Holographic Research Articles

Flexible Control of Encoded Metasurface Holographic Imaging Based on Fourier Convolution Principle

Flexible Control of Encoded Metasurface Holographic Imaging Based on Fourier Convolution Principle

3D Multiview Holographic Display with Wide Field of View Based on Metasurface

Abstract3D display technology offers a more realistic visual experience by allowing users to perceive depth and spatial awareness, enhancing interactivity and immersion. Among various approaches, multiview display technology constructs 3D images by offering multiple smooth views along the horizontal plane. Metasurfaces, with ultra‐thin physical structures and flexible functional designs, are positioned to make significant contributions to the evolution of 3D display technologies. Here, a 3D multiview holographic display system based on metasurfaces is proposed. Using generalized Snell's law, a spatially multiplexed metasurface is designed with nine views and achieves 3D display by cascading the metasurface with a spatial light modulator (SLM). By projecting holograms onto different areas of the metasurface via the SLM, corresponding reconstructed images can be observed from specific designed directions. Thanks to the large numerical aperture (NA) of the metasurface, the system successfully achieves nine views within a 120° field of view (FOV, with a theoretical maximum of 180°), validated experimentally. This system promises potential applications in VR/AR display, surgical navigation, geographic information system (GIS), and other fields.

Three-dimensional computer holography with phase space tailoring

Computer holography is a prominent technique for reconstructing customized three-dimensional (3D) diffraction fields. However, the quality of optical reconstruction remains a fundamental challenge in 3D computer holography, especially for the 3D diffraction fields with physically continuous and extensive depth range. Here, we propose a 3D computer-generated hologram (CGH) optimization framework with phase space tailoring. Based on phase space analysis of the space and frequency properties in both lateral and axial directions, the intensity of the 3D diffraction field is adequately sampled across a large depth range. This sampling ensures the reconstructed intensity distribution to be comprehensively constrained with physical consistency. A physics-informed loss function is constructed based on the phase space tailoring to optimize the CGH with suppression of vortex stagnation. Numerical and optical experiments demonstrate the proposed method significantly enhances the 3D optical reconstructions with suppressed speckle noise across a continuous and extensive depth range.

High-resolution transcranial optical imaging of in vivo neural activity

Rapid sub-nanometer neuronal deformations have been shown to occur as a consequence of action potentials in vitro, allowing for optical registration of discrete axonal and synaptic depolarizations. Such optically-measured deformations are a novel signature for recording neural activity. We demonstrate this signature can be extended to in vivo measurements through recording of rapid neuronal deformations on the population level with holographic, optical phase-based recordings. Our system demonstrates, for the first time, non-invasive recordings of in vivo tissue deformation associated with population level neuronal activity, including through-skull. We confirmed this technique across a range of neural activation models, including direct epidural focal electrical stimulation, anesthetic-induced cortical deactivation, activation of primary somatosensory cortex via whisker barrel stimulation, and pharmacologically-induced seizures. Collectively, we show holographic imaging provides a pathway for high-resolution, label-free, non-invasive recording of transcranial in vivo neural activity at depth, making it highly advantageous for studying neural function and signaling.

ALHK: Integrating 3D Holograms and Gesture Interaction for Elementary Education

The integration of technology in elementary education offers innovative ways to enhance learning. One such advancement is the use of three-dimensional holograms (3DH), which provide immersive displays that merge seamlessly with the learner’s environment, creating a dynamic and engaging atmosphere. Educators have found that 3D visual tools significantly improve student comprehension, with 94.4% agreeing in a preliminary study. However, using interactive 3D holography alone has limitations, such as the inability for students to physically touch or manipulate holographic objects. To address this, Active Learning with Holo-Kid (ALHK) is introduced as a desktop application for elementary school students (grades 1 to 6). ALHK combines Leap Motion technology’s precision with interactive 3D holography to overcome these limitations. The combination allows students to interact with virtual objects in a more immersive and realistic manner. Holograms provide visual representation, while Leap Motion enables precise gesture recognition and hand tracking, resulting in a seamless and intuitive user experience. Initial evaluations demonstrate improved student engagement and comprehension. Future iterations aim to enhance scalability by incorporating features like custom object upload, multi-user interaction, and broader age applicability. ALHK shows promise as a tool for creating an immersive and intuitive learning environment using 3D holograms and interactive technology in elementary education.

