Studies of development kinetics in volume photopolymers typically use transmission holography to quantify the index distribution. This method has advantages including simplicity, quantitative index data and natural mapping onto theories using harmonic expansion of the material response. A particular disadvantage is that the low spatialfrequency response corresponding to the intensity of the writing beams can never be Bragg matched and thus remains invisible. In configurations where the exposure is not primarily sinusoidal, the holographic method is not applicable. Important examples include bit-oriented data storage, direct-write lithography, and the object beam of page-based holography. In these cases the exposure intensity is essentially arbitrary and there is a need for metrology tools that can quantitatively measure the real and imaginary parts of the weak 3D index perturbation. Images produced by bright-field and phase-contrast microscopes are generally not quantitative and are corrupted by objects out of the focal plane. We have developed two methods, a form of optical diffraction tomography and a scanning transmission microscope, that are specifically designed to measure the 3D index response of holographic materials. Both are optimized to measure the extremely weak absorption and phase structures typical of photopolymers and have passbands that match the expected spatial frequencies.

We report the photorefractive properties of tetraphenyldiaminobiphenyl (TPD) based polymer composites that have been developed for single pulse laser operation at 532 nm. With an optimized composite, we demonstrate more than 50% diffraction efficiency using 4 mJ/cm² single shot writing and 633 nm continuous wave (cw) beam reading. The present devices showed a 300 μs fast response time. This reveals the potential for these polymer devices in applications which require fast writing and erasure. Since the writing pulse-width is in nanosecond time scale, the recording is totally insensitive to vibrations. These devices can also be used as a stepping stone to realize all-color holography since they are sensitive to both green (532nm) and red (633nm) wavelengths. The holograms can be written with either of these two wavelengths and can be read by the same wavelength or the other wavelength with high diffraction efficiency. This demonstrates that these devices have the advantage of performing two-color holography, a step closer to a dynamic full-color holographic recording medium.

The good optical properties of PQ (phenanthrenequinone)-doped PMMA (poly methylmethacrylate) and the ability to form it in a wide range of substrate configurations makes it attractive as a holographic recording material. Previously Wavelength Division Multiplexing (WDM) and Optical Code Division Multiple Access (OCDMA) filters were demonstrated in this material operating near 1550 nm using edge-illuminated geometry. In this paper we investigate the temperature dependence of edge-illuminated holographic filters formed in PQ/PMMA. It was found that both the volume and refractive index of the material changes as a function of temperature. It was also found that changes to the refractive index dominate the wavelength selectivity of the grating. Experimental measurements and a theoretical model for the grating behavior as a function of temperature are presented.

Tilt tolerance of media is compared for bit-based and page-based holographic storage systems having an equal diffraction efficiency per bit detector, dynamic range of the medium and surface recording density. We have formalized the diffraction efficiency degradation caused by aberrations of a reconstructing reference beam induced by tilt of the medium, using a coupled wave theory in the Fourier domain. The bit-based holographic storage system has a larger media tilt tolerance compared to a page-based system with relatively large page size.

Holographic data storage materials based on a dye-doped thermoplastic that could find application in professional archival and consumer applications are described. The dye is selected from the class of o-nitrostilbenes, which irreversibly bleaches under exposure to light and shows high thermal stability before and after exposure. The reduction in concentration of the dye in the host after exposure induces refractive index variations over a wide range of wavelengths and extends well away from the dye absorption peak conforming to the Kramers-Kronig relationship. The materials are injection moldable into the standard disc format and have negligible shrinkage during data storage. Samples were produced using different dyes and various concentrations in a polycarbonate host and processed on professional CD/DVD equipment. The refractive index change is as high as 0.04, with a measured instantaneous sensitivity of 0.5 cm/J and M/# = 0.3.

