This PDF file contains the front matter associated with SPIE Proceedings Volume 11710, including the Title Page, Copyright information and Table of Contents

Bayfol HX photopolymer films prove themselves as easy-to-process recording materials for volume holographic optical elements (vHOEs) and are available at industrial scale. Their full-color (RGB) recording and replay capabilities are two of their major advantages. Bayfol HX is compatible to plastic processing techniques like thermoforming, film insert molding and casting. Therefore, Bayfol HX made 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. Bayfol HX can be adopted for a variety of applications. To offer access to more applications, we address the sensitization into the Near Infrared Region (NIR) and increase the achievable index modulation Δn₁ beyond 0.06. In this paper, we will report on our latest developments in these fields.

Diffractive optical elements (DOE) and holograms based on diffractive optics use diffracted light generated by the interaction between light and the periodic structures such as gratings. For the fabrication of these structures, the researchers have widely used the materials that can modulate the refractive index. Recently, the photochromic materials have attracted a surge of interests for reversible holograms or DOE that can be controlled by light or heat. Especially, azobenzene molecules, which can undergo photo-isomerization under the specific wavelength of the light, are widely used for fabrication of surface relief gratings (SRGs). When the interference light is illuminated, azobenzene-containing polymer (azopolymer) films can form the SRGs via mass migration rather than lithographic etching. More strikingly, these already recorded SRGs as depending on mass migration, can be further inscribed via second mass migration, which can be also guided via another interference light. However, it has been accepted that this overwriting of SRGs needs to be performed after the erasing process of the already recorded SRGs. This limitation has in turn significantly restricted the hierarchical integration of the various SRGs with different structural features. In this work, we demonstrate that overwriting of SRGs on azopolymeric film can be possible without erasing of the previously recorded SRGs. By using this method, we can greatly advance not only the versatility of the process but also the accessible design of the SRGs and the resultant range of DOE-based light molding. In particularly, the pixelated SRGs with the unprecedented structural integrity can be achieved with a successive overwriting of SRGs without erasing process, which can serve to promote the augmented reality (AR) or virtual reality (VR) technologies.

Typically, commercially available Head-up display (HUD) systems use Pepper's ghost, "floating hologram", systems. Our proposed system uses holographic optical element (HOE) to minimize the volume of conventional systems, provide high-depth and large-screen augmented images, and propose a method to measure that from a human factor perspective..

Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the strong form birefringence of these nanostructures, metasurfaces provide a fascinating platform to realize novel polarization optics. Recently, we propose and implement a general design strategy for polarization-dependent holograms with metasurfaces, using Fourier optics and phase retrieval principles applied to the Jones calculus. We use this to design metasurface holograms with arbitrarily chosen polarization responses. We fabricate these gratings (for operation at visible wavelengths) and test them with Mueller matrix polarimetry, showing agreement with design.

Metasurfaces have gained considerable attention due to their control over light properties like phase, amplitude, and polarization, which benefitted the industry for their applications in digital displays and multimedia related applications. Miniaturization of the devices has always been an interesting domain for researchers that can be accomplished by enabling a device to perform multifunctional behavior. Here, we propose a meta-atom by breaking symmetry of spin orbit interactions resulting in polarization sensitive device that transmits and reflects simultaneously under different circular polarizations. A z-shaped silicon-based meta-atom is designed, which provides asymmetric transmission of 80 % and 74 % in reflection and transmission, respectively. We demonstrated polarization multiplexed holograms in transmission and reflection for proof of concept that reflects its potential in spin-controlled imaging and sensing devices.

Supramolecular azopolymer thin films are a promising material for the one-step fabrication of optical microstructures. Here we report the application of these materials to the fabrication of micrograting surface arrays, also known as dotmatrix holograms. The films were fabricated using commercially available azobenzene and polymeric components and were spin-coated on glass. The gratings were photopatterned using two-beam interference at 488 nm with 2.5 mW optical power and exposure times under 10 s. The gratings appear immediately, require no post-exposure processing, and their amplitude can be precisely controlled via exposure time. This was exploited to create two-dimensional dot-matrix arrays by mapping gray-scale images to exposure time. Individual surface relief gratings were 50 μm in diameter, with a sinusoidal amplitude up to 600 nm. The dot spacing was controlled by mechanically translating the film between exposures, with resolutions up to 800 dpi possible. The dot matrix structures are stable in ambient conditions and can be replicated using nanoimprint lithography.

Holographic reconstruction algorithms based on wave propagation typically require the object’s Z-plane location. To automate reconstruction, a focus metric is required to iteratively determine the Z-plane location. The 1951 USAF resolution test chart is often used to evaluate holographic reconstruction and focus metric performance. However, plankton present a more difficult subject, as they are dense three-dimensional objects with lower contrast and greater gray-scale variance. In addition, we are using a direct inline red laser and image sensor without optics, operating below lasing threshold to avoid speckle, resulting in modest fringe production. These factors make autofocusing more difficult. In this paper we evaluate six focus methods tested on eight classes of plankton and microfiber (n = 64), measuring Z prediction accuracy and computation time. We show that focus method performance varies with class, suggesting that best performance can be achieved by selecting the focus metric based on the specimen class of interest.

