Digital Holograms Research Articles

Y-Net: a one-to-two deep learning framework for digital holographic reconstruction

In this Letter, for the first time, to the best of our knowledge, we propose a digital holographic reconstruction method with a one-to-two deep learning framework (Y-Net). Perfectly fitting the holographic reconstruction process, the Y-Net can simultaneously reconstruct intensity and phase information from a single digital hologram. As a result, this compact network with reduced parameters brings higher performance than typical network variants. The experimental results of the mouse phagocytes demonstrate the advantages of the proposed Y-Net.

The experimental generation of Lorentz beam with sine amplitude and vortex phase modulation wavefront

The Lorentz beam with sine amplitude and vortex phase modulation wavefront is produced by employing digital hologram technology in this beam generation experiment. The high-efficiency digital holograms and the final high-quality beams generated by the spatial light modulator are obtained. By changing the topological charge number, amplitude parameter or beam order, many novel intensity distribution patterns are obtained in the experiment, such as center-symmetrical profiles, rotation symmetric profiles, a triangle with a fan hole, a square with a cross hole and a disc with round holes and so on. The experiment results show the topological charge number, amplitude parameter and beam order all have a considerable impact on the experimentally generated intensity profile. The topological charge number is equal to the number of the local intensity minimum holes under some condition. To verify the experimental results, a comparison shows that the shapes and evolution principles of the experimental results are in accord with the desired simulation focal intensity distributions. The generated beam with the tunable property benefits the tunable optical trap application, and it is convenient for a further application. The generation and calculation methods of the beam can pave the way for the related domain.

8.3: Invited Paper: Ultra High Resolution Display for Digital Holography

Ultra high resolution display panels are one of the technical trends for future display and essential for the realization of digital hologram. Two approaches for the development toward 1um pixel pitch are introduced. SLM panel with 3µm pixel pitch based on reflected TFT‐LCD was fabricated. Reconstructed hologram images were successfully demonstrated. SLM based on phase change materials was under development. In this case the driving circuitry was consist of Si CMOS backplane. Due to the scalability of PCM materials, accomplishment of pixel pitch with 1µm is very promising.

Interferenceless and motionless method for recording digital holograms of coherently illuminated 3D objects by coded aperture correlation holography system.

Optical recording of digital holograms by coherent light traditionally involves interference between object and reference waves, which complicates the image acquisition process and decreases the power efficiency. In this work, we take the coded aperture correlation holography technique one step forward to record coherent digital holograms of three-dimensional scenes, without wave interference and in a motionless working mode. In addition to the explicit benefits of integrating interferenceless holographic imaging system with coherent illumination, the suggested method enables fast image acquisition implied by its inherent high signal-to-noise ratio. Experimental validation for diffusely reflective objects is also provided, making this relatively simple system appropriate for studying and using the speckle phenomena in coherent digital holography.

Digital video watermarking algorithm robust against video container format changes

A digital watermark embedding algorithm robust against any changes of a video container format with the use of a three-dimensional (3D) discrete cosine transform is proposed. For embedding the three-dimensional (3D) method based on Koch and Zhao’s two-dimensional (2D) method is applied. The image of a digital watermark and its digital hologram as embedded information are used. Embedding is carried out in a YUV color scheme. Computer-simulation experiments are made. The proposed method proved to be robust against attacks of video container format changes.

Wave atoms for digital hologram compression.

Compression of macroscopic digital holograms is a major research problem, which if unresolved will continue to limit the possible applications of holography in multimedia contexts. The quest of searching for the most suitable representation for compression is still an open problem. In this work, we study sparsification by the wave atom transform, introduced in 2006 by Demanet etal., and experiment on four large-scale representative diffuse macroscopic holograms while testing compressibility in the object plane, Fourier plane, and defocused plane representations, respectively. We demonstrate that it is a suitable nonadaptive, sparsifying transform for Fourier or defocused content, and by integration into the wave atom coding (WAC) method, we sketch a full-fledged codec for the compression of macroscopic holograms. WAC is compared to two variants of JPEG 2000, with equal complexity of coding tools, and the more recent High Efficiency Video Coding (H.265/HEVC). For Fourier and defocused holograms, WAC outperforms the JPEG 2000 variants by 0.9-7.9dB Bjøntegaard-Delta peak signal to noise ratio, especially in the former case, while it is as good as or better than even H.265/HEVC for very deep computer-generated holograms, thus improving on existing approaches.

