A Holographic Versatile Disc (HVD) system, using Collinear Technologies for a high capacity and high data transfer rates storage system, is proposed. With its unique configuration the optical pickup can be designed as small as a DVD's, and can be placed on one side of the disc. With the HVD's special structure, the system can servo the focus/track and locate reading/writing address. A unique selectable capacity recording format of HVD and its standardization activity are also introduced. Experimental and theoretical studies suggest that the tilt, wavelength, defocus and de-track margins are wide enough to miniaturize the HVD system at a low cost. HVD systems using Collinear Technologies will be compatible with existing disc storage systems, like CD and DVD, and will enable us to expand its applications into other optical information storage systems.

Holographic devices are expected to have a much larger capacity than conventional optical storage systems such as CD, DVD or blue diode laser based HD-DVD or BD. Recent developments in the field of dedicated recording materials and advanced optical enabling technologies are now opening the door for the realization of commercial products. One of the major technical challenges is the development of a robust and reliable system concept, which allows easy exchangeability of the medium. We developed a holographic tester system with common paths for the reference and the signal beams based on a single mode blue laser diode and a commercial CMOS detector. The system will be used to evaluate various multiplexing schemes, to investigate the influence of system tolerances on the reading performance and to estimate fundamental system limitations.

Edge illuminated holographic Bragg filters formed in phenanthrenequinone (PQ) doped poly (methyl-methacrylate) (MMA) are evaluated for optical code division multiple access (OCDMA) coding and decoding applications. The polymer characteristics are optimized using a factorial design technique. Experimental cascaded Bragg filters are formed to select two different wavelengths with a fixed distance between the gratings and are directly coupled to a fiber measurement system. The configuration and tolerances of the cascaded gratings are shown to be practical for time/wavelength OCDMA applications.

A poly(N-vinylcarbazole) (PVK) based photorefractive (PR) composite has been used as recording medium in a holographic setup designed for time gated holographic imaging (TGHI). A loss of sensitivity is observed when the performance of the material is probed with a femtosecond (fs) laser and a superluminescence diode (SLD) as short coherence light sources. It is known that the reduction in sensitivity can be compensated by different chemical and physical approaches. Here we report on a first step of a comprehensive pre-illumination (PI) series experiments with red and near infrared (NIR) laser light to gain deeper insight into the microscopic mechanism of the PI effect and to overcome the loss of sensitivity. PI with red laser light increases the recording time while simultaneous PI with one of the write beams affects the response time only slightly.

The optically induced birefringence in different block copolymers containing azobenzene and mesogen side groups has been studied with holographic methods. In the materials, the light-sensitive blocks carrying the azobenzene moieties are embedded in a matrix of polystyrene. This has the advantage that the reorientation of the chromophores does not lead to the formation of surface relief gratings. In addition, it is possible to reduce the macroscopic chromophore concentration to any desired value while, at the same time, maintaining the stabilization effect due to cooperative reorientation of the chromophores inside the photo-addressable phases. These short-range interactions give rise to long-term stability of the inscribed gratings. Angular multiplexing of holographic plane-wave gratings as well as of two-dimensional images has been demonstrated in samples with thicknesses up to 1.1 mm. The achievable refractive-index modulation, the photo-sensitivity, and the stability of the inscribed gratings were compared for different materials. In contrast to photopolymers, our materials do not exhibit shrinkage upon illumination. Instead, a weak light-induced volume expansion was detected and studied in detail.

We describe a new type of nanocomposite photopolymer system in which nanoparticles having a large refractive-index difference from formed polymers are dispersed in monomers for permanent volume holographic recording. A model for the holographic grating formation based on the mutual diffusion of monomers and nanoparticles is discussed. The diffraction properties of volume holograms recorded in the nanocomposite photopolymer system are described. Experimental evidence of holographic control of nanoparticle-distribution morphology in a photopolymer is also shown.

The growing prevalence of digital technologies has led to increased data generation so that new storage technologies must be developed to handle expanding capacity demand. Holographic data storage is a very promising candidate with the potential to provide ultra-high density data storage. Currently, many teams are developing holographic storage technology, with much of the emphasis on professional archival applications. However, consumer-oriented applications are also growing rapidly and the requirements for these applications are different from those for professional archival storage. In particular, a holographic medium for consumer applications must be simple, cheap, and easy to process. In addition, where content distribution is the intended application, the medium must also be compatible with mastering and replication processes. We present a new holographic medium designed to meet the requirements of consumer oriented applications. The media is based on thermoplastic materials that are modified by the inclusion of photo-chemically active dyes. A series of 0.6 and 1.2 mm thick discs were injection molded and characterized for holographic storage capacity and sensitivity. The first series of samples showed large refractive index modulations of 0.03 but a poor sensitivity of 0.1 cm/J. Analysis of the data showed that the low sensitivity limited the usable capacity of the media to M/# values of ~1. A new series of dyes were synthesized with optimized efficiency and injection molded in 1.2 mm substrates. These substrates demonstrated comparable usable capacity but with significantly increased sensitivities. The results of the measurements of the injection-molded thermoplastic media are presented.

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 is presented. Progress toward high-density implementations as well as the development of a functional prototype is presented. These systems are the first fully functional holographic recordable drives developed. Their development paves the way for the commercialization of this technology.

Reflection gratings have been recorded and investigated in H-PDLC materials by means of real-time spectroscopy during the polymerization process in view of possible application in optical data storage. High spatial frequency gratings (>6000lines/mm) with diffraction efficiency up to 45% and index modulation over 0.01 were obtained. The effects of the shrinkage of the reflection gratings has been detected showing a displacement of the reflected wavelength from the expected value of about 3.8%. Finally recording of microgratings has been carried out observing some optimal agreement between the microscopic and the macroscopic parameters.

