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Crystals
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Liquid-Crystal Polarization Gratings
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Liquid-Crystal Polarization Gratings

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

Deadline for manuscript submissions: closed (25 June 2021) | Viewed by 45514

Special Issue Editors

Dr. Yun-Han Lee

E-Mail Website
Guest Editor
Facebook Reality Labs, United StatesFacebook Reality Labs, US
Interests: liquid crystals; polarization volume gratings; AR/VR devices
Dr. Guanjun Tan

E-Mail Website
Guest Editor
Apple Inc., Cupertino, CA, USA
Interests: AR/VR Optics; display optics; polarization volume gratings
Dr. Yishi Weng

E-Mail Website
Guest Editor
School of Electronic Science and Engineering, Southeast University, Nanjing, China
Interests: near-eye displays; polarization gratings; holographic optical elements

Special Issue Information

Dear Colleagues,

Liquid-crystal polarization gratings (LCPGs) are attracting wide interests in both liquid-crystals and optics fields due to its intriguing formation process, unique optical properties, and potential applications in emergent wearable devices such as Augmented/Virtual Reality headsets.

Depending on the formation process, LCPGs can be categorized into two major types. The first method utilizes polarization interference to pattern a thin photo-alignment layer, and the subsequently coated/filled liquid crystals can self-align into gratings following the patterned surface. The second method utilizes the photocycloaddition of cinnamate moieties or similar process to record the volumetric polarization field during polarization interference into the body of the material, and then subject to annealing process to induce birefringence. The behaviors of LCPGs are highly dependent on materials, interference patterning and processing. In the simplest case, linear gratings can be formed, while complicated, exotic gratings may also be generated. In the past, significant amount of efforts had been put into liquid crystal researches on electrically switchable non-polymer liquid crystal materials for display, phase modulation or shutter applications. Polymerizable materials, molecular kinematics and the consequent optical properties for both type of LCPGs are comparatively still an uncharted territory with new challenges and opportunities.

The unique properties of LCPGs open new possibilities in various field such as imaging, display, beam-shaping, beam-steering, communication, sensing, spectroscopy, AR/VR etc. With new optical component, it is an exciting time to explore novel optical systems that tackles these challenges and re-think classic optical designs.

This Special Issue of Crystals serves to provide a platform for researchers to report results and findings in liquid-crystal or liquid-crystal-polymer LCPGs in the aspects of material, processing, patterning, polymerization, molecular kinematics, optical properties and their applications.

Potential topics include but are not limited to:

- materials for LCPGs

- interplay between materials and LCPGs structures

- effect of processing and patterning on LCPGs

- optical characteristics of LCPGs

- novel structures of LCPGs

- applications of LCPGs

- optical systems based on LCPGs

Dr. Yun-Han Lee
Dr. Guanjun Tan
Dr. Yishi Weng
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Liquid-crystal gratings
  • Polarization volume gratings
  • Polarization gratings
  • Near-eye displays

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Published Papers (9 papers)

