scholarly journals Magnetically Tunable Liquid Crystal-Based Optical Diffraction Gratings

Polymers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2355 ◽  
Author(s):  
Dejan Bošnjaković ◽  
Nerea Sebastián ◽  
Irena Drevenšek-Olenik
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Optical Transmission ◽  
Optical Element ◽  
Optical Diffraction ◽  
Rigorous Coupled Wave Analysis ◽  
Diffraction Structure ◽  
Rigorous Coupled Wave ◽  
The One ◽  
Orientational Structure

We present a theoretical analysis of optical diffractive properties of magnetically tunable optical transmission gratings composed of periodically assembled layers of a polymer and a ferromagnetic liquid crystal (LC). The orientational structure of the LC layers as a function of an applied magnetic field is calculated by minimization of the Landau-de Gennes free energy for ferromagnetic LCs, which is performed numerically and also analytically by using the one-constant approximation and the approximations of the high and the low magnetic fields. Optical diffractive properties of the associated diffraction structure are calculated numerically in the framework of rigorous coupled-wave analysis (RCWA). The presented methodology provides a basis for designing new types of diffractive optical element based on ferromagnetic LCs and simulating their operation governed by the in-plane magnetic field.

scholarly journals Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2292
Author(s):  
Dejan Bošnjaković ◽  
Mathias Fleisch ◽  
Xinzheng Zhang ◽  
Irena Drevenšek-Olenik
Keyword(s):  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Optical Diffraction ◽  
Polymer Scaffold ◽  
Inhomogeneous Surface ◽  
Optical Elements ◽  
Surface Anchoring ◽  
Rigorous Coupled Wave Analysis ◽  
Anchoring Energy ◽  
Rigorous Coupled Wave

We present an experimental and theoretical investigation of the optical diffractive properties of electrically tuneable optical transmission gratings assembled as stacks of periodic slices from a conventional nematic liquid crystal (E7) and a standard photoresist polymer (SU-8). The external electric field causes a twist-type reorientation of the LC molecules toward a perpendicular direction with respect to initial orientation. The associated field-induced modification of the director field is determined numerically and analytically by minimization of the Landau–de Gennes free energy. The optical diffraction properties of the associated periodically modulated structure are calculated numerically on the basis of rigorous coupled-wave analysis (RCWA). A comparison of experimental and theoretical results suggests that polymer slices provoke planar surface anchoring of the LC molecules with the inhomogeneous surface anchoring energy varying in the range 5–20 μJ/m2. The investigated structures provide a versatile approach to fabricating LC-polymer-based electrically tuneable diffractive optical elements (DOEs).

scholarly journals Extraordinary Optical Transmission by Hybrid Phonon–Plasmon Polaritons Using hBN Embedded in Plasmonic Nanoslits

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1567
Author(s):  
Shinpei Ogawa ◽  
Shoichiro Fukushima ◽  
Masaaki Shimatani
Keyword(s):  
Optical Transmission ◽  
Hexagonal Boron Nitride ◽  
Incident Angle ◽  
Optical Filters ◽  
Extraordinary Optical Transmission ◽  
Light Manipulation ◽  
Rigorous Coupled Wave Analysis ◽  
Fabry Perot ◽  
Hyperbolic Dispersion ◽  
Rigorous Coupled Wave

Hexagonal boron nitride (hBN) exhibits natural hyperbolic dispersion in the infrared (IR) wavelength spectrum. In particular, the hybridization of its hyperbolic phonon polaritons (HPPs) and surface plasmon resonances (SPRs) induced by metallic nanostructures is expected to serve as a new platform for novel light manipulation. In this study, the transmission properties of embedded hBN in metallic one-dimensional (1D) nanoslits were theoretically investigated using a rigorous coupled wave analysis method. Extraordinary optical transmission (EOT) was observed in the type-II Reststrahlen band, which was attributed to the hybridization of HPPs in hBN and SPRs in 1D nanoslits. The calculated electric field distributions indicated that the unique Fabry–Pérot-like resonance was induced by the hybridization of HPPs and SPRs in an embedded hBN cavity. The trajectory of the confined light was a zigzag owing to the hyperbolicity of hBN, and its resonance number depended primarily on the aspect ratio of the 1D nanoslit. Such an EOT is also independent of the slit width and incident angle of light. These findings can not only assist in the development of improved strategies for the extreme confinement of IR light but may also be applied to ultrathin optical filters, advanced photodetectors, and optical devices.

