Aprilis HMD-050-G-C-400 photopolymerizable holographic recording material for card and disk media, based upon cationic ring-opening polymerization (CROP), has been further optimized for recording in an increased film thickness of 400 µm. A storage density, S_2D, of 150 bits/μm² for digital data recorded holographically as pages and a dynamic range of at least M/# = 22 have been achieved, which are substantially greater than previously reported for photopolymerizable media, while concurrently the inherent low shrinkage, high image fidelity and high sensitivity characteristics of the material have been retained. Dynamic range or cumulative grating strength, Ση_i0.5, has been determined from co-locationally recorded peristrophic and planar-angle multiplexed 262 kbit data pages that exhibit low raw bit-error-rates (BER) having an average value of 1E-3 and 5.5E-3 for ~100 and ~150 bits/μm², respectively. Good Bragg selectivity consistent with the imaged thickness and sinc² function behavior is observed for the multiplexed digital data page holograms, and both the Bragg selectivity and the diffraction efficiency are stable without the need for post-imaging fixing procedures. Sensitivity during recording of digital data page holograms is in the range of 6.75 cm/mJ diminshing to 0.5 cm/mJ for 87% of the cumulative grating strength that is attained during co-locational recording.

With today’s organic photopolymer materials allowing high resolution, it is possible to record subwavelength volume holographic index gratings, i.e. index gratings with a period much smaller than the wavelength operating in the form birefringence regime. Such components are of interest for the direct view liquid crystal displays that suffer from a narrow viewing angle. In fact, by providing high birefringence, they compensate the intrinsic birefringence of the liquid crystal and thus, improve the viewing angle properties of the liquid crystal displays. Recently, we introduced a hybrid holographic compensator combining an “in plane” commercially available birefringent film and a slanted optical-axis subwavelength volume index grating recorded in a DuPont photopolymer. In this paper, we present the hybrid holographic compensation and its interesting features for TN-LCD viewing angle improvement. More particularly, a hybrid holographic compensator is designed for avionics application. It is based on a 120nm-period volume index gratings achieving an index modulation of 0.045 with a 33°-slant angle of the optical axis. The hybrid holographic compensator was manufactured and implemented on an avionics equipment from Thales Avionics. Visual inspection as well as contrast measurements showed a good improvement of the viewing angle characteristics.

We present a study of the real-time formation of volume holographic reflection gratings in a liquid-crystal/photopolymer mixture. The diffraction efficiency for s- and p-polarization, Bragg wavelength, and laser scattering are monitored as the grating is formed. We present a model of grating formation that incorporates the photophysics of the initiator dye, reaction-diffusion equations of the monomer-polymer-liquid crystal system, phase separation of the liquid crystal, nematic order evolution, and volume shrinkage of the polymer. The model yields good qualitative agreement with experimental data. We discuss the physics of the system as it evolves in time and describe the effects of various phenomena on the diffraction efficiency of holographic polymer-dispersed liquid crystal gratings.

The characteristics of Phenanthrenquinone (PQ) doped Polymethyl methacrylate (PMMA) for recording edge-illuminated holographic spectral filters for dense wavelength division multiplexing applications are evaluated. Filter design includes the effects of material absorption and apodization of the index profile. Rigorous coupled wave theory and transfer matrix methods are used to simulate the performance of the filters for dense wavelength division multiplexing functions. The experimentally measured spectral FWHM bandwidths were 0.20 nm and the primary limitation of the grating performance was found to be residual material absorption.

We proposed a method for measuring the magnitude of the space-charge field of the polymeric photorefractive materials. In the case of polymeric photorefractive material with low glass transition temperature, optically anisotropic chromophores are known to be reoriented under space-charge field. Simply by adding a pair of crossed polarizers unit to a conventional degenerated four wave mixing setup, we could measure the birefringence of the photorefractive materials induced by a newly formed space-charge field. Since the birefringence of a given material is governed by the applied electric field, the space-charge field can be determined from the variation of birefringence using the oriented gas model. We investigated the dependence of the grating formation on temperature in photorefractive polymeric composite, especially the index contrast of the grating. The diffraction efficiency of the photorefractive polymeric composite decreased with increasing the temperature, and it could be explained with the magnitude of space-charge field and the electro-optic behavior at various temperatures.

