Special Issue "Localized Optical Modes in Liquid Crystals"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (30 June 2020).

Special Issue Editors

Prof. Dr. Vladimir A. Belyakov
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Guest Editor
Landau Institute for Theoretical Physics, Russian Academy of Sciences, Moscow, Russia
Dr. Sergei V. Semenov
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Guest Editor
National Investigation Centre Kurchatov Institute, Moscow, Russia
Interests: spiral media; liquid crystals; localized optical modes; DFB lasing

Special Issue Information

Dear Colleagues,

A new field of optical research has emerged over the last three recent decades that relates to the optics of periodic structures, with the value of periodicity comparable to the optical wavelength, which has been named photonics. Photonics has revealed many important phenomena that are well applied in the optical wavelength range. The reason for this is related to the fact that virtually all photonics-related effects are within the capacity of experimental observation at the contemporary level of optical techniques, while most of the corresponding effects in the X-ray wavelength range (where photonics was invented in the beginning of 20th century, under the name "X-ray diffraction") are out of the capacity of experimental observation at the present level of X-ray techniques. Photonics researches have shown that many photonics-related optical processes are more efficient than the corresponding processes in homogeneous media; a known example is a low threshold lasing. The photonics terminology proposes the term "photonic crystal", related to a periodic medium whose period value is in the range of the optical wavelengths, in order to distinguish the photonic crystals from the conventional crystals. In the proposed issue, a special type of photonic crystal is studied, namely spiral photonic liquid crystals. This kind of photonic crystal has, at any rate, two essential advantages compared with the conventional crystals. One of them, a theoretical one, is connected with the existence of a simple exact solution of the Maxwell's equations, allowing for the development of an analytical theory of the photonic liquid crystal optics. The second, an experimental one, is connected with the liquid crystal softness, allowing for their parameters to be easily modified by weak external actions (applied electric and magnetic fields, temperature changing, and so on), which is important for achieving a needed set of parameters for the experiment. It is why the studies of the photonic effects in liquid crystals are of interest, not only for the physics of liquid crystals themselves, but also for the whole solid-state physics, because liquid crystals may be regarded as model objects in studies of solid-state effects. The main objects of study for the proposed issue are localized optical modes in liquid crystals, so called, edge (EM) and defect (DM) modes. It was demonstrated that many optical phenomena occurring at the frequencies of localized modes revealed unusual properties that could be used for efficient applications of the corresponding phenomena—for example, efficient frequency conversion, low threshold lasing, and so on. These features are the main reasons for producing the proposed Special Issue. The Special Issue on “Localized Optical Modes in Liquid Crystals” is intended to provide a unique international forum aimed at covering a broad description of the results, involving the optics of photonic crystal as linear or nonlinear, and, especially, lasing. Scientists working in a wide range of disciplines are invited to contribute to this cause.

The topics summarized under the keywords broadly cover examples of the greater number of sub-topics in mind. The volume is open for any innovative contributions involving all aspects of the photonic crystal optics in particular related to the edge (EM) and defect (DM) modes.

Prof. Dr. Vladimir A. Belyakov
Dr. Sergei V. Semenov
Guest Editors

Manuscript Submission Information

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Keywords

  • Interaction of radiation with the matter
  • Liquid crystals
  • Localized optical modes
  • Surface anchoring in liquid crystals

Published Papers (8 papers)

