Crystals

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14 pages, 2589 KiB

Open AccessArticle

Electrical Control of Optical Liquid-Crystal-Guided Microstructures

by Michal Kwasny and Urszula A. Laudyn

Crystals 2022, 12(3), 325; https://doi.org/10.3390/cryst12030325 - 26 Feb 2022

Cited by 2 | Viewed by 2645

This work investigates nematic liquid crystal (NLC) optical guiding structures designed in typical sandwich-like NLC cells. With the support of an electrically controlled spatial topology of director orientation, we manage a linear and nonlinear light propagation with the realization of optical beam switching. [...] Read more.

This work investigates nematic liquid crystal (NLC) optical guiding structures designed in typical sandwich-like NLC cells. With the support of an electrically controlled spatial topology of director orientation, we manage a linear and nonlinear light propagation with the realization of optical beam switching. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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9 pages, 2462 KiB

Open AccessArticle

Fabrication of Polarization Grating on N-Benzylideneaniline Polymer Liquid Crystal and Control of Diffraction Beam

by Mizuho Kondo, Kyohei Fujita, Tomoyuki Sasaki, Moritsugu Sakamoto, Hiroshi Ono and Nobuhiro Kawatsuki

Crystals 2022, 12(2), 273; https://doi.org/10.3390/cryst12020273 - 17 Feb 2022

Cited by 1 | Viewed by 1987

Abstract

Photoresponsive photoalignable liquid crystalline polymers composed of phenyl benzoate terminated with N-benzylideneaniline were evaluated. These polymers are capable of axis-selective photoreaction, photoinduced orientation, and surface relief grating formation. Polarization holography using an He-Cd laser beam at a wavelength of 325 nm demonstrated [...] Read more.

Photoresponsive photoalignable liquid crystalline polymers composed of phenyl benzoate terminated with N-benzylideneaniline were evaluated. These polymers are capable of axis-selective photoreaction, photoinduced orientation, and surface relief grating formation. Polarization holography using an He-Cd laser beam at a wavelength of 325 nm demonstrated the formation of a surface relief grating with a molecularly oriented structure based on periodic light-induced reorientation and molecular motion. Electrical switching of diffracted light using an electric field response of twisted-nematic cell containing a low-molecular-weight liquid crystal in combination was also demonstrated. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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12 pages, 4350 KiB

Open AccessArticle

Stabilization of Long-Pitch Supertwisted Nematic Structures

by Masahiro Ito, Satoshi Ohmi and Kohki Takatoh

Crystals 2021, 11(12), 1541; https://doi.org/10.3390/cryst11121541 - 9 Dec 2021

Cited by 1 | Viewed by 2174

Abstract

Stabilized reverse twisted nematic liquid crystal devices (RTN-LCDs) were fabricated using formation of a polymer matrix under UV irradiation with an applied voltage (sustain voltage) in the vicinity of the alignment layers. In the absence of an applied voltage, the non-stabilized RTN structure [...] Read more.

Stabilized reverse twisted nematic liquid crystal devices (RTN-LCDs) were fabricated using formation of a polymer matrix under UV irradiation with an applied voltage (sustain voltage) in the vicinity of the alignment layers. In the absence of an applied voltage, the non-stabilized RTN structure gradually returns to a splay twist structure. The sustain voltage was decreased with an increase in temperature. A stabilized long-pitch supertwisted nematic (LPSTN) structure could also be formed during the RTN structure stabilization process with a much lower sustain voltage at a temperature near the clearing point. The chiral pitch for the LPSTN structure is longer than that for a typical STN structure. LPSTN-LCDs similar to RTN-LCDs show a large reduction in both the threshold and saturation voltage compared with those for TN-LCDs consisted of the same LC materials. Furthermore, a notable feature of LPSTN-LCDs is a change to a TN structure when a high voltage is applied. A black state can be realized due to the change from the LPSTN structure to the RTN structure unlike the typical STN mode under the crossed nicols condition. In contrast STN-LCDs retain their color due to the retardation because the RTN and LPSTN states are considered topologically equivalent. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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10 pages, 3727 KiB

