A Switchable Cholesteric Phase Grating with a Low Operating Voltage

We demonstrate a simple fabrication method of a uniform-lying-helix (ULH) cholesteric liquid crystal (ChLC) cell for phase grating device applications. To utilize a stable ULH state, we set the pitches of ChLCs as half of the cell gap to obtain the fingerprint texture with homeotropic anchoring. With the given grating period, the diffraction efficiency of the ULH cell can be maximized by optimizing the cell gap. We found that the fabricated grating device can provide a large diffraction angle of 10° and a low operating voltage of 3 V with a diffraction efficiency of 30%. We expect potential applications of the device for diffraction optics, optical interconnects, and beam steering devices.

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Relaxation Polarization Dependence of Circular Vector Gratings in Azobenzene Glassy Molecular Films

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.850.285 ◽

2020 ◽

Vol 850 ◽

pp. 285-290

Author(s):

Andris Ozols ◽

Peteris Augustovs ◽

Kaspars Traskovskis ◽

Valdis Kokars ◽

Lauma Laipniece ◽

...

Keyword(s):

Diffraction Efficiency ◽

Relaxation Times ◽

Grating Period ◽

Volume Density ◽

Laser Beams ◽

Relaxation Polarization ◽

Polarized Beam ◽

Sandwich Type ◽

Phd Thesis ◽

532 Nm

Holographic grating recording and relaxation is studied in different azobenzene molecular glassy films by circularly orthogonally polarized 532 nm laser beams L and R. The readout was made by circularly polarized (R or L) 632.8 nm laser beam. Sandwich-type samples (glass-film-glass) were also studied. Maximum diffraction efficiency of 81% has been achieved in sandwich-type AR-173 film. The following relaxation features have been found: after reaching diffraction efficiency (DE) maximum no DE decay took place; DE read out by R-polarized beam was always higher than that by L-polarized beam; in sandwich-type samples DE decayed until zero when read out by R-polarization whereas DE was zero when read out by L-polarization. 50% relaxation times varied from 4 to 44 minutes, and they mainly decreased when grating period was increased. The observed relaxation peculiarities can be understood if one assumes that volume birefringence grating (VBG) is recorded followed by volume density grating (VDG) and surface relief grating (SRG) recording. R-polarization "feels" all gratings whereas L-polarization only VDG and SRG. At large exposures VDG and SRG dominate. These results confirm the conclusion made by J.Mikelsone in her 2018 PhD thesis that birefringence grating recording in azobenzene materials is a neccessary condition for SRG appearance.

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A DoD Perspective on Left Handed Negative Index Materials and Potential Applications

MRS Proceedings ◽

10.1557/proc-0919-j01-02 ◽

2006 ◽

Vol 919 ◽

Author(s):

Valerie Browning ◽

Minas H Tanielian ◽

Richard W. Ziolkowski ◽

Nader Engheta ◽

David R. Smith

Keyword(s):

Composite Structures ◽

Beam Steering ◽

Electromagnetic Response ◽

Electromagnetic Spectrum ◽

Negative Index ◽

Negative Index Materials ◽

Left Handed ◽

Potential Applications ◽

Novel Approaches ◽

Electromagnetic Transport

AbstractIn the quest for ever smaller, lighter weight, and conformal components and devices for radar and communication applications, researchers in the RF community have increasingly turned to artificially engineered, composite structures (or “metamaterials”) in order to exploit the extraordinary electromagnetic response these materials offer. One particularly promising class of metamaterials that has recently received a great deal of attention are “left-handed” or negative index materials. Because these metamaterials exhibit the unique ability to bend and focus light in ways no other conventional materials can, they hold great potential for enabling a number of innovative lens and antenna structures for a broad range of commercial and DoD relevant applications. Exploring the possible implementation of negative index materials for such applications will require significant enhancements in the properties of existing Negative Index Materials (NIM) (bandwidth, loss, operational frequency, etc.), as well as improved understanding of the physics of their electromagnetic transport properties. For this reason the Defense Advanced Research Project Agency (DARPA) has initiated a program that seeks to further develop and demonstrate NIM for future DoD missions including, but not limited to, the following: 1) lightweight, compact lenses with improved optics; 2) sub wavelength/high resolution imaging across the electromagnetic spectrum; 3) novel approaches to beam steering for radar, RF, and/or optical communications; and 4) novel approaches for integrating optics with semiconductor electronics. A brief overview of the salient properties of NIM will be presented as well as a general discussion of a few of their potential applications.

