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We present an optically addressed non-pixelated spatial light modulator. The system is based on reversible photoalignment of a LC cell using a red light sensitive novel azobenzene photoalignment layer. It is an electrode-free device that manipulates the liquid crystal orientation and consequently the polarization via light without artifacts caused by electrodes. The capability to miniaturize the spatial light modulator allows the integration into a microscope objective. This includes a miniaturized 200 channel optical addressing system based on a VCSEL array and hybrid refractive-diffractive beam shapers. As an application example, the utilization as a microscope objective integrated analog phase contrast modulator is shown. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 1001

The high coherence of laser light sources is a key to the application of diffractive optics usable in holographic AR/VR displays. This can be combined with switchable diffractive elements, which are advantageous for several optical functions used in immersive holographic displays such as shutters, polarization filters, for rapid beam deflection and selection. We demonstrate a compact, effective and robust diffraction wide-angle switchable beam-deflecting device based on circular polarization gratings possessing Bragg-performances (Bragg-PG) and a polarization switch. Such grating/polarization switch pair may, for instance, be a discrete switchable deflection element or as a switching element for pre-deflection with field lenses for application in holographic AR/VR displays. Micrometer-thick circular polarization gratings characterized by high diffraction efficiency (DE > 95%), large diffraction angles ( 95% in the vis spectral range) and stable symmetric and slanted circular Bragg polarization gratings were fabricated using the developed material and processing technique. The high usable diffraction angles combined with high DE make the Bragg-PG attractive for HMD AR/VR applications because of the system inherent short focus lengths and large numerical apertures needed to meet the low space budget in HMD and other optical systems.

For the first time the cholesteric mixture containing nematic polymer with small amount of chiral-photochromic dopant is used for electroinduced diffraction gratings production. The gratings are obtained by applying electric field to the planar-aligned cholesteric polymer layer causing its periodical distortion. Material developed permits manipulating supramolecular helical structure by means of UV exposure resulting in helix untwisting. Photo-controlling of helix pitch brings to change parameters of the electroinduced gratings. Due to macromolecular "nature" of the material one can easily stabilize electroinduced gratings by fast sample cooling. All-known cholesteric grating types are realized in the studied polymer material. It is observed that the grating vector can be oriented along or perpendicular to the rubbing direction of the cell. It is shown that the diffraction efficiency is dictated by grating type and the amplitude of the applied electric field and can achieve about 80%. Moreover, the period of gratings can be tuned upon UV light illumination. The possibility of 2D gratings creation is also demonstrated. The described material and approach gives an opportunity to easily fabricate a variety of diffraction gratings with flexibly controllable parameters. Such gratings can be potentially applied in optics, optoelectronics, and photonics as intelligent diffraction elements.

A novel type of rotatable diffraction volume gratings based on cholesteric liquid crystals with phototunable helix pitch is elaborated. For this purpose the cholesteric liquid crystalline mixture with high helix pitch tunability and reversible photoinduced helix handedness inversion containing azobenzene-derivative of the chiral-photochromic dopant is developed. It was shown that the prepared cholesteric mixture under the hybrid (homeotropic – planar) boundary conditions spontaneously forms a well-oriented striped domain texture which acts as a phase grating. Under the effect of light the changes of helix pitch take place due to the molecular photoreaction of chiral-photochromic dopant causing the variation of the period of striped domain structure and its rotation. The clockwise and counterclockwise rotation of the obtained gratings can be achieved by switching between UV and visible light, correspondingly. The maximum angle of the continuous rotation is ≈690°, while the total rotation caused by UV light illumination reaches ≈1220°. The creation of a variety of complex-organized structures by local light exposure of the cholesteric domain texture is demonstrated. The observed advanced photooptical effects have potentially wide and important applications from scientific and applied points of view.

Passive and active polarization elements were created by surface and bulk photo-alignment of LCs, reactive LCs, photo-sensitive LCP and photo-curable monomer/LC composites. The use of different photo­sensitive liquid crystalline materials for the development of highly anisotropic elements with high spatial resolution and stability or, alternatively, fast switch ability will be discussed. Photo-active and voltage tunable polarization and diffraction elements are presented. For active micro-optic application a photo-addressed patterned retarder was created. Electrically switchable diffraction gratings were generated by interference exposure of photo-curable LC composites at room temperature characterized by droplet free morphology. These polarization sensitive diffraction elements are characterized be excellent optical properties and low switching times.