Reprogrammable metasurface holographic image encryption technology based on a three-dimensional discrete hyperchaotic system

The emergence of metasurfaces provides a secure and efficient platform for optical encryption technology as they have broad prospects in the field of information security. However, the limited number of channels available on metasurfaces and the insufficient security of keys make them vulnerable to attacks by eavesdroppers. In this work, a reprogrammable metasurface optical encryption scheme based on a three-dimensional hyperchaotic system is proposed. The three-dimensional discrete hyperchaotic system has strong ergodicity, initial value sensitivity, and pseudorandomness compared to previous chaotic systems that can pass NIST randomness testing well. Additionally, based on this hyperchaotic property, we designed a metasurface encryption structure based on the geometric phase. The research results show that the introduction of the hyperchaotic system greatly improves the randomness and flexibility of key generation. This scheme can encrypt multiple images with high security. Decryption is only possible when the attacker steals the complete chaotic system and parameters, as well as over 70% of the correct incident light phase information. Our research results have great potential applications in the field of metasurface optical encryption.

Dynamic 3D Fresnel incoherent correlation holography imaging based on single-shot mirrored phase-shifting technology.

Fresnel incoherent correlation holography (FINCH) records coaxial holograms for wide-field 3D imaging with incoherent light, but its temporal phase-shifting strategy makes dynamic imaging challenging. Here, we present a compact, portable single-shot mirrored phase-shifting (SSPMS) module that can be easily integrated into the FINCH system, achieving secondary modulation of self-interference beams to enable the simultaneous acquisition of four phase-shift holograms in a single exposure. Compared with previously reported methods that use diffraction gratings to spatially separate self-interference beams at specific angles, this module duplicates a laterally shifted mirrored beam using a simply modified Michelson interferometer, so the phase-shifting holograms obtained via this module are free from optical aberrations or higher-order diffracted light noises. The feasibility of the proposed method is experimentally demonstrated through imaging dynamic 3D grayscale scenes.

Deep learning and genetic algorithm driven accelerated design for frequency-multiplexed complex-amplitude coding meta-hologram

Frequency-multiplexed metasurfaces represent a significant innovation in breaking the functional limitations of traditional metasurfaces, showing immense potential in multi-channel communication. However, existing frequency-multiplexed metasurfaces primarily focus on pure phase and linear polarization modulation, neglecting the modulation for complex amplitude and circularly polarized waves. Additionally, crosstalk suppression between dual-frequency channels often requires meticulous tuning of the meta-atom structure. Therefore, manually designing a set of meta-atoms that satisfies both complex amplitude modulation and low crosstalk at dual frequencies is extremely challenging and time-consuming. Here, we utilize the method of deep learning and genetic algorithm to design a kind of meta-atom capable of bi-spectral 2-bit amplitude and arbitrary phase modulation, which greatly reduces the design difficulty and achieves excellent low-crosstalk performance. This method can be easily generalized to the design of other complex meta-atoms to improve the design efficiency. Furthermore, we propose a frequency-multiplexed complex-amplitude coding meta-hologram for modulating left-handed circularly polarized (LCP) waves. When illuminated with LCP light, it can reconstruct two distinct holographic images at two different frequencies in the near field with high quality. The independent modulation capability of the metasurface for multiple degrees of freedom of frequency, amplitude and phase gives it broad application prospects in multi-channel communication, data storage and perfect holography.

Pattern self-referenced single-pixel computational holographic imaging

Pattern self-referenced single-pixel computational holographic imaging

Vibration analysis of 3D printed cymbals and Tzouras top plates

An integrated method of determining the vibration characteristics of musical instruments is here presented. The method includes modal measurements and holographic imaging, FEM modelling and simulations. Parts of musical instruments made of composite materials have been simulated, printed and measured. The vibrational response of 3D printed cymbals and Tzouras top plates, a Greek traditional stringed musical instrument, is experimentally measured and computationally simulated. The PLA printed parts vary in geometry and thickness. The frequency response functions, and the vibrational modes are presented and further studied in relation to the aforementioned geometry variations. The experimental findings provide inputs to FEM modeling and simulation parameters.

