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4 pages, 191 KiB

Open AccessEditorial

Special Issue: Soft Photonic Crystals and Metamaterials

by Ivan V. Timofeev and Wei Lee

Materials 2022, 15(22), 8096; https://doi.org/10.3390/ma15228096 - 16 Nov 2022

Viewed by 979

Abstract

Soft matters include polymers, liquid crystals, colloids, biological tissues, and many smart materials [...] Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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7 pages, 6198 KiB

Open AccessEditor’s ChoiceArticle

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton

by Rashid G. Bikbaev, Dmitrii N. Maksimov, Kuo-Ping Chen and Ivan V. Timofeev

Materials 2022, 15(17), 6014; https://doi.org/10.3390/ma15176014 - 31 Aug 2022

Cited by 11 | Viewed by 1616

Abstract

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The [...] Read more.

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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21 pages, 8165 KiB

Open AccessArticle

Synthesis and Spatial Order Characterization of Controlled Silica Particle Sizes Organized as Photonic Crystals Arrays

by Silvia Adriana Estrada Alvarez, Isabella Guger, Jana Febbraro, Ayse Turak, Hong-Ru Lin, Yolanda Salinas and Oliver Brüggemann

Materials 2022, 15(17), 5864; https://doi.org/10.3390/ma15175864 - 25 Aug 2022

Cited by 3 | Viewed by 1896

Abstract

The natural occurrence of precious opals, consisting of highly organized silica particles, has prompted interest in the synthesis and formation of these structures. Previous research has shown that a highly organized photonic crystal (PhC) array is only possible when it is based on [...] Read more.

The natural occurrence of precious opals, consisting of highly organized silica particles, has prompted interest in the synthesis and formation of these structures. Previous research has shown that a highly organized photonic crystal (PhC) array is only possible when it is based on a low polydispersity index (PDI) sample of particles. In this study, a solvent-only variation method is used to synthesize different sizes of silica particles (SiPs) by following the traditional sol-gel Stöber approach. The controlled rate of the addition of the reagents promoted the homogeneity of the nucleation and growth of the spherical silica particles, which in turn yielded a low PDI. The opalescent PhC were obtained via self-assembly of these particles using a solvent evaporation method. Analysis of the spatial statistics, using Voronoi tessellations, pair correlation functions, and bond order analysis showed that the successfully formed arrays showed a high degree of quasi-hexagonal (hexatic) organization, with both global and local order. Highly organized PhC show potential for developing future materials with tunable structural reflective properties, such as solar cells, sensing materials, and coatings, among others. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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11 pages, 2419 KiB

Open AccessArticle

Size-Controllable Synthesis of Monodisperse Magnetite Microparticles Leading to Magnetically Tunable Colloidal Crystals

by Toya Seki, Yutaro Seki, Naoto Iwata and Seiichi Furumi

Materials 2022, 15(14), 4943; https://doi.org/10.3390/ma15144943 - 15 Jul 2022

Cited by 2 | Viewed by 1275

Abstract

Colloidal crystals (CCs) are periodic arrays of monodisperse microparticles. Such CCs are very attractive as they can be potentially applicable as versatile photonic devices such as reflective displays, sensors, lasers, and so forth. In this article, we describe a promising methodology for synthesizing [...] Read more.

Colloidal crystals (CCs) are periodic arrays of monodisperse microparticles. Such CCs are very attractive as they can be potentially applicable as versatile photonic devices such as reflective displays, sensors, lasers, and so forth. In this article, we describe a promising methodology for synthesizing monodisperse magnetite microparticles whose diameters are controllable in the range of 100–200 nm only by adjusting the base concentration of the reaction solution. Moreover, monodisperse magnetite microparticles in aqueous suspensions spontaneously form the CC structures under an external magnetic field, leading to the appearance of Bragg reflection colors. The reflection peak can be blue-shifted from 730 nm to 570 nm by the increase in the external magnetic field from 28 mT to 220 mT. Moreover, the reflection properties of CCs in suspension depend on the microparticle concentration in suspension and the diameter of the magnetite microparticles. Both fine-control of microparticle diameter and investigation of magneto-optical properties of CCs would contribute to the technological developments in full-color reflective displays and sensors by utilizing these monodisperse magnetite microparticles. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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11 pages, 3265 KiB

Open AccessArticle

Effect of Host Structure on Optical Freedericksz Transition in Dye-Doped Liquid Crystals

by Junki Yokota, Kohsuke Matsumoto, Koji Usui, Shoichi Kubo and Atsushi Shishido

Materials 2022, 15(12), 4125; https://doi.org/10.3390/ma15124125 - 10 Jun 2022

Cited by 2 | Viewed by 1918

Abstract

The optical Freedericksz transition (OFT) can reversibly control the molecular orientation of liquid crystals (LCs) only by light irradiation, leading to the development of all-optical devices, such as smart windows. In particular, oligothiophene-doped LCs show the highly sensitive OFT due to the interaction [...] Read more.

