Hologram Memory Quality Key For Optical Data Storage

A research team has applied magnetic assist recording technology to magnetic-holographic memory, reducing recording energy consumption and achieving non-error data reconstruction. Their work could pave the way for practical application of magnetic-holographic memory for storing large volumes of data at ultrahigh recording density and at ultrahigh speed.

Reconstructed image with and without magnetic assist. Courtesy of Toyohashi University of Technology.

In magnetic hologram recording, a medium is magnetized in one direction, then irradiated with a signal beam and a reference beam. The resulting interference pattern is recorded in the form of the difference in magnetization directions. When this recording proceeds with an external magnetic field applied to it, the recording of the difference in magnetization directions becomes clearer — a process known as magnetic assist recording.

Researchers at Toyohashi University of Technology, led by professor Yuichi Nakamura, investigated the effects of magnetic assist (MA) recording through numerical simulation and experiment to improve the diffraction efficiency and the resulting reconstructed images.

The stray magnetic field distribution was calculated for the nonmagnetized region. Researchers found that the intensity of the stray magnetic field depended on garnet film thickness or substantially on the aspect ratio of the nonmagnetized region. The improvement of diffraction efficiency was more effective in garnet films thinner than the width of a fringe. A suitable value of the assist magnetic field was identified for the improvement.

Through further experiments, researchers found that MA recording improved the intensity of reconstructed images and broadened the non-error recording conditions to the low energy region.

This research could enable a significant reduction in errors in data recording and reconstruction using only a small amount of energy, as well as non-error recording and reconstruction using magnetic holographic memory.

“Until now it has been difficult to obtain a clear reconstruction image with a magnetic hologram, due to strict requirements for material characteristics, optical conditions, and so on. Using magnetic assist recording, we have relaxed these requirements and also improved the reconstruction performance of recording media. This technology is promising for the future application of magnetic-holographic memory,” said researcher Zen Shirakashi.

Associate professor Yuichi Nakamura (left) and Ph.D. candidate Zen Shirakashi. Courtesy of Toyohashi University of Technology.

The researchers will continue looking for ways to improve recording density. Their goal is to use this technology to make a portable, ultrahigh-density, high-speed optical information storage medium that outperforms Blu-ray discs and that is capable of storing high-volume contents from various sources, including 8K Super Hi-Vision broadcasting and 3D films. The team hopes to enable wide application of this technology in various types of storage systems, including archive and cold storage for storing information such as medical image data, social networking service data on the internet, and high-volume data in data centers.

The research was published in Scientific Reports (doi: 10.1038/s41598-017-12442-z).