This PDF file contains the front matter associated with SPIE Proceedings Volume 12910, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Real time generation has been achieved for 4K full color rainbow hologram with normal PC. A line source approximation can accelerate computation speed 1.3 to 2.6 times faster than the previous result, depending on object points. In the approximation, each point in the object is converted to truncated line source. It makes 2D hologram calculation to 1D and calculation speed is increased. Although the rainbow hologram sacrifices vertical parallax, it can be generated faster than image hologram and full color image can be reconstructed with single SLM. Experimental results show that holograms are generated and displayed about 50 frames per second with 140,000 points and full color reconstructed images are observed.

Computer-generated hologram (CGH) techniques have advanced in the field of display technology, capable of reproducing three-dimensional images. The reconstructed three-dimensional images of the CGHs, however, usually contain speckle noises due to random phase distribution applied in the CGH synthesis. The random distribution of the speckle noise makes the traditional metrics like peak signal-to-noise ratio (PSNR) and structural similarity index map (SSIM), which are generally used in image quality evaluation, become less reliable. In this paper, we propose a novel method to evaluate the speckled CGHs using a deep neural network.

A stereoscopic image consists of a left and a right view, produced by two optical sensors, of the same scene from two slightly distant viewpoints, but imperatively at the same height and distance from the foreground. These two views are then presented to an observer in such a way that the image from the left camera is seen only by the left eye, and the image from the right camera by the right eye, to give a relief effect. This effect is created by parallax. Since the mid-nineteenth century, various manufacturers have produced dual-lens cameras, and entire collections of stereoscopic photographs of great historical and artistic interest still exist, but are rarely shown. This research demonstrates that it is possible to create 3D holograms from any pair of stereoscopic images, using the latest artificial intelligence techniques, combined with CHIMERA, the latest generation of digital holographic printing system, and to make this heritage more accessible to the general public.

Digital holography (DH) has become a promising tool in various research fields for acquiring quantitative phase information (QPI). However, its reliance on high-coherence light sources such as lasers often leads to speckle noise, which degrades image quality. Although low-coherence sources like light-emitting diodes (LEDs) can mitigate this noise, they struggle to create complete interference patterns for specimens with optical path differences exceeding their coherence length. This trade-off between high coherence and low speckle noise presents a significant challenge in DH, particularly in applications requiring long coherence lengths for accurate QPI. Our research addresses this challenge with an AIpowered approach. By training an AI model with paired hologram data from lasers and LEDs operating at the same peak wavelength, we have developed a method to reduce speckle noise while preserving the coherence length. The newly proposed method has been verified on reflective specimens using a Michelson interferometer. The resulting holograms from this AI model exhibit clear interference patterns over depths that match the laser’s coherence length, while simultaneously achieving significantly reduced speckle noise, akin to that observed in LED holography.

Multi-wavelength holography is a convenient method for the inline inspection of industrially machined parts. Compared with the single-wavelength approach, the unambiguity range can be extended by orders of magnitude. This is typically achieved by using multiple lasers. The smaller their wavelength difference, the larger is the unambiguity range. Reaching the centimeter or even meter range is difficult with individual lasers because of their relative wavelength drift. Here, we demonstrate multi-wavelength holography with 37.5 cm unambiguity range using only one single laser. The wavelength shifts are achieved with acousto-optic modulators driven at 200 MHz and 1 GHz. This provides unambiguity ranges of 37.5 and 7.5 cm respectively. Importantly, the perturbation caused by a possible long-term drift of the laser is significantly reduced. For a proof-of-concept demonstration, we determine the shape of a metallic object comprising height differences between 1 and 100 mm. The scheme can be extended to larger frequency shifts, i.e. better axial resolution, by using electro-optic modulators. This would enable to conveniently select the measurement range between some millimeters and meters although only one laser is used.

High-precision applications of multiwavelength holography typically requires stable laboratory-like environments, which is hard to achieve in industrial applications. The influence of schlieren is crucial, especially in large fieldof-view applications, where long working distances can result in optical paths up to one meter. Schlieren is a well-known effect in interferometry and can be seen in the reconstructed object wavefronts. Small perturbations in temperature change the refractive index of air resulting in local variations of the optical path. Proper encapsulation or vacuum techniques are typically employed to compensate for this. In this work, we investigate the impact of schlieren on multiwavelength holography and propose a compensation method. The sensor used is a Mach-Zehnder-based interferometer with a field-of-view of 17.9 mm × 13.4 mm and a camera with 9344 px×7000 px. A mirror was positioned at a distance of 1 m in front of the sensor. We performed holographic and interferometric measurements with and without an encapsulating pipe around the beam to investigate the influence of schlieren. The deviations of the phase shifts of the holographic data were laterally resolved using a modified version of the algorithm proposed by Cai et al. The fringe patterns of the interferometric data captured with different exposure times and frame rates were analyzed using a sinusoidal fit and discrete Fourier transformations (DFT) to show lateral frequency deviations. Both methods show that encapsulation leads to improved measurements. A potential compensation method is proposed.