The optical Freedericksz transition (OFT) can reversibly control the molecular orientation of liquid crystals (LCs) only by light irradiation, leading to the development of all-optical devices, such as smart windows. In particular, oligothiophene-doped LCs show the highly sensitive OFT due to the interaction between dyes and an optical-electric field. However, the sensitivity is still low for the application to optical devices. It is necessary to understand the factors in LCs affecting the OFT behavior to reduce the sensitivity. In this study, we investigated the effect of the host LC structure on the OFT in oligothiophene-doped LCs. The threshold light intensity for the OFT in trifluorinated LCs was 42% lower than that in LCs without fluorine substituents. This result contributes to the material design for the low-threshold optical devices utilizing the OFT of dye-doped LCs. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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12 pages, 5505 KiB

Open AccessEditor’s ChoiceArticle

Photoaligned Liquid Crystal Devices with Switchable Hexagonal Diffraction Patterns

by Inge Nys, Brecht Berteloot and Kristiaan Neyts

Materials 2022, 15(7), 2453; https://doi.org/10.3390/ma15072453 - 26 Mar 2022

Cited by 3 | Viewed by 1726

Abstract

Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns [...] Read more.

Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns at the surfaces, we experimentally stabilize two dimensional periodic LC configurations with switchable hexagonal diffraction patterns. The alignment direction follows a one-dimensional periodic rotation at both substrates, but with a 60° or 120° rotation between both grating vectors. The resulting LC configuration is studied with the help of polarizing optical microscopy images and the diffraction properties are measured as a function of the voltage. The intricate bulk director configuration is revealed with the help of finite element Q-tensor simulations. Twist conflicts induced by the surface anchoring are resolved by introducing regions with an out-of-plane tilt in the bulk. This avoids the need for singular disclinations in the structures and gives rise to voltage induced tuning without hysteretic behavior. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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15 pages, 4526 KiB

Open AccessArticle

Polymer Stabilization of Uniform Lying Helix Texture in a Bimesogen-Doped Cholesteric Liquid Crystal for Frequency-Modulated Electro-Optic Responses

by Chia-Hua Yu, Po-Chang Wu and Wei Lee

Materials 2022, 15(3), 771; https://doi.org/10.3390/ma15030771 - 20 Jan 2022

Cited by 3 | Viewed by 1880

Abstract

A polymer network (PN) can sustain the uniform lying helix (ULH) texture in a binary cholesteric liquid crystal (LC) comprising a calamitic LC and a bimesogenic LC dimer. Upon copolymerization of a bifunctional monomer with a trifunctional monomer at a concentration of 5 [...] Read more.

A polymer network (PN) can sustain the uniform lying helix (ULH) texture in a binary cholesteric liquid crystal (LC) comprising a calamitic LC and a bimesogenic LC dimer. Upon copolymerization of a bifunctional monomer with a trifunctional monomer at a concentration of 5 wt% to create the desired polymer network structure, the PN-ULH was obtained with high stability and recoverability even when cycles of helical unwinding-to-rewinding processes were induced after the electrical or thermal treatment. Utilizing dielectric spectroscopy, the flexoelectric-polarization-dominated dielectric relaxation in the PN-ULH state was characterized to determine two frequency regions, f < f_flexo and f > f_di, with pronounced and suppressed flexoelectric effect, respectively. It is demonstrated that the cell in the PN-ULH state can operate in the light-intensity modulation mode by the flexoelectric and dielectric effects at f < f_flexo and phase-shift mode by the dielectric effect at f > f_di. Moreover, varying the voltage frequency from f < f_flexo to f > f_di results in a frequency dispersion of transmittance analogous to that of flexoelectric-polarization-dominated dielectric relaxation. The unique combination of the bimesogen-doped cholesteric LC with a stable and recoverable PN-ULH texture is thus promising for developing a frequency-modulated electro-optic device. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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9 pages, 1310 KiB

Open AccessEditor’s ChoiceArticle

Chiral-Selective Tamm Plasmon Polaritons

by Meng-Ying Lin, Wen-Hui Xu, Rashid G. Bikbaev, Jhen-Hong Yang, Chang-Ruei Li, Ivan V. Timofeev, Wei Lee and Kuo-Ping Chen

Materials 2021, 14(11), 2788; https://doi.org/10.3390/ma14112788 - 24 May 2021

Cited by 12 | Viewed by 2541

Abstract

Chiral-selective Tamm plasmon polariton (TPP) has been investigated at the interface between a cholesteric liquid crystal and a metasurface. Different from conventional TPP that occurs with distributed Bragg reflectors and metals, the chiral–achiral TPP is successfully demonstrated. The design of the metasurface as [...] Read more.

