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A modified nonlinear reconstruction technique with a noise modulation parameter is proposed for interferenceless coded aperture correlation holography (I-COACH), and thus the signal-to-noise ratio of a reconstructed image is improved without sacrifice of the field of view and temporal resolution of the system. In order to obtain the optimal reconstructed image, no-reference structural sharpness (NRSS) is introduced as the evaluation metric of reconstructed image quality during nonlinear reconstruction. On the other hand, the noise modulation function is built in order to analyze the effect of phase on noise when the amplitude of the point spread hologram and object hologram is unity of 1. Both the NRSS and noise modulation functions are combined with nonlinear reconstruction in I-COACH for improving imaging performance. The validities of the proposed method under different experimental conditions have been demonstrated by experiments.

Dual-wavelength arbitrary phase-shifting digital holography with automatic phase-shift detection is first proposed in this study. Holograms with two wavelengths and the interference fringes used to detect the phase-shifting amount for each wavelength were simultaneously recorded in one image using the space-division multiplexing technique. Compared with conventional methods, the proposed approach can achieve simultaneous phase shifting of the reference beams of two wavelengths, which substantially reduces recording time and does not require excessive phase-shifting device precision. The proposed and conventional methods were quantitatively evaluated with numerical simulations, and a dynamic deformation measurement was obtained using the system. In the quantitative evaluation of the simulation, the root-mean-square errors of amplitude and phase images reconstructed by the proposed method were reduced by 12% and 19% compared to the conventional method, respectively. Both numerical simulations and experiments verified the effectiveness of the proposed method.

A digital lensless holographic microscope (DLHM) sensitive to the linear diattenuation produced by biological samples is reported. The insertion of a linear polarization-states generator and a linear polarization-states analyzer in a typical DLHM setup allows the proper linear diattenuation imaging of microscopic samples. The proposal has been validated for simulated and experimental biological samples containing calcium oxalate crystals extracted from agave leaves and potato starch grains. The performance of the proposed method is similar to that of a traditional polarimetric microscope to obtain linear diattenuation images of microscopic samples but with the advantages of DLHM, such as numerical refocusing, cost effectiveness, and the possibility of field-portable implementation.

Dennis Gabor’s seminal idea of a simple all-optical setup aimed at reconstructing the object wavefront stored on a photographic plate gave birth a little over seven decades ago to the field of holography. In 1971 Gabor obtained the Nobel Prize in Physics for this invention. Still, the road in the early days after his two first papers on the subject was one full of obstacles, so his scientific and engineering contemporaries put his idea to rest for more than 10 years, until the invention of the laser. This fact made his holographic concept take off to new and unsuspected applications. This invited review paper is a homage to Dennis Gabor’s 50th anniversary of his Nobel Prize accolade. For this purpose, the review departs from the typical common route, i.e., those written following a timeline fashion, and instead is written with the intent to cover only a few of the holography applications in optics while scanning the electromagnetic spectrum. In doing this, the authors are aware that other invited papers for this special issue will tackle other subjects not dealt with in this review non-timeline paper.

The description, implementation, and validation of an ImageJ plugin that allows the realistic simulation and real-time reconstruction of digital holographic microscopy (DHM) experiments are presented. The simulation module implements a telecentric image-plane DHM recording scheme with fully configurable imaging system, interference, and scaling parameters, including the possibility of defining an estimate of the roughness distribution of the sample to produce realistic coherent-noise affectations. The reconstruction module allows the computation of amplitude, intensity, or phase, from digital holograms’ input as either single images or video streams for real-time processing; this module also implements user-defined fine-tuning parameters, allowing subpixel linear phase compensations and digital refocusing of the complex-valued reconstructed fields. In this note, the functionality of the plugin is illustrated by simulating the noisy DHM recording of a phase-only resolution test target and the reconstruction of both the resulting synthetic hologram and an equivalent experimental recording; the results show good agreement between the simulation and the experimental recording, and accurate measurements on the reconstructed information, thus granting the use of either module with full confidence according to needs and possibilities.

