Holographic Scheme Research Articles

Single-Pixel Compressive Digital Holographic Encryption System Based on Circular Harmonic Key and Parallel Phase Shifting Digital Holography

An encryption system that combines compressive sensing (CS) and two-step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two-step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two-step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single-pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two-step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single-pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.

Holographic Integrated Sensing and Communication

To overcome spectrum congestion, a promising approach is to integrate sensing and communication (ISAC) functions in one hardware platform. Recently, metamaterial antennas, whose tunable radiation elements are arranged more densely than those of traditional multiple-input-multiple-output (MIMO) arrays, have been developed to enhance the sensing and communication performance by offering a finer controllability of the antenna beampattern. In this paper, we propose a holographic beamforming scheme, which is enabled by metamaterial antennas with tunable radiated amplitudes, that jointly performs sensing and communication. However, it is challenging to design the beamformer for ISAC functions by taking into account the unique amplitude-controlled structure of holographic beamforming. To address this challenge, we formulate an integrated sensing and communication problem to optimize the beamformer, and design a holographic beamforming optimization algorithm to efficiently solve the formulated problem. A lower bound for the maximum beampattern gain is provided through theoretical analysis, which reveals the potential performance enhancement gain that is obtained by densely deploying several elements in a metamaterial antenna. Simulation results substantiate the theoretical analysis and show that the maximum beamforming gain of a metamaterial antenna that utilizes the proposed holographic beamforming scheme can be increased by at least 50% compared with that of a traditional MIMO array of the same size. In addition, the cost of the proposed scheme is lower than that of a traditional MIMO scheme while providing the same ISAC performance.

Reconfigurable Metasurface Hologram of Dynamic Distance via Deep Learning

Reconfigurable metasurfaces have been regarded as an emerging subfield of metasurfaces that can manipulate electromagnetic wave information in a smart manner. They stimulate a gradual transition in metasurface holography from passive to active elements. To date, intelligent dynamic holographic imaging schemes typically rely on iterative or data-driven methods to obtain holograms at a fixed imaging distance, which significantly hinders the development of intelligent dynamic holographic imaging in practical scenarios involving high demands for dynamic imaging distances. Herein, a computer-generated hologram algorithm with a dynamic imaging distance and a reconfigurable metasurface are proposed, which is referred to as a generator and physical diffractive network. Simulation results of time–distance division for three-dimensional imaging are provided to demonstrate the reliability and high efficiency of the proposed algorithm.

HDMA: Holographic-Pattern Division Multiple Access

The next generation wireless communications aiming at enhancing capacity and massive connectivity significantly over high-frequency bands urge the development of novel multiple access technologies. In this paper, we propose a new type of space-division multiple access (SDMA), called holographic-pattern division multiple access (HDMA). We develop the principle for HDMA with the main idea of mapping the intended signals for receivers to a superposed holographic pattern. The multi-user holographic beamforming scheme for HDMA is then presented. Based on the theoretical analysis, we find that there exists an optimal holographic pattern such that the sum rate with simple zero-forcing precoding can achieve the asymptotic capacity of the HDMA system. Simulation results verify the theoretical analysis and show that the HDMA scheme outperforms the traditional SDMA scheme in terms of both the cost-efficiency and the sum rate.

Label‐free single‐shot imaging with on‐axis phase‐shifting holographic reflectance quantitative phase microscopy

Quantitative phase microscopy (QPM) has been emerged as an indispensable diagnostic and characterization tool in biomedical imaging with its characteristic nature of label-free, noninvasive, and real time imaging modality. The integration of holography to the conventional microscopy opens new advancements in QPM featuring high-resolution and quantitative three-dimensional image reconstruction. However, the holography schemes suffer in space-bandwidth and time-bandwidth issues in the off-axis and phase-shifting configuration, respectively. Here, we introduce an on-axis phase-shifting holography based QPM system with single-shot imaging capability. The technique utilizes the Fizeau interferometry scheme in combination with polarization phase-shifting and space-division multiplexing to achieve the single-shot recording of the multiple phase-shifted holograms. Moreover, the high-speed imaging capability with instantaneous recording of spatially phase shifted holograms offers the flexible utilization of the approach in dynamic quantitative phase imaging with robust phase stability. We experimentally demonstrated the validity of the approach by quantitative phase imaging and depth-resolved imaging of paramecium cells. Furthermore, the technique is applied to the phase imaging and quantitative parameter estimation of red blood cells. This integration of a Fizeau-based phase-shifting scheme to the optical microscopy enables a simple and robust tool for the investigations of engineered and biological specimen with real-time quantitative analysis.