scholarly journals Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 138 ◽  
Author(s):  
Jordi Ignés-Mullol ◽  
Marc Mora ◽  
Berta Martínez-Prat ◽  
Ignasi Vélez-Cerón ◽  
R. Santiago Herrera ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Boundary Conditions ◽  
Isotropic Phase ◽  
Director Field ◽  
Line Defects ◽  
The One ◽  
Bulk Structures ◽  
Microscopy Images

Spherical confinement of nematic liquid crystals leads to the formation of equilibrium director field configurations that include point and line defects. Driving these materials with flows or dynamic fields often results in the formation of alternative metastable states. In this article, we study the effect of magnetic field alignment, both under static and dynamic conditions, of nematic gems (nematic droplets in coexistence with the isotropic phase) and emulsified nematic droplets of a lyotropic chromonic liquid crystal. We use a custom polarizing optical microscopy assembly that incorporates a permanent magnet whose strength and orientation can be dynamically changed. By comparing simulated optical patterns with microscopy images, we measure an equilibrium twisted bipolar pattern within nematic gems that is only marginally different from the one reported for emulsified droplets. Both systems evolve to concentric configurations upon application of a static magnetic field, but behave very differently when the field is rotated. While the concentric texture within the emulsified droplets is preserved and only displays asynchronous oscillations for high rotating speeds, the nematic gems transform into a metastable untwisted bipolar configuration that is memorized by the system when the field is removed. Our results demonstrate the importance of boundary conditions in determining the dynamic behavior of confined liquid crystals even for configurations that share similar equilibrium bulk structures.

scholarly journals On Deuling's Transition in a Nematic Liquid Crystal

1984 ◽  
Vol 39 (6) ◽  
pp. 571-574
Author(s):  
G. Barbero ◽  
A. Strigazzi
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Electric Field ◽  
Explicit Expression ◽  
Nematic Liquid Crystal ◽  
Applied Magnetic Field ◽  
The One ◽  
Strong Anchoring

We analyse Deuling's problem both in the one constant approximation and in the general case. An explicit expression is found for the electric field threshold vs. the crossed applied magnetic field, in the strong anchoring hypothesis.

Reflection performance research of grating with polarization independence based on a sandwiched structure

2018 ◽  
Vol 32 (04) ◽  
pp. 1850042
Author(s):  
Hao Pei ◽  
Bo Wang ◽  
Wenhua Zhu ◽  
Sufang Yin ◽  
Li Chen ◽  
...  
Keyword(s):  
High Efficiency ◽  
Optical Element ◽  
The Novel ◽  
First Order ◽  
Rigorous Coupled Wave Analysis ◽  
Rigorous Coupled Wave ◽  
Sandwiched Structure ◽  
The Given ◽  
Performance Research ◽  
Modal Method

The novel reflective grating was studied under Littrow incidence as one sort of high-efficiency optical element. A covering layer and a dielectric layer are employed in this structure to achieve higher efficiency and wider bandwidth. For the given wavelength of 1550 nm, by using two-beam-interference theory of modal method, duty cycle and period of grating can be calculated, where the physical essence of high efficiency in the first-order is well explained by the modal method. The other grating parameters are optimized by using rigorous coupled-wave analysis. The optimized grating has an appropriate aspect ratio and shows that diffraction efficiencies of TE and TM polarizations in the first-order are greater than 97%. Compared with the reported surface-relief high-efficiency grating, the diffraction efficiencies of the proposed grating for TE and TM polarizations can be greatly improved.

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