The recording of polarization gratings in films of a cholesteric liquid crystalline polymer with different helix pitch was studied in detail. For this purpose, the cholesteric mixture of the nematic azobenzene-containing copolymer with a chiral- photochromic dopant was prepared. The utilization of such mixture has made possible to realize dual optical photorecord- ing in one system, first due to the phototuning of the helix pitch by UV light and second the polarization grating recording process by exposure with polarized visible light. The diffraction efficiency strongly depends on the cholesteric helix pitch and films thickness: the increase of the confinement ratio d/p (where d, film thickness; p, helix pitch) results in growth of the diffraction efficiency. Comparison of the induction of polariza- tion gratings in cholesteric, nematic (copolymer without chiral dopant), and amorphous (nonannealed) cholesteric films revealed that only the cholesteric films were characterized by significant oscillations in the diffraction efficiency signal as well as by the presence of the maximum in the first-order dif- fraction efficiency in the initial stage of the grating recording process. It was found that in addition to the polarization gra- ting surface relief gratings (SRGs) were also formed in the studied systems, however, the amplitude of the SRG inscribed in the cholesteric films was lower (� 20 nm) compared to the grating amplitude obtained in nematic films (� 60 nm). More- over, increasing helix pitch resulted in a decrease of the SRG amplitude. The obtained experimental data demonstrate the great potential of cholesteric LC mixtures of such type for dif- ferent applications as photoactive materials for photonics. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 773-781

We considered the mechanism by which bulk periodic structures are formed in polymer-nanoparticle nanocomposites. Phase bulk gratings are formed due to the diffusion transfer of nanoparticles between illuminated and nonilluminated regions of a composite upon polymerization in an interference field. We found that, for the majority of studied nanocomposites containing nanoparticles of different natures, the relative modulation of the concentration of nanoparticles exceeds 80%. We showed that the initial composition should be optimized with respect to the mass of nanoparticles, which ensures a maximal recording efficiency at a minimal level of light scattering in the grating. We found that, for each medium, there exist optimal recording conditions (the intensity and period of the field) under which n 1 is determined only by the parameters of the medium and does not depend on the parameters of the field. Examples of the practical use of periodic structures based on developed holographic nanocomposites are given.

5 pages, 3 figures.-- et al., An efficient procedure to create oriented polymer films with strongly anisotropic properties is described. It is based on a two-step process combining a photochemical and a thermal aligning step. The orientation of the polymer parallel or perpendicular to linearly polarised incident light can be adjusted. The method presented allows for simple fabrication of films with anisotropic absorption and emission characteristics with a dichroism of 0.7 and a fluorescence anisotropy of about 8.

In this letter we report a simple technique to produce volume holographic gratings based on photopolymerizable composites containing TiO2 nanoparticles. Diffraction gratings with high refractive index modulation amplitude (up to 1.25 × 10−2) have been formed due to the periodic distribution of high refractive index nanoparticles in a low refractive index polymer matrix. The diffraction efficiency increases strongly on increasing the nanoparticle concentration. Taking the mixture with 10 wt.% TiO2 nanoparticles, gratings with high diffraction efficiency, low level of scattering and high transparency in the visible-wavelength range have been obtained. This will ultimately lead to different applications of diffractive optical elements based on nanocomposites. The dependence of the gratings’ diffraction efficiency on the intensity of probe laser pulses at 1064 nm has been explored. It is shown that the nonlinear response of the gratings is attributed mainly to the nonlinear properties of the TiO2 nanoparticles embedded in the polymer matrix. The mechanism of the grating formation and the reasons for the nonlinear behavior of the diffraction efficiency are discussed.

Optically anisotropic films of side-group liquid crystalline copolysiloxane doped with photochromic azobenzene and stilbene derivatives were prepared by using standard liquid crystal cells of 4 μm in thickness. The films were irradiated with high power density laser light with the electric field vector creating an angle equal to 45° with the initial optical axis of the samples. As a result of irradiation, the photoorientation of the photochromic molecules, and the cooperative reorientation of the copolysiloxane side groups occurred. In the case of the copolymer layers containing azobenzene, the optical axis was turned by an angle of 45° during sufficiently long irradiation. The angle of reorientation and the degree of anisotropy were determined for the irradiated areas of the samples.

The 3D anisotropy generated by photoorientation of thin films of azobenzene containing polymers can be determined using waveguide spectroscopy [1-4]. Irradiation of the films in the glassy state of the polymers with polarized light resulted in almost perfectly oblate index ellipsoids. Recently [5], we have found, that in the case of LC polymers the anisotropy can be amplified by annealing. The investigation of a number of polymers shows, that various types of 3D orientations (biaxial and uniaxial, oblate and homeotropic) can be obtained by such a annealing procedure. The film interfaces seem to play a crucial role for the respective behaviour.