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Polymer Electroluminescent Devices

MRS Bulletin ◽

10.1557/s0883769400033601 ◽

1997 ◽

Vol 22 (6) ◽

pp. 31-38 ◽

Cited By ~ 78

Author(s):

Yang Yang

Keyword(s):

New York ◽

Quantum Efficiency ◽

Operating Voltage ◽

Organic Crystals ◽

New York University ◽

Research Activity ◽

Information Displays ◽

Potential Applications ◽

Bandgap Semiconductors ◽

The 1960S

Electroluminescence (EL) is the emission of light generated from the radiative recombination of electrons and holes electrically injected into a luminescent semiconductor. Conventional EL devices are made of inorganic direct-bandgap semiconductors, such as GaAs and InGaAs. Recently EL devices based on conjugated organic small molecules and polymers have attracted increasing attention due to easy fabrication of large areas, unlimited choice of colors, and mechanical flexibility. Potential applications of these organic/polymeric EL devices include backlights for displays, alphanumeric displays, and high-density information displays.Electroluminescence from an organic material was first demonstrated in the 1960s on anthracene crystals by Pope et al. at New York University. Subsequently several other groups also observed this phenomenon in organic crystals and thin films. These organic EL devices had high operating voltages and low quantum efficiency. Consequently they did not attract much attention. In 1987 a breakthrough was made by Tang and VanSlyke at Eastman Kodak who found that by using multilayers of sublimated organic molecules, the operating voltage of the organic EL devices was dramatically reduced and the quantum efficiency was significantly enhanced. This discovery touched off a flurry of research activity, especially in Japan. The Japanese researchers, as welt as the group at Kodak, have since improved the device efficiency and lifetime to meet commercial requirements. This progress is reviewed by Tsutsui in this issue.

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Vertically integrated diffractive gratings on photonic crystal surface emitting lasers

Scientific Reports ◽

10.1038/s41598-021-82194-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Lih-Ren Chen ◽

Kuo-Bin Hong ◽

Hsiu-Ling Chen ◽

Kuan-Chih Huang ◽

Tien-Chang Lu

Keyword(s):

Photonic Crystal ◽

Crystal Surface ◽

Beam Steering ◽

Azimuthal Angle ◽

Three Dimensional ◽

Grating Period ◽

Single Chip ◽

Output Beam ◽

Optical Elements ◽

Emitting Lasers

AbstractWe designed and fabricated a photonic crystal surface emitting laser (PCSEL) with vertically integrated diffractive optical elements on their top to study the mechanism of static beam steering on a single chip. The deflected output beam by the self-formed periodic ITO cladding layer of the PCSEL can be further steered by changing the grating period and azimuthal angle of the diffractive gratings relative to the photonic crystal. Through the analysis of photonic band structure and lasing characteristics, the periodic ITO structure is coupled to the photonic crystal band, whereas the integrated grating serves the diffractive function only. The findings pave the way for the design of PCSELs enabling single or multiple output beam with varying direction capability. This type of laser is regarded as an ideal light source for various applications, such as light detection and ranging and three-dimensional sensing systems.

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Control of the Induced Handedness of Helical Nanofilaments Employing Cholesteric Liquid Crystal Fields

Molecules ◽

10.3390/molecules26196055 ◽

2021 ◽

Vol 26 (19) ◽

pp. 6055

Author(s):

Ju-Yong Kim ◽

Jae-Jin Lee ◽

Jun-Sung Park ◽

Yong-Jun Choi ◽

Suk-Won Choi

Keyword(s):

Liquid Crystal ◽

Crystal Field ◽

Driving Force ◽

Cholesteric Liquid Crystal ◽

Powerful Method ◽

Cholesteric Phase ◽

Crystal Fields

In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness.

