Optical data storage has had a major impact on daily life since its introduction to the market in 1982. Compact discs (CDs), digital versatile discs (DVDs), and Blu-ray discs (BDs) are universal data-storage formats with the advantage that the reading and writing of the digital data does not require contact and is therefore wear-free. These formats allow convenient and fast data access, high transfer rates, and electricity-free data storage with low overall archiving costs. The driving force for development in this area is the constant need for increased data-storage capacity and transfer rate. The use of holographic principles for optical data storage is an elegant way to increase the storage capacity and the transfer rate, because by this technique the data can be stored in the volume of the storage material and, moreover, it can be optically processed in parallel. This Review describes the fundamental requirements for holographic data-storage materials and compares the general concepts for the materials used. An overview of the performance of current read-write devices shows how far holographic data storage has already been developed.
Photoaddressable polymers (PAPs) are side‐chain copolymer systems functionalized with azobenzene chromophores and mesogenic side groups. They show very large birefringence values after illumination with polarized light. The molecular mechanisms involved are photoinduced isomerization cycles of the azo side groups, which induce strong molecular reorientations (cooperative motion of light‐absorbing azobenzene chromophores and non‐absorbing mesogenic groups). Due to the long‐term and high‐temperature stability of their light‐induced birefringence, PAPs are very promising recording materials for optical data storage applications such as high‐capacity DVDs and holographic memory.
The paper presents the synthesis of azobenzene-functionalized block copolymers based on a poly-(methyl methacrylate) (PMMA) segment and an azobenzene-functionalized poly(hydroxyethyl methacrylate) segment, and a basic study of blending these block copolymers with homopolymers is given. Two diblock copolymers, prepared via different routes, were synthesized by a living anionic polymerization followed by a polymer analogous reaction to attach the azobenzene side groups. Self-assembly of the block copolymers resulted in phase-separated morphologies on the nanometer scale. The photoaddressable azobenzene segments are dispersed in the PMMA matrix and locally confined. Special focus is given to the preparation and characterization of block copolymer blends with PMMA homopolymer in order to dilute the phase-separated azobenzene morphology and reduce the optical density while maintaining the confinement. The block copolymer blends were characterized with respect to their morphology and initial holographic experiments were performed.
This paper describes a new class of recording materials for volume holographic applications suitable to meet commercial manufacturing needs. These next-generation holographic photopolymers have the ability to satisfy the unmet demand for color and depth tuning that is only possible with volume holograms. Unlike earlier holographic photopolymers, these new materials offer the advantages of no chemical or thermal processing combined with low shrinkage and detuning. Furthermore, these materials exhibit high transparency, a high resolution of more than 5000 lines/mm and are environmentally robust. Bayer MaterialScience plans to commercialize these materials, which combine excellent holographic characteristics with compatibility to mass-production processes. In this paper, we will briefly discuss the potential markets and applications for a new photopolymer, describe the attributes of this new class of photopolymers, relate their ease of use in holographic recording, and discuss potential applications of such materials..
We present results of the feasibility study on photoaddressable polymers (PAPs) applied to optical disc systems. PAPs represent a new class of organic rewritable materials that exhibit a huge signal birefringence (Δ
n) at the readout wavelength. By optimizing the disc structure and the readout optics, the signal amplitude is proved to be sufficient for the optical disc systems. A low noise profile and sharp recording profile led to a maximum carrier-to-noise ratio (C/N) of 58 dB and a clear eye-pattern. They also showed a potential for multi-level recording, since the recording was dominated by a pure photon mode.
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