Chiral-selective Tamm plasmon polariton (TPP) has been investigated at the interface between a cholesteric liquid crystal and a metasurface. Different from conventional TPP that occurs with distributed Bragg reflectors and metals, the chiral–achiral TPP is successfully demonstrated. The design of the metasurface as a reflective half-wave plate provides phase and polarization matching. Accordingly, a strong localized electric field and sharp resonance are observed and proven to be widely tunable. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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12 pages, 1021 KiB

Open AccessArticle

Influence of Rugate Filters on the Spectral Manifestation of Tamm Plasmon Polaritons

by Victor Yu. Reshetnyak, Igor P. Pinkevych, Timothy J. Bunning and Dean R. Evans

Materials 2021, 14(5), 1282; https://doi.org/10.3390/ma14051282 - 08 Mar 2021

Cited by 11 | Viewed by 1679

Abstract

This study theoretically investigated light reflection and transmission in a system composed of a thin metal layer (Ag) adjacent to a rugate filter (RF) having a harmonic refractive index profile. Narrow dips in reflectance and peaks in transmittance in the RF band gap [...] Read more.

This study theoretically investigated light reflection and transmission in a system composed of a thin metal layer (Ag) adjacent to a rugate filter (RF) having a harmonic refractive index profile. Narrow dips in reflectance and peaks in transmittance in the RF band gap were obtained due to the excitation of a Tamm plasmon polariton (TPP) at the Ag–RF interface. It is shown that the spectral position and magnitude of the TPP dips/peaks in the RF band gap depend on the harmonic profile parameters of the RF refractive index, the metal layer thickness, and the external medium refractive index. The obtained dependences for reflectance and transmittance allow selecting parameters of the system which can be optimized for various applications. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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10 pages, 14804 KiB

Open AccessArticle

Smart Window with Active-Passive Hybrid Control

by Heng-Yi Tseng, Li-Min Chang, Kuan-Wu Lin, Cheng-Chang Li, Wan-Hsuan Lin, Chun-Ta Wang, Chien-Wen Lin, Shih-Hsien Liu and Tsung-Hsien Lin

Materials 2020, 13(18), 4137; https://doi.org/10.3390/ma13184137 - 17 Sep 2020

Cited by 25 | Viewed by 3290

Abstract

Dimming and scattering control are two of the major features of smart windows, which provide adjustable sunlight intensity and protect the privacy of people in a building. A hybrid photo- and electrical-controllable smart window that exploits salt and photochromic dichroic dye-doped cholesteric liquid [...] Read more.

Dimming and scattering control are two of the major features of smart windows, which provide adjustable sunlight intensity and protect the privacy of people in a building. A hybrid photo- and electrical-controllable smart window that exploits salt and photochromic dichroic dye-doped cholesteric liquid crystal was developed. The photochromic dichroic dye causes a change in transmittance from high to low upon exposure to sunlight. When the light source is removed, the smart window returns from colored to colorless. The salt-doped cholesteric liquid crystal can be bi-stably switched from transparent into the scattering state by a low-frequency voltage pulse and switched back to its transparent state by a high-frequency voltage pulse. In its operating mode, an LC smart window can be passively dimmed by sunlight and the haze can be actively controlled by applying an electrical field to it; it therefore exhibits four optical states—transparent, scattering, dark clear, and dark opaque. Each state is stable in the absence of an applied voltage. This smart window can automatically dim when the sunlight gets stronger, and according to user needs, actively adjust the haze to achieve privacy protection. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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10 pages, 1202 KiB

Open AccessArticle

Chiral Optical Tamm States at the Interface between a Dye-Doped Cholesteric Liquid Crystal and an Anisotropic Mirror

by Anastasia Yu. Avdeeva, Stepan Ya. Vetrov, Rashid G. Bikbaev, Maxim V. Pyatnov, Natalya V. Rudakova and Ivan V. Timofeev

Materials 2020, 13(15), 3255; https://doi.org/10.3390/ma13153255 - 22 Jul 2020

Cited by 5 | Viewed by 2070

Abstract

The resonant splitting of optical Tamm state numerically is demonstrated. The Tamm state is localized at the interface between a resonant chiral medium and a polarization-preserving anisotropic mirror. The chiral medium is considered as a cholesteric liquid crystal doped with resonant dye molecules. [...] Read more.

The resonant splitting of optical Tamm state numerically is demonstrated. The Tamm state is localized at the interface between a resonant chiral medium and a polarization-preserving anisotropic mirror. The chiral medium is considered as a cholesteric liquid crystal doped with resonant dye molecules. The article shows that the splitting occurs when dye resonance frequency coincides with the frequency of the Tamm state. In this case the reflectance, transmittance, and absorptance spectra show two distinct Tamm modes. For both modes, the field localization is at the interface between the media. The external field control of configurable optical and structural parameters paves the way for use in tunable chiral microlaser. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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