Showing papers on "Organic photorefractive materials published in 2003"
TL;DR: In this article, an extremely large electro-optically induced photorefractive effect in a nematic liquid crystal doped with single-walled carbon nanotubes and fullerene C60 was observed.
Abstract: We have observed an extremely large electro-optically induced photorefractive effect in nematic liquid crystal doped with single-walled carbon nanotubes and fullerene C60. The effective refractive index change coefficient can be as large as 7 cm2/W, which is >1000 times larger than previous observations. We describe the basic mechanisms and conditions necessary for occurrence of such nonlinearities.
95 citations
TL;DR: In this paper, a photorefractive brown Sn2P2S6 crystal was grown by the vapor-transport technique with SnI2 as the transport agent and showed that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement.
Abstract: A significant improvement of the ring-cavity self-pumped phase conjugation response time in the near-infrared cw regime with a photorefractive brown Sn2P2S6 crystal is reported. Brown Sn2P2S6 is grown by the vapor-transport technique with SnI2 as the transport agent. With our Sn2P2S6 samples response times below 50 ms and phase-conjugate reflectivities of 25% can be achieved at a wavelength of 780 nm with a moderate light intensity of 1 W/cm2. We show that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement. Reaching this limit is possible because of the large two-wave mixing gain of 18 cm-1 measured in this crystal.
46 citations
TL;DR: This work reports the first observation, to their knowledge, of self-trapping of light as well as optically induced focusing-to-defocusing switching in an organic photorefractive glass, owing to the orientationally enhanced photoreFractive nonlinearity of the material.
Abstract: We report the first observation, to our knowledge, of self-trapping of light as well as optically induced focusing-to-defocusing switching in an organic photorefractive glass, owing to the orientationally enhanced photorefractive nonlinearity of the material.
34 citations
TL;DR: In this article, a set of organic glasses has been synthesized and evaluated for photorefractive performance and optical nonlinearity, birefringence, and charge transport were built into a single molecule by attaching an NLO chromophore to a charge transport moiety with an adjustable linking group.
Abstract: A set of organic glasses has been synthesized and evaluated for photorefractive performance The functions of optical nonlinearity, birefringence, and charge transport were built into a single molecule by attaching an NLO chromophore to a charge transport moiety with an adjustable linking group The longer linking group not only lowers the glass transition temperature Tg but also influences the photorefractive performance of the samples The photorefractive gain coefficient is larger for longer linkers with about a 2-fold increase going from the 2-carbon atom linker to 12 The glass stability and chemical stability of the materials was adequate for full photorefractive characterization
30 citations
TL;DR: In this article, solid-state photorefractive compositions consisting of the aromatic polyimide (T g is about 230 °C) and the thiacarbocyanine dyes were prepared.
26 citations
23 Dec 2003
TL;DR: In this paper, a two-beam coupling with hybrid photorefractive cells comprising a nematic liquid crystal layer adjacent to inorganic windows is described. And the authors obtained Bragg matched liquid crystal gain coefficients of more than 1600 cm-1, grating periods of less than 300 nm and a wide range of beam intersection angles.
Abstract: The very high birefringence of liquid crystals makes them attractive for photorefractive applications. However, the drawbacks of using liquid crystals as photorefractives include a small phase shift between the optical and refractive index gratings, coarse grating spacings with narrow beam intersection angles, operation usually restricted to the Raman-Nath regime, a need to apply an external electric field, and, with most geometries, a need to tilt the cell at an angle to the grating k-vector. In this paper, we describe two-beam coupling with hybrid photorefractive cells comprising a nematic liquid crystal layer adjacent to inorganic photorefractive windows. In this arrangement, the underlying photorefractive properties are determined by the inorganic windows while the liquid crystal molecules amplify the overall refractive index modulation. Using this technique we have obtained Bragg matched liquid crystal gain coefficients of more than 1600 cm-1, grating periods of less than 300 nm and a wide range of beam intersection angles without the need to apply an external field.
25 citations
TL;DR: In this article, the photorefractive effect is fully reversible, meaning that the recorded holograms can be erased with a spatially uniform light beam, which can be reconstructed by diffracting a third laser beam on the periodic index modulation.
