Hologram Image Research Articles

Generating high-quality phase-only holograms of binary images using global loss and stochastic homogenization training strategy

Deep learning presents a highly effective for computer-generated holography (CGH). However, existing learning-based CGH algorithms may encounter significant obstacles in generating high-quality holograms for binary images. This study proposes a novel diffraction model-driven neural network, termed load sharing yielding holography (LSY-Holo), which leverages a dual-branch architecture and a global structural similarity index measure (Global_SSIM) loss function to generate phase-only holograms (POHs). LSY-Holo framework facilitates capturing global information, enhancing the network’s performance to address the ill-posed inverse problem. To further optimize the model for binary images, the research introduces a custom Binary dataset alongside a stochastic homogenization preprocessing method (SHPM), which mitigates the prevalent issue of excessive noise in reconstructed images. Additionally, this deep learning approach is integrated with an iterative algorithm, which employs holograms rapidly generated by LSY-Holo as the initial phase of the AdamW Holography (AH) algorithm. This strategy significantly accelerates the convergence of the iterative process. LSY-Holo is further extended to 3D scenes, enabling dynamic defocusing and focusing effects at varying depths. Results from numerical simulations and full-color optical reconstruction experiments demonstrate that the proposed method can enhance image quality and effectively reduce the artifacts in reconstructed images.

Use of a platform with lens-free shadow imaging technology to monitor natural killer cell activity

Natural killer (NK) cells are a crucial component of the innate immune system. This study introduces Cellytics NK, a novel platform for rapid and precise measurement of NK cell activity. This platform combines an NK-specific activation stimulator cocktail (ASC) and lens-free shadow imaging technology (LSIT), using optoelectronic components. LSIT captures digital hologram images of resting and ASC-activated NK cells, while an algorithm evaluates cell size and cytoplasmic complexity using shadow parameters. The combined shadow parameter derived from the peak-to-peak distance and width standard deviation rapidly distinguishes active NK cells from inactive NK cells at the single-cell level within 30 s. Here, the feasibility of the system was demonstrated by assessing NK cells from healthy donors and immunocompromised cancer patients, demonstrating a significant difference in the innate immunity index (I3). Cancer patients showed a lower I3 value (161%) than healthy donors (326%). I3 was strongly correlated with NK cell activity measured using various markers such as interferon-gamma, tumor necrosis factor-alpha, perforin, granzyme B, and CD107a. This technology holds promise for advancing immune functional assays, offering rapid and accurate on-site analysis of NK cells, a crucial innate immune cell, with its compact and cost-effective optoelectronic setup, especially in the post-COVID-19 era.

Multiple-image authentication based on metasurface and phase retrieval with sparsity constraints

In this paper, a multiple-image authentication method is proposed based on metasurface and phase retrieval with sparsity constraints. In the encryption process, multiple plaintext images are firstly encrypted to a phase-only hologram by using phase retrieval algorithm with sparsity constraints and iterative Fourier transform algorithm, and then the phase-only hologram is converted into a metasurface hologram for multiple-image authentication with the help of a geometric-phase metasurface unit, greatly expanding the encoding information capacity of metasurface for authentication. In the authentication process, the reconstructed image of metasurface hologram is respectively authenticated with multiple plaintext images through nonlinear correlation authentication such that multiple identities of the user holding this metasurface can be simultaneously verified, overcoming the problem that the metasurface for authentication and user identity can only be one-to-one, and substantially improving the efficiency of identity authentication. In order to demonstrate the feasibility of the proposed multiple-image authentication method, a series of numerical simulations are performed, and the simulation results show that the proposed method exhibits high feasibility and security as well as authentication efficiency, and the metasurface for multiple-image authentication has strong robustness against cropping attack.

Single‐Panel Complex Holographic Display with Three‐Phase Covalent Macropixel

AbstractA single‐panel complex holographic display with a three‐phase covalent macropixel featuring ultralow noise and high‐efficiency 3D image generation is proposed. The essential feature of the proposed three‐phase covalent macropixel is the point‐symmetric covalent concatenation of sub‐pixels and an adaptive computer‐generated hologram encoding algorithm. The proposed single‐panel holographic display exhibits three times signal efficiency enhancement, 1/38 reduction of DC noise, and 1/50 reduction of conjugate noise compared to conventional holographic displays in the generation of full‐color computer‐generated hologram images. This noise reduction leads to three times the optical efficiency enhancement of holographic displays.