The number of channels of an optical communication system is increasing rapidly. In this paper, the demonstration of a 130-channel demultiplexer based on the cascaded volume holographic gratings is presented. Those gratings are recorded separately in 100-μm thickness photopolymer films, which attached on both sides of a glass substrate. They have different grating periods, slant angles, and center wavelengths. By ultilizing this configuration, the operating wavelength range of the optical demultiplexer could be expanded, and therefore, the number of channels of the holographic demultiplexer is increased. As a result of the experiment, a 0.4-nm-spaced demultiplexer with the channel uniformity of 3.5 dB, the 3dB-bandwidth of 0.12 nm, and the channel crosstalk of -20 dB is experimentally achieved.

We report on the use of a photorefractive polymer composite as the active material for a planar photo- EMF detector suitable for the adaptive detection of optical phase modulated signals in the audio range (10Hz-10KHz). The composite is based on a conjugated triphenyldiamine- phenylenevinylene polymer (TPD-PPV) and is sensitized with a highly soluble fullerene derivative (PCBM). We demonstrate experimentally that the responsitivity of such polymer based detectors can be remarkably enhanced if the polymer sample is biased by an external dc field. This effect is theoretically explained by the strong dependence of the charge carrier generation rate on the external dc field, which is an inherent property of organic photoconductors.

Development of a theoretical model of the processes present during the formation of a holographic grating in photopolymer material is crucial in enabling further development of holographic applications. To achieve this, it is necessary to understand the photochemical and photo-physical processes involved and to isolate their effects enabling them to be modelled accurately. Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing. Understanding the recording mechanisms will allow their limitations for certain processes to be improved and a more efficient, environmentally stable material to be produced. In this paper we further develop our Non-local Polymer Driven Diffusion (NPDD) model to include the effects of absorption and inhibition effects. Thus we attempt to increase the accuracy of our existing model.

The effect of field component perpendicular to the surface (longitudinal fields) on the photo-induced molecular migration and surface deformations in azobenzene polymer films are investigated. Case of tip-enhanced near-field illumination of the polymer surface is first discussed. In order to rule out the possible influence of mechanical interaction between tip and polymer, tightly focused higher-order laser beams are then used. We demonstrate that the surface topography is principally induced by longitudinal fields. Our findings can be explained by the translational diffusion of isomerized chromophores when the constraining effect of the polymer-air interface is considered.

Models of the index response of diffusion photopolymers typically assume that polymerization is proportional to optical intensity. However, common radical initiators self-terminate. This reduces the polymerization rate and has been shown in steady state to result in polymerization that is proportional to the square root of intensity. We examine the impact of sublinear polymerization rate on the spatial distribution of index in volume photopolymers. In contrast to previous work based on spatial frequency harmonics, we consider a Gaussian focus and examine the index in the spatial domain. This can thus be thought of as the impulse response of the material which, due to the nonlinear response, is not the Fourier transform of the previous studies. We show that sublinear polymerization rate dramatically impacts the spatial confinement of the index response. A case of particular interest to applications such as shift-multiplexed holography is a Gaussian beam translated orthogonal to its axis. In this geometry, a square-root material response yields an index profile of infinite axial dimension. We verify this prediction experimentally. The axial confinement of cationic (linear) photopolymer is shown to be significantly smaller than a radical (sublinear) photopolymer under the same writing conditions, confirming the prediction.

The promise of using volume holography to deliver high performance optical storage systems is at hand. The possibility of extremely large storage capacities and fast transfer rates make holographic storage ideal for high performance video applications. An overview of advances at InPhase Technologies toward the first drive product is presented. InPhase Technologies is developing a holographic recordable optical drive and associated disk media for professional archive applications. The target user capacity for the first product is 300GB of user data with sustained write and read user transfer rates of 20MByte/s. The architecture, design and implementation of the holographic drive are described here.

