liquid crystals and negative cholesteric liquid crystals for energy‐saving smart windows. This innovation enables electrically switchable and stable scattering‐mode light modulators, offering dynamic control over light transmission. The approach enhances homogeneity, alignment quality, and stability, providing versatile applications in energy‐saving windows, privacy control, and advanced display devices.
Multidimensional and large‐scale parallel manipulation of light, especially on‐demand tailoring of the working frequency and spatial phase front, is highly pursued in modern optics. Here, broadband ...tunable planar optics is demonstrated by electrically driving the nanohelix of photopatterned heliconical cholesterics. By preprogramming the initial orientation of the helixes using a dynamic‐mask photoalignment technique, spatial geometric phases can be arbitrarily encoded to the reflected light in a reconfigurable way. Due to the reversible electrically variant pitch of the heliconical superstructures, the reflective Bragg band can be precisely selected in the range from 380 to 1550 nm. In addition to wavelength selection and geometric phase modulation, spatial amplitude modulation and spin reversion can be further expected. This may offer a platform for full‐dimensional manipulation of light, including wavelength/frequency, phase, amplitude, time, and spin, thus upgrading optical information processing techniques.
A strategy for a spatial phase modulator with an electrically customizable working band is proposed via heliconical cholesterics. The photoalignment technique is adopted to realize arbitrary geometric phases. Electrically controllable heliconical superstructures enable working band selectivity over a broad range from near‐UV to near‐IR. This work enriches chiral superstructure manipulation and will upgrade present optical systems.
PyLlama is a handy Python toolkit to compute the electromagnetic reflection and transmission properties of arbitrary multilayered linear media, including the case of anisotropy. Relying on a ...4×4-matrix formalism, PyLlama implements not only the transfer matrix method, that is the most popular choice in existing codes, but also the scattering matrix method, which is numerically stable in all situations (e.g., thick, highly birefringent cholesteric structures at grazing incident angles). PyLlama is also designed to suit the practical needs by allowing the user to create, edit and assemble layers or multilayered domains with great ease. In this article, we present the electromagnetic theory underlying the transfer matrix and scattering matrix methods and outline the architecture and main features of PyLlama. Finally, we validate the code by comparison with available analytical solutions and demonstrate its versatility and numerical stability by modelling cholesteric media of varying complexity. A detailed documentation and tutorial are provided in a separate user manual. Applications of PyLlama range from the design of optical components to the modelling of polaritonic effects in polar crystals, to the study of structurally coloured materials in the living world.
Program Title: PyLlama – Python Toolkit for the Electromagnetic Modelling of Multilayered Anisotropic Media
CPC Library link to program files:https://doi.org/10.17632/dzw8x5vyrv.1
Developer's repository link:https://github.com/VignoliniLab/PyLlama
Licensing provisions: GPLv3
Programming language: Python
Supplementary material: User guide and tutorials at https://pyllama.readthedocs.io/
Nature of problem: Computation of the optical reflection and transmission coefficients of arbitrary multilayered linear media, composed of an arbitrary number of layers, possibly mixing isotropic and anisotropic, absorbing and non-absorbing materials, for linearly or circularly polarised light.
Solution method: Implementation of both the transfer matrix method (faster) and the scattering matrix method (more robust) relying on a 4×4 matrix formalism.
Additional comments including restrictions and unusual features: Integration of a physical model to handle cholesteric structures, blueprint for the integration of user-created custom systems, hassle-free export of spectra for non-programmers even for complex and/or custom systems. External routines include: Numpy 1, Scipy 2, as well as Sympy 3 (optional).
1Numpy, https://numpy.org/.2Scipy, https://www.scipy.org/.3Sympy, https://www.sympy.org/.
Large‐scale color changes (100s of nm) in polymer‐stabilized cholesteric liquid crystals with a negative dielectric anisotropy are presented. Reflection peak tuning is enabled with DC electric fields ...through a unique peak splitting behavior. This simple approach can be applied in a variety of photonic applications.
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