We present a novel approach for on-axis range selective phase shifting digital holographic imaging using a Timeof-flight (TOF) camera and temporal heterodyning (TH). The modulated arrayed detection of a TOF camera allows for integration of holograms at a selected range using chirped frequency modulated continuous wave (FMCW) techniques. The achieved range resolution is significantly better than the optical system’s depth of field. Each pixel of the TOF camera is equipped with a photonic mixing device (PMD) that facilitates gated integration with an internal reference frequency. Our innovative technique leverages the unique capabilities of a TOF camera where the required four phase shifted images, used in phase shifting digital holography (DH) reconstruction, are recorded by changing the phase shift of the TOF camera’s internal modulation frequency. The heterodyne method of recording the phase shifted holograms also filters out any background light not at the internal modulation frequency of the TOF camera. Our range selective TH FMCW DH system successfully performs imaging for both image and Fresnel holograms for target distances of approximately 80 centimeters and 95 centimeters. In this experiment we used a 2.39 GHz FMCW chirp bandwidth, which resulted in an achieved range resolution of 6.3 cm. The performance of range selectivity is further analyzed by computing extinction percentages, which quantify the amount of light removed from unselected targets. In all recording geometries, we achieved extinction percentages of over 96%.

The use of a frequency modulated continuous wave (FMCW) coherent source for both the illumination and reference beam enables range-selective digital holographic imaging. When the frequency of the reference beam is shifted by the FMCW beat frequency associated with an object at a particular range, only the light scattered from objects at that selected range forms a temporally stable interference pattern on the sensor. Thus, only objects at the selected range are present in the reconstructed image. Interference patterns from light scattered from objects outside the selected range integrate towards zero. This enables the removal of foreground scattered light from particles (for example, dense fog) that obstructs the object of interest and reduces contrast. To demonstrate this, a four-meter-tall range-extending tower with mirrors at the top and base (which create multiple reflections, and multiple passes through the tower), is used to achieve beam path lengths up to 50 meters on the optical bench. Scattering plates in the tower are used to emulate volumetric Mie scattering, analogous to dense fog. The holographic images are recorded using an off-axis digital holography setup that operates at 1550 nanometers. We demonstrate range-selective digital holographic imaging of objects up to 24 meters with range selectivity much shorter than the optical system’s depth of field.

Volume holographic optical elements (vHOES) are currently used in various applications, like augmented reality displays or wearables. Yet, the use of vHOEs as illumination optics has not found its way into products. In automotive exterior lighting vHOEs could enable unique styling, reduction of installation space, weight, and material. However, in headlamps, rear lamps, or signal lamps, several technical and conceptional challenges must be addressed. One of these challenges is to replace lasers, which are expensive and have high safety demands, by light emitting diodes (LEDs), which are widely used in the field of automotive lighting. The reconstruction of volume holograms with LEDs is straightforward for graphical holograms showing a three-dimensional scene. For automotive exterior lighting, however the hologram is not just a design element, but in addition must feature a light distribution fulfilling all the legal requirements. The vHOE thus becomes the most important functional element of the lighting system. For instance, the low beam distribution must provide a sharp, asymmetric cutoff line and white color, which turns out to be difficult. We have developed an improved manufacturing technique of such vHOEs, using two spatial light modulators (SLMs). In this paper we present the design, the holographic printer setup, and first experimental results of vHOE samples.