Open AccessArticle

Optical Filter with Large Angular Dependence of Transmittance Using Liquid Crystal Devices

by Kohki Takatoh, Masahiro Ito, Suguru Saito and Yuuta Takagi

Crystals 2021, 11(10), 1199; https://doi.org/10.3390/cryst11101199 - 3 Oct 2021

Cited by 3 | Viewed by 2057

Abstract

This study proposed a new type of optical device with variable transmittance based on the incident angle direction. These devices consist of two liquid crystal devices (LCDs) with a half-wave plate between them. Hybrid aligned nematic (HAN)-type guest-host (GH) LCDs or GH-LCDs with [...] Read more.

This study proposed a new type of optical device with variable transmittance based on the incident angle direction. These devices consist of two liquid crystal devices (LCDs) with a half-wave plate between them. Hybrid aligned nematic (HAN)-type guest-host (GH) LCDs or GH-LCDs with antiparallel alignment of high pretilt angles were used. The use of a half-wave plate allowed for the control of the p- and s-waves. Using these devices, a wide range of transmittances were obtained because no polarizer was used. The newly proposed LCDs have a wide range of applications, including use on buildings, vehicles, and glasses. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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9 pages, 2340 KiB

Open AccessEditor’s ChoiceArticle

Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers

by Yi-Hong Shih, Xin-Yu Lin, Harry Miyosi Silalahi, Chia-Rong Lee and Chia-Yi Huang

Crystals 2021, 11(9), 1100; https://doi.org/10.3390/cryst11091100 - 10 Sep 2021

Cited by 8 | Viewed by 3013

Abstract

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with [...] Read more.

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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8 pages, 2338 KiB

Open AccessArticle

UV Durable LCOS for Laser Processing

by Yasuki Sakurai, Masashi Nishitateno, Masahiro Ito and Kohki Takatoh

Crystals 2021, 11(9), 1047; https://doi.org/10.3390/cryst11091047 - 30 Aug 2021

Cited by 4 | Viewed by 2668

Abstract

Liquid-Crystal-On-Silicon (LCOS) Spatial Light Modulator (SLM) is widely used as a programmable adaptive optical element in many laser processing applications with various wavelength light sources. We report UV durable liquid-crystal-on-silicon spatial light modulators for one-shot laser material processing. Newly developed LCOS consists of [...] Read more.

Liquid-Crystal-On-Silicon (LCOS) Spatial Light Modulator (SLM) is widely used as a programmable adaptive optical element in many laser processing applications with various wavelength light sources. We report UV durable liquid-crystal-on-silicon spatial light modulators for one-shot laser material processing. Newly developed LCOS consists of UV transparent materials and shows a lifetime 480 times longer than the conventional one in 9.7 W/cm² illumination at 355 nm. We investigated the durability of polymerization inhibitor mixed liquid crystal in order to extend its lifetime. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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8 pages, 2761 KiB

Open AccessArticle

Polymer-Stabilized Blue Phase and Its Application to a 1.5 µm Band Wavelength Selective Filter

by Seiji Fukushima, Kakeru Tokunaga, Takuya Morishita, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi and Hidehisa Tazawa

Crystals 2021, 11(9), 1017; https://doi.org/10.3390/cryst11091017 - 25 Aug 2021

Cited by 2 | Viewed by 1894

Abstract

The use of polymer-stabilized blue phase (PSBP) including a tolane-type liquid crystal was investigated to develop a voltage-controlled wavelength selective filter for wavelength-division-multiplexing optical fiber network. It was found that the tolane-type liquid crystal introduction can increase both a blue-phase temperature range and [...] Read more.

