Holographic Method Research Articles

Capturing holographic images in extreme light-starved environments

New 3D holography method requires less than one photon per pixel.

A quantum cosmology approach to cosmic coincidence and inflation

This work studies the quantum cosmology of a closed, spatially homogeneous, and isotropic FLRW minisuperspace model with electromagnetic radiation as a matter content. We solve the associated Wheeler-DeWitt (WDW) equation using the holographic regularization method and show that the electromagnetic zero-point energy forms the vacuum energy and provides a unified resolution to the horizon, flatness, singularity, and cosmic coincidence problems. This quantum cosmology approach composes an alternative to the usual inflationary paradigm and can be extended to more general matter contents and emergent gravity schemes.

Ku/Ka Dual-Band Shared-Aperture Leaky-Wave Antenna With Fixed-Frequency and Wide-Angle Beam Scanning Based on Ridged SIW

In this communication, a novel ridged substrate integrated waveguide (RSIW) structure is reported, to realize the transmission of electromagnetic waves in dual bands in a shared aperture. The structure is consisting of two substrate integrated waveguides (SIW) operating in Ka and Ku bands, respectively, by integrating the Ka-SIW into the Ku-SIW like an embedded ridge. Therefore, the Ku-SIW operates like a ridge waveguide with single-mode transmission. Based on the RSIW structure, a leaky-wave antenna (LWA) is developed with fixed-frequency and wide-angle beam scanning in dual bands (Ka and Ku). Two types of slot arrays are arranged on the RSIW, and PIN diodes are adopted to control the states of slots. Two transitions from waveguide to SIW have been designed in Ka and Ku bands, respectively, to excite the RSIW. A binary holographic method based on isotropic-point-source array is developed to quickly obtain the excitation schemes of the slot array for desired beam angles. The measured results verify that the LWA can achieve beam scanning ranges of -72°~39° and -48°~42° at 31.5 GHz and 12.1 GHz, respectively. The proposed RSIW LWA has the feature of dual-band compact shared aperture, and may have a potential application in the dual-band communication systems.

Light Beam Transformation and Material Diagnostics by Dynamic Holography Methods

Light Beam Transformation and Material Diagnostics by Dynamic Holography Methods

Schwinger-Type Pair Production in Non-SUSY AdS/CFT

We study pair production of particles in the presence of an external electric field in a large N non-supersymmetric Yang-Mills theory using the holographic duality. The dual geometry we consider is asymptotically AdS and is effectively parametrized by two parameters, u 0 and − 5 / 2 < δ ≤ 0 , both of which can be related to the effective mass of quark/antiquark for non-supersymmetric theories. We numerically calculate the interquark potential profile and the effective potential to study pair production and analytically find out the threshold electric field beyond which one gets catastrophic pair creation by studying rectangular Wilson loops using the holographic method. We also find out the critical electric field from DBI analysis of a probe brane. Our initial investigations reveal that the critical electric field necessary for spontaneous pair production increases or decreases w.r.t. its non-supersymmetric value depending on the parameter δ . Ultimately, we find out the pair production rate of particles in the presence of an external electric field by evaluating circular Wilson loops using perturbative methods. From the later investigation, we note the resemblance with our earlier prediction. However, we also see that for and below another certain value of the parameter δ , the pair production rate of particle/antiparticle pairs blows up as the external electric field is taken to zero. We thus infer that the vacuum of the non-SUSY gauge theory is unstable for a range of non-supersymmetric parameter δ and that the geometry/non-SUSY field theory under consideration has quite different characteristics than earlier reported.

Two-beam phase correlation spectroscopy: a label-free holographic method to quantify particle flow in biofluids

We introduce two-beam phase correlation spectroscopy (2B-ΦCS) as a label-free technique to measure the dynamics of flowing particles; e.g., in vitro or in vivo blood flow. 2B-ΦCS combines phase imaging with correlation spectroscopy, using the intrinsic refractive index contrast of particles against the fluid background in correlation analysis. This method starts with the acquisition of a time series of phase images of flowing particles using partially coherent point-diffraction digital holographic microscopy. Then, phase fluctuations from two selected circular regions in the image series are correlated to determine the concentration and flow velocity of the particles by fitting pair correlation curves with a physical model. 2B-ΦCS is a facile procedure when using a microfluidic channel, as shown by the measurements on flowing yeast microparticles, polymethyl methacrylate microparticles, and diluted rat blood. In the latter experiment, the concentration and average diameter of rat blood cells were determined to be (4.7±1.9)×106 μL−1 and 4.6±0.4 μm, respectively. We further analyzed the flow of mainly red blood cells in the tail vessels of live zebrafish embryos. Arterial and venous flow velocities were measured as 290±110 μm s−1 and 120±50 μm s−1, respectively. We envision that our technique will find applications in imaging transparent organisms and other areas of the life sciences and biomedicine.