Abstract: Photorefractive polymers exhibit large refractive index changes when exposed to low power laser beams. When the optical excitation consists of two interfering coherent beams, the periodic light distribution produces a periodic refractive index modulation. The resulting index change produces a hologram in the volume of the polymer film. The hologram can be reconstructed by diffracting a third laser beam on the periodic index modulation. In contrast to many physical processes that can be used to generate a refractive index change, the photorefractive effect is fully reversible, meaning that the recorded holograms can be erased with a spatially uniform light beam. This reversibility makes photorefractive polymers suitable for real-time holographic applications. The mechanism that leads to the formation of a photorefractive index modulation involves the formation of an internal electric field through the absorption of light, the generation of carriers, their transport and trapping over macroscopic distances. The resulting electric field produces a refractive index change through orientational or non-linear optical effects. Due to the transport process, the index modulation amplitude is phase shifted with respect to the periodic light distribution produced by the interfering optical beams that generate the hologram. This phase shift enables the coherent energy transfer between two beams propagating in a thick photorefractive material. This property, referred to as two-beam coupling, is used to build optical amplifiers. Hence, photorefractive materials are also playing a role in imaging applications. Discovered and studied for several decades mainly in inorganic crystals and semiconductors, the photorefractive effect has not yet found wide spread commercial applications. This can be attributed to the difficulties associated with the growth of crystals, and to the high cost of optical and optomechanical components necessary for the development of complete optical systems. With the emergence of novel low cost plastic optical components that can be mass produced by techniques such as injection molding, the cost and the weight of optical components is decreasing rapidly. This trend together with the advances made in fabricating integrated laser sources at lower cost provide a great momentum to the development of new optical processing technologies. As real-time optical recording and processing media, photorefractive polymers are expected to play a major role in these technologies. The optical, physical, and chemical properties of photorefractive polymers are outlined and discussed. Current material classes and their respective merits and future challenges are presented together with examples of applications.
25 citations
TL;DR: In this paper, the photorefractive effect in polymeric systems, which involves the creation, upon a primary photochemical reaction, of a phase grating shifted in space relative to the fringe pattern, is considered.
Abstract: The review concerns the photorefractive effect in polymeric systems, which involves the creation, upon a primary photochemical reaction, of a phase grating shifted in space relative to the fringe pattern. The interaction of interfering laser beams accompanied by energy transfer from one beam to the other as well as salient features of the refractive index modulation in polymeric systems with low and high glass transition temperatures are considered. Particular attention is given to the photorefractive polymers with high glass transition temperatures containing nanocrystalline J-aggregates of cyanine dyes, which are characterised by high third-order nonlinear electric susceptibilities and induce modulation of the refractive index due to the Kerr electrooptic effect. The prospects for application of polymeric photorefractive materials are outlined. The bibliography includes 113 references.
23 citations
TL;DR: In this article, the composites are composed of PPT-CZ and are doped with the sensitizer C60 and nonlinear optical chromophores, and the two-wave mixing gain Γ exceeds 100 cm-1 at an applied field of 50 V/μm.
Abstract: High-performance photorefractive materials based on the layered photoconductive polymers PPT-CZ [rigid backbone of poly(p-phenyleneterephthalate) with pendent carbazole groups] are studied. The composites are composed of PPT-CZ and are doped with the sensitizer C60 and nonlinear optical chromophores. Despite the absence of a plasticizer and the lower concentration of the carbazole photoconductive moieties as compared with poly(N-vinyl carbazole), these materials show high photorefractive sensitivity, i.e., Sn2 of 70± 7 cm2/kJ at E0=100 V/μm for PPT-CZ(n=12):diethylaminodicyanostyrene:C60. The low glass transition temperature (<0°C) leads to a high rotational mobility of the chromophores that results in large refractive-index changes. For all the composites that were investigated, the two-wave mixing gain Γ exceeds 100 cm-1 at an applied field of 50 V/μm.
15 citations
TL;DR: In this article, the sidechains located in the electron-withdrawing group of small molecules were systematically changed in order to investigate their influence on the photorefractive properties.