A cholesteric mixture based on the nematic liquid crystalline side-chain polymer doped with a chiral-photochromic compound was prepared and used as an active medium for creation of stable polarization selective gratings by phototunable modulation of the helix pitch. Such modulation was fabricated in the polymer mixture by a nonpolarized UV-irradiation with spatially modulated intensity that causes E-Z isomerization of a chiral-photochromic dopant, decreasing its helical twisting power. It was shown that the gratings recorded by UV-exposure through a mask are strongly selective to the handedness of circular polarized light. The studied polymer film forms a right-handed helical structure and, correspondingly, the diffraction of only the right-circularly polarized light was found in the transmittance mode. The maximum diffraction efficiencies were found for the wavelength values between the maxima of selective light reflection. The films obtained open very interesting possibilities for further development of materials with stable gratings operating in the entire visible spectral range. Both the position and the width of the spectral range of an efficient diffraction can be easily controlled by the UV exposure and concentration of the dopant. The materials obtained and methods developed can be used for creation of specific diffraction elements for optics and photonics.

We present a device for tunable spatial polarization shaping, based on a red light photo-addressable cell. Such a cell compartment is based on a bisazobenzene containing photoaligning layer and a rubbed PI aligning and is filled with the LC mixture E5. Switchable spatial addressing patterns are generated by a 200 channel micro optical addressing unit based on a red VCSEL array (λ = 650 nm) and diffractive beam shapers.

In the present work we report low-threshold distributed feedback (DFB) lasing from electrically tunable holographic polymer?liquid crystal transmission gratings of POLIPHEM type doped with pyrromethene 567. Due to their uniform droplet-free micro-morphology, the POLIPHEM gratings possess high diffraction efficiency and excellent optical quality. Second-order lasing with a threshold of ~0.8??J/pulse and a bandwidth of ~1?nm was achieved under the excitation of a frequency-doubled Nd:YAG laser operating at 532?nm. The laser emission wavelength was tuned from 572?625?nm by varying the grating period. Application of an electric field switches off or tunes the lasing intensity. An electrically-induced blue-shift of the output laser emission was observed.

This letter reports on the optimized design and operation performance of a second order distributed feedback (DFB) dye laser based on an active organic waveguide with a volume Bragg grating. The DFB gratings were inscribed holographically in a dye-doped organic nanocomposite containing high refractive index inorganic nanoparticles. In this work we experimentally investigated and theoretically analyzed the influence of waveguide and grating parameters on the spectral and energy characteristics of this kind of DFB laser in order to obtain a narrow-band emission of low divergence. We will show that a tailored improvement of the waveguide and grating parameters provides a low-threshold laser emission in the spectral range of 570–620 nm with a linewidth of less than 0.05 nm and an output beam profile close to a Gaussian distribution.

Phase holographic materials based on phenanthrenquinone (PQ) in poly(methylmethacrylate) (PMMA) matrices additionally doped with laser dyes (LD) have been developed and investigated. It was found that the holographic properties of the dye-doped materials are almost the same as that of pure PQ-PMMA. In particular, the amplification of the holographic gratings due to post-exposure diffusion was demonstrated. An amplitude of the refractive index modulation of about 3 x 10(3) was achieved for the enhanced gratings with periods in the range of 0.3-30 mu m. Homogeneous distribution of PQ and LD in the enhanced gratings was found by means of a microscope-spectrometer. Such doped volume gratings can be used for different optical and photonic applications. As one possible application of the gratings distributed feedback lasing was tested. A narrow-band second-order laser emission has been demonstrated in 18 mu m thick volume gratings based on optimized PQ-PMMA materials doped with pyrromethene laser dyes.

The capability of the method of immersion transmission ellipsometry (ITE) (Jung et al. Int Patent WO, 2004/109260) to not only determine three-dimensional refractive indices in anisotropic thin films (which was already possible in the past), but even their gradients along the z-direction (perpendicular to the film plane) is investigated in this paper. It is shown that the determination of orientation gradients in deep-sub-mu m films becomes possible by applying ITE in combination with reflection ellipsometry. The technique is supplemented by atomic force microscopy for measuring the film thickness. For a photo-oriented thin film, no gradient was found, as expected. For a photo-oriented film, which was subsequently annealed in a nematic liquid crystalline phase, an order was found similar to the one applied in vertically aligned nematic displays, with a tilt angle varying along the z-direction. For fresh films, gradients were only detected for the refractive index perpendicular to the film plane, as expected.

