We describe the material characteristics and photorefractive properties of novel tetraphenyldiaminobiphenyl (TPD) based polymer composites that were developed for operation wavelengths up to 1 micron. With an optimized composite, we demonstrated more than 50% external diffraction efficiency coupled with a fast response time of about 35 ms at 980 nm. In addition to this high performing composite, we have developed a composite with high two beam coupling gain (300 cm^-1). To accomplish these attractive photorefractive properties in the near-infrared, we explored the chemical flexibility of the guest-host approach. We employed a new dye with enhanced near-infrared absorption to extend the sensitivity into this long wavelength range. Styrene-based chromophores were utilized to enable high refractive index modulation. We explored ellipsometry as well as photo-conductivity measurements to optimize the composition of the composites. In addition to the composites that contain a single chromophore species, we also analyzed samples prepared with a mixture of chromophores. Our studies reveal the potential of this new polymer-composite family to extend the operation wavelength of the photorefractive materials to even longer wavelengths. Attractive photorefractive properties coupled with long wavelength sensitivity make these materials potential candidates for imaging and communication applications.

We investigated the carrier transport and photorefractive properties in multi-component materials containing 9-(2-ethylhexyl)carbazole (EHCz), so-called liquid carbazole. The electric-field dependence of the carrier mobility for EHCz and polyvinylcarbazole (PVK) was measured by the time-of-flight (TOF) technique. We obtained the higher carrier mobility of 4.2 x 10^-6 cm²/Vs with an electric field of 2.5 x 10⁵ V/cm for EHCz than that of 6.4 x 10^-7 cm²/Vs for PVK. We also performed the two-beam coupling (TBC) technique to investigate photorefractive responses for the guest-host polymers containing PVK, EHCz, the electro-optic chromophore 4-piperidinobenzylidene malonitrile (PDCST), and the sensitizer C₆₀. The measurement showed that the TBC gain depended on the mixture ratio of PVK and EHCz. The TBC gain was enhanced from 31 to 85 cm^-1 at an electric field of 60 V/μm by increasing the concentration of EHCz from 10 to 15 wt%. These results show that EHCz plays important role for the optoelectronic and photorefractive materials as a hole transport materials as well as a plasticizer.

Novel photorefractive (PR) hybrid composites have been developed, based on a functional polymer poly(N-vinylcarbazole) (PVK) sensitized with nanocrystalline lithium niobate (LiNbO₃). A comparison study between traditional organic PR material sensitized with 2,4,7-trinitro-9-fluorenone (TNF) and novel composites mentioned above was made with respect to their photorefractive behavior at 633 nm. The steady-state and the kinetics of the photorefractive gratings in the materials under study were investigated in degenerate four-wave mixing (DFWM) and two-beam-coupling (TBC) experiments in a tilted geometry. It was shown that photorefractive properties of new composites are strongly influenced by the concentration of nanocrystals. The effect of co-sensitization, by the traditional 2,4,7-trinitrofluorenone and the LiNbO₃ nano-crystals, was discovered. This yields materials with improved PR performance compared to that of the standard PR polymer material sensitized by TNF only.

We present two applications of volume holographic filters in the reflection geometry. A passive athermal holographic filter design is realized through the mutual compensation between the temperature coefficients of the bulk hologram and a variable incident angle controlled by a bimetallic cantilever. Seven holograms are multiplexed to constitute a multi-line filter which can be used to emulate specific absorption or emission spectra for spectroscopic applications.

An overview of the InPhase Technologies holographic demonstration platform is reviewed and a new holographic multiplexing technique presented. The platform is a compact, mobile system and the first fully functional, portable; holographic recordable drive complete with custom optics and control and channel electronics. In addition a description of "POLYTOPIC MULTIPLEXING" is presented. This innovation allows us to simplify the system geometry and optimize the media usage enabling a sustainable product road map. These developments pave the way for the commercialization of this technology.