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Research

Jump to: Review

17 pages, 4664 KiB  
Article
Effect of Doping of Cd1−xZnxS/ZnS Core/Shell Quantum Dots in Negative Dielectric Anisotropy Nematic Liquid Crystal p-Methoxybenzylidene p-Decylaniline
by Ayushi Rastogi, Fanindra Pandey, Rajiv Manohar and Shri Singh
Crystals 2021, 11(6), 605; https://doi.org/10.3390/cryst11060605 - 27 May 2021
Cited by 10 | Viewed by 2548
Abstract
We report the effect of the doping of Cd1−xZnxS/ZnS core/shell quantum dots (CSQDs) in nematic liquid crystal p-methoxybenzylidene p-decylaniline (MBDA) at 0.05 wt/wt%, 0.1 wt/wt%, 0.15 wt/wt%, 0.2 wt/wt%, 0.25 wt/wt%, and 0.3 wt/wt% concentrations of CSQDs [...] Read more.
We report the effect of the doping of Cd1−xZnxS/ZnS core/shell quantum dots (CSQDs) in nematic liquid crystal p-methoxybenzylidene p-decylaniline (MBDA) at 0.05 wt/wt%, 0.1 wt/wt%, 0.15 wt/wt%, 0.2 wt/wt%, 0.25 wt/wt%, and 0.3 wt/wt% concentrations of CSQDs in MBDA. Dielectric parameters with and without bias with respect to frequency have been investigated. The change in electro-optical parameters with temperature has also been demonstrated. The increase in the mean dielectric permittivity was found due to the large dipole moment of CSQDs, which impose stronger interactions with the liquid crystal molecules. The dielectric anisotropy changes sign on doping CSQDs in MBDA liquid crystal. It was concluded that the CSQD doping noticeably increased the dielectric permittivity of nematic MBDA in the presence of an electric field. The doping of CSQDs in nematic MBDA liquid crystal reduced the ion screening effect effectively. This phenomenon is attributed to the competition between the generated ionic impurities during the assembling process and the ion trapping effect of the CSQDs. The rotational viscosity of nematic liquid crystal decreased with increasing concentration of the CSQDs, with a faster response time observed for the 0.05 wt/wt% concentration. The birefringence of the doped system increased with the inclusion of CSQDs in MBDA. These results find application in the field of display devices, phase shifters, LC—gratings, TIR waveguide, industries, and projectors. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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10 pages, 2125 KiB  
Article
Influence of X7GeS5I (X = Ag, Cu) Superionic Nanoparticles on Structural Changes in Nematic Liquid Crystal
by Peter Bury, Marek Veveričík, Peter Kopčanský, Milan Timko, Ihor P. Studenyak and Artem I. Pogodin
Crystals 2021, 11(4), 413; https://doi.org/10.3390/cryst11040413 - 12 Apr 2021
Cited by 2 | Viewed by 1819
Abstract
The effect of two types of superionic nanoparticles; Cu7GeS5I and Ag7GeS5I, respectively on nematic liquid crystal (6CB) behavior under an external electric field is investigated. The response of both attenuation of surface acoustic waves propagating [...] Read more.
The effect of two types of superionic nanoparticles; Cu7GeS5I and Ag7GeS5I, respectively on nematic liquid crystal (6CB) behavior under an external electric field is investigated. The response of both attenuation of surface acoustic waves propagating along with the substrate/liquid crystal interface and light transmission are used to study the structural changes induced by applied electric field. The increasing/decreasing regime as well as jumped change of applied field were used. The light transmission was investigated using linearly polarized laser beam (532 nm) propagating through the liquid crystal. Results obtained from both measurements for three different concentrations (0.01, 0.05 and 0.10 wt%) and in addition two different sizes of nanoparticles are compared and results, relying on structural changes, suspension stability and switching behavior are evaluated. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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11 pages, 5119 KiB  
Article
Exit Pupil Expansion Based on Polarization Volume Grating
by Jingyi Cui and Yuning Zhang
Crystals 2021, 11(4), 333; https://doi.org/10.3390/cryst11040333 - 25 Mar 2021
Cited by 15 | Viewed by 3985
Abstract
In this paper, we demonstrate a waveguide display structure which can realize a large field of view on a two-dimensional plane and a larger exit pupil size at the same time. This waveguide structure has three polarization volume gratings as its coupling elements. [...] Read more.
In this paper, we demonstrate a waveguide display structure which can realize a large field of view on a two-dimensional plane and a larger exit pupil size at the same time. This waveguide structure has three polarization volume gratings as its coupling elements. We use Zemax to simulate the effect of monochromatic and full-color two-dimensional exit pupil expansion and actually prepared a monochromatic waveguide with a two-dimensional exit pupil expansion structure. For the red, green, and blue light beams, it can achieve a large diffraction angle and can achieve diffraction efficiency of more than 70%. The waveguide structure shown can have an angle of view of 35° in the horizontal direction and 20° in the vertical direction, and an exit pupil of 18 mm long and 17 mm wide was achieved at the same time. As measured, the overall optical efficiency was measured as high as 118.3 cd/m2 per lumen with a transparency of 72% for ambient light. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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7 pages, 3288 KiB  
Article
Design and Realization of a Compact Efficient Beam Combiner, Based on Liquid Crystal Pancharatnam–Berry Phase Gratings
by Boxuan Gao, Jeroen Beeckman and Kristiaan Neyts
Crystals 2021, 11(2), 220; https://doi.org/10.3390/cryst11020220 - 23 Feb 2021
Cited by 9 | Viewed by 3099
Abstract
We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the [...] Read more.
We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the layer is controlled by spacers. The beam combiner can bring two parallel laser beams closer to each other while remaining parallel. This work shows the potential to realize components based on flat optical LC devices. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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8 pages, 2417 KiB  
Article
Enhancing the Optical Efficiency of Near-Eye Displays with Liquid Crystal Optics
by Tao Zhan, En-Lin Hsiang, Kun Li and Shin-Tson Wu
Crystals 2021, 11(2), 107; https://doi.org/10.3390/cryst11020107 - 26 Jan 2021
Cited by 13 | Viewed by 4040
Abstract
We demonstrate a light efficient virtual reality (VR) near-eye display (NED) design based on a directional display panel and a diffractive deflection film (DDF). The DDF was essentially a high-efficiency Pancharatnam-Berry phase optical element made of liquid crystal polymer. The essence of this [...] Read more.
We demonstrate a light efficient virtual reality (VR) near-eye display (NED) design based on a directional display panel and a diffractive deflection film (DDF). The DDF was essentially a high-efficiency Pancharatnam-Berry phase optical element made of liquid crystal polymer. The essence of this design is directing most of the display light into the eyebox. The proposed method is applicable for both catadioptric and dioptric VR lenses. A proof-of-concept experiment was conducted with off-the-shelf optical parts, where the light efficiency was enhanced by more than 2 times. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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Review

