Rotatable diffractive gratings based on hybrid-aligned cholesteric liquid crystals

Lin, Chi‐Huang; Chiang, Ru-Hsien; Liu, Shu-Hao; Kuo, Chie‐Tong; Huang, Chi Yen

doi:10.1364/oe.20.026837

Cited by 42 publications

(24 citation statements)

References 21 publications

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“…Another obvious way to change the cholesteric helix pitch is by applying electric field that leads to the unwinding of helix, i.e., P increases. Using the above‐mentioned system, the grating rotation angle of ≈48° was achieved (Figure b) . In this case, rotation in opposite (clockwise) direction was observed.…”

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 88%

“…The vertically aligned LC layer model proposed in ref. describes the rotation of the stripes in the direct vicinity to the substrate with homeotropic boundary conditions. The azimuthal angle of LC director orientation (φ) near the vertically aligning substrate governs the orientation of the periodic striped pattern (diffraction grating) according to Equation

φ = 2 π (d normal/ P)

…”

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

“…The easiest way to control cholesteric pitch is by temperature, which often leads to helix winding, i.e., P decreases. So, the authors used nematic E7 doped with chiral molecules CB15 and were able to achieve ≈101° of continuous counterclockwise rotation of the DG, while increasing the thickness of the sample (or d / P ) brought about an increase in the maximum angle of grating rotation ( Figure a). The authors noted that for a good quality of the gratings, the confinement ratio ( d / P ) should be in the range of 2÷3.…”

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

“…Rotation of striped texture (DG) of hybrid‐aligned CLC layer of 5 µm thickness upon a) increasing temperature and b) applied voltage. a,b) Reproduced with permission . Copyright 2012, OSA Publishing.…”

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

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Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Ryabchun

Bobrovsky

2018

Advanced Optical Materials

196

106

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refractive, diffraction and optical fiber components. In particular, diffraction grating (DG) is one of the key elements for the design and creation of modern optoelectronic devices. One of the most prominent materials for the creation of DGs is liquid crystals. The main feature of these systems is that liquid crystals combine properties such as optical anisotropy inherent for crystals and molecular mobility. High sensitivity to an external field, in particular to an electric field, makes liquid crystals very useful for the creation of DGs with tunable properties. The combination of these properties enables easy control of optical characteristics of such systems and opens wide perspectives for the design of new materials for diffractive optics.Among the different types of liquid crystalline (LC) phases, cholesteric liquid crystal (CLC) phase possesses intrinsic periodicity in the form of the helical supramolecular structure (Figure 1). With the realization of definite alignment conditions, this periodicity has been exploited for generation of DGs. [8,9] Another remarkable feature of the cholesteric mesophase is selective light reflection with the reflection wavelength determined by the simple Equation (1) where n is the average refractive index, and P is the helix pitch. The specific value of helix pitch depends on the chemical structure of the molecules forming the cholesteric phase and concentration of chiral moieties. One of the easiest ways to obtain the cholesteric mesophase is by doping the nematic matrix with chiral components (Figure 1). Variation of structure of chiral molecules by external stimuli leading, for examples, to the photoisomerization, is effectively used for fine tuning of the helix pitch. [10][11][12][13][14][15][16][17] In addition, the application of an electric field also provides a convenient opportunity to change optical properties of the CLC phase. [18][19][20][21] These unique properties enable to design a great variety of optical elements and devices based on CLC layers, films, or cells. Among them it is necessary to mention the media for photo-optical data recording, [22][23][24][25] electrically switchable mirrors, [26,27] optically controllable linearpolarization rotators, [28] coatings with controllable friction and adhesion, [29] materials for display technology, [23,30] secure Modern optics and photonics constantly require break-through materials and designs in order to achieve miniature, lightweight, highly tunable, and effective optical devices. One of the basic optical components is the diffraction grating (DG), widely used for the dispersion of light, beam steering, etc. This review gathers research efforts on diffractive optical elements based on cholesteric liquid crystal (CLC) materials with a supramolecular helical architecture. All main types and fabrication approaches of periodic diffractive structures from CLCs are classified and described. Key optical properties of DGs, their advantages and drawbacks are considered. Special attention is paid on the tunability of DG...

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Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 88%

φ = 2 π (d normal/ P)

…”

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

Section: Periodic Structures Spontaneously Forming In Clc Layersmentioning

confidence: 99%

See 2 more Smart Citations

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Ryabchun

Bobrovsky

2018

Advanced Optical Materials

196

106

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“…Cholesteric helical superstructures with uniform lying helical axes are very suitable to be used as self‐assembled phase gratings due to their periodic phase profiles . Recently, multivariant controlling methods have been proposed to effectively tune the hierarchical architectures of CLCs 39b,74. Accordingly, such CLC gratings are endowed with a wide tunability of grating period and rotation, which is highly promising in beam steering applications …”

Section: Photonic Applicationsmentioning

confidence: 99%

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

Zheng

et al. 2019

Advanced Optical Materials

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remarkable structure results in a helical-variant dielectric tensor, thus contributing to a natural 1D photonic crystal. [7] It is endowed with a broadband Bragg reflection with a unique circular-polarization selectivity. Blue phase (BP) is another fantastic phase with 3D stacked lattice ( Figure 1D). [8] Such an elegant state-of-matter is energetically preferred in a high chirality system, commonly existing in a narrow temperature range of less than 1 K, between the cholesteric and isotropic phases. It has an exotic arrangement characteristic of LCs, which twists around two helical axes forming cylinders including hierarchically twisted molecular architectures. Such double twisted cylinders are impossible to tile the whole 3D space, which leads to inevitable disclinations and results in frustrated structures.Self-organization is an intrinsic ability of LC molecules. However, the precise control and generation of large-area desirable hierarchical superstructures require state-of-the-art techniques that usually combine the "top-down" microfabrication with the "bottom-up" self-assembly. Here, we review various hierarchical architectures in SLCs, CLCs, and BPLCs, especially recent progresses in light-activated LC hierarchical superstructures, as well as their optics and photonics applications in optics and photonics. In this review, we will see the controllable spatial smectic layer curving via 2D anchoring confinement, 3D topographic confinement, and external field guidance, with which the domain size, shape, orientation, and lattice symmetry of focal conic domain (FCD) arrays are well manipulated. The control of helix direction or fluctuation of CLC layers and the growth of unique fingerprint textures including spiral and wave-like continuous gratings are presented. The 3D manipulation of BPLC hierarchical architecture is accomplished photoalignment and various light-driven azobenzene molecular motors. The construction of these unique hierarchical superstructures brings new opportunities to the design of novel optic and photonic devices. Corresponding applications, including traditional microlens array, beam steering, and more advanced specific optical field generation and LC lasers are comprehensively reviewed as well.

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Stimuli‐Directed Helical Axis Switching in Chiral Liquid Crystal Nanostructures

2018

Functional Organic and Hybrid Nanostructured Materials

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Rotatable diffractive gratings based on hybrid-aligned cholesteric liquid crystals

Cited by 42 publications

References 21 publications

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

Stimuli‐Directed Helical Axis Switching in Chiral Liquid Crystal Nanostructures

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