Geometric-phase-based shearing interferometry for broadband vortex state decoding

Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin–orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally.

Single-shot multiwavelength digital holography using Bragg diffraction of light by several ultrasound waves [Invited

We report on wavelength-multiplexed digital holographic imaging based on simultaneous Bragg diffraction of wideband light by several ultrasound waves of different frequencies in crystalline media. This technique is easy to implement, avoids spectral scanning, and is applicable in various digital holography schemes. It also enables single-shot acquisition of a few spectral fringe patterns by a single monochrome sensor and wavelength demultiplexing of the resulting interferogram. We have assembled a Mach-Zehnder interferometer with an acousto-optical tunable filter operating in the multifrequency mode and have validated the proposed technique by dual-, three-, and four-wavelength quantitative phase imaging of the test samples.

Approach to the approximation of the transfer characteristic and correlation response of Fourier holography scheme

An approach for approximating the transfer characteristic and response in the +1th order of diffraction of a 4f Fourier holography scheme by a Gaussian-like model as applied to image processing with power-law spatial-frequency power spectra is proposed. The relations between the parameters of the approximation models and the reference image spectra are found by numerical simulation depending on the reference spectrum exponent. The approximation errors and the possibility of their optimization in the required range of spatial frequencies, determined by the nonlinearity of the exposure characteristics of holographic recording media, are shown. The validity of the approach is confirmed by comparing the results of numerical simulation with experimental data. Keywords: holography, Fourier transform, spatial frequency spectrum, impulse response, recording media, exposure characteristic.

Recovery and Characterization of Orbital Angular Momentum Modes with Ghost Diffraction Holography

Orbital angular momentum (OAM) of optical vortex beams has been regarded as an independent physical dimension of light with predominant information-carrying potential. However, the presence of scattering environment and turbulent atmosphere scrambles the helical wavefront and destroys the orthogonality of modes in vortex beam propagation. Here, we propose and experimentally demonstrate a new basis for the recovery of the OAM mode using a holographic ghost diffraction scheme. The technique utilizes the speckle field generated from a rotating diffuser for optical vortex mode encoding, and the fourth-order correlation of the speckle field for the efficient recovery of the associated modes. Furthermore, we successfully demonstrate the complex-field recovery of OAM modes by the adoption of a holography scheme in combination with the ghost diffraction system. We evaluate the feasibility of the approach by simulation and followed by experimental demonstration for the recovery of various sequentially encoded OAM modes. Finally, the efficacy of the recovered modes was quantitatively analyzed by an OAM mode analysis utilizing orthogonal projection scheme.

Trichromatic shaper-based quantum state holography

Phases play an important role in ultrafast dynamics. In this paper, the authors present an ultrafast quantum state holography scheme based on the interference of photoelectron wave packets from multiphoton ionization using shaper-generated trichromatic pump-probe-reference pulse sequences. Independent control of the phase, the time delay, and the central wavelength of all three sub-pulses are demonstrated in a proof-of-concept experiment on the multiphoton ionization of potassium atoms.

A wavefront division multiplexing holographic scheme and its application in looking through diffuser

We present a spatial light modulator (SLM) assisted compact holographic method and illustrate its application by imaging through a random scattering medium. The merit of the proposed method is wavefront division multiplexing, i.e. the dual wavefront modulations over a single SLM. Two different wavefront shapes: a reference-light shape and a phase object, are combined over the SLM. One advantage of this scheme is the flexible modulation of the reference light. The experimental implementation of this method is demonstrated by quantitatively reconstructing different phase objects from the randomly scattered light. This new scheme greatly simplifies the experimental configuration and presents a better stability even in presence of external vibrations, opening avenues for the holography-based scattering imaging application.

Alternative constraints for improved multiplane hologram generation.

In this work, we introduce a modified hologram plane constraint to improve the accuracy of the global Gerchberg-Saxton (GGS) algorithm used for multiplane phase-only hologram generation. This constraint consists of a modified phase factor that depends on the amplitude of the field in the hologram plane. We demonstrate that this constraint produces an increase in the mean correlation coefficient between the reconstructed planes from a multiplane hologram and the corresponding amplitude targets for each plane. Furthermore, this constraint can be applied together with a mixed constraint in the reconstruction planes, leading to a more uniform and controllable reproduction of a target intensity distribution. To confirm the validity of our proposal, we show numerical and experimental results for multiplane holograms with six discrete planes, using both high and low contrast targets. For the experimental results, we implement a holographic projection scheme based on a phase-only spatial light modulator.

