Holographic Data Research Articles

Compression strategies for digital holograms in biomedical and multimedia applications

While 60 years of successful application of holography is celebrated in this special issue, efficient representation and compression of holographic data has received relatively little attention in research. Notwithstanding this observation, and particularly due to the digitization that is also penetrating the holographic domain, interest is growing on how to efficiently compress holographic data such that interactive exchange of content, as well as digital storage can be facilitated proficiently. This is a particular challenge, not only because of its interferometric nature and the various representation formats, but also the often extremely large data volumes involved in pathological, tomographic, or high-end visualization applications. In this paper, we provide an overview of the state of the art in compression techniques and corresponding quality metrics for various practical applications in digital holography. We also consider the future by analyzing the emerging trends for addressing the key challenges in this domain.

Secure storage and matching of latent fingerprints using phase shifting digital holography

This paper describes the secure storage and matching of latent fingerprints using phase shifting digital holography. A phase shifting digital holographic system is proposed for imaging of latent fingerprints, which can be applied in the criminal investigation field. Digital holography is one of the accurate and fast technique for measuring 3D information, by acquiring both amplitude and phase information from the object. Digital holography uses a Charge-Coupled Device (CCD) to record the interference pattern. In digital holography, the reconstructed image unavoidably contains the conjugate image and the zeroth order beam, resulting in low resolution. This problem can be overcomed by using phase shifting digital holography. Phase shifting digital holography is a technique by which multiple holograms are taken corresponding to the various phase differences between the object beam and the reference beam. One of the most secure storage methods is digital holographic data storage which provides a credible way in the fingerprint acquisition in the criminal investigation field. The phase shifting digital holograms of the latent fingerprint are acquired and then numerically reconstructed. The reconstructed fingerprint is then compared with the database after further processing to find whether it is a match or no match. The investigations have been conducted through experiments and computer simulations. The parameters used for analyzing the performance of the system are False Matching Rate (FMR), False Non-Matching Rate (FNMR) etc. This system shows a remarkable performance improvement over digital holographic techniques. The method can be explicitly used in forensic applications.

Quality Evaluation of Holographic Images Coded With Standard Codecs

Recently, a larger interest in the different plenoptic formats, including digital holograms, has emerged. Aside from other challenges that several steps of the holographic pipeline, from digital acquisition to display, have to face, visual quality assessment of compressed holograms is particularly demanding due to the distinct nature of this 3D image modality when compared to regular 2D imaging. There are few studies on holographic data quality assessment, particularly with respect to perceptual effects of lossy compression. This work aims to study the quality evaluation of digital hologram reconstructions, presented on regular 2D displays, in the presence of compression distortions. As there is no established or generally agreed compression methodology for digital holograms compression on the hologram plane with available implementations, a set of state-of-the-art compression codecs, namely HEVC, AV1, and JPEG2000, were used for compression of the digital holograms on the object plane. Both computer generated and optically generated holograms were considered. Two subjective tests were conducted to evaluate distortions caused by compression. The first subjective test was conducted on the reconstructed amplitude images of central views, while the second test was conducted on pseudo-videos generated from the reconstructed amplitudes of different views. The subjective quality assessment was based on mean opinion scores. A selection of objective quality metrics was evaluated, and their correlations with mean opinion scores were computed. The VIFp metrics appeared to have the highest correlation.

Invited Paper] Enhanced Recording Density via Multilevel Phase Retrieval and Correlation-based Multiplexed Recording in Computer-generated Holographic Data Storage

Invited Paper] Enhanced Recording Density via Multilevel Phase Retrieval and Correlation-based Multiplexed Recording in Computer-generated Holographic Data Storage