The use of polymer-stabilized blue phase (PSBP) including a tolane-type liquid crystal was investigated to develop a voltage-controlled wavelength selective filter for wavelength-division-multiplexing optical fiber network. It was found that the tolane-type liquid crystal introduction can increase both a blue-phase temperature range and a Kerr coefficient. A Fabry–Perot etalon filled with PSBP functioned as a wavelength selective filter, as expected. The tuning wavelength range was 62 nm although peak transmission was not as high as expected. Numerical analysis suggested that light absorption in transparent electrodes may cause the issue. Minor change to the etalon structure will result in improved performance. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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8 pages, 2456 KiB

Open AccessArticle

Beam Shaping for Wireless Optical Charging with Improved Efficiency

by Lei Tian, Jiewen Nie and Haining Yang

Crystals 2021, 11(8), 970; https://doi.org/10.3390/cryst11080970 - 17 Aug 2021

Cited by 1 | Viewed by 2157

Abstract

Optical wireless charging is a nonradiative long-distance power transfer method. It may potentially play an important role in certain scenarios where access is challenging, and the radio frequency power transfer is less efficient. The divergence of the optical beam over distances is a [...] Read more.

Optical wireless charging is a nonradiative long-distance power transfer method. It may potentially play an important role in certain scenarios where access is challenging, and the radio frequency power transfer is less efficient. The divergence of the optical beam over distances is a key limiting factor for the efficiency of any wireless optical charging system. In this work, we propose and experimentally demonstrate a holographic optical beam shaping system that can restrict the divergence of the optical beam. Our experimental results showed up to 354.88% improvement in the charging efficiency over a 10 m distance. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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10 pages, 3418 KiB

Open AccessArticle

Identifying a Unique Communication Mechanism of Thermochromic Liquid Crystal Printing Ink

by Maja Strižić Jakovljević, Branka Lozo and Marta Klanjšek Gunde

Crystals 2021, 11(8), 876; https://doi.org/10.3390/cryst11080876 - 28 Jul 2021

Cited by 4 | Viewed by 2559

Abstract

Thermochromic liquid crystal materials are commonly used in printing inks, opening up a wide range of possible applications. In order to ensure and control the most accurate application, the occurrence of the so-called colour play effect, i.e., the appearance of iridescent (rainbow) colours [...] Read more.

Thermochromic liquid crystal materials are commonly used in printing inks, opening up a wide range of possible applications. In order to ensure and control the most accurate application, the occurrence of the so-called colour play effect, i.e., the appearance of iridescent (rainbow) colours as a function of temperature, must be determined precisely. For this purpose, the temperature-dependent reflection of a sample must be measured using a spectrometer with an integrating sphere. The same values should be obtained for each sample containing the same thermochromic liquid crystalline material, irrespective of the spectrometer used, integrating sphere, layer thickness and the surface properties of the substrate. To describe this intrinsic property of the thermochromic liquid crystal material, the term communication mechanism might be considered. The research has shown how this mechanism is obtained experimentally. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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11 pages, 3340 KiB

Open AccessArticle

Fast-Response Liquid Crystals for 6G Optical Communications

by Junyu Zou, Zhiyong Yang, Chongchang Mao and Shin-Tson Wu

Crystals 2021, 11(7), 797; https://doi.org/10.3390/cryst11070797 - 8 Jul 2021

Cited by 25 | Viewed by 4157

Abstract

We report two high birefringence and low viscosity nematic mixtures for phase-only liquid-crystal-on-silicon spatial light modulators. The measured response time (on + off) of a test cell with 2π phase change at 1550 nm, 5 V operation voltage, and 40 °C is [...] Read more.

We report two high birefringence and low viscosity nematic mixtures for phase-only liquid-crystal-on-silicon spatial light modulators. The measured response time (on + off) of a test cell with 2π phase change at 1550 nm, 5 V operation voltage, and 40 °C is faster than 10 ms. To improve the photostability, a distributed Bragg reflector is designed to cutoff the harmful ultraviolet and blue wavelengths. These materials are promising candidates for future 6G optical communications. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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