Realizing 3D Displays and Hologram Memory through Nanomagnetic Materials

Controlling light with magnetophotonic crystals

"All of my research is based on the interaction between magnetism and some other physical phenomenon. Magnetism and light, magnetism and ultrasonic sound, magnetism and heat − all combine magnetism and some other physical phenomenon. My aim is to develop systems that have never been created before." says Professor Inoue.

Professor Inoue’s research usually involves the use of magnetic garnet containing iron as a base material. Magnetic garnet is a magnetic insulator that transmits light and is heavily used in jewelry. When light is transmitted, the magnetism and light combine to develop a magneto-optical effect in which the polarization state changes. In other words, it is said that the characteristic of this material is that the magnetism can control the characteristics of light.

"However, if you break down what we mean collectively by ‘light’, it includes various wavelengths of light from infrared to visible light and ultraviolet. Far infrared light used for optical communications has a wavelength of about 1.55 μm, while ultraviolet light used for Blu-ray Discs has a wavelength as short as 0.4 μm. In order to combine magnetism and light in accordance with each wavelength, the material properties must be changed, so to that end we have been developing various materials. However, such development takes a great deal of time. In addition, most of the materials that we develop must be discarded without ever being used for reasons such as prohibitively high cost."

Faced with this situation, Inoue came to look at combining existing materials. He worked on the development of an artificial magnetic lattice with the desired characteristics by sorting magnetic substances on the nanoscale into a lattice pattern. In fact, this idea is the same as the "photonic crystal" concept proposed by Yablonovitch of the USA in 1987, which offers properties such as three-dimensional confinement of light through the periodic arrangement of materials with different refractive indices. Since magnetic material is used for the photonic crystal, Professor Inoue calls the material he has developed a magnetophotonic crystal.

"All the properties of light can be predicted, and it is a big advantage that we can perform simulations in advance on a computer even with a three-dimensional nanoscale structure. In concrete terms, we interpose magnetic substances between different kinds of dielectric multilayer films, then, by changing the thickness of the magnetic material, we can now control the light flexibly by strengthening the magnetic coupling for each wavelength of light."

Enabling ultra high density recording with holographic memory

Inoue and his colleagues are developing various new devices and systems based on these magnetophotonic crystals.

One of these is the world's first hologram memory. This technology can record and playback on media using the interference and diffraction of light from superimposing two light sources. By slightly changing the incidence angle of the reference light, it is possible to write several pieces of data in the same place, so that 200 movies can be stored on one disc the size of a DVD.

According to Professor Inoue, "In 1999 we launched a venture company from TUT called Optware and worked on the commercialization of a collinear hologram memory that can be miniaturized by coaxially arranging the signal light and the reference light, that we developed at the Research Center for Advanced Photonic Information Memories at TUT. It was certified as an international standard in 2007, and then just before commercialization the financial crisis occurred and the project stopped."

However, the R&D itself has continued until now. The information circulating in the world continues to increase, and innovative technology that can record and playback large amount of data at high density, high speed, and low energy is undoubtedly needed. For this application, the above-mentioned magnetic materials will be useful.

"Previously we used photopolymers that solidify with light on the recording medium, but since they were organic materials, we knew that they would deteriorate over time, so we decided to use a magnetic material that could ensure stable long-term recordings. We have already developed a magnetic hologram that can write and playback with zero error and zero energy."

Another part of Professor Inoue’s research that is attracting attention is the world's first 3D display using nanomagnets. In the movie "Star Wars" (1977), there is a famous scene where R2-D2 projects a three-dimensional hologram of Princess Leia. Professor Inoue says he wants to realize exactly this type of 3D imaging.

"We use a thin film magnetic material for the display, reduce the pixel size to the nanoscale, and reverse the magnetism using the heat of the light. This allows us to create a 3D image with a wide viewing angle of 30 degrees without using special glasses. Currently, the material that we can write on is small, so the playback image is as small as a few centimeters, but we are conducting research aiming at playing larger videos."

Professor Inoue and colleagues are also advancing the miniaturization of the device aiming at 3D display applications such as head up displays for vehicles and projection from mobile devices. In addition, since a huge amount of data is required to project moving images, they are also working in parallel to combine the technology with the above-mentioned hologram memory.

Developing new computers that can perform calculations without the flow of a current

In addition, since the influence of heat generated by electric current is a major problem when creating nano-scale elements in information devices that are indispensable to the advanced information age, Professor Inoue and colleagues are working in collaboration with domestic and overseas research institutions such as MIT, Moscow State University, and Keio University to develop new calculation elements and their peripheral technologies that do not require the flow of current.

"Instead of electrons, we use spin, which is a magnetic property of an electron. Spin can take two states − upward or downward, and has the property of transmitting waves into the crystal by the interaction between spins. Our idea is to try and make computations using the phase interference of this spin wave by strengthening or weakening the wave. We have already processed magnetic garnet into the form of a fork and succeeded in inputting spin waves from the three prongs, causing phase interference at the connection point and outputting the result at the main part. We have recently created the word ‘magnonics’ to accelerate research in this field."

Currently, Professor Inoue and his team are conducting studies to process small chips by cutting holes in thin garnet to create lines for miniaturization of elements. Also, although current is not used for calculation, at present it is used for exciting spin waves and detecting the results of calculations, so Inoue is trying to develop methods that do not use current.

Professor Inoue concludes, "We will actively work on launching ventures and strive to develop magnonics as a globally applicable technology."

Reporter's Note

Professor Mitsuteru Inoue majored in electromagnetics at Toyohashi University of Technology and taught at a technical college for ten years after acquiring his master's degree. During this time, he had no access to experimental or measurement equipment, so he became absorbed in calculating combinations of magnetic materials and designing devices with the mainframe computer that was the only tool available to him. He says that this became a great help to his later research. "After completing my doctoral degree, I gained confidence and went back to TUT, but I ended up leaving the laboratory after a big argument with my professor. I went back to the situation of no equipment other than a personal computer. Perhaps it is from this experience that I learned to do imaginative and original work." Inoue says, laughing.

Staying true to the philosophy of never imitating has its risks, and three of Inoue’s ventures have failed so far, but with no loss of enthusiasm, he is taking on the challenge of the fourth. We have high hopes for him!