Space‐Time Coding Metasurface For Multifunctional Holographic Imaging

AbstractHolographic imaging as one of promising image techniques reconstructs object image using the amplitude and phase information scattered from objects. Programmable metasurface composed of digitally coding unit cells can arbitrarily manipulate amplitude and phase of the scattering wave by tailoring operation states of the unit cells, and thus achieves high‐resolution imaging reconstruction. However, the conventional metasurface can only achieves a desired holographic image on an imaging plane. This paper presented a time‐space coding 2‐bit metasurface to overcome this challenge. By rapidly switching PIN diodes loaded in metasurface unit cell according to the customized time sequences, the magnitude and phase of the ±1st order harmonic fields can be fully controlled, achieving the hologram imaging at the higher order harmonics. The proof‐of‐concept measurements are given to demonstrate the versatile holographic imaging functions at the ±1st order harmonics including two different holographic images on an imaging plane, holographic imaging and beam scanning, and holographic imaging and orbital angular momentum (OAM) wave generation, which undoubtedly enriches the applications of the programmable metasurfaces in the field of the holographic imaging.

Speckle Reduction in Digital Holography by Fast Logistic Adaptive Non-Local Means Filtering

Digital holography is a promising imaging technology. However, there is speckle noise in the reconstructed image of a digital hologram. Speckle degrades the quality of the reconstructed image. Suppression of speckle noise is a challenging problem in digital holography. A novel method is proposed to reduce speckle by a fast logistic adaptive non-local means (LA-NLM) algorithm. In the proposed method, the logistic function is incorporated into the weight calculation of the NLM algorithm to account for multiplicative speckle noise. Filtering parameters are dynamically adjusted according to the statistical property of speckle in the reconstructed image. To enhance computational efficiency, the proposed algorithm takes advantage of the integral image technique to speed up the calculation of the similarity between image patches. Simulated and experimental digital holograms are obtained to verify the proposed method. The results show that the speckle noise is effectively suppressed in digital holography. The proposed method is efficient and feasible, and can be applied to such fields as three-dimensional display, holographic measurement, and medical diagnosis.

High-fidelity approximations for large holograms

Future holographic displays will require high-resolution holograms ranging from several hundred gigabytes to several terabytes. Hologram computations using the Fresnel approximation have been proposed; however, they are effective only in paraxial regions and result in significant errors for high-resolution holograms. This study proposes a high-resolution hologram calculation method using the Pade approximations, which can significantly improve the accuracy of the phase calculation despite a slight increase in computational complexity compared with the Fresnel approximation. In this study, image holograms with resolutions ranging from 10K to 30K pixels were generated using the Fresnel and Pade approximations, and the computation time and image quality of the reproduced images were evaluated. The Pade Approximation served as an effective solution for obtaining large holograms of high quality and reasonable computational complexity.

In-focus quantitative phase imaging from defocused off-axis holograms: synergistic reconstruction framework.

Digital holographic microscopy (DHM) enables the three-dimensional (3D) reconstruction of quantitative phase distributions from a defocused hologram. Traditional computational algorithms follow a sequential approach in which one first reconstructs the complex amplitude distribution and later applies focusing algorithms to provide an in-focus phase map. In this work, we have developed a synergistic computational framework to compensate for the linear tilt introduced in off-axis DHM systems and autofocus the defocused holograms by minimizing a cost function, providing in-focus reconstructed phase images without phase distortions. The proposed computational tool has been validated in defocused holograms of human red blood cells and three-dimensional images of dynamic sperm cells.

Reconfigurable chiral metasurface based on vanadium dioxide: Modulation of phase and intensity for high-quality hologram and near-field imaging

Circular dichroism (CD) has gained significant recognition in the field of artificial materials. However, there is still a need for a flexible approach to modulate CD, which would enable spin-selective multidimensional manipulation of terahertz (THz) waves. In recent years, reconfigurable metasurfaces have emerged as a prominent area of research in the field of micro/nanophotonic. This study proposes a novel reconfigurable chiral metasurface utilizing the phase transition properties of vanadium dioxide (VO2), capable of modulating CD. This metasurface not only realizes the modulation of the Pancharatnam-Berry (PB) phase in two states of VO2 but also enables the modulation of CD at the dual THz band. Based on the principle of the PB phase to control the phase of the meta-atom, the 3-bit coded metasurface arrays were proposed to achieve high-quality THz holographic imaging. Furthermore, the near-field imaging effect is realized by utilizing the differentiation property of the absorption intensity of chiral CD meta-atom. This multifunctional device, with its simple structure, exhibits tremendous potential for applications in THz holographic imaging, THz circular polarized wave detection, and image encryption.