Computational assessment of an effective-sphere model for characterizing colloidal fractal aggregates with holographic microscopy

We perform simulations to evaluate a recent experimental technique for using in-line holographic microscopy and an effective-sphere model to measure the population-averaged fractal dimension Df of an ensemble of colloidal fractal aggregates. In this technique, models based on Lorenz–Mie scattering by a uniform sphere are fit to digital holograms of a population of fractal aggregates to determine the effective refractive indices neff and effective radii aeff of the aggregates. A scaling relationship between neff and aeff based on the Maxwell Garnett effective-medium theory then determines Df. Here we use a multisphere superposition code to calculate the exact holograms produced by aggregates with tunable fractal dimensions Df. We show that neff and aeff become less sensitive to the aggregate orientation as Df increases. We also show that the Maxwell Garnett scaling relationship correctly determines Df to within 10.5% when multiple scattering is negligible and the population-averaged coefficient of determination ⟨R2⟩p > 0.6, indicating that the holograms are well-described by the effective-sphere model.

Secure storage and retrieval schemes for multiple encrypted digital holograms with orthogonal phase encoding multiplexing.

Recent developments in 3D computational optical imaging such as digital holographic microscopy has ushered in a new era for biological research. Therefore, efficient and secure storage and retrieval of digital holograms is a challenging task for future cloud computing services. In this study, we propose a novel scheme to securely store and retrieve multiple encrypted digital holograms by using phase encoding multiplexing. In the proposed schemes, an encrypted hologram can only be accessed using a binary phase mask, which is the key to retrieve the image. In addition, it is possible to independently store, retrieve, and manage the encrypted digital holograms without affecting other groups of the encrypted holograms multiplexed using different sets of binary phase masks, due to the orthogonality properties of the Hadamard matrices with high autocorrelation and low cross-correlation. The desired encrypted holograms may also be searched for, removed, and added independently of other groups of the encrypted holograms. More and more 3D images or digital holograms can be securely and efficiently stored, retrieved, and managed.

Noise suppression by controlling the sparsity of the point spread function in interferenceless coded aperture correlation holography (I-COACH).

Interferenceless coded aperture correlation holography (I-COACH) is an incoherent opto-digital technique for imaging 3D objects. In I-COACH, the light scattered from an object is modulated by a coded phase mask (CPM) and then recorded by a digital camera as an object digital hologram. To reconstruct the image, the object hologram is cross-correlated with the point spread function (PSF)-the intensity response to a point at the same object's axial location recorded with the same CPM. So far in I-COACH systems, the light from each object point has scattered over the whole camera area. Hence, the signal-to-noise ratio per camera pixel is lower in comparison to the direct imaging in which each point is imaged to a single image point. In this work, we consider the midway between the camera responses of a single point and of a continuous pattern over the entire camera area. The light in this study is focused onto a set of dots randomly distributed over the camera plane. With this technique, we show that there is a PSF with a best number of dots, yielding an image with a maximum product of the signal-to-noise ratio and the image visibility and a maximum value of structural similarity.

Multiwavelength Digital Holographic Imaging and Phase Unwrapping of Protozoa Using Custom Fiji Plug-ins

Multiwavelength digital holographic microscopy (DHM) has been used to improve phase reconstructions of digital holograms by reducing 2π phase ambiguities. However, most samples used as test images have been solid or adhered to a surface, making it easy to determine focal planes and correct for chromatic aberration. In this study we apply 3-wavelength off-axis DHM to swimming protozoa containing distinct spectral features such as chlorophyll and carotenoids. We reconstruct the holograms into amplitude and phase images using the angular spectrum method. Methods for noise subtraction, chromatic aberration correction, and image registration are presented for both amplitude and phase. Approaches to phase unwrapping are evaluated and compared to expected results from simulated holograms. The algorithms used are implemented in plug-ins using the open source Fiji platform and are available for use, significantly expanding the open-source software available for DHM.