In this study, we examine the influence of the corrugation height of surface relief gratings on the output characteristics of organic distributed feedback (DFB) lasers. A series of surface relief gratings with a constant corrugation period (410 nm) and variable corrugation heights ranging from 20 and 80 nm are fabricated by the illumination of a new developed photosensitive azobenzene containing material with an interference pattern. A blend of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo{2,1',3}-thiadiazol)] and poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] is used as organic laser active material which is deposited by spin-coating onto the grating array. The investigation of the laser output characteristics reveals an increase of the slope efficiency by a factor of 4 from 0.8% to 3.7% due to an increase of the grating height. The laser threshold decreases only slightly from 8.5 mJ/cm2 to 6.0 mJ/cm2 with increasing corrugation height. We interpret this as a result of the change of coupling between light mode and grating. The study helps to relate this to loss mechanisms of the DFB lasing process. This enables a further optimization of the DFB laser design.

This paper reports photoalignment control of discotic liquid crystal (DLC), a pentakis-(phenylethynyl)benzene derivative, using a thin film of an azobenzene-containing polymer. The polymer films was irradiated with non-polarized light obliquely, subsequently annealed at 240°C and coated with a DLC solution to give a mono-domain texture of DLC films with excellent optical quality. Photopatterning of DLC films was achieved by imagewise irradiation of the polymer film at an oblique incident.

The dependence of the Photo-orientation process on the liquid crystallinity and the molecular aggregation is studied. In the case of ordered films the photo-orientation is restricted, but this restriction can be overcome by a photochemical pre-treatment using UV light or by higher power density of the incident Vis light. The optical anisotropy increases with spacer length or the ordering tendency of the polymers.

Photoreorientation processes in photochromic LCP's are dependent on the supramolecular order. The efficiency is much higher in films of low order, which have been obtained by a suitable preparation or by an intermediate photochemical decoupling. On the other hand, a photochemically induced order in an initially isotropic film acts as initializing force, governing the direction of thermotropic self-organization. The combination of both ordering principles causes a significant amplification of the light-induced optical anisotropy.

The distributed feedback (DFB) lasers based on a waveguide with volume grating providing feedback through second order Bragg diffraction were experimentally and theoretically investigated and optimized. The gratings are readily inscribed holographically in a layer of a dye-doped organic nanocomposite containing high refractive index inorganic nanoparticles. It is shown that the improvement of the parameters of waveguide and grating provides narrow-band lasing emission with a beam profile close to Gaussian intensity distribution.

We report on a thin-film polymer distributed feedback (DFB) laser, composed of an active waveguide and an external volume Bragg grating providing second-order distributed feedback, and its output properties. The volume noncorrugated Bragg gratings were inscribed holographically in an organic–inorganic nanocomposite containing high refractive index inorganic nanoparticles. The active waveguide doped with PM576 was fabricated on top of the Bragg grating. The DFB laser presented exhibits both surface and edge emission by transverse optical pumping with nanosecond laser pulses at 532 nm. A theoretical model to analyze the influence of the parameters of the active waveguide and the Bragg grating on the laser performance has been developed.

3D arrays of latex particles (0.1– 3 μm ) have been prepared using a flow cell or a vertical deposition method. Such ordered arrays are of particular interest as model systems for photonic crystals and 3D optical gratings. They possess the properties of photonic band gap materials, can be used as templates for the fabrication of inverse structures, and their lattice constants are easily adjusted by the particle diameter. Well-ordered films of thin colloidal crystals were obtained. The arrays exhibit well-developed stop-bands in transmission and reflectance spectra covering the UV–vis–NIR–IR spectral area (0.2– 6.5 μm ) . Besides a hexagonal diffraction pattern, different pictures of trigonal symmetry were identified by diffraction microscopy using a Bertrand lens. The light intensity distribution and chromatic dispersion for different types of diffraction pattern have been analysed.

We studied peculiarities of the structural reconstruction within holographically recorded gratings on the surface of several different amorphous azobenzene-containing polymers. Under illumination with a light interference pattern, two processes take place in this type of polymer. The first process is the light-induced orientation of azobenzene units perpendicular to the polarization plane of the incident light. The second one is a transfer of macromolecules along the grating vector (i.e. perpendicular to the grating lines). These two processes result in the creation of a volume orientation grating (alternating regions of different direction or degree of molecular orientation) and a surface relief grating (SRG)-i.e. modulation of film thickness. One can assume that both orientation of molecules and their movement might change the local mechanical properties of the material. Therefore, formation of the SRG is expected to result also in modulation of the local stiffness of the polymer film. To reveal and investigate these stiffness changes within the grating, spin-coated polymer films were prepared and the gratings were recorded on them in two different ways: with an orthogonal circular or orthogonal linear polarization of two recording light beams. A combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) techniques was applied for SRG development monitoring. We demonstrate that formation of the phase gratings depends on the chemical structure of polymers being used, polymer film thickness, and recording parameters, with the height of grating structures (depth of modulation) increasing with both the exposure time and the film thickness. UFM images suggest that the slopes of the topographic peaks in the phase gratings exhibit an increased stiffness with respect to the grating depressions.

