Liquid Crystal Gratings Research Articles

Fast switchable ferroelectric liquid crystal gratings with two electro-optical modes

In this article, we reveal a theoretical and experimental illustration of the Ferroelectric liquid crystal (FLC) grating fabricated by mean of patterned alignment based on photo-alignment. The complexity related to the mismatching of the predefined alignment domains on the top and bottom substrate has been avoided by incorporating only one side photo aligned substrate while the other substrate does not have any alignment layer. Depending on the easy axis in the said alignment domains and the azimuth plane of the impinging polarized light, the diffracting element can be tuned in two modes i.e. DIFF/OFF switchable and DIFF/TRANS switchable modes, which can be applied to different applications. The diffraction profile has been illustrated theoretically that fits well with the experimental finding and thus the proposed diffraction elements with fast response time and high diffraction efficiency could find application in many modern devices.

Simple system for evaluating retardation of liquid crystal cells using grating type liquid crystal polarization splitters

We propose a unique optical system for measuring the retardation of birefringent films using a pair of liquid crystal (LC) gratings; that is, the examined birefringent films are inserted between two LC gratings. Because the LC grating functions as a polarization beam splitter for circularly polarized light, the proposed system is optically equivalent to the measurement system using a pair of two circular polarizers. First, the polarization splitting performance of the LC grating is discussed. It is found that a sufficiently high voltage (such that the retardation is less than a half wavelength) has to be applied for the almost pure circularly polarized diffracted light. Next, the measurement of the retardation of a homogeneous LC cell as an examined birefringent film was demonstrated using the proposed method. The proposed method is revealed to have the same measurement performance as that of the conventional method using a pair of linear polarizers and has an advantage that there is no need for the optic axis of the test birefringent specimen to be set at a specific angle.

Enhanced diffraction properties of photoinduced gratings in nematic liquid crystals doped with Disperse Red 1.

Diffraction properties of photoinduced gratings recorded by overlapping two coherent beams at 532 nm in nematic liquid crystals doped with Disperse Red 1 were investigated with a probe beam at 632.8 nm. The grating was formed due to the alignment of dye molecules that leaded to the reorientation of the liquid crystal phase. The diffraction efficiency of the photoinduced grating was found to increase rapidly when the sample temperature was close to the clearing point in the nematic phase and a nearly 30-fold enhancement of the first-order diffraction efficiency was obtained. The pretransitional enhancement of the diffraction efficiency was discussed in terms of the reorientation of liquid crystals, optical nonlinearity effects and the onset of critical opalescence near the nematic-isotropic phase transition. Moreover, a peak shift of diffraction efficiency towards the lower temperature was observed with the increase of recording light intensity, which was attributed to laser induced photochemical disordering.

视点可控液晶光栅的研究

视点可控液晶光栅的研究

Tri-color composite volume H-PDLC grating and its application to 3D color autostereoscopic display.

A tri-color composite volume holographic polymer dispersed liquid crystal (H-PDLC) grating and its application to 3-dimensional (3D) color autostereoscopic display are reported in this paper. The composite volume H-PDLC grating consists of three different period volume H-PDLC sub-gratings. The longer period diffracts red light, the medium period diffracts the green light, and the shorter period diffracts the blue light. To record three different period gratings simultaneously, two photoinitiators are employed. The first initiator consists of methylene blue and p-toluenesulfonic acid and the second initiator is composed of Rose Bengal and N-phenyglycine. In this case, the holographic recording medium is sensitive to entire visible wavelengths, including red, green, and blue so that the tri-color composite grating can be written simultaneously by harnessing three different color laser beams. In the experiment, the red beam comes from a He-Ne laser with an output wavelength of 632.8 nm, the green beam comes from a Verdi solid state laser with an output wavelength of 532 nm, and the blue beam comes from a He-Cd laser with an output wavelength of 441.6 nm. The experimental results show that diffraction efficiencies corresponding to red, green, and blue colors are 57%, 75% and 33%, respectively. Although this diffraction efficiency is not perfect, it is high enough to demonstrate the effect of 3D color autostereoscopic display.

Diffraction properties of a vector grating liquid crystal cell fabricated using a one-step exposure of a nonorthogonal elliptically polarized interference beam

Vector grating liquid crystal (LC) cells, with periodically intermixed 0° planar and 90° twisted nematic alignments and director distributions rotated in the grating vector, were fabricated using a one-step polarization holographic exposure. A nonorthogonal elliptically polarized interference UV beam was irradiated to the empty glass cell, which had the inner walls coated with a photocrosslinkable polymer liquid crystal film. The dependence of the diffraction properties on the birefringence of the nematic LC (E7) in the resultant vector grating LC cell was determined through experimental and theoretical analysis. The polarization azimuth and ellipticity of the diffracted beams were varied using the temperature of the nematic LC.

