Polarization Holographic Gratings Research Articles

Tunable polarization holographic gratings obtained by varying the ratio of intensities of the recording beams

Polarization holography has been extensively applied in many fields, such as optical science, metrology, and biochemistry, due to its property of polarization modulation. However, the modulated polarization state of diffracted light corresponds strictly to that of incident light one by one. Here, a kind of tunable polarization holographic grating has been designed in terms of Jones matrices, and intensity-based polarization manipulation has been realized experimentally. The proposed tunable polarization holographic grating is recorded on an azobenzene liquid-crystalline film by a pair of coherent light beams with orthogonal polarization states and asymmetrically controlled intensities. It is found that the diffracted light can be actively manipulated from linearly to circularly polarized based on the light intensity of the recording holographic field when the polarization state of incident light keeps constant. Our work could enrich the field of light manipulation and holography.

Two-Dimensional Polarization Holographic Gratings in Azopolymer Thin Films: Polarization Properties in the Presence or Absence of Surface Relief

During polarization holographic recording in azopolymer thin films, usually together with the volume anisotropic grating, a surface relief grating (SRG) is also formed. By using two consecutive exposures, it is possible to obtain a two-dimensional (2D) grating. To the best of our knowledge, the polarization properties of such gratings have not been studied yet. To determine the influence of the surface relief on the polarization selectivity of the 2D gratings, we propose two methods to suppress the SRG formation: by varying the recording conditions or varying the sample structure. In these experiments we have used the commercially available azopolymer PAZO, poly[1-4-(3-carboxy-4-hydrophenylazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] to perform the polarization holographic recording using a 442 nm He-Cd laser. As indicated by our results, when the surface relief is present, it strongly dominates the response of the 2D grating and it behaves almost as a scalar polarization insensitive grating. Conversely, when the SRG formation is suppressed, the polarization properties of the 2D grating in all four diffracted orders are very well pronounced. In this way, we demonstrate that we can easily control SRG formation and, if desired, obtain 2D grating with high surface relief modulation, or alternatively record polarization-selective 2D gratings with virtually no surface relief.

Photoalignment of sub-micrometer periodic liquid crystal polarization grating by using the optical imprinting method.

Photoalignment of liquid crystal polarization grating based on optical imprinting is a promising technique for polarization grating mass production. However, when the period of the optical imprinting grating is in the sub-micrometer level, the zero-order energy from the master grating will become high, and it will strongly affect the photoalignment quality. This paper proposes a double-twisted polarization grating structure to eliminate the zero-order disturbance of master grating and gives the design method. Based on the designed results, a master grating was prepared, and the optically imprinted photoalignment of polarization grating with a period of 0.5μm was fabricated. This method has the advantages of high efficiency and significantly greater environmental tolerance than the traditional polarization holographic photoalignment methods. It has the potential to be used for large-area polarization holographic gratings production.

Filtration Properties of Polarization Holographic Gratings Recorded in Liquid Crystal Composites

Filtration Properties of Polarization Holographic Gratings Recorded in Liquid Crystal Composites

Reversible supramolecular chiral structures induced in azopolymers by elliptically polarized light: influence of the irradiation wavelength and intensity.

Photoinduced supramolecular chiral structures in azo materials have been extensively studied for the development of all-optical switches and because of their influence on the properties of certain types of polarization holographic gratings. Here, we investigate chiral structures induced by irradiation with elliptically polarized light in thin films of four azopolymers denoted as PAZO, P1, P1-2, which are amorphous, and P2, which is liquid crystalline. Their formation is characterized in real time by the kinetics of azimuth rotation. The influence of the irradiation wavelength and intensity is also analyzed. The largest azimuth rotation per unit thickness is achieved in PAZO (33°/µm) and P1-2 (25°/µm). Reversibility of the chiral structures is demonstrated by a tenfold change in the direction of rotation. Our results also indicate that chiral structures formation occurs significantly faster than the induction of linear birefringence.

Influence of the size of Au nanoparticles on the photoinduced birefringence and diffraction efficiency of polarization holographic gratings in thin films of azopolymer nanocomposites

This study is aimed to determine the influence of the size of gold (Au) nanoparticles (NP) doped in azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) on the photoinduced birefringence of the nanocomposite thin films as well as on the diffraction efficiency of polarization holographic gratings recorded in them. For this reason, we used spherical Au NP with five different dimensions – 10, 20, 30, 40 and 50 nm. Concentrations of the NP in the nanocomposites varied from 0 a.u. (non-doped samples) to 16 a.u. where 1 a.u. corresponds to 0.015 wt %. Birefringence was induced with He–Cd laser (λ = 442 nm) and measured at 635 nm using DPSS laser. We observe an enhancement of photoinduced birefringence, which is most pronounced for the Au NP with size 20 nm. The polarization holographic gratings were inscribed with two orthogonal circular polarizations (left- and right-handed). AFM measurements were performed to determine the properties of the resulting surface relief gratings. Our results indicate that both the diffraction efficiencies and surface relief modulation of the gratings inscribed in the nanocomposite thin films are higher compared to those in the non-doped samples.