Complex defect inspection for transparent substrate by combining digital holography with machine learning

We proposed a complex defect inspection (CDI) technique for quality control of transparent substrates that uses the diffraction characteristics of digital holograms and a machine learning algorithm. A complex pattern diffraction model was built to provide two diffraction criteria, the least separation of confusion and the effective diffraction distance, to extend depth of focus in the effective diffraction regime for numerical reconstruction. On the basis of an analysis of three-dimensional diffraction characteristics of complex images, defect identification was performed to detect and classify defects (cracks, dusts, and watermarks) in transparent substrates using region-based segmentation and a machine learning algorithm. The experimental results indicated that the defect detection performance of the proposed CDI system was recall = 96.3% and precision = 92.8%. Moreover, overall multiclass classification accuracy = 95.3%, resulting in a discrimination area under the receiver operating characteristic curve (Az) of 0.96.

The new route for realization of 1‐μm‐pixel‐pitch high‐resolution displays

AbstractA new pixel structure for the realization of a 1‐μm‐pixel‐pitch display was developed. This structure, named vertically stacked thin‐film transistor (VST), was based on the conventional back‐channel etched thin‐film transistor (TFT), but all the layers except the horizontal gate line were vertically stacked on the embedded data line, enabling the implementation of high‐resolution display panels. The VST device with a channel length of 1 μm showed a high field effect mobility of more than 50 cm2/Vs and low subthreshold slope of 78 mV per decade. It also shows a high uniform electrical characteristic over the entire 6‐in. wafer. The development of a new pixel architecture is expected to enable the implementation of 1‐μm‐pixel‐pitch high‐resolution displays such as spatial light modulators for digital holograms.

Electromagnetic modeling of a reconfigurable graphene-based metasurface using MoM-GEC method for 3D digital holography

ABSTRACTViewing the trend of beam shaping, beam steering, and metasurface holograms, a reconfigurable graphene-based metasurface is proposed and modeled using the method of moments combined with the generalized equivalent circuit (MoM-GEC) approach. The scattering state of each individual unit cell of the metasurface can be controlled by applying different biased voltages into the graphene antennas. In fact, the complex surface conductivity of graphene is introduced in our mathematical formulation in order to tune the magnitude and phase of the local reflection coefficient. Benefitting from this scalability, our graphene-based metasurface will regenerate a 3D medical hologram. The proposed approach is validated and paves the way for the generation a 3D digital holograms. There are several important areas where this study makes an original contribution such as medical imaging 3D displays.

Dynamic-range compression scheme for digital hologram using a deep neural network.

This Letter aims to propose a dynamic-range compression and decompression scheme for digital holograms that uses a deep neural network (DNN). The proposed scheme uses simple thresholding to compress the dynamic range of holograms with 8-bit gradation to binary holograms. Although this can decrease the amount of data by one-eighth, the binarization strongly degrades the image quality of the reconstructed images. The proposed scheme uses a DNN to predict the original gradation holograms from the binary holograms, and the error-diffusion algorithm of the binarization process contributes significantly to training the DNN. The performance of the scheme exceeds that of modern compression techniques such as JPEG 2000 and high-efficiency video coding.

An FPGA-Based Autofocusing Hardware Architecture for Digital Holography

A novel hardware architecture for the reconstruction of digital holograms with autofocusing is presented in this paper. The architecture is based on a novel autofocusing algorithm operating on a smaller local block located at the center of the source digital holograms. By exploiting global information contained in the local block, accurate focus distance can be computed with less computational complexities. Interval search is also adopted to further accelerate the process. The circuits for the fast autofocusing algorithm and subsequent reconstruction operations are effectively integrated in the proposed architecture. Two fast Fourier transform cores are shared by the operations for parallel computations with low area costs. The architecture is implemented by field programmable gate array, and is used as a hardware accelerator in a network on chip system for performance evaluation. Experimental results demonstrate that the proposed circuit exhibits the advantages of high speed computation, low power dissipation, accurate focus distance search, and hologram reconstruction for three-dimensional rendering applications.