Simple system for measuring optical rotation of glucose solution using liquid-crystal grating

We demonstrate an optical system for measuring the concentrations of optically active media using liquid-crystal polarization gratings (LCPGs). The optical rotation angle is determined by measuring the intensities of two diffracted light beams from an LCPG combined with a quarter-wave plate (QWP). The intensity ratio is used to evaluate the optical rotation angle, minimizing the dependence on changes in light source intensity and wavelength and reducing the influence of temperature-drift-induced LC birefringence shifts. We demonstrate the system by measuring the concentration of a glucose–water solution. The measurement error caused by the slight wavelength dependence of the QWP’s retardation is assessed numerically.

PA49 キラルネマチック液晶を用いた捻れ配向回折格子液晶セルの配向欠陥形成(液晶フォトニクス・光デバイス,ポスター発表,2015年日本液晶学会討論会)

PA49 キラルネマチック液晶を用いた捻れ配向回折格子液晶セルの配向欠陥形成(液晶フォトニクス・光デバイス,ポスター発表,2015年日本液晶学会討論会)

Paper No P09: Electrically Tunable Grating Using Holographic Polymer Templated Blue Phase Liquid Crystal

AbstractIn this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer‐templated blue phase liquid crystal grating. This grating is obtained by preforming a polymer grating template, and then refilling it with the blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, its driving voltage can be reduced to 43 V, while maintaining sub‐millisecond response time.

Technique for Spectropolarimetry Based on Liquid Crystal Polarization Diffraction Grating

Technique for real-time spectropolarimetry is developed. An embedded system for circular dichroism registration is designed based on National Instruments single board reconfigurable I/O platform for ultraviolet and visible spectroscopic needs. The basic functional unit of the proposed device is liquid crystal polarization diffraction grating. In order to expand the dynamic range the control of data accumulation time is provided. Two NMOS sensor linear arrays provide an excellent linearity of response.

Holographic binary grating liquid crystal cells fabricated by one-step exposure of photocrosslinkable polymer liquid crystalline alignment substrates to a polarization interference ultraviolet beam.

Holographic binary grating liquid crystal (LC) cells, in which the optical anisotropy was rectangularly modulated even as the grating was fabricated using holographic exposure, were fabricated by one-step polarization holographic exposure of an empty glass cell, the interior of which was coated with a photocrosslinkable polymer LC (PCLC). The present study is of great significance in that three types of holographic binary grating LC cells containing twisted alignments can be fabricated by simultaneous exposure of two PCLC substrates to the UV interference beams, which are sinusoidally modulated. The polarization conversion properties of the diffracted beams are explained well by theoretical analysis based on Jones calculus.

Electrically tunable holographic polymer templated blue phase liquid crystal grating**Project supported by the National Basic Research Program of China (Grant No. 2013CB328804), the National Natural Science Foundation of China (Grant No. 61307028), the Funds from the Science and Technology Commission of Shanghai Municipality (Grant Nos. 11JC1405300, 13ZR1420000, and 14ZR1422300), and the Fundamental Research Funds for the Central Universities, China (Grant

In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer templated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal (HPTBPLC) grating is free from electrode patterning, thus leading to a lower cost and more flexible applications.

Formation of holographic gratings in polymer-dispersed liquid crystals using off-resonant light

This paper presents the electro-optical characteristics of polarization-independent holographic gratings (HGs) recorded in polymer-dispersed liquid crystals (PDLCs) using off-resonant laser beam. The key mechanism is based on the low light absorbance by the materials used, which enables a slow polymerization-induced phase separation. The off-resonant light can penetrate through the cell without much energy loss (absorbance) and can be uniformly absorbed across the LC cell to produce uniform PDLC structures. The intensity-modulated interference field, which is generated by two linearly polarized off-resonant laser beams, is adopted to record the HGs. The fabricated HGs are electrically switchable and polarization independent. Moreover, the diffractions of the HGs fabricated using off-resonant light is better than those produced by resonant light.