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Research

Open AccessArticle
Optical Kossel Lines and Fluorescence in Photonic Liquid Crystals
Crystals 2020, 10(6), 541; https://doi.org/10.3390/cryst10060541 - 24 Jun 2020
Cited by 1 | Viewed by 520
Abstract
We propose a general analytical way to describe the fluorescence peculiarities in photonic liquid crystals (revealing themselves as an optical analog of the X-ray Kossel lines in conventional crystals) based at the localized optical edge modes existing in perfect photonic liquid crystal layers. [...] Read more.
We propose a general analytical way to describe the fluorescence peculiarities in photonic liquid crystals (revealing themselves as an optical analog of the X-ray Kossel lines in conventional crystals) based at the localized optical edge modes existing in perfect photonic liquid crystal layers. The proposed approach allows us to predict theoretically the properties of optical Kossel lines in photonic liquid crystal (fluorescence polarization, spectral and angular fluorescence distribution, influence of the light absorption in liquid crystal, and, in particular, existing the optical Borrmann effect if the absorption in liquid crystal is locally anisotropic). Comparison of the theoretical results and the known experimental data shows that the theory reproduces sufficiently well the observation results on the fluorescence in photonic liquid crystals. For confirming a direct connection of the optical Kossel lines to the localized optical edge modes in perfect photonic liquid crystal, we propose the application of time-delayed techniques in studying the optical Kossel lines. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Localized Conical Edge Modes in Optics of Spiral Media (First Diffraction Order)
Crystals 2019, 9(12), 674; https://doi.org/10.3390/cryst9120674 - 16 Dec 2019
Cited by 1 | Viewed by 554
Abstract
In cholesteric liquid crystals (CLC) problems related to the localized optical modes for a non-collinear geometry are studied here in the two wave dynamic diffraction theory approximation. This approximation, which insures the results accuracy order of δ (where δ is the CLC dielectric [...] Read more.
In cholesteric liquid crystals (CLC) problems related to the localized optical modes for a non-collinear geometry are studied here in the two wave dynamic diffraction theory approximation. This approximation, which insures the results accuracy order of δ (where δ is the CLC dielectric anisotropy), is applied because for a non-collinear geometry there is no exact analytic solution of the Maxwell equations and a theoretical description of the experimental data becomes more complicated. The dispersion equation for non-collinear localized edge modes (called conical modes (CEM)) is found and analytically solved for the case of thick layers and for this case the lasing threshold and the conditions of the anomalously strong absorption effect are found. It is shown that qualitatively CEMs are very similar to the localized edge modes (EM) in CLCs related to a collinear geometry, i.e., for the case of light propagation along the spiral axis however the CEMs differ by their polarization properties (the CEM eigen polarizations are elliptical ones depending on the degree of CEM deviation from the collinear geometry in contrast to the circular eigen polarizations in the EM case). What is concerned of the CEM quantitative values of the parameters they are “worth” (the photonic effects are not so pronounced) than for the corresponding ones for EM. The CEM lasing threshold is higher than the one for EM, etc. Performed theoretical studies of possible conversion of EMs into CEMs showed that it can be due to the EM reflection at dielectric boundaries at the conditions of a high pumping wave focusing. Known experimental results on the CEM are discussed and optimal conditions for CEM observations are formulated. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Thermo-Optical Generation of Particle-Like Structures in Frustrated Chiral Nematic Film
Crystals 2019, 9(11), 574; https://doi.org/10.3390/cryst9110574 - 31 Oct 2019
Cited by 2 | Viewed by 808
Abstract
The creation of metastable particle-like structures in frustrated (unwound) chiral nematic film containing light-absorbing additive is studied. It is shown that such localized structures can be generated by the thermo-optical action of a focused laser beam or arise spontaneously at a phase transition [...] Read more.
The creation of metastable particle-like structures in frustrated (unwound) chiral nematic film containing light-absorbing additive is studied. It is shown that such localized structures can be generated by the thermo-optical action of a focused laser beam or arise spontaneously at a phase transition from an isotropic to a liquid crystal state. Observed axisymmetric patterns resemble cholesteric spherulites with toroidal double-twisted director-field configuration. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Localized Conical Edge Modes of Higher Orders in Photonic Liquid Crystals
Crystals 2019, 9(10), 542; https://doi.org/10.3390/cryst9100542 - 20 Oct 2019
Cited by 3 | Viewed by 682
Abstract
Most studies of the localized edge (EM) and defect (DM) modes in cholesteric liquid crystals (CLC) are related to the localized modes in a collinear geometry, i.e., for the case of light propagation along the spiral axis. It is due to the fact [...] Read more.
Most studies of the localized edge (EM) and defect (DM) modes in cholesteric liquid crystals (CLC) are related to the localized modes in a collinear geometry, i.e., for the case of light propagation along the spiral axis. It is due to the fact that all photonic effects in CLC are most pronounced just for a collinear geometry, and also partially due to the fact that a simple exact analytic solution of the Maxwell equations is known for a collinear geometry, whereas for a non-collinear geometry, there is no exact analytic solution of the Maxwell equations and a theoretical description of the experimental data becomes more complicated. It is why in papers related to the localized modes in CLC for a non-collinear geometry and observing phenomena similar to the case of a collinear geometry, their interpretation is not so clear. Recently, an analytical theory of the conical modes (CEM) related to a first order of light diffraction was developed in the framework of the two-wave dynamic diffraction theory approximation ensuring the results accuracy of order of δ, the CLC dielectric anisotropy. The corresponding experimental results are reasonably well described by this theory, however, some numerical problems related to the CEM polarization properties remain. In the present paper, an analytical theory of a second order diffraction CEM is presented with results that are qualitatively similar to the results for a first order diffraction order CEM and have the accuracy of order of δ2, i.e., practically exact. In particular, second order diffraction CEM polarization properties are related to the linear σ and π polarizations. The known experimental results on the CEM are discussed and optimal conditions for the second order diffraction CEM observations are formulated. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Miniaturized Metalens Based Optical Tweezers on Liquid Crystal Droplets for Lab-on-a-Chip Optical Motors