The development of an optimized scheduling technique based on an accurate model is necessary for the continued development of holographic data storage technology. In this paper we examine an algorithm based on the non-local polymerization driven diffusion model (NPDD), which determines an appropriate recording schedule for use in data storage. The NPDD model accounts for nonlocal spatial and temporal material effects present in material involving free radical chain polymerization. The model is solved using a finite difference technique and an optimized schedule determined. Results are compared to experimental work. The inverse-square scaling law of holographic diffraction is also examined and is shown to hold for low diffraction efficiency gratings but breaks down for a low number of high efficiency gratings.

As a method to record and reconstruct three-dimensional whole information of an object, holography has been used for various applications from the beginning of its invention. Recent holography technologies widen their applicability from present ongoing applications as display, data storage, and holographic lithography to near-future potential technologies as three-dimensional display, nano-particle-based optical storage, and surface plasmon lithography. In this paper, recent holographic technologies applied to various fields are discussed with respect to related simulation issues. Theoretical analysis and expectation through simulation study are inevitable for deeply understanding background principles, gaining insight, saving resources and maximizing efficiency. Simulation issues related to these holographic technologies are introduced and some our simulation studies are presented.

Diffusion model of monomers in holographic recording media was investigated to determine diffraction efficiency and the effect of the binder structure on holographic recording in an organic-inorganic hybrid photopolymers. Experimental value and rise of diffraction efficiency for the photopolymer films containing different organic sol-gel precursor (TSPEG) were compared with theoretical plot of diffraction intensity growth against recording time based on the first Harmonic diffusion model, using various material parameters, including the monomer diffusion constant, D, polymerization rate, refractive index of monomer, binder, and polymer. The initial rate of polymerizations in the photopolymer films, evaluated by FT-IR method was compared to the polymerization rate obtained from the simulation. Diffusion time of the photopolymer determined from the simulation was a function of TSPEG content, proving that the side chain in the organic hybrid media affect the diffusion of monomer from the dark area of the photopolymer (non-local polymerization).

The chromophoric materials were prepared by copolymerization of various methacrylic monomers. The incorporation of the chromophore groups was done by coupling reaction of diazonium salts of the sulfonamide such as: sulfomethazine or sulfisomidine). The copolymers having free OH groups were able to react with 3-triethoxypropyl isocyanate forming intermediates used to prepare hybrid transparent films by sol-gel technique. The films of both copolymers as well as of hybrid sol-gel structures showed photochromic properties via trans-cis isomerization of the diazo groups. The absorption maximum of the trans form was ca. 435-445 nm depending on chemical composition of the material. Illumination of the films with coherent laser beams (two-beam coupling) resulted in formation of diffraction grating. The diffraction efficiency reached 4-5 % and refractive index modulation was in the range up to 0.0032.

Two series of photochromic copolymathacrylates containing cyanoazobenzene chromophores as side chains were described. The series with shorter ethylene spacer between mesogen and main polymethacrylate chain was amorphous, whereas the second one with longer ethoxyethylene spacer was liquid crystalline forming smectic C mesophase above Tg. The materials were deposited on glass substrates via spin coating and casting technique to provide thin transparent films. The reversible change of refractive index of the films on illumination with white light was determined by ellipsometry. The difference of real part of the refractive index of the sample was in the range 0.0067-0.0210 depending on the polymer. Formation of diffraction grating was achieved by two beam coupling arrangement using a 532 nm laser diode . The diffraction efficiency for the first order diffraction was in the range of 1.5-2.1% for the homopolymers.

Incorporating the effects of volume changes into the Nonlocal Polymerization Driven Diffusion Model we examine these effects on grating evolution. The concept of free volume or hole formation is explored and the subsequent decay and diffusion of holes examined. The inclusion of a nonlocal temporal response function is also shown to be critical to the modeling of grating formation for short recording times. The model is solved using a finite difference technique and results converted initially to refractive index modulation and then to diffraction efficiency using rigorous electromagnetic theory. Fits are carried out to experimental data and model parameters determined.