How does the use of modern technologies affect students’ perception of information? The effectiveness of holographic projection technology in music education

ABSTRACT The article studies the holographic projection technology in an innovative music classroom during full-time education. The study addresses the influence of this technology on the effectiveness and efficiency of learning, as well as on the perception and memorisation of educational material by students. It describes an innovative music classroom with equipment for using a 3D Hologram (3DH) for face-to-face lectures. An educational experiment was conducted within a three-month course. The experiment enrolled 111 foreign students in the first year of studying at higher educational institutions in China. The evaluation of the emotional background of the learning environment in the innovative music classroom indicates a positive attitude of students towards educational activities. The activities aroused their interest, admiration and trust; the environment was friendly and joyful. The findings can facilitate the search for innovative solutions to improve pedagogical activity or foster the introduction of holographic innovations into teaching practice.

Increasing the space–bandwidth product of holographic displays by segmenting and combining phase masks

This paper presents a method for enlarging holographic images under the constraints of spatial light modulators. The proposed method involves using a modified Gerchberg–Saxton algorithm and spatial multiplexing to segment images and projection surfaces. Segmented element images are processed to create multiple phase masks, which are then stitched for image reconstruction. Experimental results indicated that the proposed method enabled effective magnification under different segmentation methods. This method allows the enlargement of holographic images without using additional lenses, thus enabling effective magnification to be achieved with a limited setup. Reconstruction results indicate that the proposed method can produce a magnification of up to 16 × .

Speckle reduced holographic display system with a jointly optimized rotating phase mask.

Speckle noise degrades image quality in systems with coherent light sources, which must be overcome in holographic displays. In this Letter, we introduce a holographic display system with a rotating phase mask for speckle noise reduction. The rotating phase mask works in a similar way as a conventional rotating diffuser, but its pattern is jointly optimized with the spatial light modulator to maintain the contrast of the reconstructed image. The effectiveness of our system is verified through both numerical simulations and a tabletop prototype, reducing the speckle contrast by 38.8% while preserving the image quality.

Design of a polarization-insensitive broadband achromatic metalens for mid-wave infrared detector.

Metalenses, boasting outstanding focusing efficiency and high-resolution imaging capabilities, have generated widespread usage in fields such as integrated optics, achromatic imaging, and optical holography. In this study, we have developed a broadband achromatic metalens within the detection range from 3 to 5 µm, and it has a numerical aperture (NA) of 0.71 with a remarkable maximum focusing efficiency of 63.8% at the focal plane within the specified bandwidth. We have further delved into the dispersion control mechanism that combines the geometric and transmission phases and optimized the constructed phase response simulation database using the particle swarm optimization (PSO) algorithm, ensuring a precise phase matching between the actual wavefront and the ideal focusing wavefront. This metalens with its ability to expand the array size has the potential to create a compact infrared imager, which holds significant importance in achieving efficient detection and integration within infrared detectors.

The modified Gerchberg–Saxton algorithm for subwavelength resolution holographic image with speckle suppression

Abstract The Gerchberg–Saxton algorithm is widely recognized as one of the most popular methods for calculating phase-only holograms. However, due to bandwidth limitations, this iterative method is not suitable for designing subwavelength resolution holograms. To address this challenge, we have modified the angular spectrum method (ASM) by incorporating additional information to compensate for lost high-frequency details in inverse propagation. In order to mitigate optical speckle artifacts that arise in the computational process, we have integrated the double amplitude freedom (DAF) into our approach. Furthermore, we have implemented a narrow probability distribution in the initial phase mask as a key strategy to minimize fluctuations in the intensity of the reconstructions. Our proposed method has successfully achieved subwavelength resolution reconstructions with reduced speckle noise.

Wavelength-multiplexed orbital angular momentum meta-holography

AbstractThe field of high-bandwidth holography has been extensively studied over the past decade. Orbital angular momentum (OAM) holography, which utilizes vortex beams with theoretically unbounded OAM modes as information carriers, showcases the large capacitance of hologram storage. However, OAM holography has been limited to a single wavelength, restricting its potential for full-color holography and displays. In this study, we propose wavelength and OAM multiplexed holography that utilizes the multiple dimensions of light—wavelength and OAM—to provide a multi-color platform that expands the information capacity of holographic storage devices. The proposed wavelength-OAM multiplexed holography is physically realized by a metasurface, the state-of-the-art optical element consisting of an array of artificially engineered nanostructures. Hydrogenated silicon meta-atoms, the constituents of the metasurface, are engineered to possess wavelength selectivity by tailoring the dispersion of polarization conversion. These meta-atoms are used to encode the calculated OAM-preserved phase maps based on our design. The sampling grid of the phase map is rotated by 45°, which effectively suppress higher-order diffraction, providing a great strategy for achieving large field-of-view (FOV) holography. We successfully demonstrate six holographic images that are selectively reconstructed under the illumination of light with specific wavelengths (λ = 450, 635 nm) and topological charges (l = -2, 0, 2), without high-order diffraction. Our work suggests that ultrathin meta-holograms can potentially realize ultrahigh-bandwidth full-color holography and holographic video displays with large FOV.