DWT‐SVD Based Watermarking for High‐Resolution Medical Holographic Images

Watermarking is one of the most common techniques used to protect data’s authenticity, integrity, and security. The obfuscation in the frequency domain used in the watermarking method makes the watermarking stronger than the obfuscation in the spatial domain. It occupies an important place in watermarking works in imperceptibility, capacity, and robustness. Finding the optimal location to hide the watermarking is one of the most challenging tasks in these methods and affects the method’s performance. In this article, sample identification information is processed with the method of watermaking on the hiding environment created by using a chaos‐based random number generator on biomedical data to provide solutions to problems such as visual attack, identity theft, and information confusion. In order to obtain biomedical data, a lensless digital in‐line holographic microscopy (DIHM) setup was designed, and holographic data of human blood and cancer cell lines, which are widely used in the laboratory environment, were obtained. The standard USAF 1951 target was used to evaluate the resolution of our imaging setup. Various QR codes were generated for medical sample identification, and the captured medical data were processed by watermarking it with chaos‐based random number generators. A new method using chaos‐based discrete wavelet transform (DWT) and singular value decomposition (SVD) has been developed and applied to high‐resolution data to eliminate the problem of encrypted data being directly targeted by third‐party attacks. The performance of the proposed new watermarking method has been demonstrated by various robustness and invisibility tests. Experimental results showed that the proposed scheme reached an average PSNR value of 564588 dB and SSIM value of 0.9972 against several geometric and destructive attacks, which means that the proposed method does not affect the image quality and also ensures the security of the watermarking information. The results of the proposed method have shown that it can be used efficiently in various fields.

From digital holographic microscopy to optical coherence tomography – separate past and a common goal

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Broadband digital coding metasurface holography

Digital coding metasurfaces composed of subwavelength meta-atoms can flexibly control electromagnetic waves to achieve holography, which has great potential in millimeter-wave imaging systems and data storage. In this paper, we propose a 3-bit reflective digital coding metasurface. The incident linearly polarized waves can be transformed into cross-polarized components with distinct phase responses by adjusting the rotational and open angles of the coding elements. The 3-bit phase performance can be retained over a wide bandwidth from 12 to 18 GHz by simultaneously changing the rotational and open angles. Based on the proposed broadband metasurface, broadband holography is successfully demonstrated with the optimization of a modified Gerchberg–Saxton algorithm. As a proof of concept, five schemes with different holograms integrating the letters “S,” “E,” “U,” “X,” and “Z” are simulated from 12 to 18 GHz. Good simulation results validate the performance of the proposed broadband holography, showing a relative bandwidth of 40%. Two prototypes superposing the holograms of letters “U” and “X” are fabricated and measured in a near-field microwave anechoic chamber. The experimental results corroborate well with simulated results, further supporting the demonstration. We believe that the proposed broadband holography based on the digital coding metasurface paves a way to wideband applications for microwave imaging, information processing, and holographic data storage.

Arsenic trisulfide-doped silica-based porous glass

Novel composite material based on silica porous glass as low refractive index matrix and high refractive index As2S3 nanoparticles filled in the pores has been made. Chalcogenide nanoparticles were dissolved and the porous glass matrix was impregnated in the obtained solution. Subsequently, the solvent was evaporated by annealing the porous glass. Various optical parameters of the created composite material are presented in this paper. These parameters are based on optical and structural transformations which occur under active illumination and heat treatment in such chalcogenide-containing composite and compared with thin As2S3 light-sensitive layers. New functionalities may be added this way to the composite, such as illumination and/or thermally driven optical parameters. Developing and optimizing the optical properties of the obtained As2S3-porous glass composites can be useful for creating 3D optical-structural patterns for different applications such as holographic data storage, light modulation, and/or functional, nonlinear optical elements with various parameters for VIS-NIR optics.

A common-path digital holographic microscope with a rotatable birefringent prism for synthesizing high-quality quantitative phase images from multi-angle interferograms

We propose a simple common-path off-axis interferometric system to perform high-quality quantitative phase imaging based on a rotatable birefringent prism that is placed at the output port of a conventional transmission or reflection microscope. The proposed system effectively eliminates the zero-order term of holographic data and increases the phase image reconstruction bandwidth by compounding multi-angle holograms, thereby obtaining high-quality quantitative phase images without zero-order artifacts. In addition, the proposed multi-angle phase image compounding method can eliminate the repetitive object phases caused by self-reference interferometry, thereby alleviating the problem of field-of-view reduction. Furthermore, we realize high-quality quantitative phase imaging based on multi-angle phase images without sacrificing the imaging frame rate. The concept is demonstrated by performing high-quality quantitative phase imaging of polystyrene microspheres and a freshwater alga, Pinnularia. Experimental results show that the noise level of the quantitative phase images synthesized using the proposed rotatable common-path digital holographic microscopy system is lower than that of conventional single-shot digital holographic microscope reconstruction quantitative images, and a more detailed cell internal structure can be observed.

A free field recovery technique based on the boundary element method and three-dimensional scanning measurements.