Characterization of Polarization Holographic Gratings Obtained on Azopolymer Thin Films by Digital Holographic Microscopy

Polarization diffraction gratings are formed by one-step polarization holographic recording in azopolymer thin films. The evolution of the gratings parameters, such as the modulation of diffraction efficiency and relief depth with regard to different exposure dose is analyzed. Phase-shifting digital holographic microscopy is applied for the measurement of the light-induced polarization diffraction gratings. For the accurate hologram acquisition and reconstruction of the complex amplitude transmitted by the gratings, we performed all-optical (without moving components) phase-shifting implemented within in the imaging system of the digital holographic microscope. The experimental measurement results and theoretical predictions were compared and analyzed.

Polarization holographic gratings in PAZO polymer films doped with particles of biometals

The paper presents a study of the diffraction efficiency of polarization holographic gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with Cu(II) 3-amino-5,5′-dimethylhydantoin (CLP) and Ni(II) 3-amino-5,5′-dimethylhydantoin (NLP) at three different concentrations, namely 1, 2 and 5 wt.%. The influence of the dopants composition and concentration on the parameters of the polarization holographic gratings recorded in the thin composite films has been discussed. The gratings are recorded with a He-Cd gas laser with wavelength 442 nm. The polarization of the recording beams was left and right circular and the recording angle was 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Diffraction efficiency (η) higher than 30 % was achieved for the hybrid samples, as well as 585 nm surface relief height.

Effect of molecular weight of PEG polymer matrix on the diffraction efficiency of Methyl Orange holographic media

Abstract Recording media for diffraction gratings formation based on polymer films of polyethylene glycol doped with the photoisomerisable azo-dye Methyl Orange have been developed. Holographic recording of the plane wave front for parallel and orthogonal orientation of polarization vectors of light beams have been performed at room temperature. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence the average molecular weight of polymer matrix and solvent system for thin layers formation on the diffraction efficiency. Five PEG polymers were used as host for azo-dye incorporation −1500, 4000, 6000, 10,000 and 40,000, and two solvent systems, EtOH–H2O and THF-H2O, were examined to investigate film-forming properties. It was concluded, that structure of films as well as diffraction efficiency value and curves character strongly depend on PEG molecular weight.

Polarization holographic gratings with enhanced parameters recorded in azopolymer based nanocomposite materials

We present study of the parameters of polarization holographic gratings recorded in thin films of the azopolymer PAZO (Poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) and in a composite PAZO-based organic/inorganic material with incorporated TiO2 nanoparticles with size 21 nm and different concentrations. The gratings are inscribed by two plane waves with left and right circular polarization from a He-Cd gas laser (442 nm) at recording angle 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. Gratings with different spatial frequencies are obtained by varying the recording angle. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Our results indicate that the diffraction efficiency for the hybrid samples is enhanced with respect to the pure azopolymer films. Comparison is also made between polarization response of samples deposited from water and from methanol solution.

Multi-functional two-dimensional holographic grating based on silver pattern coated by azopolymer

A two-dimensional diffraction device with the properties of polarization modulation, angular sensitivity, polarization-independent diffraction efficiency and repeatable recording has been designed and fabricated in an azopolymer-silver double-layer film by means of two-step holographic exposure. A silver pattern is formed in the light field with the sinusoidally distributed intensity, and then a polarization holographic grating is recorded in the azobenzene liquid-crystalline layer through the interference of two orthogonally linearly polarized lasers. We report here that the polarization states of the diffraction beams from the recorded two-dimensional grating are orthogonally modulated; the diffraction efficiency is related to the incident angle of the probe light and the rotation angle between the two-step recording, while independent on the incident polarization state. Furthermore, the experimental results are analyzed through the scalar diffraction theory and Jones matrices.

Effect of yttrium oxide nanoparticles on the dielectric properties and dynamics of the formation of holographic polymer–liquid-crystal composites

The electro-optic properties of highly structured polymer–liquid-crystal composites based on acrylate monomers and E7 liquid crystals doped with ${{\rm Y}_2}{{\rm O}_3}$Y2O3 nanoparticles are considered. The influence of nanoparticles on the diffraction efficiency, the driving voltage, the dielectric properties, and the dynamics of the formation of holographic and polarization holographic diffraction gratings inscribed in polymer–liquid-crystal composites is demonstrated. The diffraction efficiency of the doped holographic diffraction gratings decreases, and that of the polarization diffraction gratings increases. Doping with nanoparticles leads to a decrease in driving stresses and increases the formation time and dielectric constant of highly structured polymer–liquid-crystal composites.

Polarization Gratings in Azobenzene-Based Fully Liquid Crystalline Triblock Copolymer.