We discussed the electric and optical properties of three types of conjugated carbazole polymers: substituted polyacetylene with carbzole moiety, main-chain polymers having conjugated carbazole trimer units, and triindole units. Substituted polyacetylenes can be expected to show the enhanced optoelectronic responses due to the extended conjugated systems in the main chain and the additional chromophores in the side chain. The hole mobility of a substituted polyacetylene containing carbazole moiety was determined to be about 10^-4 cm²/Vs with the electric field of 4 x 10⁵ V/cm by time-of-flight technique, while polyvinylcarbazole showed hole mobility of about 10^-6 cm²/Vs. The carrier mobility is presumably enhanced by the extended conjugation system. Hyperbranched polymers with carbazole trimer units exhibited the enhanced two beam coupling gain of 60 cm^-1 in comparison with main-chain polymer with carbazole units. Since triindole is an electron-donative molecule containing three carbazole substructures with smaller ionization energy than that of carbazole, we can expect the application to a variety of optical and electrical materials. Main-chain polymers with triindole units exhibited the two-beam coupling gain of over 100 cm^-1. Therefore, theses conjugated carbazole polymers are one of the good candidates for the new class of electronic and photonic materials.

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.

We report on the photorefractive properties of two polymer composites that utilize a new bis-triarylamine side-chain polymer matrix. Correctly locating the frontier orbitals of the new transport manifold with respect to the HOMO levels of chromophores, allows stable continuous operation over exposure levels of more that 4 kJ/cm² when samples are electrically biased at 57 V/μm. This operational stability is combined with video-rate compatible grating build-up times and a dynamic range that allows index modulations of 3 x 10^-3 and gain coefficients on the order of 100 cm^-1 at moderate fields. The thermal stability of one of the composites reported is excellent, showing no signs of phase separation even after one week at 60°C. A comparison with the stability of composites where the new matrix was replaced by PVK is also presented.

A photoconductive sol-gel material based on the incorporation of polyvinyl carbazole (PVK) and 2,4,7-trinitro-9-fluorenone (TNF) within a silica matrix is reported. Unmatched photosensitive as large as 10^-10 cm/ΩW has been found at moderate applied electric fields (20 V/μm). The optimization of the concentration balance between the functional component (the TNF/PVK molar ratio percent) has resulted in a 300-fold increase of the photocurrent efficiency (Φ). The study of photcoductivity of sol-gel materials prepared with different PVK contents has confirmed the unneeded use of massive photoconductive materials to obtain optimum performance.

We report holographic recording in photosensitive polymer optical fibers by guided beams. The fibers are made of poly(methyl methacrylate) doped with Disperse Red 1as photosensitive element. Holographic recordings are performed with parallel- and orthogonally-polarized writing beams. Recording of Fourier-transform images in these fibers is also demonstrated. The recording mechanism is photoinduced reorientation of Disperse Red 1 molecules.

We present novel substrates for the elaboration of organic active devices for use in integrated optics. The selected materials are based on photopolymerizable matrices doped with optically active molecules. In such organic complexes, photoinduced chemical reactions initiate the polymerization of small monomers inducing an increase in density as well as in viscosity. Since these reactions are limited to the illuminated regions, the properties of these materials are easily patterned. Indeed, a refractive index increase occurs with the densification. Thus, it is possible to create a spatial modulation of the refractive index which can be used to make optical waveguides or phase holograms. Moreover, we induce quadratic non linear optical (NLO) properties by doping the photopolymers with push-pull chromophores. For this purpose, we need a non centro-symmetric alignment of the quadratic optical chromophores. This is obtained by orienting these polar entities with an external static electric field followed by the freeze of their orientation through the viscosity increase associated with the polymerization process. The non linear properties can then be patterned by irradiating the samples through appropriate masks. Long life-time periodically poled structures obtained with NLO chromophores doped photopolymers will be presented.

A holographic hybrid sol-gel material with excellent values of diffraction efficiency, index modulation and high photosensitivity (up to 93%, 10^-3, and 5 x 10^-3 cm²/mJ, respectively) is reported. Moroever, a high angular selectivity has been achieved $9 = 0.0967°) through the selection of the adequate nanoporous silica supporting matrix. Such a value has allowed to first demonstrate the capability of angular multiplexing in a holographic sol-gel media (up to five volume holograms with a resultant M/# of 0.83 in a preliminary approach). Shrinkage during UV curing processes has also been determined in order to evaluate how accurate can be the retrieval of the recorded data.