Bayfol® HX photopolymer films prove themselves as easy-to-process recording materials for volume holographic optical elements (vHOEs) and are available in customized grade at industrial scale. Their full-color (RGB) recording and replay capabilities are two of their major advantages. Moreover, the adjustable diffraction efficiency, tunable angular and spectral selectivity of vHOEs recorded into Bayfol® HX as well as their unmatched optical clarity enables superior invisible “off Bragg” optical functionality. As a film product, the replication of vHOEs in Bayfol® HX can be carried out in a highly cost-efficient and purely photonic roll-to-roll (R2R) process. Utilizing thermoplastic substrates, Bayfol® HX was demonstrated to be compatible to state-of-the-art plastic processing techniques like thermoforming, film insert molding and casting, which opened up using a variety of industry-proven integration technologies for vHOEs. Therefore, Bayfol® HX makes its way in applications in the field of augmented reality such as Head-up-Displays (HUD) and Head-mounted-Displays (HMD), in free-space combiners, in plastic optical waveguides, and in transparent screens. Also, vHOEs made from Bayfol® HX are utilized in highly sophisticated spectrometers in astronomy as well as in narrow band notch filters for eyeglasses against laser strikes and retail optics. See through applications such as, HMD and HUD, have demanding performance requirements on combiner and imaging technologies such as efficiency, optical function, and clarity. The properties of Bayfol® HX make it principally well suited to solve these challenges in primary display, and near-infrared imaging applications such as eye-tracking. Based on a customizable and available toolbox, Bayfol® HX can be adopted for a variety of such applications. To serve further sensing applications we recently extended our chemical toolbox to address the photo sensitization beyond RGB into the Near Infrared Region (NIR), and reported already on various demonstration examples. On our way to generate a standardized Bayfol® HX film sensitized in the NIR - comparable to Bayfol® HX200 sensitized for RGB - we investigated the initiation mechanism in greater detail for this tailored NIR photoinitiation system and report on the performance characteristics of the envisaged standardized NIR sensitized Bayfol® HX film fabricated on the production coating line.

This paper presents a novel multiplexing approach termed ‘hybrid-polarization-angular-depth multiplexing’, integrating angular, depth, and polarization multiplexing. The proposed multiplexing technique is successfully implemented on a highly efficient azo-carbazole polymer film. The demultiplexing of the generated holograms is achieved simply by modifying the polarization of the reading beam.

This research focuses on optimizing the TIR efficiency of an AR system using holographic optical element with a waveguide glass. Near-eye display AR with wave-guide glass overlays digital content onto the user's real world to enhance the user experience. However, effectively guiding light is a challenging task due to the limitations in reproducing the holographic angle spectrum. We analyzed the recording method of holographic optical element by angle and medium, examining the components that create interference patterns in detail. holographic optical element maximizes TIR efficiency and AR image quality by generating maximum light propagation at specific angles in each medium. Our experimental setup embeds holographic optical element into waveguide structures and creates optimized angles for holographic patterns to precisely control light. Additionally, we investigate the impact of materials and manufacturing processes on HOE performance. The results show significant improvements in TIR efficiency and light utilization when using holographic optical element. Virtual images exhibit enhanced clarity, brightness, and color accuracy, enhancing the display efficiency of AR devices by reducing light loss. In conclusion, the angle analysis of holographic optical element recording demonstrates the potential to enhance optical performance in wave-guide AR displays. This research contributes to advancements in AR technology, benefiting fields such as entertainment, education, healthcare, and industrial training.

Coherent excitation of a resonant medium yields a nonlinear response to the Fourier spectrum of the input signals. This property can be exploited to produce a 1D temporal correlator by applying two signals simultaneously, and subsequently reading out the state of the medium. This intricate process of nonlinear responses generates multiple time-delayed outputs, where we are only interested in the specific segment that pertains to the cross-correlation. To this end, the Schrödinger equation is used as a model to accurately determine the precise time code and location of the desired output. Here, we show via simulations how this may be used for 1D event recognition. By comparing a reference signal to a query signal, we can expect a prominent peak in the cross-correlation if there is a match. Such a system is inherently delay-invariant due to the properties of the Fourier transform but is not invariant to scaling in the time-domain (i.e., frequency shifting). We additionally show how frequency-shift invariant correlation can be achieved by pre-processing the input signals via the Mellin transform. This technique is tested using audio signals to achieve speech recognition, where invariance to frequency shifts means that individual phrases may be recognized independently of the voice of the speaker. This approach can be extended to three-dimensional video recognition systems for real-time event recognition. By utilizing the frequencyshift invariant technique, the system can effectively correlate videos with different time scales, making it applicable to various fields, such as surveillance and copyright plagiarism detection.

We investigate Irgacure 784/PMMA photopolymers doped with single-walled carbon nanotubes (SWCNTs) of various concentrations. Doping the photopolymer samples with SWCNTs results in an increase in the peak diffraction efficiency from 63% to 88%, as opposed to the undoped state. Holographic imaging of real objects using the SWCNT-doped photopolymer has also been performed.