Label-free detection and quantification of Giardia duodenalis cysts using a lens-free microscope

Giardiasis leads to severe diarrhea, and its impacts are especially concerning in low-income sites that lack water and sanitation infrastructure. Monitoring water quality considering the infective form of Giardia is therefore an action that strongly aligns with public health. The standard protocol for cyst quantification in water involves immunofluorescence assays (IFA), which depend on fluorescent probes coupled to antibodies, making it an observer-dependent, and a relatively expensive method. Lens-free holographic microscopy (LHM) offers a possible alternative for imaging, as it relies on portable, lightweight, and low-cost equipment. It is based on phase and amplitude images of holograms recorded with partially coherent lighting. This study, therefore, aimed to test LHM for the detection and counting of Giardia cysts. Purified suspensions of G. duodenalis cysts, with known concentration, were quantified by IFA and LHM. Holograms were acquired by transmission, using three different wavelengths, and were then submitted to automated analysis, using an algorithm developed in Python. Slide preparation and cyst counting by IFA proved to be more laborious compared to LHM. Agglomerations of cysts impaired both methods. LHM quantification showed significant similarity with the reference number of cysts in suspension, which was not obtained by standard immunofluorescence. LHM proved to be an effective technique for detecting and counting Giardia cysts in purified samples and with high concentrations, showing potential for future application in water quality assessment targeting pathogens, but limitations include low sensitivity and a demand for future work considering matrix effect on real environmental samples.

Multi-depth hologram generation from two-dimensional images by deep learning

Recently, proposals have been made to use deep learning for hologram calculations to directly infer holograms from three-dimensional (3D) data. However, this approach is expensive because it requires capturing depth information using an RGB-D camera for inference. In this study, we propose a novel approach that can infer 3D holograms directly from a color two-dimensional (2D) image without requiring depth information, using deep learning. The proposed scheme comprises three deep neural networks (DNNs). The first DNN predicts the depth information from the 2D images, the second DNN generates holograms using the 2D image and the inferred depth information, and the third DNN optimizes the quality of the holograms generated by the second CNN. The inference speed was superior to a state-of-the-art graphics processing unit. We prepared a training dataset comprising pairs of holograms and 2D images. The holograms are generated from the RGB-D image using a layer-based hologram calculation. One significant benefit of our proposed approach is that the reproduced image of the final hologram contains a natural depth cue, i.e., it can represent a natural 3D reproduced image in the depth direction. In addition, conventional image sensors can be used to create input information for inference.

Development and Evaluation of a Mixed-Reality Tele-ultrasound System.

The objective of this feasibility study was to develop and assess a tele-ultrasound system that would enable an expert sonographer (situated at the remote site) to provide real-time guidance to an operator (situated at the imaging site) using a mixed-reality environment. An architecture along with the operational workflow of the system is designed and a prototype is developed that enables guidance in form of audiovisual cues. The visual cues comprise holograms (of the ultrasound images and ultrasound probe) and is rendered to the operator using a head-mounted display device. The position and orientation of the ultrasound probe's hologram are remotely controlled by the expert sonographer and guide the placement of a physical ultrasound probe at the imaging site. The developed prototype was evaluated for its performance on a network. In addition, a user study (with 12 participants) was conducted to assess the operator's ability to align the probe under different guidance modes. The network performance revealed the view of the imaging site and ultrasound images were transferred to the remote site in 233 ± 42 and 158 ± 38 ms, respectively. The expert sonographer was able to transfer, to the imaging site, data related to position and orientation of the ultrasound probe's hologram in 78 ± 13 ms. The user study indicated that the audiovisual cues are sufficient for an operator to position and orient a physical probe for accurate depiction of the targeted tissue (p < 0.001). The probe's placement translational and rotational errors were 1.4 ± 0.6 mm and 5.4 ± 2.2º. The work illustrates the feasibility of using a mixed-reality environment for effective communication between an expert sonographer (ultrasound physician) and an operator. Further studies are required to determine its applicability in a clinical setting during tele-ultrasound.