Cross talk-free retinal projection display based on a holographic complementary viewpoint array.

In near-eye displays (NEDs), retinal projection display (RPD) is one kind of promising technology to alleviate the vergence-accommodation conflict (VAC) issue due to its always-in-focus feature. Viewpoint replication is widely used to enlarge the limited eyebox. However, the mismatch between viewpoint interval and eye pupil diameter will cause the inter-viewpoint cross talk when multiple viewpoints enter the pupil simultaneously. In this Letter, a holographic complementary viewpoint method is proposed to solve this cross talk problem. Instead of avoiding observing multiple viewpoint images simultaneously, it is designed that multiple complementary viewpoints jointly project the complete image on the retina without cross talk. To do this, the target image is segmented into multiple sub-images, each multiplied with a corresponding partial spherical phase to converge to a specific complementary viewpoint. A group of complementary viewpoint enter the eye pupil simultaneously, and each viewpoint project a corresponding sub-image on a specific area of the retina and splice to a complete image. All of the complementary viewpoints are duplicated to an interlaced two-dimensional array to extend the eyebox in both horizontal and vertical directions. Optical experiment verifies that the proposed method could present smooth transition between viewpoints to avoid both inter-viewpoint cross talk and blank image issues.

The mixed-state entanglement in holographic p-wave superconductor model

In this paper, we investigate the mixed-state entanglement in a model of p-wave superconductivity phase transition using holographic methods. We calculate several entanglement measures, including holographic entanglement entropy (HEE), mutual information (MI), and entanglement wedge cross-section (EWCS). Our results show that these measures display critical behavior at the phase transition points, with the EWCS exhibiting opposite temperature behavior compared to the HEE. Furthermore, we explore the behavior of thermodynamics and holographic quantum information at the zeroth-order phase transition point and find that it is opposite to that observed in the first-order phase transition. Additionally, we find that the critical exponents of all entanglement measures are twice those of the condensate. Our findings also suggest that the EWCS is a more sensitive indicator of the critical behavior of phase transitions than the HEE. Lastly, we uncover a universal inequality in the growth rates of EWCS and MI near critical points in thermal phase transitions, such as p-wave and s-wave superconductivity, suggesting that MI captures more information than EWCS when a phase transition first occurs.

A Cylindrical Near-Field Acoustical Holography Method Based on Cylindrical Translation Window Expansion and an Autoencoder Stacked with 3D-CNN Layers.

The performance of near-field acoustic holography (NAH) with a sparse sampling rate will be affected by spatial aliasing or inverse ill-posed equations. Through a 3D convolution neural network (CNN) and stacked autoencoder framework (CSA), the data-driven CSA-NAH method can solve this problem by utilizing the information from data in each dimension. In this paper, the cylindrical translation window (CTW) is introduced to truncate and roll out the cylindrical image to compensate for the loss of circumferential features at the truncation edge. Combined with the CSA-NAH method, a cylindrical NAH method based on stacked 3D-CNN layers (CS3C) for sparse sampling is proposed, and its feasibility is verified numerically. In addition, the planar NAH method based on the Paulis-Gerchberg extrapolation interpolation algorithm (PGa) is introduced into the cylindrical coordinate system, and compared with the proposed method. The results show that, under the same conditions, the reconstruction error rate of the CS3C-NAH method is reduced by nearly 50%, and the effect is significant.

Holographic phase-retrieval method of near-field antenna pattern measurement for bolometer-array-equipped millimeter-wave telescopes

Wide field-of-view millimeter-wave telescopes with a bolometric detector array have been developed for cosmic microwave background radiation observations. For the purpose of laboratory verification of these telescopes, several studies have demonstrated near-field antenna measurements using a phase-sensitive detector that replaces a few representative pixels of the focal-plane detector array. We present a holographic phase-retrieval method that enables near-field measurements with the bolometric detector array as it is. We place a reference emitter at a fixed position and scan a signal emitter at the telescope aperture. These two emitters are phase-locked and generate interference patterns (holograms) on the focal plane, from which the amplitude and phase of the aperture field can be retrieved. We experimentally demonstrated this method with a crossed-Dragone telescope with a field-of-view that is 18 deg × 9 deg. In the demonstration, we placed a phase-sensitive detector at three detector positions on the focal plane. The antenna patterns calculated from the hologram, neglecting the directly measured phase information, were consistent with those calculated from both intensity and phase measurements at the −60-dB level at 180 GHz. Applying this method, the antenna patterns for all of the bolometric detectors on the focal plane can theoretically be measured simultaneously.

