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13 pages, 5635 KiB

Open AccessReview

Magnetic Holography and Its Application to Data Storage

by Yuichi Nakamura

Photonics 2021, 8(6), 187; https://doi.org/10.3390/photonics8060187 - 25 May 2021

Cited by 5 | Viewed by 3968

The principle of magnetic holograms and its application to holographic memory are reviewed. A magnetic hologram was recorded through a thermomagnetic recording as a difference in magnetization direction and reconstructed with the magneto-optical effect. To achieve a bright reconstruction image, it is important to record deep magnetic fringes on the materials with large Faraday rotation coefficients. This technique was applied to the holographic memory using transparent magnetic garnets as a recording material. The first reconstruction image was dark and noisy, but improvements in the recording conditions resulted in error-free recording and reconstruction of the magnetic hologram. To form deep magnetic fringes, insertion of heat dissipation (HD) layers into recording layer was proposed. It was found that this HD multilayer medium showed diffraction efficiency higher than that of a single layer medium, and error-free recording and reconstruction were also achieved, using magnetic assisted recording. These results suggest that HD multilayer media have potential applications in recording media of magnetic holographic data storage. In future, a high recording density technique, such as multiple recording, should be developed. Full article

(This article belongs to the Special Issue Holography)

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12 pages, 4055 KiB

Open AccessArticle

Development of Heat Dissipation Multilayer Media for Volumetric Magnetic Hologram Memory

by Yuichi Nakamura, Pang Boey Lim, Taichi Goto, Hironaga Uchida and Mitsuteru Inoue

Appl. Sci. 2019, 9(9), 1738; https://doi.org/10.3390/app9091738 - 26 Apr 2019

Cited by 5 | Viewed by 3015

Abstract

Holographic memory is a strong candidate for next-generation optical storage, featuring high recording densities and data transfer rates, and magnetic hologram memory using a magnetic garnet, as the recording material is expected to be used as a rewritable and stable storage technology. However, the diffraction efficiency of magnetic holography depending on the Faraday rotation angle is insufficiently high for actual storage devices. To increase the diffraction efficiency, it is important to record deep magnetic fringes, whereas it is necessary to suppress the merging of fringes owing to heat diffusion near the medium surface. In this work, we investigated the recording process of magnetic holograms in detail with experiments and numerical simulations, and developed a multilayer media with transparent heat dissipation layers to record deep and clear magnetic holograms by controlling the heat diffusion generated during the thermomagnetic recording process. To suppress lateral heat diffusion near the medium surface, we designed and fabricated a multilayer magnetic medium in which the recording magnetic layers are discrete in a film, approximately 12-µm thick. This medium exhibited diffraction efficiency higher than that of the single-layer medium, and error-free recording and reconstruction were achieved using the magnetic assist technique. Full article

(This article belongs to the Special Issue Applications of Magneto-Optical Materials)

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