Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS

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Credit: by Yi-Long Li, Nan-Nan Li, Di Wang, Fan Chu, Sin-Doo Lee, Yi-Wei Zheng, and Qiong-Hua Wang

Holographic 3D display completely avoids the side effects of the traditional 3D display, such as the dizziness and fatigue of viewers. Therefore, it has become the frontier and hotspot of the current research. With the proposal of the metaverse concept, the development of the holographic 3D technology has attracted more attention. However, limited by the pixel pitch and size of the SLM, the viewing angle and size of the holographic image are very small.

In a new paper published in Light Science & Application, a team of scientists, led by Professor Qiong-Hua Wang from School of Instrumentation and Optoelectronic Engineering, Beihang University, China have developed a tunable liquid crystal grating based holographic 3D display system with wide viewing angle and large size. The tunable liquid crystal grating designed by the team, providing an adjustable period and the secondary diffraction of the reconstructed image, enables to simultaneously implement two different hologram generation methods in achieving wide viewing angle and enlarged size, respectively.

In the wide viewing angle holographic experiment, the system achieves the viewing angle of 57.4°, which is 7 times that of the conventional system using a single SLM. In the large size holographic reproduction, the system can realize the size magnification of 4.2 times. The proposed system structure is simple and easy to operate, and can also be applied to augmented reality (AR) display. These scientists summarize the operational principle of their system:

“We proposed a tunable liquid crystal grating based holographic 3D display system, which breaks through the limitations of narrow viewing angle and small size of holographic 3D display. The proposed system consists of a laser, a beam expander, a beam splitter, an SLM, a 4f system (including lens I and lens II), a filter, a tunable liquid crystal grating, a polarized light valve and a signal controller.”

“The proposed system realizes wide viewing angle holographic 3D display by using the following method. When the voltage is applied to the tunable liquid crystal grating, the liquid crystal molecules are arranged in the small periodic order and the diffraction image is subjected to a secondary diffraction. By adjusting the period of the tunable liquid crystal grating, M secondary diffraction images can be generated. The polarization state of the polarized light valve is adjusted, so that the secondary diffraction image can be uniformly displayed in intensity.”

“The proposed system realizes large size holographic 3D display by using the following method. The large size hologram of the 3D object is generated and equally divided into two sub-holograms, named as sub-hologram I and sub-hologram II. At moment T1, sub-hologram I is loaded on the SLM. At this time, the function of the tunable liquid crystal grating is equivalent to that of the transparent glass since no voltage is applied to it. At moment T2, sub-hologram II is loaded on the SLM, meanwhile a voltage is applied to the tunable liquid crystal grating to generate the zero-order primary maximum and ±1 order secondary maximum on the spectral plane. The polarized light valve is controlled to ensure that only the positive first-order diffracted light can pass through. When the switching time of T1 and T2 is fast enough, the reconstructed images of sub-hologram I and sub-hologram II can be spliced seamlessly in space according to the visual persistence effect of human eyes to realize a large size holographic 3D display.”

“The proposed system structure is simple and easy to operate, and can also be applied to augmented reality (AR) display. The proposed system will have wide applications in medical diagnosis, advertising, education and entertainment and other fields.”  the scientists forecast.

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Yaobiao Li Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS liyaobiao@ciomp.ac.cn Office: 86-431-861-76851

Qiong-Hua Wang Beihang University, China qionghua@buaa.edu.cn

Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS

Copyright © 2022 by the American Association for the Advancement of Science (AAAS)

Copyright © 2022 by the American Association for the Advancement of Science (AAAS)