In this paper, we expand the eyebox size of lens-less holographic near-eye-display (NED) using passive eyebox replication technique that incorporates the spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox is replicated in horizontal direction by using the horizontal high-order diffractions of the SLM under spherical wave illumination and multiplexed HOE combiner. The HOE combiner is used as a see-through reflective screen for the projected holographic virtual image, and it is fabricated based on two spherical divergent waves recording condition. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be used for eyebox expansion. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. Astigmatism distortion introduced during the HOE fabrication was counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The experimental results prove that the proposed prototype system is simple and effective to achieve distortion-free reconstruction of 3D virtual image and eyebox extension of lens less holographic NED.

Computer-generated hologram (CGH) is an ideal three-dimensional display technology. However, the problem with CGH is that it is computationally expensive. Therefore, much research has been conducted to shorten the computation time of CGH. A fast rendering technique for computer graphics is Foveated rendering. It uses human visual characteristics and reduces the resolution of images in the peripheral field of view to achieve high-speed computation without being noticed by the observer. There is also a CGH method that uses Foveated Rendering to achieve high-speed computation, but it needs to be used with a special holographic display. Therefore, it cannot be combined with other CGH methods or applied in the future. We propose a method of controlling the resolution of CGH reconstructed images and reduce the amount of computation to achieve Foveated rendering on a general holographic display and high-speed CGH computation. By computing a smaller area of the sub-holograms, the point-light sources can be larger and displayed at a lower resolution. By calculating the correction of brightness in accordance with the area of the sub-holograms, point-light sources with different resolutions can be output simultaneously. Since the area of the holograms to be calculated is smaller, calculation is faster than by conventional CGH calculation, which calculates all of the area of the holograms at high resolution. The larger the field of view of the holographic display, the more significant the effect of faster Foveated rendering. We also evaluated the effectiveness of the proposed method for observers through experiments. The experimental results indicate that a speedup of 1.9 times can be expected when computing an object with a viewing angle of 13.8°.

A novel technique is proposed for creating stacked CGVHs (computer-generated volume hologram) that reconstruct full-color holographic 3D images in full-parallax. Because of excellent wavelength selectivity of volume holograms, the stacked CGVHs can reconstruct high-quality images with white illumination. However, it is not easy to expand the size of stacked CGVHs due to limited output power of the laser, used for contact-copy to transfer the 3D images of printed high-definition CGHs (computer-generated hologram) to CGVHs. In this paper, we propose a method referred to as tiling contact-copy for extending the size of CGVHs. Using the technique, the size of a fabricated CGVH is no longer depending on the laser power. We demonstrate a full-color stacked CGVH over 10 cm × 10 cm, fabricated by the proposed technique.

Stereoscopic display techniques used in virtual reality (VR) and augmented reality (AR) do not satisfy the physiological requirements for human vision, leading to issues such as fatigue and motion sickness. Electroholography based on computer-generated hologram (CGH) is an ideal technique for a three-dimensional display. However, there are limitations of both the field of view (FOV), which is the size of the reconstructed image, and the viewing zone, which is the range of the reconstructed image that can be observed. Expanding both FOV and the viewing zone is desirable, but there is a trade-off between them. For the reasons mentioned above, holographic head-mounted display (HMD) systems have been proposed. Since HMD systems are used in a fixed position, the narrow viewing zone does not significantly affect the observation of the reconstructed image. Thus, we need to prioritize the expansion of FOV. We developed a practical holographic HMD system that includes a concave mirror to expand the FOV. Concave mirrors can reduce chromatic aberration when making full-color images because the convergence of light is independent of wavelength. Our holographic HMD system can also support three degrees of freedom (3DoF) by including a motion sensor to obtain the user’s attitude angle. To support 3DoF, we carry out phase-compensation as a fast calculation algorithm. This enabled CGH calculations to be more efficient for modifying the user’s attitude angle and was realized real-time calculation of 3DoF.

We propose an advanced layering method of integrated dept-position map for real-world object. The depth map of far field object has not contain depth information and impossible to layering the far field objects. Therefore, the position map was rendered from generated high-quality 3D model used deep neural network, it is accurately layering for far field object. However, it has field loss of 3D model depending on the color density, when layering at near field. Therefore, by combining the depth map with the position map, the proposed integrated depth-position map was obtained for accurately layering in far and near field objects.