The boundary element method- (BEM-) based free field recovery technique (FFRT) has been proposed to recover the free field radiated by an arbitrarily shaped source from the mixed field that would be measured in a noisy environment. However, that technique requires that the boundary integral equation should be established on an enclosed hologram surface surrounding the source, which means that the hologram surface should be discretized into elements and the measurement points should be located on the nodes of the elements. For large-scale or mid-high frequency problems, it makes the total number of measurement points huge since it should obey the criterion of more than six elements per wavelength, which put forward very high requirements for holographic data measurement. To overcome this problem, a more flexible BEM-based FFRT without the restriction on the locations of measurement points is proposed in this study. In virtue of this, a three-dimensional scanning measurement method can be applied to acquire holographic data with high efficiency. The effectiveness of the proposed method is validated by two numerical simulations and an experiment.

Thermally Reconfigurable Hologram Fabricated by Spatially Modulated Femtosecond Pulses on a Heat-Shrinkable Shape Memory Polymer for Holographic Multiplexing.

Optical security involving the use of light to achieve distinctive vision effects has become a widely used approach for anticounterfeiting. Holographic multiplexing has attracted considerable interest in multiplexing security due to its high degree of freedom for manipulating the optical parameters of incident laser beams. However, the complex and time-consuming fabrication process of metasurface-based holograms and the sophisticated nature of holographic imaging systems have hindered the practical application of holographic multiplexing in anticounterfeiting. Combining holography with shape memory polymers to construct reconfigurable holograms provides a simple and efficient way for holographic multiplexing. This paper proposes a reconfigurable four-level amplitude hologram fabricated on a heat-shrinkable shape memory polymer using spatially modulated femtosecond laser pulses. Simply by triggering the shape recovery of the polymer through heating, the amplitude modulation of light by the hologram is reconfigured through the shrinking of processed microcrater pixels with three diameters, which enables variation to be achieved in reconstructed holographic images. Examples of holographic multiplexing and data encryption are used to validate the proposed method. The proposed economic and simple approach for holographic multiplexing provides an integrated and single-material solution to packaging and optical security, which has extensive potential in anticounterfeiting and optical encryption.

Highly efficient dual page reproduction in holographic data storage.

We propose a simultaneous dual-page reproduction for holographic data storage (HDS) with high-efficiency and high-speed data reproduction by reusing a transmitted reference beam that passes through a recording medium after data reconstruction. The transmitted reference beam enters the recording medium at a different incident angle to reproduce different data pages; thus, this technology can double data-transfer rates without increasing the laser's output power or preparing another laser source. In the experiment, neighboring angle-multiplexed two data pages were simultaneously reconstructed and a data transfer rate of 1.0 Gbps was obtained.

Lensless phase retrieval based on deep learning used in holographic data storage.

This paper proposes a lensless phase retrieval method based on deep learning (DL) used in holographic data storage. By training an end-to-end convolutional neural network between the phase-encoded data pages and the corresponding near-field diffraction intensity images, the new unknown phase data page can be predicted directly from the intensity image by the network model without any iterations. The DL-based phase retrieval method has a higher storage density, lower bit-error-rate (BER), and higher data transfer rate compared to traditional iterative methods. The retrieval optical system is simple, stable, and robust to environment fluctuations which is suitable for holographic data storage. Besides, we studied and demonstrated that the DL method has a good suppression effect on the dynamic noise of the holographic data storage system.

CNN-based demodulation for a complex amplitude modulation code in holographic data storage

CNN-based demodulation for a complex amplitude modulation code in holographic data storage

Towards Reduced CNNs for De-Noising Phase Images Corrupted with Speckle Noise

Digital holography is a very efficient technique for 3D imaging and the characterization of changes at the surfaces of objects. However, during the process of holographic interferometry, the reconstructed phase images suffer from speckle noise. In this paper, de-noising is addressed with phase images corrupted with speckle noise. To do so, DnCNN residual networks with different depths were built and trained with various holographic noisy phase data. The possibility of using a network pre-trained on natural images with Gaussian noise is also investigated. All models are evaluated in terms of phase error with HOLODEEP benchmark data and with three unseen images corresponding to different experimental conditions. The best results are obtained using a network with only four convolutional blocks and trained with a wide range of noisy phase patterns.

Improved phase retrieval in holographic data storage based on a designed iterative embedded data.