A distributed-feedback laser, operating in the spectral range of 590-670 nm is reported. The laser device is based on surface relief grating providing a second order DFB structure. The surface relief grating is inscribed in an azobenzene-containing material and an active layer realized in high refractive index poly(phenylquinoxaline) matrix. It is shown that the design of laser device provides for the possibility of simple replacement of an active layer. This allows, in particular, laser wavelength tuning without rewriting of the surface relief grating.

Distributed feedback (DFB) lasers are produced directly in fluorescent azobenzene-containing materials using a single holographic optical step. Surface relief grating capable of producing images in fluorescence microscopy can be holographically formed in a number of materials.

Amorphous, optically isotropic films of photochromic liquid crystalline copolymers have been prepared and irradiated with linearly polarized light. In this way high values of dichroism and birefrin...

Large aspect ratio 3D microstructures (arrays of square posts and linear rectangular gratings) fabricated in a number of azobenzene-containing materials by soft lithography were manipulated by a single beam of polarized light. The materials exhibited different response to the beam orientation and the direction of light polarization. An elongation of the square posts both along and perpendicular to the polarization plane was observed depending on material. Reversibility of the deformation has been demonstrated. Broadening of the hills, amplitude and shape changing were observed for linear gratings. A slanted expose led to the blazed asymmetric structures. Some aspects of light-induced deformation mechanisms in azobenzene-containing materials are discussed. The approach developed in the paper can be useful both for the understanding of mass transport mechanism in azobenzene-containing materials and for the fabrication of diffracted optical structures.

The application of holographic photocurable organic–inorganic nanocomposites is considered for the creation of permanent polymer microlasers with second-order distributed feedback (DFB) based on volume transmission diffraction gratings. The use of inorganic nanoparticles of size < 10 nm and refractive index (RI) ≥ 2 ensures the formation of volume periodic structures of high RI contrast and, correspondingly, high feedback efficiency combined with good optical quality. To fabricate a laser we have used a composite containing ZrO2 nanoparticles dispersed in acrylate monomers, doped with Pyrromethene 567 laser dye. Transversal pumping of the gratings was performed by nanosecond laser pulses at 532 nm. The threshold, input–output and spectral characteristics of DFB lasers and their dependences on the RI contrast of the feedback structure have been investigated. The optimized values of RI contrast and concentration of the laser dye providing the lowest lasing threshold have been found. It was shown that the lasing wavelength can be tuned by varying the grating period as well as the nanoparticle concentration. Our first results demonstrate that nanocomposite gratings show promising potential for the cost-effective one-step fabrication of compact organic solid-state DFB lasers.

This Letter reports on new methods and a consistent model for voltage tunable optical transmission gratings. Elastomeric gratings were molded from holographically written surface relief gratings in an azobenzene sol-gel material. These were placed on top of a transparent electroactive elastomeric substrate. Two different electro-active substrate elastomers were employed, with a large range of prestretches. A novel finite-deformation theory was found to match the device response excellently, without fitting parameters. The results clearly show that the grating underwent pure-shear deformation, and more surprisingly, that the mechanical properties of the electro-active substrate did not affect device actuation. (C) 2011 Optical Society of America

Dielectric elastomer actuators (DEA) of poly-styrene-ethylene-butadiene-styrene (SEBS) and poly-acrylic VHB4910 were studied for voltage tunable optical transmission gratings. A new geometry is proposed, in which the grating is placed in an area without electrodes, permitting for light transmission through the device. Experiments were performed to implement surface relief gratings on DEA films from pattern masters made from holographic recorded gratings. Since the actuation strain of the DEA depends strongly on the boundary conditions, the desired voltage-controllable deformation of the grating can be achieved by choosing suitable manufacturing parameters. Conditions were found permitting a relative change up to 8.5 % in a 1 µm grating. A model based on independently measured material parameters is shown to describe the optical behavior.