Double-sided computer-generated holography.

We present a method for computer-generated holography (CGH) in which different images are reproduced on both sides of a hologram with a single illumination source. In the proposed method, we use a transmissive spatial light modulator (SLM) and a half mirror (HM) located downstream of the SLM. The light modulated by the SLM is partially reflected by the HM, and the reflected light is modulated again by the SLM for the double-sided image reproduction. We derive an algorithm for double-sided CGH and experimentally demonstrate it.

Automatic elimination of phase aberrations in digital holography based on Gaussian 1σ- criterion and histogram segmentation.

We propose a numerical and automatic quadratic phase aberration elimination method in digital holography for phase-contrast imaging. A histogram segmentation method based on Gaussian 1σ-criterion is used to obtain the accurate coefficients of quadratic aberrations using the weighted least-squares algorithm. This method needs no manual intervention for specimen-free zone or prior parameters of optical components. We also propose a maximum-minimum-average-standard deviation (MMASD) metric to quantitatively evaluate the effectiveness of quadratic aberration elimination. Simulation and experimental results are demonstrated to verify the efficacy of our proposed method over the traditional least-squares algorithm.

Photoalignment of sub-micrometer periodic liquid crystal polarization grating by using the optical imprinting method.

Photoalignment of liquid crystal polarization grating based on optical imprinting is a promising technique for polarization grating mass production. However, when the period of the optical imprinting grating is in the sub-micrometer level, the zero-order energy from the master grating will become high, and it will strongly affect the photoalignment quality. This paper proposes a double-twisted polarization grating structure to eliminate the zero-order disturbance of master grating and gives the design method. Based on the designed results, a master grating was prepared, and the optically imprinted photoalignment of polarization grating with a period of 0.5μm was fabricated. This method has the advantages of high efficiency and significantly greater environmental tolerance than the traditional polarization holographic photoalignment methods. It has the potential to be used for large-area polarization holographic gratings production.

Computer-Generated Holography Methods for Data Page Reconstruction Using Phase-Only Medium

Achievements in the field of high-speed spatial modulation electrooptic components provide the possibility to create perspective optical-digital diffractive systems for information storage and processing that outperform modern electronic counterparts by utilizing throughput, energy efficiency, and reliability. This work presents a study of computer-generated holography methods that allow the formation of spatially-modulated information signals (data pages) with high accuracy using phase-only spatial light modulators. Computer-generated Fourier hologram fringe patterns were formed using bipolar intensity and double-phase coding. Numerical and experimental results of both methods’ implementation are compared. It was determined that bipolar intensity holograms provide higher data density on the data page if complex digital modulation methods such as multilevel amplitude and phase or quadrature modulation are used to represent data points. Double-phase coding can offer perspective for multilevel amplitude or multilevel intensity modulated data page reconstruction; however, exact control of phase modulation characteristics is required to obtain high reconstruction quality.

Compact reconstruction of a Fourier hologram for a 3D object by scaling compensation.

The Fourier holographic projection method is compact and computationally fast. However, since the magnification of the displayed image increases with the diffraction distance, this method cannot be used directly to display multi-plane three-dimensional (3D) scenes. We propose a holographic 3D projection method of Fourier holograms by scaling compensation to offset the magnification during optical reconstruction. To achieve a compact system, the proposed method is also used to reconstruct 3D virtual images with Fourier holograms. Different from traditional Fourier holographic displays, images are reconstructed behind a spatial light modulator (SLM) so that the observation position can be placed close to the SLM. The effectiveness of the method and the flexibility of combining it with other methods are confirmed by simulations and experiments. Therefore, our method could have potential applications in the augmented reality (AR) and virtual reality (VR) fields.