Chirality-Assisted Phase Metasurface for Circular Polarization Preservation and Independent Hologram Imaging in Microwave Region

A chirality-assisted phase is introduced to innovatively impose separate phase profiles in two circular polarization (CP) preserving channels, namely, two co-polarized output components under left-handed and right-handed circularly polarized (LHCP and RHCP) illuminations. Such a scheme is physically implemented by a proposed multi-layered meta-atom that achieves chiral characteristics by inner twisting angles between adjacent functional elements. A proof-of-concept metasurface is constructed to realize separate holographic images in two polarization-preserved fields with different propagating distances, respectively. In order to achieve sufficient utilization of the two polarization-preserved components, a further approach that can suppress polarization conversion is proposed with a polyatomic unit composed of four separate chiral meta-atoms arranged in a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 2 array. A dual-holographic metasurface is designed to impose characters “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$</tex-math> </inline-formula> ” and “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> ” in two co-polarized fields with little energy distributed in corresponding cross-polarized fields. A prototype of the metasurface is fabricated and experimentally measured. The measurements agree well with theoretical predictions and full-wave simulations, showing in the co-polarized field a character “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$</tex-math> </inline-formula> ” under LHCP incidence and an “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> ” under LHCP incidence. The proposed mechanism provides a theoretical foundation for further CP channel expansion and modulations and has great potential in multifunctional antenna design and wireless communications.

Graphene Lithography Based on Laser Reduction and Plasma Oxidization for Rewritable Hologram Imaging

AbstractGraphene lithography is crucial for various graphene‐based devices, showing considerable potential in the fields of energy, environment, electronics, and optics. Recent reports show that graphene can be facilely fabricated and simultaneously patterned without masks via laser direct writing on a graphene oxide (GO) film. Thus, this laser‐reduced graphene oxide (LRGO) is successfully applied for graphene holograms with advantages of being ultra‐thin, wide‐angle viewing, and full‐color display. However, owing to the absence of an effective approach for oxidizing LRGO, the graphene holograms are only written once, not rewritable. This study demonstrates that LRGO can be oxidized with oxygen plasma treatment, enabling the development of rewritable graphene holograms through laser reduction and plasma oxidization. Laser irradiation can directly reduce GO and simultaneously achieve patterning. The oxygen plasma treatment gradually oxidizes and removes the as‐prepared LRGO. Using a computer‐calculated hologram pattern, the laser system can manufacture a thin graphene hologram in seconds. The fabricated graphene hologram image can be erased with oxygen plasma treatment, preparing the GO film for new hologram writing. This facile, low‐cost, erasable graphene lithography process paves the way for various graphene applications in metasurfaces, device fabrication, imaging, data storage, and displays.

Holographic display using layered computer-generated volume hologram.

The spatial frequency of the reconstructed image of planar computer-generated hologram(CGH) is limited by the sampling interval and the lack of thickness. To break through this limitation of planar CGH, we propose a new computer-generated volume hologram(CGVH) for full-color dynamic holographic three-dimensional(3D) display, and an iteration-free layered CGVH generation method. The proposed CGVH is equivalent to a volume hologram sampled discretely in three directions. The generation method employs the layered angular spectral diffraction to calculate the light field in the layered CGVH, and then encodes it into a CGVH. Numerical simulation results show that the CGVH can accurately reconstruct full-color 3D objects, where better imaging quality, more concentrated diffraction energy, denser reconstructed spatial frequency information, and larger viewing angle are achieved. The proposed CGVH is expected to be applied to realize dynamic modulation, wavelength multiplexing, and angle multiplexing in various optical fields in the future.

Holographic Optical Tweezers That Use an Improved Gerchberg-Saxton Algorithm.