We present here two approaches for the fabrication of 2D and 3D optical structures. The first one is a step-by-step fabrication process of 3D structures using thin relief gratings (stacks of thin 1D or 2D gratings). Azobenzene containing materials for the surface relief inscription have been used in the step-by-step procedure, where after holographic inscription of desired relief structure and coverage with spacer layer another correlated relief structure has been written in the next active layer etc. The method provides full flexibility of the structure type and parameters including different gratings in different layers (hierarchical structures). A technique to produce hexagonal relief gratings of enlarged diameter which can be used for layer-by-layer photonic structures is developed. The second approach is a multi-beam holographic recording using special phase masks. Such mask consists of three phase gratings arranged in plane equilateral triangle geometry with gratings vectors at 120° to each other. A simple method of fabrication of well-adjusted mask with rather high diffraction efficiency is developed. Hexagonal 2D surface relief and 3D volume phase structures were fabricated by a single laser beam exposure using UV or visible wavelengths (depending on the material) through the mask. Azobenzene containing materials and photopolymers, including new specially designed one, were used as holographic materials.

Holographic surface relief gratings written in azobenzene containing films were studied for the use as masters for polymeric thin film distributed feedback (DFB) lasers. Light induced mass transport driven by E-Z isomerization in azobenzene containing materials have shown to be attractive for all optical and one-step fabrication of periodic surface structures with varying parameters for different optical applications. Based on new azobenzene materials and their holographic processing deep surface relief gratings were generated with grating pitches in the range of 400 nm as resonant structures for second order DFB lasers emitting in the VIS range. Nanoimprint techniques enabled multiple duplications of azobenzene master gratings in UV adhesives. The replicas were coated via spin casting with thin films of red light emitting polymer layers to form DFB thin film lasers. These active layers are guest-host-systems consisting of an UV-light absorbing conjugated polymer as host transferring its excitation via Forster resonant energy transfer to a red emitting conjugated polymer. Simple adjustment of grating depth via controlling of illumination time allowed it to investigate the influence of the corrugation depth and thereby the coupling of laser light and grating on the lasing behavior of second order DFB lasers in the red region. For this purpose multiple surface structures with different corrugation depths of up to 130 nm were generated holographically, duplicated and coated.

An innovative approach for voltage-tunable optical gratings based on dielectric elastomer actuators (DEAs) using electro active polymers is presented. Sinusoidal surface gratings, holographically written into azobenzene containing films, are transferred via nanoimprinting to DEAs of different carrier materials. We demonstrate that the surface relief deformation depends on the mechanical and geometrical properties of the actuators. The tested DEAs were made using commercially available elastomers, including a tri-block copolymer poly-styrene-ethylene-butadiene-styrene (SEBS), a silicone polydimethylsiloxane rubber (PDMS) and commonly used polyacrylic glue. The polyacrylic glue is ready to use, whereas the SEBS and the PDMS precursors have to be processed into thin films via different casting methods. The DEA material was pre-stretched, fixed to a stiff frame and coated with stretchable electrodes in appropriate designs. Since the actuation strain of the DEA depends strongly upon the conditions such as material properties, pre-stretch and geometry, the desired voltage-controllable deformations can be optimized during manufacturing of the DEA and also in the choice of materials in the grating transfer process. A full characterization of the grating deformation includes measurements of the grating pitch and depth modulation, plus the change of the diffraction angle and efficiency. The structural surface distortion was characterized by measuring the shape of the transmitted and diffracted laser beam with a beam profiling system while applying an electro-mechanical stress to the grating. Such surface distortions may lead to decreasing diffraction efficiency and lower beam quality. With properly chosen manufacturing parameters, we found a period shift of up to 9 % in a grating with 1 μm pitch. To describe the optical behavior, a model based on independently measured material parameters is presented.

Dielectric elastomer actuators (DEA) of poly-styrene-ethylene-butadiene-styrene (SEBS) and commonly used VHB4910 tape were studied for voltage tunable optical transmission gratings. A new geometry is proposed, in which the grating is placed in an area without electrodes, permitting for light transmission through the device. Experiments were performed to implement surface relief gratings on DEA films from pattern masters made from holographic recorded gratings. Since the actuation strain of the DEA depends strongly on the boundary conditions, the desired voltage-controllable deformation of the grating can be achieved by choosing suitable manufacturing parameters. Conditions were found permitting a shift of up to 9 % in a 1 μm grating. A model based on independently measured material parameters is shown to describe the optical behavior.

A novel method is presented for the fabrication of 2D and 3D structures based on single beam exposure through a phase mask. The thin film mask consists of three phase gratings arranged in plane equilateral triangle geometry with grating vectors at 120° to each other. In the first step the gratings were inscribed into a film of an azobenzene containing polymer using polarization holography. The resulting complex surface relief holographic element was then duplicated into a transparent colourless surface relief element by soft lithography. 2D and 3D surface relief and volume photonic elements were fabricated by a single laser beam exposure (at UV or visible wavelengths depending on the material) through this colourless mask. Azobenzene containing materials and photopolymers, including organic–inorganic nanocomposites, were used as holographic materials. In this way an easily fabricated and cheap phase 'photonic' mask, with much higher diffraction efficiency compare to an amplitude mask, has been proposed and realized. Moreover, the method offers a control over the parameters of the resulting 2D and 3D structures (periods from sub-micrometres to a few micrometres) by changing the parameters of the gratings in the first optical element inscribed in the azobenzene polymer film. The technique has been used for one-step manufacture of hexagonal surface relief gratings, then used for layer-by-layer photonic structures.