In this paper, we demonstrate a design for a laser picoprojector with a high rate of reduction in the speckle contrast value. The method utilizes a holographic diffuser, deformable mirror, and fast electrically tunable (FET) lens. Then we compare the reduction rate of the speckle contrast value for holographic diffusers with different divergence angles and an FET lens with different optical power ranges combined with a deformable mirror. The increase in reduction rate of speckle contrast value means that the minimum value of the speckle can be reached faster. There reduction rate increases from 4.76 to 5.74 for the 5 × 5 holographic diffuser, 3.45 to 5.66 for the 10 × 10 holographic diffuser, and 1.52 to 4.58 for the 30 × 30 holographic diffuser.

Ringing artifacts are the main noise sources in holographic projection when the quadratic phase is introduced to suppress speckle noise. In this study, the mechanisms of ringing artifacts on reconstructed images are theoretically analyzed, which illustrates the ringing artifacts are related to the bandwidth properties of the reconstructed wave field. Based on the frequency analysis, a band-limited iterative algorithm is proposed to optimize the phase hologram in the Fresnel domain. The proposed method can effectively suppress the ringing artifacts as well as the speckle noise of the Fresnel hologram by optimizing the phase distribution with bandwidth constraint. Numerical simulations and optical experiments have been performed to validate the proposed method for providing quality reconstructions in lensless holographic projection.

In this study, we reveal a novel aerial display system, to the best of our knowledge, that combines volume hologram mirrors with a dihedral corner reflector array (DCRA). The suggested aerial display has a see-through capability, which allows for a new design of aerial displays by combining with other types of displays. Furthermore, the virtual image, which frequently disrupts the observation of aerial images, can be suppressed by the Bragg condition of the volume hologram. The color dispersion in the holograms is efficiently compensated by employing features of the DCRA. The findings of preliminary experiments are demonstrated using a DCRA device and full-color hologram mirrors.

Compressive holography can successfully reconstruct a three-dimensional layered object from a two-dimensional hologram. However, the extremely time-consuming reconstruction limits its range of applications. We propose a dimension reduction of measurement matrix (DRMM) method to accelerate compressive holographic reconstruction. The calculation time is substantially reduced while the reconstruction quality is improved by DRMM, which is implemented by a hologram segmentation approach and a parallel computing technique. Holograms of specific target objects are segmented from the hologram of a three-dimensional layered object, and the reconstruction can be implemented in parallel using multicore processors. We present both simulation and experimental results to show the feasibility and effectiveness of the proposed method.

The accuracy of particle detection and size estimation is limited by the physical size of the digital sensor used to record the hologram in a digital in-line holographic imaging system. In this paper, we propose to utilize the autoregressive (AR) interpolation of the hologram to increase pixel density and, effectively, the quality of hologram reconstruction. Simulation studies are conducted to evaluate the influence of AR interpolation of a hologram on the accuracy of detection and size estimation of single and multiple particles of varying sizes. A comparative study on the performance of different interpolation techniques indicates the advantage of the proposed AR hologram interpolation approach. An experimental result is provided to validate the suitability of the proposed algorithm in practical applications.

We propose a new learning and inferring model that generates digital holograms using deep neural networks (DNNs). This DNN uses a generative adversarial network, trained to infer a complex two-dimensional fringe pattern from a single object point. The intensity and fringe patterns inferred for each object point were multiplied, and all the fringe patterns were accumulated to generate a perfect hologram. This method can achieve generality by recording holograms for two spaces (16 Space and 32 Space). The reconstruction results of both spaces proved to be almost the same as numerical computer-generated holograms by showing the performance at 44.56 and 35.11 dB, respectively. Through displaying the generated hologram in the optical equipment, we proved that the holograms generated by the proposed DNN can be optically reconstructed.