Photopolymer films containing s-triazine (ST) methacrylic monomers were explored for holographic recording. Photofunctional s-triazine derivative having polymerizable group was synthesized starting from the reaction of a ST di-thiol derivative with methacryloyl chloride to give ST methacrylic monomer substituted with methylthio group (TRSM). ST methacrylic monomer substituted with ethylene oxy unit (TREGM) was synthesized from the reaction of a diamine substituted ST dichloride derivative with hydroxyl-ethyleneoxy methacarylate (HEMA). Photopolymer films prepared by mixing the s-triazine monomer with binder, additives, and photoinitiator were sensitive to a visible light and polymerized upon excitation with a visible laser. The optimization of holographic recording media was achieved by controlling the concentration and chemical structure of monomer composition in photopolymer films to control the diffusion and polymerization of monomer. The new photopolymer films containing ST methacrylic monomer substituted with ethylene oxy unit (TREGM) showed diffraction efficiency reaching ~ 90%. High diffraction efficiency and fast response for the photopolymer prepared from TREGM monomer were ascribed to the effective monomer compatibility with the binder to result in high optical clarity of the film.

Holographic data storage systems, utilising various photopolymer materials as the recording medium, are currently being developed. The photopolymer recording material used in this study is an Acrylamide/PVA based material. In this paper, having determined values for some basic properties of the material such as diffusion of Polyacrylamide and diffusion of water, we now look at chemically modifying the material and experimentally determine the impact. An important material characteristic, which determines the performance of any photopolymer medium, is the spatial frequency response of that material. Previously, applying our Non-local Photo-Polymerisation Driven Diffusion Model, (NPDD), we have discussed the effects on material behaviour of the length of the polymer chains and the rates of diffusion within the material. These parameters have been shown to be important in determining the response of the material. If the average length of the Polyacrylamide chains is shortened, an increase in the diffusion coefficient might be observed. Shorter Polyacrylamide chains should then result in an increase in the materials spatial frequency response, and ultimately in an increase in holographic data storage capacity. One possible method of doing this is to modify the chemical composition of the material to control chain length. The rates of diffusion of the material, both before and after modification of the chemical composition, are compared to determine the impact. Shortening the chain lengths should result in the possibility of creating smaller structures in the photopolymer material.

The interaction between electrons and photons satisfying a resonant condition in the boundary between metallic material and dielectric material can generate a surface-bound wave exponentially decaying away from the interface. Particularly, the intensity caused by the surface plasmon wave is considerably high on the interface when the incident angle of the monochromatic wave satisfies the resonant condition. Thus, adopting this wave makes it possible to generate a highly intense reference wave propagating along the interface in hologram. Recently, it is shown that applications and researches based on surface plasmon resonance can be applied for photonic integrated circuits and devices. However, feasible methods to fabricate a nano-scale structure using the surface confined (2-dimensional) wave caused by surface plasmon resonance require us to use thin photosensitive recording material. Some notable methods to fabricate nanoscale devices made from PMMA (polymethyl methacrylate) have been already shown. In this paper, by using the property that the incident monochromatic light can be absorbed in the interface of the metallic medium and the dielectric medium when a certain resonance condition is satisfied, we propose a wavelength selection filter fabricated by a phase mask with the pitch of 1061.1nm and phase conjugation holography. In the experiment, two monochromatic light sources, He-Ne laser with the wavelength of 633nm and second harmonic Nd-YAG laser with the wavelength of 532nm, will be used. The fabricated lamella metal-coated grating using the phase mask will be shown, and the volumetric metalcoated photopolymer grating will be used to verify our proposed wavelength selection filter.

A novel photoresponsive polymer containing bisazo chromophores have been synthesized for comparative study with monoazo polymer. Since the bisazo structure has an extended Π-conjugation electronic system, it is expected to have large intrinsic molecular birefringence that can realize large macroscopic photoinduced birefringence (Δn_PI) via photoinduced molecular re-orientation process of bisazo molecules. As a result, it was found that the large value of Δn_PI (0.17) could be obtained by using bisazo polymer at 514.5nm excitation with 1.0W/cm².