It is very important for holographic optical tweezers (OTs) to develop high-quality phase holograms through calculation by using some computer algorithms, and one of the most commonly used algorithms is the Gerchberg-Saxton (GS) algorithm. An improved GS algorithm is proposed in the paper to further enhance the capacities of holographic OTs, which can improve the calculation efficiencies compared with the traditional GS algorithm. The basic principle of the improved GS algorithm is first introduced, and then theoretical and experimental results are presented. A holographic OT is built by using a spatial light modulator (SLM), and the desired phase that is calculated by the improved GS algorithm is loaded onto the SLM to obtain expected optical traps. For the same sum of squares due to error SSE and fitting coefficient η, the iterative number from using the improved GS algorithm is smaller than that from using traditional GS algorithm, and the iteration speed is faster about 27%. Multi-particle trapping is first achieved, and dynamic multiple-particle rotation is further demonstrated, in which multiple changing hologram images are obtained continuously through the improved GS algorithm. The manipulation speed is faster than that from using the traditional GS algorithm. The iterative speed can be further improved if the computer capacities are further optimized.

Range selective phase-shifting frequency-modulated digital holography with temporal-heterodyning.

We demonstrate that a time of flight (TOF) camera can be used to perform range selective temporal-heterodyne frequency-modulated continuous wave digital holography (TH FMCW DH). The modulated arrayed detection of a TOF camera allows efficient integration of holograms at a selected range with range resolutions significantly less than the optical system's depth of field. TH FMCW DH also allows for on-axis geometries to be achieved, where background light not at the internal modulation frequency of the camera is filtered out. Range selective TH FMCW DH imaging was achieved for both image holograms and Fresnel holograms using on-axis DH geometries. A 2.39GHz FMCW chirp bandwidth resulted in a DH range resolution of 6.3cm.

A Study on Remote Detection of Turkey Digital Identity Card Hologram Element

Technological advances and the pandemic have caused an explosion in demand for remote services. In critical processes such as banking, insurance and notary public, the service to be provided remotely has to be provided as quickly and safely as the service provided in presence. In such sensitive processes, the identity card authenticity detection must be done accurately and securely. One of the techniques used in accuracy detection is the use of mobile devices that support contactless chip technology. However, the number of mobile devices using this method is limited today. This situation hinders the effective and widespread use of remotely provided services and resources. Therefore, a different solution method was needed that would be an alternative to contactless chip technology, remove the obstacles to widespread use and reduce incidents such as counterfeiting. In this study, it was investigated whether the hologram, which is one of the security elements in the identity, can be used in determining the accuracy of Turkey's digital identity cards. For this purpose, a special function and program has been developed on the MATLAB application by using 2-D neighborhood methods to detect the crescent on the hologram. 227 digital ID cards were first evaluated on a mobile device over certain threshold values such as color level and similarity ratio. Then, each card used in the test was examined one by one with the naked eye. Approximately 99.56% similar results were obtained between the test findings made over the application and the findings obtained after the controls made with the naked eye. It has been concluded that the secure hologram image, one of the security elements on the digital ID card with this high success rate, can be used as computer aided in remote services. With this solution method, it has contributed to overcome an important obstacle in front of services that are thought to be provided remotely in many fields such as banks, notaries and education.

Generation of phase-only holograms with high-diffraction-order reconstruction by a U-Net-based neural network: A phase grating perspective

Implicit periodic structure in phase-only holograms will result in many diffraction orders in the diffraction field. We analyzed the diffraction pattern from a phase gratings point of view and proved that the diffraction orders were jointly influenced by the phase factor, the single-beam diffraction factor, and the multibeam interference factor. According to the analysis, we proposed the high-diffraction-order angular spectrum method (HDO-ASM) for the numerical reconstruction of high diffraction orders. Different from the conventional methods of removing high diffraction orders, we chose to reconstruct target images in high diffraction orders with HDO-ASM and a U-Net-based neural network. Finally, the 4 K phase-only holograms with high-diffraction-order reconstruction were generated in 0.09s and had a mean reconstruction quality of 34.3 dB (PSNR) in the DIV2K valid dataset. Theoretical and experimental results demonstrated that there are few speckle noises and fringes in the reconstructed images of holograms generated by the proposed method.

Neural compression for hologram images and videos.

Holographic near-eye displays can deliver high-quality three-dimensional (3D) imagery with focus cues. However, the content resolution required to simultaneously support a wide field of view and a sufficiently large eyebox is enormous. The consequent data storage and streaming overheads pose a big challenge for practical virtual and augmented reality (VR/AR) applications. We present a deep-learning-based method for efficiently compressing complex-valued hologram images and videos. We demonstrate superior performance over the conventional image and video codecs.