Electro-holography is an ideal three-dimensional image display technology, but there is a problem with the small field of view. Various methods for enlarging the field of view have been proposed, including a method that involves using a head-mounted display (HMD). While the HMD can enlarge the field of view, it narrows the view, causing a sense of occlusion. Therefore, we propose a method of enlarging the field of view that involves using an optical system attached to the head and used as a projector to widen the view. With the proposed method, a reconstructed image is projected from the head-mounted optical system to a concave mirror placed in front of the head. The light of the reconstructed image, enlarged with the concave mirror, is then reflected almost in the direction of incidence. We can also observe this light. This method does not require the eyes to be covered, as with an HMD, so the view is widened more. Distortion of the reconstructed image, which is a characteristic of concave mirrors, can also be suppressed by reflecting light almost directly in front of the viewer. Furthermore, because this system is used with a fixed viewpoint, like an HMD, we can observe the reconstructed image in a narrow viewing zone. Experiments showed that the field of view is enlarged, demonstrating the effectiveness of the proposed method.

Augmented reality head-mounted displays (AR-HMDs) based on waveguides (WGs) are compact in size and comfortable to wear. However, conventional WG-type AR-HMD systems commonly project virtual contents onto single fixed focal plane, often leading to a vergence-accommodation conflict (VAC). This conflict can result in motion sickness and visual fatigue for the user. To mitigate the VAC, display’s depth of field (DOF) should be expanded. For this, we present a multi-focal lens holographic optical element (HOE)-based WG-type display. The multi-focal lens HOE consists of several spatial focal areas with focal lengths of -30 cm, -60 cm, and -100 cm, respectively. The configuration of HOE can be extended the DOF in AR display, as each area on HOE possesses a different refractive power relative to its recorded focal length. The proposed HOE is fabricated using a photopolymer and interferogram recording technique with photomask patterns. Experimental results demonstrate that the DOF is extended from 30 cm to 100 cm, as indicated by the fact that the virtual contents are spatially focused on different depth positions. In conclusion, we believe that the proposed optical system offers significant benefits in terms of reducing VAC while maintaining a compact form factor.

In this paper, simplified digital content generation using single-shot depth estimation for full-color holographic printing system is proposed. Firstly, digital content generation is analyzed completely before the hardware system of holographic printing is run to provide a high-quality three-dimensional (3D) scene without degrading information of the original 3D object. Here, the single-shot depth estimation method is applied, and 3D information is acquired from the estimated highquality depth data and a given single 2D image. Then the array of sub-holograms (hogels) is generated directly by implementing fully analyzed computation considering chromatic aberration for full-color printing. Finally, the generated hogels are recorded into holographic material sequentially via effectual time-controlled exposure under synchronized control with three electrical shutters for RGB laser beam illuminations to obtain full-color 3D reconstruction. Numerical simulation and optical reconstructions are implemented successfully.

Diffractive optical element (DOE) has the characteristics of lightweight, flexibility, and easy replication, which meet the needs of miniaturization, integration, and mass production of optical systems. They play and will continue to play an important role in multiple fields of modern optics. In application scenarios with different requirements, researchers need to flexibly apply design methods to customize DOE with specific functions. On the basis of reviewing the basic principles of DOE design, existing DOE design methods based on diffraction principle and interference principle are briefly described. Combined with the latest application progress of DOE in the field of imaging and display, the applicability of DOE design methods is elaborated. Finally, the difficulties faced in DOE design are summarized, and potential application directions in future technology are prospected.

The grating array-based wavefront sensor (GAWS) is a programmable version of the popular Shack-Hartmann wavefront sensor (SHWS) that consists of a 2D array of plane binary diffraction gratings and a single focusing lens. In the present work, a multiplexed GAWS (MGAWS) is proposed that generates a pair of low- and high-sampling zonal spots, simultaneously, having different dimensions and spatial frequencies. Realisation of both the low- and high-sampling zonal spots will allow to perform a sequence of zonal sensing in succession such that it results in reduced zonal cross-talk and improved dynamic range, in the presence of higher order aberrations. Proof-of-concept simulation results are presented to demonstrate the working of proposed MGAWS and its performance is also compared with conventional GAWS.

The applicability of the proposed 3-D printed lens-less digital inline holographic microscopy setup is demonstrated with bio-imaging examples. The direct object illumination with an elliptical beam from laser diode avoids the spatial filtering and beam collimation assembly which significantly reduces the setup complexity and cost. The use of Raspberry Pi camera sensor for hologram recording further reduces the cost without compromising on the hologram reconstructed image quality. The adjustable magnification in the range of 1.1X-1.8X is achieved. We believe that the proposed DIHM setup can be an important imaging tool especially in the resource constrained applications.