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Terahertz Beam Steering Concept Based on a MEMS-Reconfigurable Reflection Grating

Sensors ◽

10.3390/s20102874 ◽

2020 ◽

Vol 20 (10) ◽

pp. 2874

Author(s):

Xuan Liu ◽

Lisa Samfaß ◽

Kevin Kolpatzeck ◽

Lars Häring ◽

Jan C. Balzer ◽

...

Keyword(s):

Diffraction Grating ◽

High Speed ◽

Beam Steering ◽

Vertical Displacement ◽

Grating Period ◽

Terahertz Waves ◽

Large Area ◽

Electrostatic Actuators ◽

Reflection Gratings ◽

Reflection Grating

With an increasing number of applications of terahertz systems in industrial fields and communications, terahertz beamforming and beam steering techniques are required for high-speed, large-area scanning. As a promising means for beam steering, micro-electro-mechanical system (MEMS)-based reflection gratings have been successfully implemented for terahertz beam control. So far, the diffraction grating efficiency is relatively low due to the limited vertical displacement range of the reflectors. In this paper, we propose a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators. We vary the number of the reflectors per grating period and configure the throw of individual reflectors so that the reflection grating is shaped as a blazed grating to steer the terahertz beam with maximum diffraction grating efficiency. Furthermore, we provide a mathematical model for calculating the radiation pattern of the terahertz wave reflected by general reflection gratings consisting of subwavelength reflectors. The calculated and simulated radiation patterns of the designed grating show that we can steer the angle of the terahertz waves in a range of up to ± 56.4 ∘ with a maximum sidelobe level of −10 dB at frequencies from 0.3 THz to 1 THz.

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Effective Modulation of Optical and Photoelectrical Properties of SnS2 Hexagonal Nanoflakes via Zn Incorporation

Nanomaterials ◽

10.3390/nano9070924 ◽

2019 ◽

Vol 9 (7) ◽

pp. 924 ◽

Cited By ~ 3

Author(s):

Ganesan Mohan Kumar ◽

Pugazhendi Ilanchezhiyan ◽

Hak Dong Cho ◽

Shavkat Yuldashev ◽

Hee Chang Jeon ◽

...

Keyword(s):

Electronic Conductivity ◽

Energy Bands ◽

Hydrothermal Route ◽

Zn Doping ◽

Visible Light Absorption ◽

Photoelectrical Properties ◽

Potential Applications ◽

Device Applications ◽

Tin Sulfides ◽

The Stability

Tin sulfides are promising materials in the fields of photoelectronics and photovoltaics because of their appropriate energy bands. However, doping in SnS2 can improve the stability and robustness of this material in potential applications. Herein, we report the synthesis of SnS2 nanoflakes with Zn doping via simple hydrothermal route. The effect of doping Zn was found to display a huge influence in the structural and crystalline order of as synthesized SnS2. Their optical properties attest Zn doping of SnS2 results in reduction of the band gap which benefits strong visible-light absorption. Significantly, enhanced photoresponse was observed with respect to pristine SnS2. Such enhancement could result in improved electronic conductivity and sensitivity due to Zn doping at appropriate concentration. These excellent performances show that Sn1−xZnxS2 nanoflakes could offer huge potential for nanoelectronics and optoelectronics device applications.

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Intrinsic magnetic topological insulator phases in the Sb doped MnBi2Te4 bulks and thin flakes

Nature Communications ◽

10.1038/s41467-019-12485-y ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 54

Author(s):

Bo Chen ◽

Fucong Fei ◽

Dongqin Zhang ◽

Bo Zhang ◽

Wanling Liu ◽

...