It is difficult to find the micromirror array with desired specifications for augmented-reality displays, and the custom fabricating methods are complicated and unstable. We propose a novel, to our knowledge, three-dimensional see-through augmented-reality display system using the holographic micromirror array. Unlike the conventional holographic waveguide-type augmented-reality displays, the proposed system utilizes the holographic micromirror array as an in-coupler, without any additional elements. The holographic micromirror array is fabricated through the simple, effective, and stable method of applying the total internal reflection-based hologram recording using a dual-prism. The optical mirror and microlens array are set as references, and the specifications can be customized. It reconstructs a three-dimensional image from a displayed elemental image set without using any additional device, and the user can observe a three-dimensional virtual image while viewing the real-world objects. Thus, the principal advantages of the existing holographic waveguide-type augmented-reality system are retained. An optical experiment confirmed that the proposed system displays three-dimensional images exploiting the augmented-reality system simply and effectively.

To determine the methods of color measurement and color-difference calculation for holographic prints with light pillars, 94 pairs of holographic prints constituted by 17 different products were collected. A set of color-difference comparison experiments was organized by 64 observers with normal color vision, and a total of 86 groups of visual judgments were gathered. The CIELAB and CIEDE2000 color-difference values were calculated on the basis of the analysis of the microstructures of gratings distributed on the holographic paper. The performances of the original formulas were evaluated in terms of the standardized residual sum of squares index, and then they were optimized considering the power function effects ( a , b factors) together with a contribution from lightness ( k L factor). Meanwhile, the color-difference threshold of the holographic prints was estimated with a goal to minimize the number of wrong decision in the visual experiment; therefore, the values were set as 2.50 and 2.00 for the original CIELAB and CIEDE2000 with the consistency of 91.5% and 98.9%, respectively. The results can also provide guidance to evaluate the color quality of the holographic prints with light pillars in the packaging and printing industries.

The modal holographic wavefront sensor enables fast measurement of individual aberration modes without the need for time-consuming calculations. However, the measurement accuracy suffers greatly from intermodal crosstalk, caused when the wavefront contains more aberrations than the one to be measured. In this paper, we present sensor optimization to minimize this effect and show the improvement when using Karhunen–Lòeve instead of Zernike modes as the basis. Finally, we show in simulation that an open-loop adaptive optics system based on the optimized sensor can be used to correct the effect of realistic, dynamic atmospheric turbulence on a wavefront and increase its Strehl ratio significantly.

Single-shot higher-order transport-of-intensity quantitative phase imaging (SHOT-QPI) is proposed to realize simple, in-line, scanless, and single-shot QPI. However, the light-use efficiency of SHOT-QPI is low because of the use of an amplitude-type computer-generated hologram (CGH). Although a phase-type CGH overcomes the problem, the accuracy of the measured phase is degraded owing to distortion of the defocused intensity distributions, which is caused by a quantization error of the CGH. Alternative SHOT-QPI with the help of deep learning, termed Deep-SHOT, is proposed to solve a nonlinear problem between the distorted intensities and the phase. In Deep-SHOT, a neural network learns the relationship between a series of distorted intensity distributions and the ground truth phase distribution. Because the distortion of intensity distributions is intrinsic to an optical system, the neural network is optimized for the system, and the proposed method improves the accuracy of the measured phase. The results of a proof-of-principle experiment indicate that the use of multiple defocused intensities also improves accuracy, even the nonlinear problem.

This paper describes the dependence of the precision of digital holographic methods on measurement parameters. The predominantly discussed parameters are illumination intensity and its homogeneity, surface microroughness, the influence of measurement geometry, as well as object shape, since most of them can be optimized by experimental arrangement. Frequency sweeping digital holography as well as dual-wavelength digital holography in the Fourier arrangement are tested and the results are discussed. It transpires that the methods are not very sensitive to object microroughness or overall reflectivity. Instead, it is the similarity of signal and reference waves that has the highest impact on measurement. After parameter optimization, the holographic methods can be advantageously used for ground surface measurements in optical workshops.

One shortcoming of digital in-line holography (DIH) is the low axial position accuracy due to the elongated particle traces in the reconstruction field. Here, we propose a method that improves the axial localization of DIH when applying it to track the motion of weak phase particles in dense suspensions. The proposed method detects particle positions based on local intensities in the reconstruction field consisting of scattering and incident waves. We perform both numerical and experimental tests and demonstrate that the proposed method has a higher axial position accuracy than the previous method based on the local intensities in the reconstructed scattered field. We show that the proposed method has an axial position error below 1.5 particle diameters for holograms with a particle concentration of 4700 p a r t i c l e s / m m 3 . The proposed method is further validated by tracking the Brownian motion of 1 µ m p a r t i c l e s in dense suspensions.