Crystals 2019, 9(10), 515; https://doi.org/10.3390/cryst9100515 - 07 Oct 2019
Cited by 2 | Viewed by 1116
Abstract
Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar [...] Read more.
Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar optical components capable of focusing light. The lens made of arrays of plasmonic gold nanorods were fabricated on a glass substrate by using electron beam lithography. A 1064 nm laser was used to create a high intensity circularly polarized light focal spot through metalens of focal length 800 µm, N.A. = 0.6 fabricated based on Pancharatnam-Berry phase principle. We demonstrated that optical rotation of birefringent nematic liquid crystal droplets trapped in the laser beam was possible through this metalens. The rotation of birefringent droplets convinced that the optical trap possesses strong enough angular momentum of light from radiation of each nanostructure acting like a local half waveplate and introducing an orientation-dependent phase to light. Here, we show the success in creating a miniaturized and robust metalens based optical tweezers system capable of rotating liquid crystals droplets to imitate an optical motor for future lab-on-a-chip applications. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Chiral Optical Tamm States at the Interface between an All-Dielectric Polarization-Preserving Anisotropic Mirror and a Cholesteric Liquid Crystal
Crystals 2019, 9(10), 502; https://doi.org/10.3390/cryst9100502 - 26 Sep 2019
Cited by 7 | Viewed by 1225
Abstract
As a new localized state of light, the chiral optical Tamm state exists at the interface between a polarization-retaining anisotropic mirror and a substance with optical activity. Considering a hybrid structure comprising a metal-free polarization-preserving mirror and a cholesteric liquid crystal, we highlight [...] Read more.
As a new localized state of light, the chiral optical Tamm state exists at the interface between a polarization-retaining anisotropic mirror and a substance with optical activity. Considering a hybrid structure comprising a metal-free polarization-preserving mirror and a cholesteric liquid crystal, we highlight the high Q factor arising from the all-dielectric framework. The intensity of localized light decreases exponentially with increasing distance from the interface. The penetration of the field into the cholesteric liquid crystal is essentially prohibited for wavelengths lying in the photonic bandgap and close to the cholesteric pitch length. The dielectric mirror has its own photonic bandgap. The energy transfer along the interface can be effectively switched off by setting the tangential wave vector to zero. The spectral behavior of the chiral optical Tamm state is observed both as reflection and transmission resonance. This Fano resonance is analogous to the Kopp–Genack effect. Our analytics are well in line with precise calculations, which may pave a new route for the future development of intelligent design for laser and sensing applications. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Magnetic Field-Induced Macroscopic Alignment of Liquid-Crystalline Lanthanide Complexes
Crystals 2019, 9(10), 499; https://doi.org/10.3390/cryst9100499 - 25 Sep 2019
Cited by 3 | Viewed by 933
Abstract
We propose a theoretical approach and a numerical method for determining the Frank elastic constants based on the experimental dependence of the effective values of the permittivity components on the magnetic field. The theoretical task was to find the minimum of the free [...] Read more.
We propose a theoretical approach and a numerical method for determining the Frank elastic constants based on the experimental dependence of the effective values of the permittivity components on the magnetic field. The theoretical task was to find the minimum of the free energy and then to solve the inverse problem on finding elastic constants by the least squares root minimizing with experimental data. The proposed approach combines strong and weak models with various pretilt conditions at the boundaries. This model also describes the inhomogeneity of the electric field inside the sample. The proposed method allows to achieve higher accuracy using a small amount of experimental data. This statement is confirmed by the error estimation study, which is also presented in this research. As an experimental sample, we used the gadolinium-based liquid crystal complex, since there are no data on the Frank elastic constants for this complex. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix
Crystals 2019, 9(9), 469; https://doi.org/10.3390/cryst9090469 - 08 Sep 2019
Cited by 1 | Viewed by 841
Abstract
Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC [...] Read more.
Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC layer, is induced by an electric field in a virtual CLC cell with periodic (planar/homeotropic) boundary conditions at one of the alignment surfaces. This in-plane helical structure is stable only in a permanently applied electric field providing the helix deformation. In this work the polarized light reflectance spectra have been studied at different electric fields and light impingement into a waveguide formed by the DLH layer. It is found that for light propagating along the helix axis the reflectance spectrum has multiple stop-bands centred at wavelengths λ j = 2 p n j , which is different from set of bands located at λ j = p n j , and characteristic of CLC spectra for the Grandjean-plane textures subjected to distortion by an electric or magnetic field perpendicular to the helix axis, where j is a natural number, p is the helix pitch and n is the average refractive index. Each of the higher order (j > 1) bands consists of three polarization-dependent sub-bands. In the case of an amplifying CLC DLH layer, depending on an extent of the helix deformation, the lasing modes can be excited at different edges of the sub-bands. While at the strongest deformation the lasing is preferable at the edges of the central sub-band; a lower extent of deformation makes favourable conditions for the lasing at edges of the two other sub-bands. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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