Abstract: Single component photorefractive materials based on small molecules have been synthesized. The sidechains located in the electron-withdrawing group of these molecules were systematically changed in order to investigate their influence. It was demonstrated that the photorefractive performance of these materials could be fine-tuned by changing the length of the sidechain. Excellent optical quality and photorefractive properties were obtained. A large net optical gain of 280 cm−1 at a low external field (38.3 V/μm) and a diffraction efficiency of 82% were observed at 780 nm. The results indicate that an optimum sidechain length exists for this type of molecules.
14 citations
TL;DR: In this article, it was shown that the group velocity of light pulses can be reduced significantly by using the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process.
Abstract: We show theoretically that the group velocity of light pulses can be reduced significantly by use of the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process. The group velocity of light pulses of the order of 0.1 m/s can be achieved in typical photorefractive BSO crystals with an appropriate externally applied electric field and moving gratings of appropriate speeds. It is also shown that the slowly propagating light pulses can be set to be amplified after passing through the photorefractive material.
TL;DR: In this article, a photorefractive polymer composite containing a trapping layer was reported to have a grating life time as high as 600 s and a diffraction efficiency and gain coefficient also increased by the introduction of a trapping mechanism.
Abstract: A photorefractive polymer composite containing a trapping layer which exhibits a significant enhancement in its photorefractivity is reported. The photorefractive polymer composite containing a trapping layer showed a grating life time as high as 600 s, while the grating life time was only 7 s in the photorefractive polymer composite without a trapping layer. The grating growth rate was found to be unaffected by the introduction of a trapping layer. The diffraction efficiency and gain coefficient also increased by the introduction of a trapping layer. The enhancement in the photorefractive properties is due to the increase in the space-charge field developed in the photorefractive polymer composite containing a trapping layer.
TL;DR: In this paper, a planar photorefractive waveguide was fabricated by laser irradiation with the wavelength of 632.8 nm and 532 nm, respectively, in a KNSBN:Ce crystal, where the high refractive index regions induced by thin cylindrical or thin sheet beams propagating through the crystal were used as waveguide structures.
TL;DR: In this paper, photorefractive BaTiO3:Ru single crystals were fabricated and investigated, and the authors found that the dark conductivity is dominant in the crystal and much higher than the photo conductivity at a low intensity pumping beam.
TL;DR: In this article, the photorefractive polymer contains a second-order nonlinear optical chromophore and a charge transporting group, which exhibits low glass transition temperature of about 52 °C.
TL;DR: In this article, the effect of synchrotron light on the refractive index of poly(methyl methacrylate) (PMMA) has been investigated and shown to allow the manufacturing of waveguides in PMMA.
Abstract: Synchrotron light changes the refractive index of poly(methyl methacrylate) (PMMA). Refractive-index enhancements as well as reductions depending on dose and energy of the radiation used can be observed. This effect allows the manufacturing of, for example integrated-optical components, as is demonstrated by realization of waveguides in PMMA.
TL;DR: In this paper, a low-T g polymer with a second-order nonlinear optical chromophore and carbazole as a charge-transporting group was synthesized and characterized.
TL;DR: This work reports the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals, and identifies the dominant carrier to be holes from the direction of two-wave mixing energy transfer.
Abstract: The photorefractive effect in a nominally undoped 0.91PbZn1/3Nb2/3O3–0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm×4 mm×8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm-1, and the normalized time constant under 1-W/cm2 illumination is 12 s at a wavelength of 476 nm. The effective trap density is calculated as 5×1016 cm-3 from the Debye screening length under the assumption of Kukhtarev’s band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer.
TL;DR: In this article, an electric field is applied to the device in plane so as to coincide with the direction of a grating formed by two writing beams, and the maximum thickness was 600 μm.
Abstract: We propose a structure of a photorefractive polymer device. An electric field is applied to the device in plane so as to coincide with the direction of a grating formed by two writing beams. This structure permits us to fabricate a thick photorefractive polymer device with a high optical gain. The maximum thickness we fabricated was 600 μm. We investigate the device performance using a two-beam coupling experiment and demonstrate high-beam-coupling gain in the thick device. We also describe position dependence of the photorefractive effect for an apical electrode structure.