Sharpness metric maximization is a method for reconstructing coherent images that have been aberrated due to distributed-volume turbulence. This method places one or more corrective phase screens in the digital-propagation path that serve to increase overall sharpness of the image. As such, this study uses sharpness metric maximization on 3D irradiances obtained via frequency-diverse digital holography. We vary the number of corrective phase screens in the propagation path and sharpen images of a realistic, extended object via multi-plane sharpness metric maximization. The results indicate that image reconstruction is possible when using fewer corrective screens than aberrating screens, but that image quality increases with a greater number of corrective screens.

An off-axis digital holographic imaging polarimeter was developed to estimate the Jones matrices of an object. The Jones vector image of the electric field returned from the object is determined from a single holographic recording using the interference between the dual, nearly orthogonal, reference beams. The technique compensates for phase variations in the optical beam paths between the recorded holograms and relaxes the need to generate orthogonal illumination polarization states. A minimization algorithm was developed to compute an estimation of the Jones matrix image of an object based on a set of measured Jones vector images. A proof-of-concept demonstration was performed to compute an estimated Jones matrix image of a polarimetrically complex object using digital holograms recorded with 6 different illumination polarizations.

Modal decomposition (MD) has become an indispensable analysis approach for revealing the modal characteristics of optical fibers. A new MD approach based on the convolutional neural network (CNN) is presented to retrieve the exact superposition of eigenmodes of few-mode fibers. Using the near-field beam intensity and phase patterns obtained from digital holography, not only the amplitude of each eigenmode but also the exact phase difference between the higher-order modes and the fundamental mode can be predicted. Numerical simulations validate the reliability and feasibility of the approach. When ten modes in the few-mode fiber are considered, the similarities of the intensity and phase pattern between the reconstructed fields and the given fields can achieve to 97.0% and 85.6%, respectively.

Incoherent digital holography (IDH) requires no spatial coherence; however, it requires high temporal coherence for a light source to capture holograms with high spatial resolution. Temporal coherence is often enhanced with a bandpass filter, reducing the light utilization efficiency. Thus, there is a trade-off between spatial resolution and light utilization efficiency. In this paper, we derive a relationship between spatial resolution and temporal coherence by including a conceptual aperture, determined by temporal coherence, in our previous theory of spatial resolution for arbitrary depth planes [Opt. Express 27, 33634 (2019)OPEXFF1094-408710.1364/OE.27.033634]. Experimental evaluations verified the effectiveness of our theory, which is useful for the optimization of IDH setups and avoiding the trade-off.

We propose a method to enlarge the field of view (FOV) of holographic 3D displays in both the horizontal and vertical directions. The FOV was enlarged by using two galvano mirrors and a high-speed spatial light modulator. These optical elements were placed so that the imaging relation was satisfied among them and they were synchronously driven at a high speed to implement the time-division method. Using this method, a floating 3D object could be successfully reconstructed in mid-air near the focal point of the final lens at the rate of 10 Hz. The FOV was enlarged five times and two times in the horizontal and vertical directions, respectively.

The study focuses on a methodology providing noninvasive monitoring and evaluation of the antitumor effect of traditional Chinese medicine, cantharides complex (canth), on 4T1 breast tumor cells. Digital holographic tomography (DHT) and developed data post-processing algorithms were used for quantitative estimation of changes in optical and morphological parameters of cells. We calculated and compared data on the refractive index, thickness, and projected area of 4T1 breast tumor cells in control untreated specimens and those treated with doxorubicin hydrochloride (DOX), canth, and their combinations. Post-treatment changes in cellular morphology recorded by DHT demonstrated that the two drugs led to noticeably different morphological changes in cells that can be presumably associated with different pathways of their death, apoptosis, or necrosis. The effect of combined treatment with these two drugs strongly depended on their relative concentrations and could lead to changes characteristic either for DOX or for canth; however, being more profound than those obtained when using each drug solely. The results obtained by DHT are in a good correspondence with commonly used cell viability analysis and immunofluorescent analysis of changes in cellular cytoskeleton.