Analysis of Factors Influencing Traffic Sign Recognition Based on Multi-Sensor Perception Data

When traffic signs are blocked or faded, the ability of automated vehicles (AVs) to perceive and recognize them is lost or reduced. Previous research has improved and optimized the recognition algorithm but has not systematically analyzed the environmental and design factors that can lead to the AV’s failure to perceive and recognize traffic signs. This study uses the multiple sensors in the equipped vehicles of the Tongji University Road and Traffic Holographic Data Acquisition System to perceive and recognize traffic signs in six crash hotspots in Shanghai, China. Failure to recognize traffic signs was analyzed considering the influence of four sets of factors: traffic sign design, vehicle characteristics, environmental factors, and road design. A feature importance analysis was conducted utilizing the machine learning algorithm model CatBoost. Shapley additive explanation values were used to analyze the positive and negative relationships as well as the contribution rates of each influencing factor. The results revealed that the major factors influencing sign perception and recognition were positioning of traffic sign, lighting, blockage, cleanliness, fading, and reflectivity. Cleanliness had the most significant impact on the perception and recognition of traffic signs compared with the other influencing factors, and it also showed significant influencing interaction with the other factors. Fading was the second most important factor. The results of this study can guide designers of traffic signs to promote safety in mixed traffic environments that include both AVs and human-driven vehicles.

Survey on Unmanned Aerial Vehicle Communications for 6G

Although the application of the fifth-Generation (5G) mobile communication has brought tremendous innovations to the daily life of human beings, e.g., autonomous vehicles and internet of everything, the upcoming huger data requirement leads to the emergence of the sixth-Generation (6G) mobile communication. Compared to 5G, the transmission rate, time delay, and wireless coverage need to be improved significantly. Thus, in this paper the applications of Unmanned Aerial Vehicles (UAVs) to the ubiquitous, intelligent and coupling 6G network are surveyed. First, the utilization of UAVs in the framework of space-air-ground-sea integrated network is demonstrated, and the roles and functions of UAVs in different scenarios are emphasized, e.g., the swarm base stations, the deployment for holographic projection, the long-distance relaying and the data collection. Then, the potential 6G key techniques of terahertz, ultra-massive multiple-input and multiple-output, endogenous artificial intelligence, Intelligent Reflecting Surface (IRS), intelligent edge computing, blockchain and integrated sensing and communication for UAV communications are investigated. Finally, the future challenges of UAV communications for 6G, including the limited duration, integration of networks, compatibility of IRS, development of THz communications, and user security are discussed.

Estimating the effects of x-ray radiations on lymphocytes by minimally invasive holographic imaging flow cytometry

Estimating the effects of x-ray radiations on lymphocytes by minimally invasive holographic imaging flow cytometry

Motion-free high-resolution on-chip microscopy using LED matrix

Lensless microscopy is an imaging technique that allows high-resolution imaging over a large field of view with a cost-effective design. Conventional lensless microscopy often utilizes multi-height phase retrieval and pixel-super-resolution algorithms to reconstruct high-resolution images, requiring mechanical stages for three-dimensional relative movements between a light source, camera, and sample. However, the excessive use of stages inevitably increases the bulkiness of the system and extends the image acquisition time. Here, we propose a motion-free lensless microscope that incorporates an RGB LED matrix array. A high-resolution holographic image is reconstructed from subpixel-shifted color images obtained with LED illuminations without any mechanical movement. Using a prototype system, we have demonstrated a spatial-bandwidth product of 30 megapixels with a resolution of 0.87 µm and a field of view of 24 mm2. The usability of the proposed method has been further tested for histopathologic examination. Our system features a compact and high-performance design with inexpensive optoelectronic elements, a conventional CMOS sensor and an LED matrix, which are well-aligned with the original design motivation of lensless imaging methods.