A wavelength and polarization selective photon sieve for holographic applications

Abstract Optical metasurfaces are perfect candidates for the phase and amplitude modulation of light, featuring an excellent basis for holographic applications. In this work, we present a dual amplitude holographic scheme based on the photon sieve principle, which is then combined with a phase hologram by utilizing the Pancharatnam–Berry phase. We demonstrate that two types of apertures, rectangular and square shapes in a gold film filled with silicon nanoantennas are sufficient to create two amplitude holograms at two different wavelengths in the visible, multiplexed with an additional phase-only hologram. The nanoantennas are tailored to adjust the spectral transmittance of the apertures, enabling the wavelength sensitivity. The phase-only hologram is implemented by utilizing the anisotropic rectangular structure. Interestingly, such three holograms have quantitative mathematical correlations with each other. Thus, the flexibility of polarization and wavelength channels can be utilized with custom-tailored features to achieve such amplitude and phase holography simultaneously without sacrificing any space-bandwidth product. The present scheme has the potential to store different pieces of information which can be displayed separately by switching the wavelength or the polarization state of the reading light beam.

Modeling of quantum-like cognitive phenomena by the Fourier-holography technique under the choice of alternatives

The article is dedicated to the search for a biologically motivated mechanism of the cognitive phenomenon of violation of the classical formula of total probability for the disjunction of incompatible events, which is considered by a number of researchers as a quantum-like phenomenon. A classical mechanism implemented by the 6f Fourier holography scheme of the resonant architecture that does not require reference to quantum mechanics either in its physical nature or at the level of formalism is demonstrated. In the analysis, the decision-making is interpreted as a choice of alternatives by using the non-cooperative game "Prisoner's Dilemma". The approach to the task is based on the search for a mechanism for forming a conditional estimate under a condition that contradicts the rule of monotonous decision logic. It is demonstrated that this estimate, in contrast to the unconditional and conditional one with a non-contradictory condition, is formed by logic with exception. The ring architecture of the holographic setup corresponds to the biologically inspired neural network concept of the excitation ring and implements cognitive dissonance on logic with exception. Conditions and ranges of violation of the classical formula of total probability in relation to the correlation radius of the reference image recorded in a hologram storing the monotone logic inference rule are analytically determined. The analytical model is confirmed by a quantitative coincidence of the results of numerical modeling with the published results of natural experiments.

Tunable Polarization and Surface Relief Holographic Gratings in Azopolymer Nanocomposites with Incorporated Goethite (α-FeOOH) Nanorods

We employ two approaches to tune the properties of concurrently inscribed volume polarization and surface relief gratings in nanocomposite thin films containing the azopolymer PAZO (poly[1-4-(3-carboxy-4-hydrophenylazo)benzensulfonamido]-1,2-ethanediyl, sodium salt]) and goethite (α-FeOOH) nanorods. The first one is applied on the stage of sample preparation by varying the concentration of the goethite nanorods from 0% to 15%. Then, different angles between the recording beams are set in the holographic scheme, which allow us to obtain gratings with spatial periods in the range from 0.86 to 2.51 µm. Surface relief modulation close to 300 nm is achieved as well as total diffraction efficiency in the ±1 diffracted orders of more than 50%. The influence of the incorporated goethite nanorods on the properties of both volume birefringence and the surface relief grating are discussed.

Electrically tunable diffuser for holographic multiplexing storage

A polymer-dispersed liquid crystal (PDLC) device is fabricated to serve as a diffuser for random phase encoding of reference beams in holographic storage system. By tuning the applied voltage on the PDLC device, three individual random phase reference waves which are orthogonal to each other can be generated. Therefore, holographic multiplexing scheme can be performed using voltage modulation on the PDLC diffuser. In addition, shift multiplexing technique still can be performed in the storage system. When compared with conventional shift multiplexing, using electrically tunable PDLC diffuser offers additional multiplexing mechanism in the presented technique. Using the proposed PDLC diffuser, the multiplexing numbers can be enhanced three times owing to voltage modulation. A holographic storage system implemented using shift multiplexing and voltage modulation on PDLC diffuser is demonstrated.