Sound is an important invisible physical phenomenon that needs to be explained in several physical and biological processes, along with visual phenomena. For this purpose, multiparameter digital holography (DH) has been proposed to visualize both features simultaneously due to the phase and amplitude reconstruction properties of DH. In this paper, we present a brief review on sound field imaging techniques with special focus on the multiparameter imaging capability of DH for visualizing sound and visual features. The basic theory and several experimental results with very high-speed recordings are also presented to demonstrate sound field imaging for the audible range as well as in the ultrasound range.

Digital light-in-flight recording by holography is a promising technique for observing a propagating ultrashort light pulse as a motion picture. A typical reconstruction process of digital light-in-flight recording by holography, we extract holograms without considering the relationship between the lateral size of the extracted hologram (sub-hologram) and the size of an area where the propagating ultrashort light pulse and an image sensor overlap. The area records the image of the ultrashort light pulse at a certain moment. In this study, by considering the size of the small interference fringe image, we assessed the influence of the lateral size of the hologram on the reconstructed image. We defined the size of the area in which the interference fringe image at a moment is recorded. Then, we examined the reconstructed images by changing the lateral size of the sub-hologram. As a result, we found that the lateral size of the hologram does not affect the size of the reconstructed image but the spatial resolution of the reconstructed images.

Digital holography (DH) with two wavelengths (TW) that are close to each other was applied to height measurement of solder bumps having spherical specular surfaces with diameters of ∼ 20 µ m and heights of ∼ 20 µ m . We employed the parallel phase shifting method for instantaneous image capturing, and we improved the spatial resolution of our TW-DH system having two beams with different wavelengths that traveled in opposite directions in the interferometer. It gave 74-times higher repetition and 2.4-times higher spatial resolution than those in our previous DH system based on the Fourier transform method.

This feature issue of Applied Optics is dedicated to the international meeting of Information Photonics 2020 (IP’20), which was held September 11–12, 2020, in Taipei, Taiwan. IP’20 covered a broad range of topics, including advanced display techniques, optical computing, and optical storage. This feature issue, however, limits topics to unconventional imaging techniques, such as digital holography, artificial-intelligence associated imaging, compressive imaging, and single-pixel imaging.

Recently, an optical scanning holographic system with a polarization directed flat lens was proposed to realize coaxial scanning holography (CSH). The advantage of CSH is its small form factor and the stability. However, the diffraction efficiency of the polarization directed flat lens cannot be 100%, and thus there is always zeroth order light in the scanning beam. The imperfect diffraction property of the polarization directed flat lens results in an incomplete scanning Fresnel zone plate. Consequently, the reconstructed image is blurred and noisy. In this paper, we compared different methods, including the back propagation, the phase correlation, and inverse filtering, for the hologram reconstruction. It is demonstrated that inverse filtering is the only method that can retrieve the high-frequency component of the hologram. However, additional noise also arises with the use of inverse filtering. Therefore, the imaging performance of CSH by using a polarization directed flat lens is inherently worse than that of conventional OSH.

International audience; The purpose of this work is to provide theoretically grounded assessment on both the field-of-view and the bandwidth of a lensless holographic setup. Indeed, while previous works have presented results with super-resolution and field-of-view extrapolation, there is no well established rules to determine them. We show that the theoretical field of view can be hugely large with a spatial-frequency bandwidth only limited by the wavelength leading to an unthinkable number of degrees of freedom. To keep a realistic field of view and bandwidth, we propose several practical bounds based on few setup properties: namely the noise level and the spatio-temporal coherence of the source.

Digital holographic microscopy (DHM) is a technique that has high potential for analyzing biological samples and has been successfully applied to the study of cells and cell lines providing information about important parameters such as refractive index, morphology, and dry mass, among others; it has also found applicability to study the effects of therapeutic treatments. Finding the size and shape of cells is important since they tend to change in the presence of some pathologies. In this research work, we obtain the morphology thickness and refractive index of the A375 melanoma cell line through a slight tilting of the cell in a DHM setup. Further, the development of a novel mathematical expression based on this tilt and in the optical phase difference is presented. We show images of melanoma cells with the refractive index information included, and their morphology thickness as rendered from the holographic phase maps recorded with DHM.