The kinetics of photosensitive polymer holographic recording materials is examined. We discuss why a linear relationship between monomer concentration and polymerization rate does not satisfactorily explain current experimental results and propose a possible solution. Then, using the Rigorous Coupled Wave Model(RCWM) we examine the higher order grating components so as to more clearly understand the non-linear relationship between exposing intensity and polymerization.

The reversible reaction that takes place in the writable, readable, erasable (WRE) photosensitive materials involving fulgides (ABERCHROM 540 and 670) was investigated with a photochemical and holographic approach. It appeared that the fatigue of the photosensitive material was strongly dependent on the properties of the matrix used as a support. This was precisely established both by spectroscopic monitoring (λ_max, absorbance_max, photo-stationary state) and by following the diffraction efficiency η values. There was a nice correlation between the evolution of the spectral features of C isomer and of the η values all along the WRE cycles. This combined approach was applied to four different supports: PVK, PMMA, PEPC/PS and epoxy RESIN. So for both fulgides: (1) PVK, frequently used in optics, appears as being the worst one. The starting fulgides were destroyed after only a few WRE cycles. This was assigned to the intrinsic photoaging of PVK whose absorption in UV domain is far from negligible and leads to the formation of radical species able to attack the fulgide. (2) Holograms recorded in PMMA and PEPC/PS present similar behavior with a loss of ≈10% after 8 cycles. (3) Epoxy RESIN appears to be a very good candidate for these reversible systems; no fatigue was observed after 40 cycles. It has to be attributed to the matrix in which the detrimental rotation process, giving rise to the non photochromic Z isomer, is strongly inhibited.

When large amounts of data are stored in Bacteriorhodopsin (bR), for example with Holographic Particle Image Velocimetry (HPIV), the volatile nature of the medium can be a serious problem. The loss of information has two causes; thermal erasure and photo-induced erasure. The thermal erasure can be reduced by cooling the film. We found that by cooling a film with an optical density of 1.5 (OD₅₇₀) from 21.2°C to 1.7°C, the thermal erasure time leading to 50% loss of diffraction efficiency was increased from 31 to 185 seconds. The rate of photo-induced erasure does not only depend on the intensity of the reconstruction wave, but also on its wavelength. The influence of the shifted wavelength and the reconstruction intensity on the rate of photo-induced erasure were analysed experimentally and were found to agree with the theory. Reconstructing a hologram with 690 nm can potentially result in a 35 times larger integrated signal to be read from the hologram as when reconstructing with 532 nm.

Thick rigid polymer media with diffusive development of gratings are suitable for archive information storage, and especially for 3D holographic optical elements. Diffusion of unreacted molecules of photosensitive dye ensures postexposure growth of diffracted light, which can be followed either by secondary growth, or by some decay caused by displacement of chromophore groups photochemically attached to polymer chains (photoproduct). In a long run, extremely slow, though still finite, diffusion of macromolecules leads to destruction of a holographic grating. Not only the rate, but also the shape of postexposure kinetics noticeably depends on the choice of particular polymer, its degree of polymerization, temperature of processing and thermal history of material: in aged samples, gratings appear more efficient.

We present our results on polarization holographic data storage in thin azobenzene side chain polymers. Two different systems have been demonstrated: a read only system with red diode laser and a read&write system with green frequency doubled solid state lasers. Error free operation have been proved at 2.77 bit/µm² data density. We have also demonstrated enhanced security holographic storage by applying phase coded reference waves imaged onto the hololographic storage material. We also present the concept of extending the principle to multilayer holographic storage.

An overview of the InPhase Technologies holographic demonstration platform is presented. This compact, mobile system is a fully functional holographic recordable drive complete with custom optics and custom control and channel electronics. The development of this device paves the way for the commercialization of this technology.

