Dual-Wavelength Metasurfaces for Switchable 2D AND and XOR Logic Operations: Implications for Optical Computing and Information Encryption

Significance 

Optical computing is transforming the landscape of information processing networks and can provide advantages such as real-time operation, parallel processing, and low energy consumption. The integration of nanophotonics is central to this success because it addresses the demands for miniaturization and enhanced functionality of optical systems. metasurfaces is an important component in nanophotonics because of its ability to manipulate light at subwavelength scales with high precision and flexibility which make them ideal candidates for advanced optical computing applications. Logic operations, particularly AND and XOR, are fundamental to computing networks and play a critical role in image processing, pattern recognition, machine vision, and medical diagnostics. Traditional optical systems for performing these operations often rely on spatial filtering techniques, which involve complex setups with multiple components and precise mechanical adjustments, however, they face significant challenges with regard to operational complexity, efficiency, and scalability. To address these challenges, new study published in ACS Nano and led by Professor Guoxing Zheng from the Wuhan University and conducted by Dr. Chang Peng, Dr.  Tian Huang, Dr.  Xiao Liang, Dr.  Zile Li, and Dr.  Shaohua Yu, alongside Dr.  Chen Chen from the Suzhou Institute of Nano-Tech and Nano-Bionics and Dr.  Hongchao Liu from the University of Macau developed a novel approach to optical logic operations where they introduced a switchable two-dimensional (2D) AND and XOR operator based on dual-wavelength metasurfaces. The new innovative system utilizes two cosine gratings with distinct spatial frequencies and an initial phase difference to achieve high-precision AND and XOR operations simultaneously, simply by adjusting the incident laser wavelength.

The core of the authors’ experimental setup was the dual-wavelength metasurface which is composed of two cosine gratings with distinct spatial frequencies and an initial phase difference of π/2. They designed the metasurface to function at two specific wavelengths: 445 nm (blue light) for the AND operation and 633 nm (red light) for the XOR operation. The optimization process involved simulating the optical response of the metasurface using CST Microwave Studio. The researchers optimized the geometric parameters of the nanobricks to achieve high output efficiency at both target wavelengths, and ensure that the metasurface could effectively modulate the amplitude of incident light for precise logic operations. The researchers used 4f optical system to validate the metasurface’s functionality where they positioned input images symmetrically to the orientation axis of the grating and employed Fourier lenses to obtain the spatial frequency of these images. The metasurface, placed at the confocal plane, performed amplitude modulation based on the cosine gratings’ spatial frequencies. The team used simple geometric figures (a triangle and a rectangle as input images). When illuminated with blue light (445 nm), the system produced a bright trapezoid at the center of the output plane, indicating the AND operation and such result demonstrated that the metasurface could effectively highlight the common features between the input images. Conversely, when they used red light (633 nm), the system yielded a black trapezoid at the center, representing the XOR operation and this result confirmed the system’s ability to emphasize the distinct characteristics of each image through destructive interference. Afterward and building on the success of the simple figures, the authors tested the system with more complex patterns where they used images of compasses with varying outer arc angles and distinct pointer shapes as input images. The metasurface-based system successfully performed the AND and XOR operations on these complex patterns as well. When illuminated with blue light, the system revealed a hexagon shape at the center, along with additional arcs, demonstrating the AND operation’s capability to extract common features. Under red light, the system produced a cross-shaped pattern with additional arcs, confirming the XOR operation’s ability to highlight differences. They reported that their experimental results for both simple and complex patterns closely matched the numerical simulations, showcasing the metasurface’s high precision and reliability. The successful demonstration of AND and XOR operations with varying levels of image complexity highlighted the system’s robustness and versatility.

Another important application the researchers investigated in their studies is the use of the metasurface-based system for information encryption. The team devised a scheme where initial messages were transmitted to two separate receivers and each receiver held part of the information, and keys were distributed to decrypt the hidden message. Receiver 1 held the metasurface (Key 1) and Receiver 2 had a vector containing critical   setup details (Key 2).  Now, when the correct Key 2 (with the accurate experimental parameters and operating wavelength) was used, the system successfully revealed the hidden message. In contrast, a falsified Key 2 will provide decoding of incorrect information and this confirmed the security of the encrypted message.  In conclusion, Professor Guoxing Zheng and colleagues developed a switchable 2D AND and XOR operator based on dual-wavelength metasurfaces which overcome challenges associated with traditional optical logic systems. It is considered to have enhanced precision, more efficient for logic operations and simplifies the design and fabrication process, which makes the system more scalable and user-friendly. There are several practical implications of the new system, for instance, it can lead to more efficient and integrated optical chips with more reliable information processing. Moreover, the reported high precision and versatility of the new metasurface-based system is ideal for advanced image processing tasks such as edge detection, pattern recognition, and image interpretation which are important in machine vision. Furthermore, it could be used to enhance the readability of medical images and aids in the accurate diagnosis of diseases because it will be able to highlight small differences in imaging data that might otherwise go unnoticed. Additionally, the exciting system’s ability to hide and reveal information based on specific keys enhances overall security, making it extremely suitable for applications in data protection and cybersecurity.

About the author

Guoxing Zheng is a professor at the Electronic Information School, Wuhan University. He received his Ph. D from the Institute of Optics and Electronics, Chinese Academy of Sciences in 2005.  Dr Zheng’s current research focuses on metamaterials/metasurfaces and their applications in scientific research and industry. He has published over 135 Chinese inventive patents and more than 130 research papers in optical related fields including Nature Nanotechnology, Nature Communications, Science Advances, Light: Science & Applications, Advanced series, etc. He has undertaken more than 30 research projects including 5 funds from National Natural Science Foundation of China (NSFC), two from National Key Research and Development Program of China. He was continuously honored as Elsevier Most Cited Chinese Researchers since 2020. His major academic jobs include: standing member of Optical Education Committee of China Optical Society, member of Optical Communication Committee of China Communications Society, standing director of Hubei Optical Society, editorial board member of two SCI journals (Journal of Optics, and Electronics), and Associate editor of Frontiers in Nanotechnology. He is a senior member of IEEE and OPTICA.

Reference

Peng C, Huang T, Chen C, Liu H, Liang X, Li Z, Yu S, Zheng G. Switchable Two-Dimensional AND and Exclusive OR Operation Based on Dual-Wavelength Metasurfaces. ACS Nano. 2024 Feb 6;18(5):4424-4431. doi: 10.1021/acsnano.3c10723.

Go to ACS Nano.

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