Rotatable Diffraction Gratings Based on Cholesteric Liquid Crystals with Phototunable Helix Pitch

Ryabchun, Alexander; Bobrovsky, Alexey; Stumpe, Joachim; Shibaev, Valéry

doi:10.1002/adom.201500159

Cited by 91 publications

(66 citation statements)

References 41 publications

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“…Since the considered optical texture does not get dark completely during the sample rotation on the microscope stage relative to the crossed polarizers (Figure 1b, c), it means that the twisted orientation structure is formed within the LC layer. Thus, the optical textures of the LC layer presented in Figure 1b,c correspond to the hybrid aligned cholesteric [29][30][31][32][33]. Its orientational structure is shown in Figure 2b.…”

Section: Resultsmentioning

confidence: 99%

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

et al. 2016

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A reorientation of cholesteric liquid crystal with a large helix pitch induced by the electrically controlled ionic modification of the surface anchoring has been studied. In initial state, the cholesteric helix is untwisted completely owing to the normal surface anchoring specified by the cations adsorbed at the substrates. As a result, the homeotropic director configuration is observed within the cell. Under the action of dc electric field, one of the substrates becomes free from the layer of surface active cations, therefore, setting the planar surface anchoring. The latter, in turn, leads to the formation of the hybrid chiral structure. The threshold value and dynamic parameters have been estimated for this process as well as the range of control voltages, which do not allow the electrohydrodynamic instabilities. The twisted hybrid director configuration observed in the experiment has been analyzed by means of the simulation of polarization change of light propagating through the cholesteric layer with asymmetric (planar and homeotropic) surface anchoring on the cell substrates.

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Section: Resultsmentioning

confidence: 99%

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

et al. 2016

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“…A similar approach has also been employed, [259] but with far reaching outcome. Under UV irradiation, the twisting power of the tunable dopant weakens and the mixture goes through the nematic LC and then to the CLC with opposite handedness.…”

Section: Light-switched Cholesteric Lc Gratingmentioning

confidence: 99%

“…Lin et al designed a rotatable grating [270] whose working principle is similar to the light-driven rotatable grating, [259] but the driving stimulus was heat. The authors used two commercially available components, namely, E7 (nematic host) and 4-(2-methylbutyl)-4-cyanobiphenyl (CB15) chiral dopant, to produce CLCs with the d/P ratio ranging from 2.2 to 3.0 and filled the mixtures in hybrid aligned cells.…”

Section: Thermally Switched Cholesteric Lc Gratingsmentioning

confidence: 99%

Dynamic Control of Light Direction Enabled by Stimuli‐Responsive Liquid Crystal Gratings

et al. 2018

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the duality consolidation, the idea of controlling light and how it interacts with matter has always been an exciting topic. Visible light, as we perceive it, is a small portion of the electromagnetic spectrum composed of mutually perpendicular oscillating electric and magnetic fields that propagate through space and presents wave-like and particle-like behavior. Since the elements comprising matter possess dynamic electron clouds, the electromagnetic nature of light prompts different responses when it interacts with different materials, depending on its intensity, frequency, the arrangement of molecules, and so on. Whenever light interacts with matter, it might be absorbed, re-emitted, scattered, or transmitted. Although these effects are well known, the combination of them with new, innovative materials pushes optics forward. In fact, advances in optics have often occurred through the development of materials with improved optical properties, thus creating remarkable applications that tremendously influence our daily lives. These exciting applications include image processing and recording, lasing, data storage, display devices, detector systems, propulsion systems, and optical tweezers, which have enabled remote micromanipulation of colloidal particles and promising applications in various biomedical and biological applications. [1][2][3] There is, however, one component that stands out: the diffraction grating. It is generally regarded as one of the most important devices in the development of several fields of science. [4] Such importance comes from the fact that a diffraction grating is a device with a periodic structure capable of changing the propagation and splitting the spectrum The ability to control light direction with tailored precision via facile means is long-desired in science and industry. With the advances in optics, a periodic structure called diffraction grating gains prominence and renders a more flexible control over light propagation when compared to prisms. Today, diffraction gratings are common components in wavelength division multiplexing devices, monochromators, lasers, spectrometers, media storage, beam steering, and many other applications. Next-generation optical devices, however, demand nonmechanical, full and remote control, besides generating higher than 1D diffraction patterns with as few optical elements as possible. Liquid crystals (LCs) are great candidates for light control since they can form various patterns under different stimuli, including periodic structures capable of behaving as diffraction gratings. The characteristics of such gratings depend on several physical properties of the LCs such as film thickness, periodicity, and molecular orientation, all resulting from the internal constraints of the sample, and all of these are easily controllable. In this review, the authors summarize the research and development on stimuli-controllable diffraction gratings and beam steering using LCs as the active optical materials. Dynamic gratings fabricated by applying external f...

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“…Beam steering of more than one dimension could be achieved in some optical phased arrays [17][18][19] and cholesteric liquid crystal grating; [16,[20][21][22] however, grating-based deflectors usually suffer from strong dispersion in deflection angle and low deflection efficiency which results from light leakage to other orders of diffraction. Beam steering of more than one dimension could be achieved in some optical phased arrays [17][18][19] and cholesteric liquid crystal grating; [16,[20][21][22] however, grating-based deflectors usually suffer from strong dispersion in deflection angle and low deflection efficiency which results from light leakage to other orders of diffraction.…”

Section: Doi: 101002/adom201600824mentioning

confidence: 99%

Arbitrary Beam Steering Enabled by Photomechanically Bendable Cholesteric Liquid Crystal Polymers

Chen

et al. 2017

Advanced Optical Materials

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Beam-steering technology is now in widespread use in a variety of optical systems, spanning from fiber-optic interconnector to Lidar. Most current techniques are based on optical grating diffractions; they are thus subject to not only finite tuning range, direction, and efficiency but also complex inorganic fabrication and circuit design. A high-degree-of-freedom beamsteering element makes such operations more efficient and versatile. Azobenzene cholesteric liquid crystal polymer (azo-ChLCP) can be regarded as a soft self-assembled Bragg mirror capable of being bent photomechanically. With proper control of pump polarization and exposure time, the output beam can be directly steered to an arbitrary direction. The deflection efficiency was achieved to be at least 90% with an angular tuning range of ≈54°, which is markedly superior to conventional grating-based devices. Additionally, the angle of deflection is independent of wavelength, preventing the deflected beam from spreading out with colors. This work demonstrates and characterizes the azo-ChLCP beam deflector, which features optical tunability, high efficiency, wide tuning range, and polarization-selective deflection direction, making a significant breakthrough in beam-steering technology.

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Rotatable Diffraction Gratings Based on Cholesteric Liquid Crystals with Phototunable Helix Pitch

Abstract: a chiral additive (dopant) characterized by the defi nite helical twisting power, β ; this phenomenological parameter shows an ability of the dopant to twist the nematic structure (Equation ( 1) ):

Cited by 91 publications

References 41 publications

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

Dynamic Control of Light Direction Enabled by Stimuli‐Responsive Liquid Crystal Gratings

Arbitrary Beam Steering Enabled by Photomechanically Bendable Cholesteric Liquid Crystal Polymers

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