TL;DR: In this paper, a numerical analysis of a waveguide Bragg reflector is presented based on a homemade modelling technique, which allows for the possibility of realizing complex integrated optical components, such as Bragg-reflection lasers and amplifiers.
TL;DR: In this paper, the appearance of the photorefractive effect on all optical polling (OP) of a bulk glass is investigated, considering the geometry of formation of the refractive-index grating in glass upon interaction of the intersecting Gaussian beams.
Abstract: The appearance of the photorefractive effect on all optical polling (OP) of a bulk glass is investigated. During OP, a refractive-index grating accumulates in the glass and radiation effectively diffracts through it. The theory of the self-diffraction of light has been developed and the resultant expression for the amplitude of the diffracted light has been deduced, considering the geometry of formation of the refractive-index grating in glass upon interaction of the intersecting Gaussian beams. The results of the experimental investigation of the diffraction of light on the photorefractive gratings induced in some oxide glasses have been presented. The experimental results obtained are in agreement with the theory, based on a model of formation of a spatially periodic electrostatic field in glass via the coherent photogalvanic effect. The phenomenon of light diffraction can be used to investigate the physical properties of all OP in different glass media and to search for new, effective photorefractive materials.
TL;DR: In this paper, a simplified model is used to describe the nonlinear optical behaviors of absorption and refractive index change of semiconductors, and a trade-off of optical absorption and index change should be taken for the practical non-linear optical devices.
TL;DR: In this paper, an atomic force microscope (AFMEM) was used for the detection of free and trapped charge carrier density, ferroelectric domains and the topography of the sample.
Abstract: Electrostatic force detection with an atomic force microscope (AFM) is ideally suited for the study of the surface properties of dielectric materials. The AFM allows simultaneous detection of many physical quantities like free and trapped charge carrier density, ferroelectric domains and, of course, the topography of the sample. Usually, photorefractive materials are optically investigated: volume refractive index gratings are observed by light diffraction. In contrast, the AFM offers the possibility of directly observing the physical steps for the development of a photorefractive grating. Due to the high sensitivity and the unprecedented lateral resolution, the AFM provides a wealth of new possibilities for the investigation of photorefractive materials. We present results obtained with Sr0.61Ba0.39Nb2O6 (SBN) crystals. The samples had as-grown as well as polished surfaces. Spatial distribution and temporal dynamics of photorefractive charge patterns are successfully resolved. Furthermore, additional cha...
Patent•
06 Mar 2003TL;DR: In this article, a method for treating photorefractive effect of an optical device, which comprises irradiating an optical devices comprising a lithium niobate single crystal or a lithium tantalate single-crystal with an ultraviolet light having a wavelength of at least 300 nm and at most 400 nm, was proposed.
Abstract: A method for treating a photorefractive effect of an optical device, which comprises irradiating an optical device comprising a lithium niobate single crystal or a lithium tantalate single crystal with an ultraviolet light having a wavelength of at least 300 nm and at most 400 nm so as to suppress and control a photo-induced refractive index change (photorefractive effect) caused on the device.
10 Dec 2003
TL;DR: In this paper, the synthesis, the molecular properties and an evaluation of the photorefractive performance of different types of polymer composites were reported, including Narylated carbazoles as bifunctional chromophores to demonstrate the importance of the relative orientation of dipole moment and polarizability tensor.
Abstract: We report on the synthesis, the molecular properties and an evaluation of the photorefractive performance of different types of polymer composites. Samples were C60 and (2, 4, 7-trinitro-9-fluorenylidene)malonitrile (TNFDM) sensitized and characterized by four-wave mixing and two-beam coupling experiments at 680 and 780 nm. In a first type of composite, new synthesized N-arylated carbazoles were used as bifunctional chromophores to demonstrate the importance of the relative orientation of dipole moment and polarizability tensor on the Figure-of-Merit (FOM) of photorefractive experiments. Investigations were performed on mixed inorganic/organic nanocomposites to extend the photosensitivity of the samples to longer wavelengths, photoconductivity at 980 nm was studied on PbS colloids/PVK samples. Finally, a fully functionalized photorefractive polymer was synthesized and analyzed by four-wave mixing and two beam coupling experiments. The polymer showed a strange oscillating behavior in diffraction efficiency and gain. Thus far the temporally oscillation couldn’t be explained properly.