Photosensitive liquid crystalline (LC) block copolymers are a universal platform for designing functional materials for optics and photonics. Here, azobenzene LC ABA triblock copolymer containing mesogenic groups in each block is studied as a medium for the recording of polarization holographic gratings. The fast recording of polarization gratings is successfully performed with two orthogonally circularly polarized light beams of a 532-nm laser. It is shown that annealing of the recorded polarization grating increases diffraction efficiency considerably, by a factor of 70, and provokes simultaneous erasing of the surface relief grating if it has been recorded. Holographic behavior of the triblock copolymer is compared with that of an azobenzene homopolymer and a random copolymer, which has the same monomer ratio as the triblock copolymer. The obtained results are expected to allow designing new materials for the polarization of optical elements and holographic data storage.

Design of an all-optical logic sequence generator based on polarization holographic gratings

In this Letter, an all-optical logic sequence generator based on two different polarization holographic gratings has been proposed and demonstrated, which has one input port and four output ports. The polarization state of input light signal determines logic output signals. It can produce four kinds of logic sequence output signals: 1000, 0100, 0010, and 0001, corresponding to the input light signal of four different polarization states: the p-linear, s-linear, left-handed circular, and right-handed circular. The two polarization gratings have been fabricated, and the working principle of the logic sequence generator has been proved by diffraction pattern analysis of polarization gratings.

Effect of Yttrium Oxide Nanoparticles on the Diffraction Efficiency of Holographic Polymer-liquid Crystal Gratings

Electro-optical properties of the holographic and polarization holographic diffraction gratings formed in polymer-liquid crystal composites doped with Y2O3 nanoparticles are considered. The effect of impurities on the diffraction efficiency and operated electric field is shown. The diffraction efficiency of doped holographic diffraction gratings decreases, whereas the diffraction efficiency of polarization diffraction gratings increases. Doping with nanoparticles leads to a decrease in the operated electric field.

Polarization holographic gratings with high diffraction efficiency recorded in azopolymer PAZO

Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used − 10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the + 1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.

Polarization modulation by means of tunable polarization gratings in an azobenzene side-chain liquid-crystalline polymer film.

Polarization modulation was achieved by means of a new type of grating recorded with two 532nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged. With the polarization angle changing from 0 to 90deg, the ± first-order diffraction efficiency increased from 5.15% to 10.53%. Diffraction properties of the recorded gratings were attributed to the combination of polarization holographic gratings and amplitude gratings based on the calculation of Jones matrices and polarization holographic theory.

Polarization holographic gratings in PAZO azopolymer recorded with different recording-beams polarizations

Polarization holographic gratings (PHG) were recorded using a laser emitting a wavelength of 491 nm in thin films of the (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]) azopolymer, shortly denoted as PAZO. Thin azopolymer films with various thicknesses were spin-coated on plastic and glass substrates. Four different polarization states of the recording beams were used, and the results compared: a) two vertical linear polarizations, b) horizontal and vertical linear polarizations, c) linear polarizations at +45° and –45° relative to the recording plane, and d) two orthogonal circular polarizations – left- and right-handed (LCP and RCP). The diffraction efficiency in the +1 diffraction order was monitored in real time by a probing laser beam at the wavelength of 635 nm. The results indicate that the highest diffraction efficiency is achieved when recording with orthogonal polarizations – linear at ±45° or left and right circular. This is explained by the ability of the azopolymer material to record the variations in the polarization state of light better than the variations in its intensity. The holographic gratings obtained can be used to enhance the light-extraction efficiency of an OLED device.

Photoinduced Anisotropy of IWK-2D Azobenzene Molecular Glassy Films

We have experimentally studied photoinduced anisotropy (PA) of holographic gratings in IWK-2D [precise chemical notation: 2-(3-(4-((4-(bis (2-(trityloxy) ethyl) amino) phenyl) diazenyl) styryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile] azobenzene molecular glassy films in transmission and reflection modes using a special simultaneous holographic recording and readout setups which enabled measurements of PA time evolution. PA manifested itself by diffraction efficiency difference with linear s- and p-polarizations. Three different types of polarization holographic gratings were recorded and studied using p-p, L-L and L-R polarized beams creating different recording interference patterns. Atomic force microscope (AFM) was used to study the surface profile changes. Experimental evidence was obtained that the transmission mode PA was due to the both recorded surface relief and volume polarization gratings whereas the reflection mode PA was due to the recorded surface relief gratings. The main PA features were similar for all three types of polarization gratings whereas details were different. PA properties of IWK-2D films were notably distinctive from those of previously studied films.

Enhanced diffraction efficiency of polarization holographic gratings in Au nanoparticles-doped methyl orange film

The polarization holographic gratings recorded in Au nanoparticles-doped methyl orange/polyvinylpyrrolidone (MO/PVP) composite films were investigated. The polarization state of diffraction beams was controlled by a probe light and holographic gratings together. The first-order diffraction efficiency of the MO/PVP film doped with Au nanoparticles was measured to be 3.2 times larger than that of pure composite film. Meanwhile, an obvious enhancement of photoinduced birefringence of MO molecules was also demonstrated. This enhancement of diffraction efficiency and photoinduced birefringence was discussed in terms of the localized field effect via the surface plasmon resonance of Au nanoparticles, which was confirmed by finite-difference time-domain simulation.