Keyword(s):

First Principles ◽

Magnetic Order ◽

Photoemission Spectroscopy ◽

First Principles Calculations ◽

New Device ◽

Angle Resolved Photoemission Spectroscopy ◽

Potential Applications ◽

Device Applications ◽

Physical Phenomena ◽

Promising Avenue

Abstract Magnetic topological insulators (MTIs) offer a combination of topologically nontrivial characteristics and magnetic order and show promise in terms of potentially interesting physical phenomena such as the quantum anomalous Hall (QAH) effect and topological axion insulating states. However, the understanding of their properties and potential applications have been limited due to a lack of suitable candidates for MTIs. Here, we grow two-dimensional single crystals of Mn(SbxBi(1-x))2Te4 bulk and exfoliate them into thin flakes in order to search for intrinsic MTIs. We perform angle-resolved photoemission spectroscopy, low-temperature transport measurements, and first-principles calculations to investigate the band structure, transport properties, and magnetism of this family of materials, as well as the evolution of their topological properties. We find that there exists an optimized MTI zone in the Mn(SbxBi(1-x))2Te4 phase diagram, which could possibly host a high-temperature QAH phase, offering a promising avenue for new device applications.

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Submillisecond-Response Polymer Network Liquid Crystal Phase Modulators

Polymers ◽

10.3390/polym12122862 ◽

2020 ◽

Vol 12 (12) ◽

pp. 2862

Author(s):

Yannanqi Li ◽

Zhiyong Yang ◽

Ran Chen ◽

Lingchao Mo ◽

Juanli Li ◽

...

Keyword(s):

Liquid Crystal ◽

Light Scattering ◽

Beam Steering ◽

Polymer Network ◽

Infrared Region ◽

Dielectric Anisotropy ◽

Spatial Light Modulators ◽

Operating Voltage ◽

Scattering Loss ◽

Light Modulators

A submillisecond-response and light scattering-free polymer-network liquid crystal (PNLC) for infrared spatial light modulators is demonstrated. Our new liquid crystal host exhibits a higher birefringence, comparable dielectric anisotropy, and slightly lower visco-elastic constant than a commonly employed commercial material, HTG-135200. Moreover, the electro-optical performance of our PNLCs with different monomer concentrations, cell gaps, and liquid crystal (LC) hosts is compared and discussed from four aspects: operating voltage, hysteresis, relaxation time, and light scattering loss. The temperature effect on hysteresis is also analyzed. Potential applications of PNLCs for laser beam steering and spatial light modulators especially in the infrared region are foreseeable.

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Recent Progress of Electro-optic Polymers for Device Applications

MRS Proceedings ◽

10.1557/proc-488-193 ◽

1997 ◽

Vol 488 ◽

Cited By ~ 1

Author(s):

Alex K-Y. Jen ◽

Qing Yang ◽

Seth R. Marder ◽

Larry R. Dalton ◽

Ching-Fong Shu

Keyword(s):

Data Storage ◽

High Speed ◽

Stable State ◽

Optical Data Storage ◽

Device Fabrication ◽

Optical Data ◽

Material System ◽

Electro Optic ◽

Potential Applications ◽

Device Applications

AbstractElectro-optic (E-O) polymers have drawn great interest in recent years because of their potential applications in photonics devices such as high speed modulators and switches, optical data storage and information processing1–2. In order to have suitable materials for device fabrication, it is essential to design and develop polymeric material systems (active and passive polymers) with matched refractive indices, large E-O coefficients, good temporal and photochemical stability3–8 The E-O response of an active polymer commonly arises from the electric field induced alignment of its second-order nonlinear optical (NLO) chromophore, either doped as a guest/host system or covalently bonded as a side-chain. Because of the strong interaction among the electric dipoles, the poled structure is in a meta-stable state; the poled NLO chromophores which possess large dipole moment will tend to relax back to the randomly oriented state. As a result, the stability of the poled structure strongly depends on the rigidity of the overall material system. As it might be expected, the continuous increases of the rigidity and Tg of poled polymers imposes constraints on the selection of suitable chromophores that can survive the hightemperature poling and processing conditions. To circumvent this problem, we have developed a series of chromophores that possess conformation-locked geometry and perfluoro-dicyanovinylsubstituted electron-accepting group which demonstrate both good thermal stabilty and nonlinearity. This paper provides a brief review of these highly efficient and thermally stable chromophores and polymers for device applications.

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