To computer-generate high-quality holographic stereograms, a huge number of images must be provided: several hundred for a horizontal parallax and the square of this number for a full parallax. In this paper, we propose to drastically reduce this number to four input images with depth maps (or equivalently, four groups of neighboring images used to compute a depth map) in any pose, in order to create the missing images with depth image-based rendering. We evaluate the view synthesis method objectively before providing visual results of the corresponding holographic stereograms. We believe this method outperforms shearlet-based approaches in objective view synthesis quality metrics and in the number of required input images (7×7)., info:eu-repo/semantics/published

In this work, quality evaluation of a reconstructed amplitude image in digital holography is presented. The digital holograms are recorded using three different digital holographic experimental configurations, namely, conventional off-axis digital holography, concave-lens-based digital holography, and the digital holographic camera developed for non-destructive testing applications [Opt. Lasers Eng. 137, 106359 (2021)OLENDN0143-816610.1016/j.optlaseng.2020.106359]. The quality of reconstructed images is measured by calculating the quality evaluation parameters such as speckle index, peak signal-to-noise ratio, and structural similarity index measure for these experimental configurations. Optimization of the power of the light source and exposure time of the recording sensor is performed for the three configurations based on the quality evaluation of reconstructed images. A comparison of the quality of reconstructed images is made for the three experimental configurations to analyze their performance for different source power and exposure time of the recording image sensor.

This paper describes the experiment on multiplexing recording using a phase mask to create augmented reality waveguides. The study is distinguished by the application of photo-thermo-refractive glass as both holographic and substrate materials. The presented approach allows us to obtain the diffraction efficiency above 15% in each of the multiplexed gratings for sevenfold recording. The images output with the manufactured planar waveguide prototype are presented.

Lookup table (LUT) and wavefront recording plane (WRP) methods are proposed to accelerate the computation of fully computed hologram stereograms (HSs). In the LUT method, we precalculate large and complete spherical wave phases with varying depths, and each complex amplitude distribution segment of the object point can be obtained quickly by cropping a specific and small part of the precalculated spherical wave phases. Then, each hologram element (hogel) can be calculated by superposing all the related segments. In addition, setting a WRP near the 3D scene can further accelerate computation and reduce storage space. Because the proposed methods only replace the complex calculation using referencing LUT, they are accurate and have no limitation on the size of hogel compared with some methods of paraxial approximation. Simulations and optical experiments verify that the proposed methods can reconstruct quality 3D images with reduced computational load.

The demand for single-shot and common-path holographic systems has become increasingly important in recent years, as such systems offer various advantages compared to their counterparts. Single-shot holographic systems, for example, reduce computational complexity as only a single hologram with the object information required to process, making them more suitable for the investigation of dynamic events; and common-path holographic systems are less vibration-sensitive, compact, inexpensive, and high in temporal phase stability. We have developed a single-shot common-path off-axis digital holographic setup based on a beam splitter and pinhole. In this paper, we present a concise review of the proposed digital holographic system for several applications, including the quantitative phase imaging to investigate the morphological and quantitative parameters, as a metrological tool for testing of micro-optics, industrial inspection and measurement, and sound field imaging and visualization.

We present color fluorescence imaging using an incoherent digital holographic technique in which holographic multiplexing of multiple wavelengths is exploited. Self-interference incoherent digital holography with a single-path in-line configuration and the computational coherent superposition scheme are adopted to obtain color holographic three-dimensional information of self-luminous objects with a monochrome image sensor and no mechanical scanning. We perform not only simultaneous color three-dimensional sensing of multiple self-luminous objects but also color fluorescence imaging of stained biological samples. Color fluorescence imaging with an improved point spread function is also demonstrated experimentally by adopting a Fresnel incoherent correlation holography system.