A new material based on 1,2-naphthoquinone in polymethylmethacrylate is proposed for phase holograms showing diffusion enhancement. The spectral sensitivity of this material allows forming holograms using 488?530?nm wavelengths, while the hologram reconstruction can be implemented at 633?nm. The amplitude of the refractive index modulation achieved makes it possible to reach diffraction efficiencies close to 100% at a thickness of several hundreds of ?m. It was found by means of UV?visible and NMR spectroscopy that the diffusion of 1,2-naphthoquinone caused by photoproduct attachment to macromolecules of a polymer matrix is the main reason for the hologram enhancement. A relatively high diffusion coefficient (4.8 ? 10?17?m2?s?1 at 50??C) was measured, leading to fast enhancement at moderate temperature.

The in situ observation of thermal alteration of photoinduced optical anisotropy of ultrathin films of polymethacrylates having p-cyanoazobenzene side chains exhibiting amorphous, crystalline, and liquid-crystalline phases was performed by means of temperature scanning ellipsometry. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photoinduced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers, amplified optical anisotropy was maintained even at 300 °C.

We present here novel easily processible organic-inorganic nanocomposites suitable for holographic fabrication of diffraction optical elements (DOE). The nanocomposites are based on photocurable acrylate monomers and inorganic nanoparticles (NP). The compatibility of inorganic NP with monomers was achieved by capping the NP surface with proper organic shells. Surface modification allows to introduce up to 50wt.% of inorganic NP in organic media. Depending on the NP nature (metal oxides, phosphates, semiconductors, noble metals) and their properties, the materials for both efficient DOE and multifunctional elements can be designed. Organic-inorganic composites prepared have been successfully used for the effective inscription of periodic volume refractive index structures using the holographic photopolymerization method. The nanocomposite preparation procedure, their properties and optical performance of holographic gratings are reported. The use of functional NP makes it possible to obtain effective holographic gratings having additional physical properties such as light-emission or NLO. Some examples of such functional polymer-NP structures and their possible application fields are presented. The combination of easy photo-patterning of soft organic compounds with physical properties of inorganic materials in new nanocomposites and the flexibility of the holographic patterning method allow the fabrication of mono- and multifunctional one- and multi-dimensional passive or active optical and photonic elements.

A novel process of photo-induced orientation and optical anisotropy in the whole matrix of a photochromic liquid-crystalline polymer (LCP) in the glassy state via angular-dependent photoselection by the absorption of linearly polarized light with low intensity is presented. Spectroscopical and conoscopical studies give information about the interaction between azochromophores and the mesogenic side chains in homeotropic and homogeneous LCP monodomain films as a result of the photoselection process. Novel variations of erasable optical storage are described using photochromic LCPs in combination with polarized light

Light-induced mass transport in azobenzene functionalized polymers has been used for generation of surface relief gratings (SRG) for different optical applications. The effect of grating formation has been ascribed to the light-induced motion of the azobenzene chromophores involving the covalently bound polymer chains. We propose a concept of supramolecular materials for the effective all-optical generation of surface relief structures and optical anisotropy. The materials are based on the non-covalent interactions between charged photochromic azobenzene units and oppositely charged polymer matrix, for example polyelectrolytes including charged alkoxysilanes. This new supramolecular approach opens a new way for the simple, cost effective and environment friendly preparation from building blocks of a variety of materials for the effective formation of SRG. Up to 1.65 μm deep relief gratings were inscribed onto a few micrometers thick films of these materials. The high thermal stability of the induced structures has been explained in terms of the network of oppositely charged ions inherent to the materials. Also 2D-structures, for example square and hexagonal gratings, were inscribed by the successive recordings. The latter possibility was also used to generate gratings with non-sinusoidal profiles by Fourier transform technique. A new technique to control the grating profile has been developed based on the real-time process of grating formation in these materials. The gratings with sow-tooth like profiles were induced by this method. The diffraction efficiencies up to 60 % in one diffraction order were achieved.