Generation and experimental reconstruction of optimized Fresnel random phase-only holograms

In this paper, we demonstrate a method for random phase optimization in the Fresnel domain that enables the fast generation of phase-only holograms (POHs). Our proposal consists of applying the iterative Fresnel transform algorithm (IFrTA) to optimize a random phase with the parameters of a given holographic projection system. Then, the resulting optimized Fresnel random phase is used for the generation of POHs of several objects. We compare the performance of our proposed method to the direct generation of holograms using IFrTA, and quantitatively study the quality of the reconstructed object varying the generation parameters. Our results show significantly improved computation speed and minor loss of accuracy compared with the direct application of the IFrTA. We present both numerical and optical reconstructions obtained with a holographic projection scheme based on a phase-only spatial light modulator to verify the validity and effectiveness of our proposal.

Experimental Fresnel and Fourier digital holography using a digital micro-mirror device

We present an experimental off-axis optical holographic scheme employing a digital micromirror device (DMD) as projecting media instead of a liquid crystal spatial light modulator (SLM). The DMD allows projecting information through light reflection. We perform holographic recording in the Fourier and the Fresnel domains under similar experimental configurations to test our experimental scheme and verify the DMD performance as a binary amplitude SLM. For the digital holographic recovery process of Fourier holograms, we applied a non-linear modification that allows reducing the degradation in the recovered data. We also implement a multiplexing protocol enabling the packaging of an entire holographic dynamic scene into a single data. Furthermore, we use QR codes as information containers to achieve noise-free information recovery after holographic reconstruction. Experimental results demonstrate the viability and versatility of a DMD in an experimental holographic scheme.

Dynamically reconfigurable high-efficiency terahertz metasurface holograms

A reflective, dynamically reconfigurable, high-efficiency metasurface holographic scheme is presented in this paper, which is realized by pumping thin gallium arsenide wafers with a structured femtosecond laser. When the terahertz (THz) passes through the gallium arsenide wafer (GaAs), the pattern carried by the pump light is converted into the complex permittivity of the light carrier density distribution on the gallium arsenide wafer, which modulates the wafer, thereby changing the transmittance of the THz wave. The wavefront of the THz beam is determined by changing the shape and direction of the projected resonator on the DMD by Pancharatnam-Berry (P-B) phase principle. The numerical simulation results show that different holograms can be obtained by dynamically switching the projection on the DMD, and the orthogonal conversion efficiency of circularly polarized light can reach 90%. The holographic scheme proposed in this paper is convenient and fast and may advance the real-time dynamic conversion and dynamic display of holograms.

The Theoretical and experimental study of the bending of a thin substrate during electrolytic deposition

The present paper is aimed at the theoretical and experimental study of the shape distortion of thin substrates during electrolytic deposition and gaccumulation of residual stresses in them. The theoretical modeling is provided in the framework of the theory of solids with variable material composition. The result of the deposition process is modeled with a continuous family of elastic bodies, which local deformations are incompatible. These deformations act as internal sources for stresses. Formally they are equivalent to the field of distributed defects. Unlike the classical approach adopted in nonlinear elasticity, the elements of the family which present a body with a variable material composition don’t have a global reference natural (free of stresses) form. Instead we used the continuous family being only locally free from stresses. To formulate the boundary value problem, continuous families of reference, intermediate and actual forms and corresponding families of deformations are defined. The deformations, belonging to these families, locally represent implants (local deformations of reference forms into intermediate ones) and deformations that bring intermediate forms into actual ones. Relations for stresses and strains in such bodies are obtained under the assumption that the displacement gradients are small with respect to unity and satisfy the kinematic hypothesis of the technical plate theory. Under these assumptions the equilibrium equations are derived. They include specific terms which determine formal loading that is caused by incompatible deformations. Axisymmetric problems for a circular substrate under various types of fixing and tension on the boundary, which characterize the conditions of the experiment, are obtained. The theoretical distribution for displacements of the substrate surface is formulated upon the obtained solution. They are intended to identify incompatible deformations that cause bending during the deposition process. The experimental measuring setup is constructed according to a holographic scheme of displacement measurements in real time. The deposition process is carried out in a cylindrical chamber with flange fastening of the cathode. The electrochemical process is implemented in sulphate electrolyte. As a result of comparing the theoretically obtained relations for bending surfaces of the substrate with the experimental results, the parameters that characterize the substrate shrinkage and tension are estimated.