Повышение пространственного разрешения цифровых голограмм с помощью одномерного субпиксельного сканирования

The article considers the issue of increasing the spatial resolution during the registration of digital holograms. In practice, discretization is carried out by measuring signal samples using sensors with a certain finite aperture. The resolution is determined by the size of the aperture area over which the averaging takes place. The resolution enhancement method is based on the sampling equation for signals obtained by the subpixel shift method using generalized functions. A subpixel shift is carried out using a spatial shift by a value less than the element of resolution. Apertures of various shapes are used, for example, elliptical, diamond-shaped, hexagonal, but rectangular apertures are most commonly used. The discretization equation involves the use of a two-dimensional aperture function. Below is a way to increase the resolution when using a one-dimensional function. This can be done based on the structure of the holographic signal. In this case, you can use a subpixel shift in only one direction. Digital holography is distinguished by the fact that photodetector matrices which have a spatial resolution much lower than photographic media used in traditional holography methods are used to register the signal,. Therefore, digital holography uses optical schemes with small angles between interfering beams. However, certain restrictions are imposed on the shape of the objects under study. If the objects have a shape that is significantly different from a flat one, it is necessary to use traditional schemes. The article presents mathematical modeling of the resolution enhancement method based on the recovery of signals from a real hologram obtained in the usual way. The increase in resolution is achieved using a one-dimensional subpixel shift. The use of a one-dimensional subpixel shift makes it possible to significantly simplify the optical scheme of the holographic setup.

Spherical crown holographic display with planar SLM

Spherical holography can expand the viewing angle, while the unavailability of spherical spatial light modulators (SLM) and the huge sampling number are challenges for spherical holography. In this paper, we propose a spherical crown holographic display method based on planar SLM. First by analyzing the diffraction formula of concentric spheres, the relationship between it and the plane diffraction is found. Then it is proposed that a spherical hologram loaded on a commercial planar SLM can reproduce the target object correctly with a reasonable number of sampling points. The method can be combined with spatiotemporal multiplexing and curved multiplexing to further expand the viewing angle and information capacity, respectively. It provides a new perspective for spherical holography, and has broad prospects in the field of 3D holographic display.

Fractional Fourier-transform filtering and reconstruction in off-axis digital holographic imaging.

An off-axis digital holographic reconstruction method with fractional Fourier transform domain filtering is proposed. The theoretical expression and analysis of the characteristics of fractional-transform-domain filtering are given. It is proven that the filtering in a lower fractional-order transform domain can utilize more high-frequency components than that in a conventional Fourier transform domain under the same size of filtering regions. In simulation and experiment, the results demonstrate that the reconstruction imaging resolution can be improved by filtering in the fractional Fourier transform domain. The presented fractional Fourier transform filtering reconstruction provides a novel (to our knowlede) optional way for off-axis holographic imaging.

Statefinder diagnosis for Barrow agegraphic dark energy

Here, by employing a Barrow entropy and the standard holographic method at a cosmic framework, we formulate Barrow agegraphic dark energy (BADE), taking the Universe age as an IR cutoff scale in a flat FLRW Universe. For evaluation of statefinder parameters in [Formula: see text] and [Formula: see text] planes, trajectories have been plotted for BADE and discovered that for various values of [Formula: see text], the model exhibits both the behavior of Chaplygin gas and quintessence. Moreover, as a supplement to the statefinder study, we looked at the BADE model without interaction in the plane [Formula: see text], which might offer us a dynamic study using the energy density BADE parameter [Formula: see text] and [Formula: see text], as per VI-[Formula: see text]CDM observational data without interaction from Planck 2018 results.

An equivalent source method for holographic visualization of acoustic sources in an apertured enclosure based on exterior measurements

Most acoustical holography techniques are developed to visualize sound sources or reconstruct sound field in a free-space environment, where no boundary reflected or scattered sound are present. However, in some engineering applications, a sound scatter is an inseparable part of source mechanism. For example, for a centrifugal fan, the aerodynamic noise sources are the turbulent pressure inside the fan shell, but the source distribution is significantly altered if the fan shell is removed. Thus, in order to visualize the sources inside the fan shell by holography methods based on exterior sound measurements, the measurements need to be performed with the presence of the shell (which is a sound scatter). This obviously violates the free-space assumption for most acoustical holography methods. In this work, traditional free-space equivalent source methods are extended to visualize acoustic sources situated in an enclosure with openings based on sound measurements exterior to the enclosure. The key step is to replace the free-space Green’s function used in traditional equivalent source methods by a Green’s function that satisfies the boundary condition of the apertured enclosure. Simulations are performed to prove the concept of the proposed acoustical holography method.