Research Background
Computer-Generated Holography (CGH) represents a cutting-edge technology that employs computer algorithms to dynamically reconstruct virtual objects. This technology has found extensive applications across diverse fields such as three-dimensional display, optical information storage and processing, entertainment, and encryption. Despite the broad application spectrum of CGH, contemporary techniques predominantly rely on projection devices like Spatial Light Modulators (SLMs) and Digital Micromirror Devices (DMDs). These devices inherently face limitations in display capabilities, often resulting in narrow field-of-view and multilevel diffraction in projected images.
In recent developments, metasurfaces composed of an array of subwavelength nanostructures have demonstrated exceptional capabilities in modulating electromagnetic waves. By introducing abrupt changes to fundamental wave properties like amplitude and phase through nanostructuring at subwavelength scales, metasurfaces enable modulation effects that are challenging to achieve with traditional devices. Advances in metasurface-based holography have led to significant achievements such as large viewing angles, achromatic imaging, full-color displays, increased information capacity, and multidimensional multiplexing, making them potent tools for dynamic holographic displays.
Nonetheless, dynamic metasurface holography, still faces great challenges in realizing real-time, highly fluid dynamic display effects required for advanced displays such as advanced human-computer interaction. The key to fluid metasurface holographic displays lies in achieving high computational and display frame rates. Computational frame rate refers to the speed of data calculation, processing, and preparation for display, ensuring the system can compute the required content in real time. Most current holographic display solutions depend heavily on performing rapid Fourier transforms (FFTs) multiple times, usually requiring dedicated computational units like Graphics Processing Units (GPUs) to meet the demands for high-refresh rates, making computational power and energy consumption critical bottlenecks for widespread application. On the other hand, the display frame rate, the speed at which display devices refresh and present new content, is crucial for the smoothness of visual content. At present, most dynamic holographic display strategies based on metasurfaces struggle to achieve high display frame rates, which hampers their ability to deliver a fluid visual experience.
Research Highlights
Addressing the aforementioned challenges, a team led by Professor Wei Xiong and Associate Professor Hui Gao from the Wuhan National Laboratory for Optoelectronics at Huazhong University of Science and Technology has introduced a dynamic interactive bitwise metasurface holography (Bit-MH) technique with high computational and display frame rates. They have constructed the world's first practical interactive metasurface holographic display system. Their work, titled "Dynamic interactive bitwise meta-holography with ultra-high computational and display frame rates," has been published in the 1st issue of Opto-Electronic Advances in 2023.
In their study, the team segmented the display functionality of metasurfaces into distinct spatial regions or channels, with each capable of projecting a reconstructed sub-holographic pattern. Utilizing optical addressing for spatial channel multiplexing, they mapped the on/off states of all channels to a set of bit values, thus transforming the dynamic updating process of holography into the manipulation of these bit values to control the corresponding channels. This approach significantly enhances computational efficiency by using mapped bitwise operations instead of relying on frequent FFT calculations required by traditional dynamic holography updates, resulting in efficient dynamic refreshing.
The researchers performed benchmark tests of the core algorithm for bitwise dynamic holography on a low-power Raspberry Pi computing platform, revealing that the maximum computational frame rate of the bitwise dynamic holography approach can reach up to 800 kHz. Additionally, by employing high-speed DMD optical addressing devices, they achieved a maximum display frame rate of 23 kHz.
To demonstrate the concept, the research team built an interactive holographic gaming system for playing Tetris within the visible light spectrum. The system's core components include a spatially segmented metasurface device, DMD, Raspberry Pi controller, gaming controller, and necessary optical components. The proposed design for bitwise dynamic holography allows for efficient updating of holographic images and real-time interaction with external input devices. This efficient and programmable Bit-MH method is expected to pave the way for future smooth and efficient metasurface holographic display systems.
Fig. 1. System architecture diagram of an interactive holographic Tetris game implemented with bitwise dynamic metasurface holography.
Corresponding Author Biography
Professor Wei Xiong is currently a professor at Huazhong University of Science and Technology, identified as a national high-level young talent by the Organization Department of the Central Committee, and the director of the Laser and Terahertz Function Laboratory at the Wuhan National Laboratory for Optoelectronics. His research focuses on micro/nanoscale laser 3D/4D printing, micro/nano-optical devices, and ultrafast laser imaging and characterization. In recent years, he has published over 100 papers in internationally renowned journals such as Science Advances, International Journal of Extreme Manufacturing, Nature Communications, Advanced Materials, Light: Science & Application, and Nano Letters, and holds more than fifty authorized and published patents domestically and internationally. He has received the Best Paper Award at the ICALEO conference organized by the Laser Institute of America, served as the chair of the Laser Nano Fabrication and Manufacturing sessions at the ICALEO, co-chair of the laser sessions at the POEM international conference, and is currently a member of the Extreme Manufacturing Division Committee of the Chinese Mechanical Engineering Society, editorial board member of Chinese Journal of Lasers and Frontiers of Optoelectronics (FOE), youth editorial board member of International Journal of Extreme Manufacturing (IJEM), and the vice-chairman of the Hubei and Wuhan Laser Societies.
Associate Professor Hui Gao is with the Wuhan National Laboratory for Optoelectronics at Huazhong University of Science and Technology. He is a recipient of the "Young Talents Support Project" by the China Association for Science and Technology and a member of the China Democratic Promotion Association. He completed his undergraduate studies at Zhejiang University and his doctoral degree at the University of Chinese Academy of Sciences and National University of Singapore. He won the National Excellent Doctoral Dissertation Award of the China Instrument and Control Society in 2020. His research interests include holographic display, micro/nano-optical light field modulation, and laser micro/nano manufacturing. He has published more than twenty papers in journals like Science Advances and his research has been recognized as ESI Highly Cited Papers. He has undertaken several national and provincial projects such as the National Natural Science Foundation of China and the Hubei Provincial Youth Fund, and has been selected for the Wuhan Morning Light Plan. Currently, he holds positions such as the youth editorial board member/office director in Wuhan for the journal Opto-Electronic Advances, youth editorial board member of the Chinese Journal of Lasers, member/deputy secretary-general of the Micro/Nano Committee of the Chinese Society of Optical Engineering, committee member/science popularization expert of the Science Popularization Committee of the China Instrument and Control Society, and scientific advisor for Light SciPop.
Professor Wei Xiong's Research Group at Huazhong University of Science and Technology