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22 pages, 6071 KiB  
Review
Recent Advances in Photoalignment Liquid Crystal Polarization Gratings and Their Applications
by Tiegang Lin, Jin Xie, Yingjie Zhou, Yaqin Zhou, Yide Yuan, Fan Fan and Shuangchun Wen
Crystals 2021, 11(8), 900; https://doi.org/10.3390/cryst11080900 - 31 Jul 2021
Cited by 29 | Viewed by 6783
Abstract
Liquid crystal (LC) circular polarization gratings (PGs), also known as Pancharatnam–Berry (PB) phase deflectors, are diffractive waveplates with linearly changed optical anisotropy axes. Due to the high diffraction efficiency, polarization selectivity character, and simple fabrication process, photoalignment LC PGs have been widely studied [...] Read more.
Liquid crystal (LC) circular polarization gratings (PGs), also known as Pancharatnam–Berry (PB) phase deflectors, are diffractive waveplates with linearly changed optical anisotropy axes. Due to the high diffraction efficiency, polarization selectivity character, and simple fabrication process, photoalignment LC PGs have been widely studied and developed especially in polarization management and beam split. In this review paper, we analyze the physical principles, show the exposure methods and fabrication process, and present relevant promising applications in photonics and imaging optics. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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21 pages, 6132 KiB  
Review
Non-Mechanical Beam Steering with Polarization Gratings: A Review
by Christopher Hoy, Jay Stockley, Janelle Shane, Kelly Kluttz, Douglas McKnight and Steven Serati
Crystals 2021, 11(4), 361; https://doi.org/10.3390/cryst11040361 - 30 Mar 2021
Cited by 30 | Viewed by 5663
Abstract
Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining [...] Read more.
Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining characteristics of this beam steering architecture and highlight several applications of the technology. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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Graphical abstract

16 pages, 6492 KiB  
Review
Twisting Structures in Liquid Crystal Polarization Gratings and Lenses
by Shiyuan Zhang, Wan Chen, Yang Yu, Qidong Wang, Quanquan Mu, Shixiao Li and Jin Chen
Crystals 2021, 11(3), 243; https://doi.org/10.3390/cryst11030243 - 27 Feb 2021
Cited by 13 | Viewed by 6372
Abstract
Recently, diverse twisting structures have been discovered to be a potential approach to design liquid crystal polarization gratings and lenses (LCPGs and LCPLs) with a high diffraction efficiency, broad bandwidth, wide view, and large diffraction angle. In this review, we divide these twisting [...] Read more.
Recently, diverse twisting structures have been discovered to be a potential approach to design liquid crystal polarization gratings and lenses (LCPGs and LCPLs) with a high diffraction efficiency, broad bandwidth, wide view, and large diffraction angle. In this review, we divide these twisting structures into two main types, namely, multi-layer twisting structures with phase compensation and twisting structures forming Bragg diffraction. We found that multi-layer twisting structure LCPGs and LCPLs presented a broader bandwidth and a wider view angle by phase compensation. While for transmissive or reflective Bragg LCPGs, a large diffraction angle with high diffraction efficiency could be achieved. Based on the theoretical analysis in the review, potential research directions on novel twisting structures were prospected. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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Graphical abstract

18 pages, 5406 KiB  
Review
Polarization Volume Gratings for Near-Eye Displays and Novel Photonic Devices
by Kun Yin, Tao Zhan, Jianghao Xiong, Ziqian He and Shin-Tson Wu
Crystals 2020, 10(7), 561; https://doi.org/10.3390/cryst10070561 - 1 Jul 2020
Cited by 46 | Viewed by 8239
Abstract
Liquid crystal-based reflective polarization volume grating (PVG), also known as a linear Bragg–Berry phase optical element or a member of volume Bragg gratings (VBGs), is a functional planar structure with patterned orientation of optical axis. Due to the strong polarization selectivity, nearly 100% [...] Read more.
Liquid crystal-based reflective polarization volume grating (PVG), also known as a linear Bragg–Berry phase optical element or a member of volume Bragg gratings (VBGs), is a functional planar structure with patterned orientation of optical axis. Due to the strong polarization selectivity, nearly 100% diffraction efficiency, large diffraction angle, and simple fabrication process, PVGs have found potential applications in novel photonic devices and emerging near-eye displays. In this review paper, we describe the operation principles, discuss the optical properties, present the fabrication methods, and provide promising applications of PVGs for near-eye displays and novel photonic devices. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
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