Gratings: Light‐Driven Wide‐Range Nonmechanical Beam Steering and Spectrum Scanning Based on a Self‐Organized Liquid Crystal Grating Enabled by a Chiral Molecular Switch (Advanced Optical Materials 2/2015)

Gratings: Light‐Driven Wide‐Range Nonmechanical Beam Steering and Spectrum Scanning Based on a Self‐Organized Liquid Crystal Grating Enabled by a Chiral Molecular Switch (Advanced Optical Materials 2/2015)

FDTD Modelling of Silver Nanoparticles Embedded in Phase Separation Interface of H‐PDLC

We report localized surface plasmon resonance (LSPR) of silver nanoparticles (NPs) embedded in interface of phase separation of holographic polymer‐dispersed liquid crystal (H‐PDLC) gratings using Finite‐Difference Time Domain method. We show that silver NPs exhibit double resonance peak at the interface, and these peaks are influenced by the angle of incident light. We observe a blue shift of the wavelength of resonance peak as the incident angle increases. However, the location of silver NPs at the interface has nearly no effect on the wavelength of resonance peak. Also we show near‐field and far‐field properties surrounding silver NPs and find that field distribution can be controlled through rotation of incident angle. Therefore, LSPR properties of silver NPs within H‐PDLC gratings can be excited by appropriate wavelength and angle of the incident light.

时分全分辨率可控液晶光栅设计

时分全分辨率可控液晶光栅设计

Topologically patterning of polyvinyl alcohol microstructures for vertical-/hybrid-aligned nematic liquid-crystal gratings doped with polyhedral oligomeric silsesquioxane nanoparticles

We demonstrate a soft lithography approach for fabrication of a topographically patterned polyvinyl alcohol (PVA) liquid-crystal (LC) alignment layer. This specific approach employs modified micromolding in capillaries for negative replication of the PVA microstructures on indium tin oxide (ITO) substrates from patterned poly(dimethylsiloxane) molds in a single step, leading to planar alignment on the desired regions. By doping with polyhedral oligomeric silsesquioxane nanoparticles, which can induce vertical alignment on bare ITO surfaces, periodic LC phase gratings based on an alternating vertical-aligned/hybrid-aligned nematic geometry are presented as an application, and a theoretical model was used to simulate and examine the experimental results.

Blazed vector grating liquid crystal cells with photocrosslinkable polymeric alignment films fabricated by one-step polarizer rotation method

Blazed vector grating liquid crystal (LC) cells, in which the directors of low-molar-mass LCs are antisymmetrically distributed, were fabricated by one-step exposure of an empty glass cell inner-coated with a photocrosslinkable polymer LC (PCLC) to UV light. By adopting a LC cell structure, twisted nematic (TN) and homogeneous (HOMO) alignments were obtained in the blazed vector grating LC cells. Moreover, the diffraction efficiency of the blazed vector grating LC cells was greatly improved by increasing the thickness of the device in comparison with that of a blazed vector grating with a thin film structure obtained in our previous study. In addition, the diffraction efficiency and polarization states of ±1st-order diffracted beams from the resultant blazed vector grating LC cells were controlled by designing a blazed pattern in the alignment films, and these diffraction properties were well explained on the basis of Jones calculus and the elastic continuum theory of nematic LCs.

Improvement on the Performance of Holographic Polymer-Dispersed Liquid Crystal Gratings with Surface Plasmon Resonance of Ag and Au Nanoparticles

An investigation and comparison of the characteristics of holographic polymer-dispersed liquid crystal (H-PDLC) gratings doped with Ag and Au nanoparticles (NPs) is presented. The experimental results show that the diffraction efficiency and electro-optical properties of holographic gratings are improved through the addition of Ag and Au NPs. It is notable that Ag NP-doped gratings have far superior performance than those containing Au NPs. Furthermore, we find that the diffraction efficiency improvement can be explained as being due to the surface plasmon resonance of the metal NPs embedded in the PDLC. We theoretically simulate the surface plasmon resonance (SPR) wavelengths of the Ag and Au NPs within the PDLC and find that the laser wavelength used to fabricate the holographic gratings is much closer to the SPR wavelength of Ag NPs than that of Au NPs. Atomic force microscopy images show that the phase separation of the Ag-doped grating is improved, and the grating structure is much smoother than those of the undoped samples and the Au NP-doped samples, because of the SPR properties of the Ag NPs in the PDLC microstructure during the holographic recording process.

Light‐Driven Wide‐Range Nonmechanical Beam Steering and Spectrum Scanning Based on a Self‐Organized Liquid Crystal Grating Enabled by a Chiral Molecular Switch

Light‐Driven Wide‐Range Nonmechanical Beam Steering and Spectrum Scanning Based on a Self‐Organized Liquid Crystal Grating Enabled by a Chiral Molecular Switch