Embedded data are used to retrieve phases quicker with high accuracy in phase-modulated holographic data storage (HDS). We propose a method to design an embedded data distribution using iterations to enhance the intensity of the high-frequency signal in the Fourier spectrum. The proposed method increases the antinoise performance and signal-to-noise ratio (SNR) of the Fourier spectrum distribution, realizing a more efficient phase retrieval. Experiments indicate that the bit error rate (BER) of this method can be reduced by a factor of one after 10 iterations.

Quality guided alternative holographic data representation for high performance lossy compression

We analyze several representations for holographic data and determine the effectiveness of a common lossy compression algorithm for each representation. We demonstrate that a phase–amplitude representation, when used to represent holograms of diffuse objects, can be combined with a phase unwrapping algorithm to achieve much higher compression ratios (CRs) than direct compression of the complex valued holographic data. We compare the compression performance of the JPEG algorithm for several conventional and alternative holographic data representations. Additionally, we test two different phase unwrapping algorithms to improve phase compression performance. In particular, we propose and evaluate an alternative phase representation based on a quality guided phase unwrapping algorithm. This alternative representation offers higher performance to the other tested approaches, achieving CRs over 6 with a limited quality loss after reconstruction. We add the experimental reconstruction of the processed holograms to further validate our proposal.

Common-path angular-multiplexing holographic data storage based on computer-generated holography.

An unconventional angular-multiplexed recording technique is proposed for holographic data storage based on a computer-generated hologram (CGH) technique. While general angular-multiplexed recording techniques require a Mach-Zehnder interferometer to record data pages as volume holograms, the proposed method records ones with a common-path configuration with the help of a CGH technique, which prevents the optical setup from being bulky. In the proposed method, the CGH reconstructs signal and reference beams simultaneously, and these beams interfere in a recording medium. By changing the diffraction angle of the reference beam from the CGH, angular multiplexing is accomplished with a common-path optical setup without additional optical elements. Multiplexed recording of four data pages is demonstrated in a proof-of-principle experiment, which indicates the feasibility of the proposed method.

Significant Enhancement of the Polarization Holographic Performance of Photopolymeric Materials by Introducing Graphene Oxide.

Relying on various defects and functional oxygen-containing groups on the basal planes, graphene oxide (GO) is commonly unitized for intimate mixing with a polymer matrix to fabricate high-performance nanocomposite polymeric materials with the characteristics of graphene. Herein, by introducing GO nanosheets in a phenanthraquinone-doped polymethyl methacrylate (PQ/PMMA) photopolymer, we demonstrate that the polarization holographic diffraction efficiency of nanocomposite materials can be dramatically enhanced up to nearly 10 times and the photosensitivity can also be enhanced by more than 3 times. Experimental observations reveal that the incorporation of GO nanosheets serves as a polymerization initiator not only to promote the polymerization of MMA monomers and induce the drafting behavior of the PMMA polymer on its surface but also to effectively modulate the molecular weight of the PQ/PMMA photopolymer by adjusting the doping concentration of GO nanosheets. The current study, for the first time, demonstrates that the modulation of molecular weight for PQ/PMMA photopolymers here exerts a significant impact on their holography performance. In addition, due to the strong physisorption of PQ photosensitizers onto GO nanosheets, the aggregation of PQ around GO-graft-PMMA also facilitates the formation of GO-graft-PMMA/PQ and is beneficial to the enhancement of holographic performance. The emergence of GO-graft-PMMA/PQ nanocomposite materials here is expected to fulfill the requirement of high-performance polarization-sensitive materials in the field of polarization holographic data storage and provide a facile but effective nanocomposite doping strategy to modulate the holographic performance of photopolymers from micro- and mesoscopic levels.

Reduction of spatio-temporal phase fluctuation in a spatial light modulator using linear phase superimposition

Spatio-temporal phase modulation with a phase-only liquid-crystal spatial light modulator (SLM) plays an important role in the optics and photonics community. SLMs are generally affected by either or both spatial and temporal phase fluctuations, depending on driver electronics, thereby reducing the quality of a generated beam. In this study, to reduce phase fluctuations, we present an optical-based linear phase superimposition method with spatial bandpass filtering. We experimentally investigate the method’s effectiveness, particularly for holographic data storage applications. Experimental results show that the presented method is useful in robustly generating phase distributions against fluctuations, regardless of the SLM driving scheme.