Friedrich Bruder

Holographic recording aspects of high-resolution Bayfol HX photopolymer

We have been developing a new class of recording materials for volume holography, offering the advantages of full color recording and depth tuning without any chemical or thermal processing, combined with low shrinkage and detuning. These photopolymers are based on the two-chemistry concept in which the writing chemistry is dissolved in a preformed polymeric network. This network gives the necessary mechanical stability to the material prior to recording. In this paper we describe several aspects of holographic recording into Bayfol® HX which are beneficial for its effective use and discuss them within a more elaborate reaction-diffusion model. Inhibition phenomena and the influence of precure are studied within this model and are investigated experimentally for single hologram recording and angular multiplexed hologram recordings. Also the dark reaction after the exposure period and the minimum allowable waiting time for full hologram formation are addressed. The proper understanding of these phenomena is important for the optimal usage of these new materials, in for example step-and-repeat mass production of holograms.

Materials in optical data storage

Abstract Optical Data Storage has become the mainstream technology for distributing audio, video and computer software content as well as recording and archiving personal data during the past two and a half decades. The continuous demand for ever higher storage capacities and faster data transfer rates has led to the development of three disc format families Compact Discs, Digital Versatile Discs and Blu-ray Disc, which have become established in the market. Research and development for future high density formats exploits the already well established “bit-wise” recording and volume storage approaches like holographic and “page-wise” recording. Each existing and future technology imposes specific requirements on materials that can facilitate functioning and reliable products for the consumer. In this review several aspects of the interrelation between technological requirements and materials are highlighted.

Development of Organic Recording Media for Blue High Numerical Aperture Optical Disc System

Organic write once media is developed for the Blu-ray disc format, namely, a system comprising a blue wavelength laser diode of 405 nm and a high numerical aperture (NA) lens of 0.85. The first generation Blu-ray disc format employs phase change media. Thus, the organic write once media was designed with a reflectivity modulation scheme in order to retain compatibility. A very simple layer structure is proposed, SiO2/Dye/SiO2 without any metal reflective layer, and the media showed sufficient modulation amplitude and signal quality. The optical constants before and after the recording were measured to clarify the recording mechanism, and the result matched well with the readout waveform in the optical disc system. The measured jitter level after random pattern recording at a density of 23.3 GB per disc was 6.7% using a limit equalizer, which satisfies the Blu-ray disc format.

Water Absorption and Transient Tilt of Polymeric Substrates for Optical Data Storage Media

A mechanical model for determining water absorption and transient tilt of a polymeric optical disk is established. Experimental data on disks fabricated from different substrate materials are in quantitative agreement with the model predictions. Consequences of transient tilt for the readout signals of future high density optical data storage media are discussed. Modified polycarbonates with reduced water absorption can make transient tilt less critical for the readout signal. This holds true especially in the case of future high-density optical data storage media.

Optimizing Substrate Polymers to Optical Disk Requirements by Computer Simulations

The dynamic development of optical devices for the future blue laser compact disk (CD-) technology calls for a projection of the usability of the appropriate substrate polymers. As the new hardware is not yet available, a direct examination of the substrate polymers is not possible. Computer simulations may present a useful tool to predict substrate properties parallel to the development of the hardware components and prior to the chemical synthesis of polymers. With methods of polymer physics and computer simulations, important open questions are worked out. These are, the birefringence of CDs for different polymer materials, their mechanical strength and melt flow, the influence of the pit replication on the optical disk readout-signals and the influence of water absorption on the dishing of the disk. An outlook on some recent results on structurally modified polycarbonates with lower birefringence levels, that might become important in the near future is given.