Holographic Data Storage Media Research Articles

Acrylate dendritic monomers for fabricating holographic data storage media with high performance

Photopolymer is well-recognized as an ideal holographic data storage medium. In order to improve the holographic performance of a two-stage photopolymer, five acrylate dendritic monomers (DM-1/2/3/4/5) with high refractive indices (1.590–1.634) are designed and synthesized in this study. Their structures are characterized by 1H NMR, 13C NMR, FTIR and HR-MS spectra, and their photopolymerization kinetics are investigated through real-time FTIR. Using these DMs as one recording monomer, a series of photopolymer samples with different formulations are fabricated. The influence of DM-1/2/3/4/5 on the holographic performances of these samples are explored under holographic exposure of a 532 nm laser. The results show that the photosensitivity and angle selectivity of these samples can be improved by adding these DMs. The most excellent holographic characteristics are obtained by a sample with 4% DM-1. Using it as a data storage medium, a volume holographic grating with high diffraction efficiency of 90% and narrow selection angle of 0.11° is recorded. Moreover, the sample achieves a high dynamic range of 13.7 and a low volume shrinkage of 0.36% after recording 60 holograms through angular-multiplexing with low record/read exposure dose, indicating its great application potential in holographic data storage.

A Review of the Optimisation of Photopolymer Materials for Holographic Data Storage

Photopolymers are very interesting as optically sensitive recording media due to the fact that they are inexpensive, self-processing materials with the ability to capture low-loss, high-fidelity volume recordings of 3D illuminating patterns. We have prepared this paper in part in order to enable the recognition of outstanding issues, which limit in particular the data storage capacity in holographic data storage media. In an attempt to further develop the data storage capacity and quality of the information stored, that is, the material sensitivity and resolution, a deeper understanding of such materials in order to improve them has become ever more crucial. In this paper a brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described. The key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymer material discussed are presented.

Shift-multiplexed holographic digital data page storage in a nanoparticle-(thiol–ene) polymer composite film

We demonstrate shift-multiplexed holographic storage of 180 digital data pages with low symbol-error rates in a thick (250 μm) SiO2 nanoparticle-polymer composite film using step-growth thiol-ene photopolymerization. A two-dimensional 2:4 modulation code was employed for formatting digital data pages in order to reduce the average intensity of code block without decreasing the coding efficiency. This study clearly shows the feasibility of the thiol-ene based nanoparticle-polymer composite system as a holographic data storage medium.

Holographic testing of fluorescent photosensitive glass–ceramics

In this paper we investigate the holographic recording properties of the fluorescent photosensitive glass–ceramics. The materials described here, stable up to 400 °C, represent a substantial advancement in the development of long lifetime media for holographic data storage. A detailed physical–chemical characterization of the proposed material is presented. It is shown that volume holograms were obtained after the recording process using a continuum high power laser in an off-axis setup.

Temperature Compensation Servo Algorithm for Holographic Data Storage

Photopolymers are widely used as media for holographic data storage because of their high dynamic range, high photosensitivity and availability. However, the most photopolymers have a large coefficient of linear thermal expansion. Therefore, it is known that the temperature changes cause deterioration of readout image under the Bragg-mismatch conditions. This paper proposes a new servo algorithm which includes both the servo error signals detection method and the automatic compensation procedures with feedback servo for the holographic data storage system. Experimental results for the proposed technique are demonstrated for temperature changes of up to +25 K successfully.

Two-dimensional simulation of holographic data storage medium for multiplexed recording

In this paper, we propose a new analysis model for photopolymer recording processes that calculate the two-dimensional refractive index distribution of multiplexed holograms. For the simulation of the photopolymer medium, time evolution of monomer diffusion and polymerization need to be calculated simultaneously. The distribution of the refractive index inside the medium is induced by these processes. By evaluating the refractive index pattern on each layer, the diffraction beams from the multiplexed hologram can be read out by beam propagation method (BPM). This is the first paper to determine the diffraction beam from a multiplexed hologram in a simulated photopolymer medium process. We analyze the time response of the multiplexed hologram recording processes in the photopolymer, and estimate the degradation of diffraction efficiency with multiplexed recording. This work can greatly contribute to understanding the process of hologram recording.

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.

UV-Patterned Polysilane Films as a Phase Mask in Optical Correlation System

Entirely transparent polysilane films, which were modified by ultraviolet (UV) light exposure to decrease their refractive index, were used as phase masks. The phase modulation amount of the transmitted laser, which was estimated using a Mach–Zehnder interferometer, can be modified linearly by UV exposure dose, indicating that the polysilane films have a very useful property of controllability by UV light exposure. Optical correlation using the polysilane phase masks as the information-carrying medium was then demonstrated. A matched-filter four-wave-mixing optical correlator using a photorefractive (PR) polymer as a real-time holographic data storage medium was used. A large correlation signal difference of over 3.6-fold was obtained for the striped polysilane phase masks that were arranged orthogonally or in parallel. This is due to the distinct encoded images in the polysilane phasemasks originating from the large refractive index modification in polysilane films of approximately Δn=-0.14 at λ=633 nm. The high transparency in the entire visible region and such large refractive index modification make polysilane films difficult to forge, and allow us to use phase masks in pattern recognition systems for security verification.

Polymeric photorefractive composite for holographic applications

Applications of photorefractive polymeric composite for holographic data storage medium and phase conjugation mirror were demonstrated. Polymeric material composed of photoconducting carbazole-substituted polysiloxane matrix, 2,4,7-trinitro-9-fluorenone, and 2-{3-[( E)-2-(dibutylamino)-1-ethenyl]-5,5-dimethyl-2-cyclohexeny liden}malononitrile chromophore exhibited a diffraction efficiency of 92% at an electric field of 30 V/μm. Holographic recording, reading, and erasing of single page image were demonstrated using the 100 μm thick polymeric composite. We also demonstrated that the distorted phase of the object beam introduced by a image distorter was successfully restored using a phase conjugation mirror.

New chlorin-e6 trimethyl ester compounds as holographic data storage media at liquid helium temperature

The chlorin–polyvinylbutyral (PVB) guest–host system has been the workhorse for most of the previously reported holographic hole burning experiments. In order to extend the spectral range and to improve on some of its properties we synthesized chlorin-e 6 trimethyl ester 1 and brominated chlorin-e 6 trimethyl ester 2, which require a much shorter synthesis pathway than chlorin. We studied the hole burning behaviour of these new dyes with different matrix materials and film preparation methods at liquid helium temperature and measured important properties like hole width and burning kinetics. One result was that we found the methyl ester compounds embedded into a photopolymer to have a five times faster burning rate than the chlorin–photopolymer system.