The method of step-by-step formation of correlated 3D phase optical structures is presented. Surface relief gratings (SRG) recorded in azobenzene polymer layers are alternated with layers of a spacer polymer with a different refractive index. A pair of azobenzene and spacer polymers with excellent compatibility makes it possible to prepare layers of good optical quality in a stack without destruction of SRG in the previous layer. A correlated stack of six layers (three active and three spacer layers) with 2D structures of different types (linear, tetragonal, and hexagonal) were built. In this way hierarchical 3D structures with different grating periods or different shapes of SRG can be also produced, resulting in full flexibility of the structure type and grating parameters.

Volume phase gratings in the photopolymerisable composites, containing luminescent nanoparticles have been fabricated for the first time. Nanoparticles of LaPO4, doped by Ce3+ and Tb3+ ions (the trade name is REN-X-green) with high luminescence quantum yield were used as a luminescent inorganic additive. The holographic gratings in such materials are formed as a result of the diffusion distribution of the nanoparticles during exposure of photopolymerisable composites to interference pattern. The influence of the pre-polymer formulation and the holographic patterning parameters on the grating formation is comprehensively investigated. The use of the optimised pre-polymer syrup containing two monomers with sufficiently different polymerisation rates allows fabrication of gratings with diffraction efficiency up to 80% at low optical losses (< 5%) (20 μm film thickness). To obtain maximum diffraction efficiency the intensity and the period of the interference pattern were optimised for each formulation. In addition maximum diffraction efficiency was achieved with the nanocomposites containing 30–32 wt.% of nanoparticles. On the other hand the highest possible modulation of the nanoparticles' concentration was obtained for the concentration of about 20 wt.%. In this case maximum ordering of the nanoparticles in the polymer matrix is achieved. The photoluminescence of the nanoparticles within the homogeneous polymer film and within the grating has been measured. The example application of the photopolymerisable composite containing luminescence inorganic nanoparticles in holographic security technology has been demonstrated.

We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer – liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

The ordering of nanoparticles in polymer matrix using holographic photopolymerization is investigated. The general approach to the selection of the photopolymerizable compounds is proposed. The nonlinear and luminescent properties of obtained gratings are studied.

Liquid-crystalline properties of the ionic self assembled complex benzenehexacarboxylic-(didodecyltrimethylammonium)(6)[BHC-(C12D)(6)] were investigated by polarizing microscopy, differential scanning calorimetry (DSC), x-ray analysis, null ellipsometry, UV and IR spectroscopy. The complex exhibits a bilayer smectic Sm-A(2) liquid-crystalline phase and aligns spontaneously. Alignment properties do not depend on the hydrophobic or hydrophilic treatment of the surfaces. The aligned complex possesses a negative (Delta n=-0.02) homeotropically oriented optical axis, with layers aligned parallel to the surface. X-ray analysis of the aligned sample revealed a lamellar structure with a d spacing of 3.15 nm, consisting of sublayers of thicknesses d(1)=1.41 and d(2)=1.74 nm. This was confirmed by simple geometrical calculations and detailed temperature-dependent investigations, revealing that the first layer contains the BHC molecules and oppositely charged groups of the surfactants, and the second the alkyl tails of the surfactant. Changes in the order parameters (as calculated from the IR investigations) are correlated with the phase transitions as found by DSC. The properties of the complex are strongly influenced by the ionic interactions within the complex. The presence of these groups slows down the dynamics within the material sufficiently to allow for crystallization of the complex from an aligned LC phase into a single crystal domain, as well as restricting the transition to the isotropic phase.

The new method of immersion transmission ellipsometry (ITE) [1] has been developed. It allows the highly accurate determination of the absolute three-dimensional (3D) refractive indices of anisotropic thin films. The method is combined with conventional ellipsometry in transmission and reflection, and the thickness determination of anisotropic films solely by optical methods also becomes more accurate. The method is applied to the determination of the 3D refractive indices of thin spin-coated films of an azobenzene-containing liquid-crystalline copolymer. The development of the anisotropy in these films by photo-orientation and subsequent annealing is demonstrated. Depending on the annealing temperature, oblate or prolate orders are generated.

Norland UV-adhesive NOA68 was studied as a material for holographic optical elements fabrication. Permanent transmission diffractive gratings were inscribed by the exposure to the interference field of UV Ar-ion laser. The contributions of the volume and the surface parts of the phase modulation to the efficiency of the gratings were investigated for different gratings periods. The depth of the surface relief grows up to 250 nm with an increase in the grating period. For relatively small periods ⩽2.5 μm the contribution of the surface relief part to the total diffraction efficiency is negligible and gratings can be considered as volume diffractive structures. The deep (up to 1.5 μm) surface relief with almost square profile was manufactured by the UV exposure through a mask. Both techniques do not require any subsequent wet or thermal developing process. The mechanism of the holographic image formation is discussed.