High density polarization holographic demonstrator system has been developed using ~2 µm thick azobenzene polyesters on reflective card form media. One possible development of the system is the introduction of phase encoding into the reference arm that provides enhanced security applications. Simulations were carried out with a custom computer program based on mathematical model of the system to generate code sets optimal in terms of code number and security level. The model is suitable also for the prediction of expected tolerances necessary before the definition of a working system. Performed experiments proved applicability of the model for possible system considerations. We also present our concept of extending thin-film holographic principle to multilayered holographic storage of increased capacity.

Traditional planar lightwave circuits fabricated from lithographically-patterned waveguides in glasses, semi-conductors or polymers cannot accommodate the wide range of materials required by typical optical devices. In addition, such waveguides are nearly always defined in the material surface and thus can support only a limited density of interconnects and suffer poor performance at waveguide crossings. Furthermore, the inflexibility of lithographic approaches -- including both waveguides and "silicon-bench" methods -- requires optical sub-components with unreasonable and expensive tolerances. We propose an alternative integrated optics platform based on 3D direct-write lithography into an optically addressable encapsulant. Arbitrary micro-optics are first embedded in a liquid monomer which is then cured into a semi-solid pre-polymer. It is essential that this step take place with minimal shrinkage to avoid stresses. A scanning confocal microscope then nondestructively identifies the component locations and their tolerances. The controller customizes the circuit design to accommodate these tolerances and then scans a 0.3 to 0.6 NA focus within the volume of the holographic polymer to create waveguides, lenses or other passive interconnects with one micron resolution. A final incoherent exposure cures and solidifies the polymer, finishing the process. The resulting hybrid optoelectronic circuits contain 3D routed waveguides interconnecting active and passive micro-optic devices in environmentally robust, hermetically sealed packages. A feature of particular interest is the ability to write waveguides directly off of the tips of embedded fibers, passively interfacing the circuits to fiber. We show that polymers developed for holographic data storage have the properties required for this application.

The optically induced birefringence in different azobenzene and mesogen containing block copolymers has been studied with holographic methods as well as with measurements between crossed polarizers. The influence of various parameters for possible applications as holographic data storage materials was investigated. In the block copolymers, the functionalized blocks are confined in a matrix of polystyrene. This has the advantage that no surface relief gratings appear when the chromophores are reoriented. Also liquid-crystalline stabilization due to cooperative reorientation occurs inside the functionalized blocks. These short-distance interactions in the blocks give rise to long-term stability of the inscribed gratings. So far injection-molded blends with azobenzene containing block copolymers were capable to store up to 200 holograms on one spot. On such a sample we could also demonstrate a fundamental physical effect which generally plays a role for light diffraction on thick gratings. According to the Kramers-Kronig relations, an attenuation of light is always coupled with a phase shift. In the case of a thick holographic grating, the intensity of the transmitted wave (of diffraction order zero) is a function of the angle of incidence, because part the light is diffracted into the first order when the Bragg condition is fulfilled. We measured the phase shift of the transmitted wave as function of the Bragg mismatch angle and found good agreement with analytical calculations.

Many new high-tech consumer products that are now under development require micro-optical elements. The development of these micro-optical devices has been carried out by many different researchers working in a variety of areas. This has lead to a large number of different fabrication techniques. We examine a novel fabrication technique that may allow the development of large arrays of elements quickly and cheaply. It is known that the exposure of dye sensitised Acrylamide layers to light can lead to material refractive index and volume changes. It is therefore proposed that a patterned exposure can be used to form a mixture of volume and surface relief patterning, enabling the production of optical elements. The examination of this fabrication technique, in particular the study of the processes that result in this volume change, may also lead to improvements in the photopolymer material so as to control shrinkage of these materials. The development of low shrinkage holographic recording materials is an active area in holography as most current photopolymer materials exhibit some volume change during the recording process. This has implications for the fidelity of the replayed image. This is of crucial importance in areas such as data storage systems. The further study of this process also has implications for the wider holographic research community. It is important to understand the surface relief profile of the holographic element prior to extracting grating parameters as surface relief effects may influence the experimental data. In this paper we describe initial experimental attempts to produce micro-optical elements for use in the visible spectrum using patterned exposure of an Acrylamide based photopolymer material.