In this work, a numerical method to enhance the contrast of intensity hologram reconstructions of digital lensless holographic microscopy (DLHM) is presented. The method manipulates the in-line hologram and reference images through mathematical operations between them; additionally, a sharpening operation, functionalized in terms of the parameters of the recording setup, is applied to the said images. The preprocessing of the recorded images produces a modified in-line hologram and a reference wave image from which an intensity reconstruction with a 25% improvement of its contrast, with respect to the conventional reconstruction procedure, is achieved. The method is illustrated with intensity reconstructions of a hologram of a monolayer of polystyrene spheres 1.09 µm in diameter. Finally, the preprocessing method is validated with a modeled hologram, successfully applied to holograms of the section of the head a Drosophila melanogaster fly and its results are contrasted with those obtained via bright-field microscopy.

In a digital hologram, the maximum viewing angle of a computer-generated hologram (CGH) is limited by pixel pitch due to the diffraction grating equation. Since reducing pixel size of display panel is challenging and costly, we propose a method to expand the viewing angle of a digital hologram by attaching an aligned pixelated random phase mask (PRPM) onto the CGH pattern based on analysis of simulation results. By introducing a phase-averaging process to the widely used iterative Fourier transform algorithm, an optimized CGH pattern can be obtained in conjunction with a PRPM. Based on scalar diffraction theory, viewing angle enhancement characteristics were verified by comparing the perspective views of a two-plane hologram using a virtual eye model. In addition, we performed full electromagnetic simulations that included effects due to potential fabrication errors such as misalignment, thickness variation, and internal reflections and diffractions between the CGH and random mask patterns. From the simulation results, by attaching a 1.85 µm-sized pixel pitch PRPM to a 3.7 µm CGH, the viewing angle can be easily expanded almost identical to that of a CGH with 1.85 µm-pixel pitch.

We present spatially resolved measurements of the below-band-gap carrier-induced absorption and concurrent phase change in a semiconductor with the help of transmission digital holography. The application is demonstrated for a bulk GaAs sample, while the holograms are recorded with a conventional CMOS sensor. We show that the phase information enables spatially resolved monitoring of excess carrier distributions. Based on that, we discuss a phase-based approach for separation of carrier and heat related effects in the semiconductor optical response.

Remote detection of spectral line emission is an important capability in a number of areas, including defense and environmental science. In this paper, we report on a mechanism for spectral line emission detection that is not based on narrow bandpass filters or hyperspectral imagers, but is instead based on the use of switchable spectral filters. The use of a switchable filter enables a single sensor to perform remote sensing tasking in a broad passband, while also detecting emission in a particular spectral line. In this case, the switchable spectral filter studied is a holographic polymer dispersed liquid crystal (HPDLC) reflection grating. The concept is demonstrated through modeling a sensor with an integrated HPDLC filter and building a detection algorithm capable of detecting spectral line emission. The modeling framework is built upon four components: the background scene, the spectral line source, the HPDLC filter, and the sensor. Results from the model show probability of detection and probability of false alarm for spectral line sources of varying strength for a particular background scene.

The performance of direct and unwrapped phase retrieval, which combines digital holography with the transport of intensity, is examined in detail in this paper. In this technique, digital holography is used to numerically reconstruct the intensities at different planes around the image plane, and phase retrieval is achieved by the transport of intensity. Digital holography with transport of intensity is examined for inline and off-axis geometries. The effect of twin images in the inline case is evaluated. Phase-shifting digital holography with transport of intensity is introduced. The performance of digital holography with transport of intensity is compared with traditional off-axis single- and dual-wavelength techniques, which employ standard phase unwrapping algorithms. Simulations and experiments are performed to determine and compare the accuracy of phase retrieval through a mean-squared-error figure of merit as well as the computational speeds of the various methods.

We introduce the digital holographic microscope for recording in vivo human eye retinal structures. Current eye imaging technologies cannot provide images with resolutions better than 1 µm within depths of a few hundred micrometers. This can be improved with digital holography, in which a hologram of the eye captured with digital camera contains information about structures over the full depth of the eye. This information can be reconstructed either optically or numerically. Our hologram recording scheme utilizes working principles of the off-axis digital holographic microscope, designed for reflective micro-object investigation. The eye cornea and lens form the microscope objective. We can record in vivo digital holograms of the human eye retina with resolution after reconstruction of at least 1.3 micrometer.