Proceedings Article•
01 Jun 2003
TL;DR: In this article, the first observation of optical spatial solitons in an organic photorefractive monolithic glass was reported, and self-trapping of light as well as optically induced focusing-to-defocusing switching was observed.
Abstract: We report the first observation of optical spatial solitons in an organic photorefractive monolithic glass. Self-trapping of light as well as optically induced focusing-to-defocusing switching was observed, owning to the orientationally enhanced photorefractive nonlinearity.
17 Jun 2003
TL;DR: In this article, the first observation of self-trapping of an optical beam in an organic photorefractive monolithic glass was reported, which brought about the possibility of using organic materials for soliton-based applications.
Abstract: We report the first observation of self-trapping of an optical beam in an organic photorefractive monolithic glass. The orientationally enhanced photorefractive nonlinearity that gives rise to spatial solitons can be switched from self-focusing to self-defocusing simply by changing the polarization of the optical beam. Our experiment brings about the possibility of using organic materials for soliton-based applications.
01 Jan 2003
TL;DR: In this article, it was shown that the group velocity of light pulses can be reduced significantly by using the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process.
Abstract: We show theoretically that the group velocity of light pulses can be reduced significantly by use of the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process. The group velocity of light pulses of the order of 0.1 m/s can be achieved in typical photorefractive BSO crystals with an appropriate externally applied electric field and moving gratings of appropriate speeds. It is also shown that the slowly propagating light pulses can be set to be amplified after passing through the photorefractive material.
18 Nov 2003
TL;DR: In this paper, the propagation and coupling of electromagnetic waves in photorefractives materials:Bil2SiO2o (BSO), Bi 12TiO2O (BTO), and LiNbO3-doped and -undoped; both in bulk and fibers form.
Abstract: The purpose of this work is the Study of Photorefractives Materials and their Applications in Optical andHolographic Information Processing The process that makes possible these applications is the photorefractiveeffect Thus, we study the propagation and coupling of electromagnetic waves in photorefractives materials:Bil2SiO2o (BSO) and Bi 12TiO2O (BTO), and LiNbO3-doped and -undoped; both in bulk and fibers form Weuse techniques of holographic characterization and nonlinear optics, for determination of parameters andfigures of merit of these photorefractive medium Also, present some applications, as: the use as holographicmemories ofhigh capacity of storage; and Non-Destructive Tests, as Real-Time Holographic Interferometry 1 STUDY OF PHOTOREFRACTIVES MATERIALSThe Photorefractive Effect[1][2] is a phenomenon where the local refractive index is changed by the illumination of light intensity modulation It consists of the migration of carriers of regions illuminated fordark regions in the crystal and alteration of the refractive index caused for the new space-charge distribution,or either, the photo-induction and the electro-optics effect The theoretical model that better explains thisphenomena is the Band Transport Model11 Determination ofParameters in PRC's for 2WMIn incidence of two laser beams in photorefractive medium an interference pattern is formed, or either, formsa holographic gratting in medium (Fig 1) The solution for the space-charge field as function ofr and t, in thesteady-state situation, will be gotten making the secular derivatives to tend the zero in the basic equations ofthe Band Transport Model of Kukhtarev[1] In formation of photorefractive grafting, the presence of inelectric field in this way introduces a change in the refractive index by through Pockels effect The difractionefficiency and relation of intensities two beams in photorefractive medium can be obtained experimentally12 Determination ofThermo-optics Properties in PRC's for Thermal Lens TechniquesIn the measures of thermal lens in unmarried mode[3], the sample illuminated by a Gaussiam laser beamTEMoo As a result of the energy of optical absorption, one local temperature variation and produced in thesample due to a non-radiative process The refractive index change with the temperature produces a lens waistbeam sample We made experiments of LT in photorefractives crystals Of transient signal thermal lens gottenthe values of D, the thermal diffusivity; and ds/dT, the optical path variation withthe temperature (Fig 1)