A series of novel chiral azodye homo- and copolymers has been investigated for applications in optical data processing and display technology. Supramolecular chirality in those systems due to helical superstructure leads to specific photo-optical response to circularly polarized light and, therefore, for creation of advanced photorecording media, especially for polarization holography. Highly twisted smectic-like mesophases of side chain homo- and copolymers (short pitch TGB A* phase) appear visually transparent and optically isotropic but possess a hidden liquid crystalline ordering, giving rise to rewriteable photorecording in relatively thick polymer films with high photoinduced phase retardation and diffraction efficiency. The amplitude gratings were written in polymer films with linearly polarized light but the phase gratings with circularly polarized light. Evolution of the photoinduced birefringence and diffraction efficiency, η₁, is studied. For some polymers, polarization gratings are obtained with η₁ value above 30%; overmodulation effects of the grating recording are observed and discussed. The effect of dark self-amplification is reported.

We report on the trapping mechanisms in bis-triarylamine (PATPD) based polymer composites. Although exceptional stability under continuous operation has been reported in PATPD-based composites, a small degradation of the response time in photorefractive devices under continuous operation has been found when improved styrene-based chromophores, with high figure-of-merit, are used. The accumulation of relatively large densities (~10¹⁷ cm^-3) of filled traps is observed even though to first approximation the transport manifold has the lowest ionization potential of all the moieties in the composite, so no apparent deep trapping sites are to be present. The results of spectroscopic studies where the formation of chromophore aggregates is explored and correlated with the formation of hole-trapping sites that dominate the temporal evolution of the photogenerated current density and C₆₀ anion accumulation after several minutes of continuous operation will be presented and compared with numerical simulations considering a two-trapping site model in materials containing the chromophore DBDC.

We present results on the photorefractive performance of cyclometalated complexes in which a central metal atom (Pd or Pt) coordinates two different molecular sub-units in a single species. Depending on the details of their structure, these molecules aggregate in crystals, glasses or liquid crystalline phases. The photorefractive properties of the complexes are discussed by treating separately results obtained in different phases. Crystalline compounds can be dissolved in suitable polymers and we show how phase separation in polymeric composites, which is usually detrimental for sample stability, can be controlled and used to increase photorefractive performance parameters by orders of magnitude. In addition, we present a method for estimating the itensity of the space-charge field in chiral smectic phases without using any of the standard models developed for crystalline or amorphous materials.

Non-local and non-linear models of photopolymer materials, which include diffusion effects, have recently received much attention in the literature. The material response is non-local as it is assumed that monomers are polymerised to form polymer chains and that these chains grow away from a point of initiation. The non-locality is defined in terms of a spatial non-local material response function. The numerical method of solution typically involves retaining either two or four harmonics of the Fourier series of monomer concentration in the calculation. In this paper a general set of equations is derived which allows inclusion of higher number of harmonics for any response function. The numerical convergence for varying number of harmonics retained is investigated with special care being taken to note the effect of the; non-local material variance σ, the power law degree k, and the rates of diffusion, D, and polymerisation F₀. General non-linear material responses are also included.

The inclusion of a nonlocal spatial response function in the Nonlocal Polymer Driven Diffusion model (NPDD) has been shown to predict high spatial frequency cut-off in photopolymers. Here the nature of the temporal response of photopolymer is discussed and a nonlocal temporal response function proposed. The extended model is then solved using a finite element technique and the results discussed. Based on this model we examine the nature of grating evolution when illumination is stopped during the grating recording process. Refractive indices of the components of the photopolymer material used are determined and predictions of the temporal evolution of the refractive index modulation described.

Holographic and diffractive optical elements (D.O.E.’s) have a variety of engineering applications. However, the availability of an inexpensive, self-processing, environmentally stable material with good spatial frequency response is crucial for further development in successful applications of holography. A number of different materials are currently being examined. In this paper we examine an Acrylamide-based photopolymer recording material, as it is one of the promising materials currently available. The material is self-processing and can be sensitised to different recording wavelengths using a dye. The self-processing capability simplifies the recording and testing processes and enables holographic interferometry to be carried out without the need for complex realignment procedures. The material requires further improvement as it has a number of limitations, e.g. it has a poor spatial frequency response range (500-2500 l/mm). The improvement of this material will require bulk testing of the material. Therefore a LabView controlled automated fabrication and testing system was developed. Arrays of D.O.E.’s were recorded in the Acrylamide based photopolymer material using the automated system and the refractive index modulation and the thickness of the grating were extracted.