23‐3: Distinguished Paper: The New Route for Realization of 1µm‐pixel‐pitch High Resolution Displays

We present a new pixel structure to realize the 1μm‐pixel‐pitch display. This structure is based on the conventional back‐channel etched thin‐film transistor (TFT), but all layers except the horizontal gate line are vertically stacked on the embedded data line, enabling the implementation of high resolution display panels. The vertically‐stacked TFT with 1μm‐channel length shows a high field effect mobility over 50 cm2/Vs, low subthreshold slope of 78 mV/decade. It also shows a high uniform electrical characteristic over the entire 6‐inch wafer. The development of new architecture enables the implementation of a 1μm‐pixel‐pitch high resolution displays such as digital hologram.

Rapid deformation analysis in digital holographic interferometry using graphics processing unit accelerated Wigner-Ville distribution.

High-speed measurement of temporally varying displacement derivatives of a deformed object is an important and challenging problem in precision metrology. This paper proposes an approach for temporal deformation analysis using digital holographic interferometry, where a series of digital holograms is recorded corresponding to a test object subjected to variable load. Numerical reconstruction followed by superposition of these holograms provides a huge stack of interference or fringe pattern data, which needs to be processed to extract the displacement derivative information. This operation involves great computational complexity, and we propose a highly efficient Wigner-Ville distribution method based on a graphics processing unit to address the challenge. Experimental results clearly demonstrate the viability of the proposed approach for high-speed deformation analysis in digital holographic interferometry.

Wavelet compression of off-axis digital holograms using real/imaginary and amplitude/phase parts

Compression of digital holograms allows one to store, transmit, and reconstruct large sets of holographic data. There are many digital image compression methods, and usually wavelets are used for this task. However, many significant specialties exist for compression of digital holograms. As a result, it is preferential to use a set of methods that includes filtering, scalar and vector quantization, wavelet processing, etc. These methods in conjunction allow one to achieve an acceptable quality of reconstructed images and significant compression ratios. In this paper, wavelet compression of amplitude/phase and real/imaginary parts of the Fourier spectrum of filtered off-axis digital holograms is compared. The combination of frequency filtering, compression of the obtained spectral components, and extra compression of the wavelet decomposition coefficients by threshold processing and quantization is analyzed. Computer-generated and experimentally recorded digital holograms are compressed. The quality of the obtained reconstructed images is estimated. The results demonstrate the possibility of compression ratios of 380 using real/imaginary parts. Amplitude/phase compression allows ratios that are a factor of 2–4 lower for obtaining similar quality of reconstructed objects.

Recent Advances in the Processing and Rendering Algorithms for Computer-Generated Holography

Digital holography represents a novel media which promises to revolutionize the way the users interacts with content. This paper presents an in-depth review of the state-of-the-art algorithms for advanced processing and rendering of computer-generated holography. Open-access holographic data are selected and characterized as references for the experimental analysis. The design of a tool for digital hologram rendering and quality evaluation is presented and implemented as an open-source reference software, with the aim to encourage the approach to the holography research area, and simplify the rendering and quality evaluation tasks. Exploration studies focused on the reproducibility of the results are reported, showing a practical application of the proposed architecture for standardization activities. A final discussion on the results obtained is reported, also highlighting the future developments of the reconstruction software that is made publicly available with this work.

Single-shot in-line holographic authentication using phase and amplitude modulation

In this paper, single-shot in-line holographic authentication using phase and amplitude modulation is presented. Amplitude modulation and phase modulation are presented and conducted at reference wave path to obtain noise-like reference wavefront and to generate the parameters (masks) at reference wave path as security keys for single-shot in-line digital holography, and its application, i.e., optical authentication, is presented to show validity of the proposed digital holographic system. A reference optical path using the cascaded random amplitude-only and phase-only masks is applied as an example. Only one in-line digital hologram is used for object reconstruction, and the recovered objects can be effectively authenticated. It is illustrated that parameters (e.g., masks) flexibly designed at reference wave path can facilitate wavefront retrieval in the CCD plane and also can act like security keys for optical information authentication. @ Elsevier, 2019.