The effect of monomer functionality on the diffraction efficiency of the photopolymer containing multi- and monofunctional monomers was investigated. A mixture of tri-, di-, and mono functional monomers were dispersed in a solution of polysulfone dissolved in organic solvent containing a photo initiator. The monomer contents were varied by changing the ratio between them. The average functionality (F_av = Σ φ_iF_i) was determined, where φ_i is the mol fraction of the monomer with functionality F_i. The holographic recording was performed and diffraction efficiency (η) of each film was determined by using a 532 nm laser. In the photopolymer film having an optimized composition, η was increased within 20 sec and reached a maximum of >90% with an exposure power of 5 mW laser. The rise of η (response time), maximum η, and stability of η value over prolonged recording were dependent on the monomer structure and composition and the average functionality. The result could be ascribed to the reactivity and functionality of monomers under interference light, to generate refractive index contrast.

In this paper we analyze the evolution of the refractive index modulation when recording gratings in an acrylamide based photopolymer. A nonlocal diffusion model is used to predict theoretically the grating evolution. The model has been developed to account for both nonlocal spatial and temporal effects in the medium which can be attributed to polymer chain growth. Previously it was assumed that the temporal effect of chain growth could be neglected. However temporal effects both due to chain growth and monomer diffusion are shown to be significant, particularly of short recording periods. The diffusion model is solved using a Finite-Difference Time-Domain technique to predict the evolution of the monomer and polymer concentrations throughout grating recording. Using independently measured refractive index values for each component of the recording medium, the Lorentz-Lorenz relation is used to determine the corresponding refractive index modulation. Gratings recorded for short exposure times with the diffraction efficiency growth monitored in real time both during and after recording are presented. The effect of volume shrinkage of polymer on grating evolution is also examined. The temporal response of the material and monomer diffusion is shown to influence refractive index modulation post-exposure. The inclusion of the nonlocal temporal response and the use of the Lorentz-Lorenz relation are shown to be necessary to accurately describe this polymerization process.

A red-sensitive acrylamide-based photopolymer based on multiple polymerizable monomers is developed in this paper for holographic applications. In order to improve the spatial resolution of this photopolymer system, a new strategy of employing low molecular-weight polyvinyl alcohol as binder is proposed. The comparative experiments of different photosensitive system with various molecular weights (72000,15000, 9000) are conducted to study their effects on the diffraction efficiency and spatial resolution. The experimental results show that the photosensitive system with low molecular weight of 9000 has much higher resolution and diffraction efficiency, and bright volume transmission grating with spatial frequency of 3000 lines/mm and diffraction efficiency higher than 85% can be recorded successfully on the optimum photopolymer material at the exposure level of 40 mJ/cm². Some preliminary applications of spatial and angular multiplexing holographic storage for storing multiple binary and grey-tone optical images, are successfully demonstrated.

Tir- and mono functional monomers were dispersed in a solution of polysulfone in organic solvent containing a photo initiator and other additives. New photopolymer film was prepared by dispersing acrylic monomer in a polysulfone matrix. The Polysulfone was adopted as a binder since it affords transparent thick films with low dimensional changes during holographic recording. Optical property of the photopolymer showed high diffraction efficiency (>90%) under an optimized optical condition at 532nm laser. The angular selectivity for angular multiplexing page oriented holographic memories (POHMs), the maximum diffraction efficiency of the material during holographic recording, the diffraction efficiency of the films as a function of an incident angle of two beams, exposure energy for saturation of the holographic material and application for holographic data storage will be discussed.

Near field optical nano patterning was investigated using azobenzene based amorphous molecular glass material, which shows fast response to the light and higher diffraction efficiency for short irradiation time compared to common azo polymers. Optical patterning was performed using NSOM equipped with a He-Cd laser as the light source and a cantilever with 100 nm aperture diameter. Macroscopic motion of photoresponsive materials containing azobenzene groups was useful to fabricate the well defined nano structures such as dots and line array without nanomask and development process by control of irradiation time and scan speed.

In recent years developments in holographic materials have lead to an increasing interest in many areas such as data storage and metrology. Materials such as Acrylamide-based photopolymers are good holographic recording materials, as they are inexpensive and self-processing. The diffusion rate of monomer and the molecular weight of polymerised monomer determine many material characteristics. The length (size) of the polymer chains has a direct effect on the diffusion rate of the polymer and shortening the chain length leads to an increase in the diffusion rate. Shorter chains also decrease the non-local material response parameter and, in consequence, lead to an increase in the spatial frequency response of the material. Thus it is expected that by controlling the polymer chain length (molecular weight) one might control the material spatial frequency response. In this paper we look at the effect of varying the quantity of crosslinking agents on the material and its impact on the rate of diffusion. We then look at determining the rate of diffusion of water within the material to provide a lower limit to the maximum rate of monomer diffusion.

Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing. Understanding the mechanisms present during the fabrication of gratings in these materials is crucial in enabling further development. One such mechanism is the presence of an inhibition period at the start of grating growth during which the formation of polymer chains is suppressed. Some previous studies have indicated possible explanations for this effect and mathematical models have been proposed to approximate the observed behaviour. We examine the kinetic behaviour involved within the photopolymer material during recording to enable a clear picture of the photochemical processes present. Sets of experiments were carried out with the specific aim of developing an improved understanding of these processes. Here we discuss these experimental results and provide a theoretical model, which attempts to describe the inhibition process in our Acrylamide based photopolymer and predicts this behaviour under certain conditions.