Reversible holographic storage media are very useful for temporal storage of a buffer hologram, in associative retrieval, and photo-EMF detection. A particularly interesting application is optical coherence tomography (OCT), a noninvasive medical imaging method. Skin tissue or bone are highly scattering media, but nevertheless exhibit a transparence window in the NIR of the light spectrum (800-850 nm). Ballistic photons coming from a certain depth within the medium can be separated from diffusely scattered photons by holographic time gating enabling depth-resolved holographic imaging. Due to the extremely low number of ballistic in comparison with scattered photons, this technique requires holographic storage media with very high sensitivity in the NIR. The necessity to use NIR light excludes most commonly used reversible holographic media, such as Bakteriorhodopsin or azo-dye-containing systems to name only a few. By contrast, photorefractive (PR) materials, in particular amorphous organic PR systems, are highly promising for this application. However, their NIR performance is insufficient so far. In this paper, we introduce a novel organic PR material, a composite based on the poly(arylene vinylene) copolymer TPD-PPV (inset Fig. 2). Under normal conditions, the material exhibits a reasonably fast hologram recording speed in the NIR, much faster than more traditional (e.g. PVK-based) materials under identical conditions. With this material, we discovered that pre-illumination (“gating”) improves the sensitivity by a factor of > 50. These effects are reversible, but can be partly permanent by redox-chemical doping. We demonstrate multiple-video-rate holographic recording under practical conditions, underlining the outstanding NIR-sensitivity of the new material.

Predictions made by two models describing dynamic processes in organic photorefractive materials are verified for a photorefractive polymer, consisting of a Poly-TPD, a dicyano dye and the sensitizer C₆₀. One of the models can describe our measurements under the assumption of optically active traps as dominant trap species. This is confirmed by altering the sensitizer concentration, which has an influence on the charge transport properties of the material. Also, increasing the sensitizer concentration yielded a significant increase of the grating erasure rate in our material.

The photorefractive effect of 14 ferroelectric liquid crystals (FLCs) mixed with a photoconductive compound was investigated by two-beam coupling experiments. The influence of the properties of low-molecular-weight FLCs on the photorefractive iffect was examined, and it was found that the photorefractive two-beam coupling gain coefficients and the refractive index grating formation time are strongly dependent on the properties of FLCs. The effects of the magnitude of the spontaneous polarization, viscosity, and the homogeneity of the surface-stabilized state on the photorefractivities of FLCs are discussed based on these findings.

We report on an efficient and fast hybrid photorefractive polymer sensitized with CdSe quantum dots. The surface of the quantum dots was treated with 4-methylbenzenethiol. This surfactant allows the quantum dots to have an efficient photoinduced charge generation when mixed with a mixture of chromophores. The enhanced photoconductive properties lead to fast grating build-up times of 100 ms and below. In four-wave mixing experiments, overmodulation of the diffraction efficiency was observed at an applied field of 60 V/μm and gain coefficients on the order of 20 cm^-1 at moderate fields.

In this paper, a new technique is presented for adjusting the playback wavelength of Lippmann holograms recorded in methylene-blue sensitized dichromated gelatin (MBDCG). The main feature of this technique is introducing a water-soluble organic reagent into MBDCG photosensitive layer as preswelling reagent and wavelength adjuster. This method has wide wavelength adjustment range and high signal-to-noise ratio, can be applied to adjust the playback wavelength of reflection hologram quantitatively by changing the concentration of preswelling reagent. Its possible applications include color image display, holographic optical elements, and optical anti-counterfeiting.

A holographic polymer-dispersed liquid crystal (HPDLC) thin film is composed of multifunctional acrylate monomer blended with the nematic liquid crystal mixture, and then investigated the real-time diffraction efficiencies for various physical parameters of amount of liquid crystals and applied AC electric fields. It is experimentally shown that the holographic gratings recorded in HPDLC film can be reversibly erased and reconstructed by switching on and off of appropriate applied AC electric field. By using these electro-optic properties we have developed bifocal holographic lenses having two different focal lengths of 300 mm and 400 mm.

The paper presents the results of a study of the spatial structure of Si-containing [poly(ethynediyl-arylene-ethynediyl-silylene)] composites in the nanometer scale, as well as of an optical study of photorefractive effects in the visible and near-infrared ranges in these composites. The compositions have been examined using transmission/diffraction electron microscopy. The results suggest the existence of an extraordinary self-organisation in conjugated silicon organometallic polymers (nano-structured layers with a spatial period of several nanometers and the length of more than 100 nm). The most probable mechanism of the structure formation is π-stacking of the aromatic groups with the poly(phenylsilsesquioxane) matrix as a template. The observed self-organisation is very important for the understanding of the infrared photorefractive effect in the organometallic polymer compositions. Two-wave mixings in the Raman-Nath and Bragg modes were used to study non-linear optical properties in the visible (632 nm) and near-infrared (1500 nm) spectral ranges. Both local and non-local types of refractive index gratings have been observed.