Holography has become of increasing interest in recent years with developments in many areas such as data storage and interferometry. Photopolymer materials such as acrylamide-based photopolymers are ideal materials for the recording of holographic optical elements, as they are inexpensive and self-processing. There are many experiments reported in the literature that describe the diffraction efficiency and angular selectivity of various materials. The majority of these discuss the performance of the holographic optical element after the recording stage. It has been noted however, sometimes, the recording beams are seen to modulate in intensity during fabrication of the grating. In this paper we discuss our current work and improvements on our previous model. This paper incorporates the growth of an absorption grating during the recording process and deals with a non-ideal beam ratio illustrating the effects this has on the modulation. Our new model attempts to better explain the modulation of the recording beams during grating formation resulting in a more accurate approximation to this behaviour.

A novel approach to 3D optical information storage based on writing and reading of microscopic holographic gratings in a photopolymer layer is presented. Strongly localized reflection gratings created by two highly focused laser beams are used to replace the pit and land structure of the CD/DVD technology. The holographic recording method presented here allows employing various multiplexing methods. A combination of wavelength multiplexing and multilayer storage is proposed to achieve storage densities similar to page-oriented holographic data storage. In this paper we report on recording and readout of submicron-sized gratings using diffraction limited laser beams. The transversal extent of a micrograting corresponds to the optical resolution limit. Track spacing and bit-to-bit separation are about 500 nm. The interlayer spacing through the depth of the photopolymer is less than 8 micron. This way a 3D structure is realized that even refines the surface data structure of current DVDs.

We have demonstrated an optical novelty filter based on the two-beam coupling effect in photorefractive polymers. The photorefractive polymer composition was optimized for response time and two-beam coupling gain by changing the ionization potential and polarizability of various components. In this study, a photorefractive polymer composition was simultaneously optimized for response time and gain, and employed as a key element in a two-beam coupling novelty filter with a high contrast ratio and a limiting frequency of 14Hz, considerably higher than any previously reported in a two-beam coupling photorefractive novelty filter.

A new type of volume holographic gratings based on polymer-liquid crystal composite named POLIPHEM (POlymer LIquid Crystal Polymer Holograms Electrically Manageable) is presented. The new composite material in combination with the proper holographic fabrication results in switchable holographic gratings with high diffractive and electro-optical parameters. Periodic structures consisting of alternating polymeric and LC-rich regions with aligned mono-domain morphology of the LC are formed due to photopolymerisation and phase separation of the initially homogenous film of photo-curable monomers and liquid crystals under illumination with an interference field (λ_rec=364 nm) at room temperature. Compared to typical holographic polymer-dispersed liquid crystals (H-PDLCs) POLIPHEM films are characterized by the absence of light-scattering, strong anisotropy after holographic exposure, low driving voltages and fast electro-optic time-response. The kinetics of the holographic recording under different irradiation intensities were investigated at λ_test=632.8 nm, the microstructure and the electro-optical response of POLIPHEM transmission gratings have been analyzed. POLIPHEMs were realized in the pitch range of 0.28-6 μm. The diffraction efficiency of more than 96% was achieved for p-polarized probe light (for λ_test=632.8 nm). Possible mechanism of POLIPHEM formation is discussed briefly.

Investigating dynamics in a disordered solid material below, at, and well above glass transition temperature, we show that (1) to describe glass dynamics entirely it has to be regarded over a long range on logarithmic time scale, (2) a single stretched exponential function (Kohlrausch-Williams-Watts) can never describe the data, (3) stretching exponents do not cover the ranges previously suggested (from 0 to 1, e.g. as a sigmoid function). Optically recorded dynamics (measured by ellipsometry) is brought into connection with dielectric spectroscopy.