Atomization of low temperature fuel is of great importance in a jet engine combustor, and its visualization and diagnostics are challenging, especially in the presence of shreds and ligaments. A 25 kHz picosecond pulsed digital inline holography system is applied to measure the spray produced by an airblast atomizer with low temperature kerosene. The breakup process of shreds and ligaments of − 37 ∘ C kerosene are visualized and analyzed, revealing the transition of liquid jet disintegrating into droplets under the atomizing air film. Three-dimensional positions and size distributions of droplets in spray are acquired. It is found that a decrease in the kerosene temperature increases shreds and ligaments in the spray, which eventually leads to reduction of droplet density and increase of droplet size, while increasing the air pressure can compensate the degradation. This work also demonstrates that high speed holographic imaging is a powerful tool in spray diagnostics and liquid breakup visualization.

Time average digital holography under random excitation or square wave excitation is established as an on-site non-destructive testing tool for defect detection in large metallic and composite sandwich structures due to its high sensitivity, single exposure interferogram, and fast inspection capability. However, extensive calibration studies are necessary to corroborate the defect type and defect size with the excitation frequency range and excitation magnitude. In this paper, a method to simulate a time average digital holographic fringe pattern under random excitation is proposed with the idea to minimize the number of calibration experiments and also for better evaluation of the size and type of defect. The proposed method circumvents the requirement for a closed form expression for the complex characteristic fringe function for time average interferometry under random excitation. The computed fringe pattern is illustratively compared with an experimental time average digital holographic fringe pattern.

Pupil expansion using waveguide propagation and pupil replication has been a popular method of developing head-up displays and near-to-eye displays. This paper examines one of the limits of pupil replication, which involves projecting images at a finite distance through a single waveguide by holographic optical elements and seeing the image doubling artifact. A Zemax model and a demonstrator were developed to determine the cause of image doubling. A relationship between the designed outcoupled image distance of a waveguide, pupil size, optical path length, and angle of image doubling is established. In waveguide pupil replication, the internally propagating light should be close to collimated to mitigate image doubling. We also provide a solution to project the image at different distances, which is an important factor for some applications, such as automotive head-up display and the seamless integration of augmented reality information with the natural environment.

Digital micro-mirror devices (DMDs) are a popular alternative to liquid crystal spatial light modulators for laser beam shaping due to their relatively low cost, high speed, and polarization and wavelength independence. Here we describe in detail how to convert a low-cost digital light projector (DLP) evaluation module that uses a Texas Instruments DLP4710 DMD into a spatial light modulator using a 3D printed mount. The resulting device is shown to accurately shape Laguerre–Gauss modes, is able to operate in real-time over HDMI without modification with a 180 Hz hologram refresh rate, and has a resolution of 1920 × 1080 pixels and diagonal screen size of 0.47 inches (11.9 mm).

In this work, we introduce a mixed complex and phase only constraint to the Gerchberg–Saxton (G–S) algorithm, leading to improvements in the generation of holograms from multiplane light field distributions. To achieve this, we determine the optimal weight factor for the complex and phase only part of a light field in every plane to achieve the best accuracy. We also demonstrate how this approach can be used to generate encrypted holograms that can only be reconstructed by illumination with a determined phase profile. In this way, we enable the possibility for secure, high-quality multiplane projection and display. We show numerical results for the generation of standard and encrypted seven-plane holograms, as well as the comparison with the conventional G–S algorithm.

We show an in-line digital holographic image reconstruction from subsampled holograms with resolution improvement and lensless magnification with high noise immunity by a compressive sensing approach. Our method treats the sensed field as subsampled, low-pass filtered and projected on a Fresnel–Bluestein base in an inverse problem approach to image reconstruction with controlled lensless magnification. So, we have demonstrated by simulation and experimental results that the approach can reconstruct images with quality even when used in holograms obtained from unusual subsampling schemes.