The holographic system is usually used for imaging, so it can be attributed to imaging optical systems. This analogy allows using a well-developed computational optics technique to design and analyze real digital holographic systems, as well as to solve the measuring tasks of digital holography. The work presents a mathematical model that establishes a one-to-one correspondence between dimensional and spatial parameters of a digital holographic image and a holographing object for the given case of an in-line scheme. The values of the model constants used to determine the real size and the longitudinal coordinate of an object according to its holographic image are found through calibration. The described approach is used to calibrate and analyze the imaging properties of a submersible digital holographic camera designed to study plankton in its habitat. The paper also shows the results obtained in situ using the holographic sensor of plankton.

My research has been about the aesthetics of light, as an entity in itself, and how the viewer interacts with it; holography is one of the media that I have used in this process. For example, in "Specific Light Objects" installation, the viewer is allowed to immerse itself in an experience where visual and sound sensations are intermingled in the exploration of the holographic image, and invite the self-knowledge of the relativity of our perception and consequently of the vision of our cognitive universe. The dialogue of holography with other media is adequate to the demands of contemporary art, in the form of multimedia hybrids, and in the form of installations, in which the holographic work constitutes one more element of the whole. Developments in production techniques of pulsed holograms and holographic stereograms have combined to provide high-quality three-dimensional illusions and movement. Currently considering the new era of holographic image and the creation of digital holograms, where image systems are being developed to capture dimensional content and also possible software to edit it, in this paper we are analysing the creative process and experimental techniques of holographic image from the point of view of the visual arts.

Laser-based holographic techniques continue to grow into commercial markets, used in the production of holographic optical elements (HOEs), for image projection in virtual reality (VR) and augmented reality (AR) devices as well as in white-light analog holography for the generation of ultra-realistic full-color replicas of three-dimensional objects such as museum artefacts. These rapidly developing holographic techniques and holography-based technologies require reliable light sources at multiple wavelengths simultaneously, often in the same optical path. The individual laser performance requirements for holography applications are met by commercially available, extremely reliable, single-frequency or single-longitudinal-mode (SLM) lasers in the visible spectrum with long coherence length, excellent wavelength stability and accuracy, and high, stable output powers. However, the optical alignment and beam combining necessary in multi-wavelength systems can be technically challenging and time consuming. Elaborate assembly and constant maintenance can divert valuable resources away from the more fundamental work necessary to improve quality of the holograms and HOEs. The aim is to develop a laser combiner that provides the necessary performance per laser line with robust beam alignment stability during exposure, and repeatability between exposures, which requires strict control of opto-mechanical component design and thermal management. The performance of a laser combiner, which integrates up to four laser lines with up to 1.5 W of optical power per laser, collinearly aligned with high precision position overlap, angular overlap, and beam pointing stability, and repeatability over long periods of time, is evaluated in this paper. This laser combiner includes the laser sources, control electronics, and beam combining optics and is designed to be easily transportable, providing the ideal combined laser solution to facilitate advancements of holographic techniques.

CHIMERA is the third generation of digital holographic printing systems. CHIMERA is based on the use of three lowpower red, green, and blue continuous lasers combined with the Ultimate U04 ultra-fine grain silver-halide holographic glass plates. Acquisition of perspective images can be done with an in-house designed cylindrical scanner for real still objects or with software for computer-generated objects. This holoprinter is capable of printing at a frequency equal or greater than 50 hogels per second, full-color, 120° full-parallax digital reflection holograms or holographic optical elements with a size of up to 60×80 cm and a hogel size ranging from 250 to 500 μm. The color rendition and the parallax—horizontal and vertical—of this printer are so good that, with a 250 μm hogel size, an observer can hardly detect a difference between an analog ultra-realistic full-color Denisyuk hologram and a digital CHIMERA hologram. This paper discusses and compares the different characteristics of the two techniques—CHIMERA and Denisyuk—for still object recording and analyzes their advantages, benefits, and limitations.

A holographic stereogram printing system is a valuable method to output the natural-view holographic three-dimensional images. Here, the 3D information of the object such as parallax and depth information, are encoded into the elemental holograms, i.e. hogels, and recorded onto the holographic material via the laser illumination of the holographic printing process. However, according to the low resolution of the hogels, the quality of the printed image is reduced. Therefore, in this paper, we propose the real object-based fully automatic high-resolution light field image acquisition system using the one-directional moving camera array and smart motor-driven stage. The proposed high-resolution light field image acquisition system includes interconnected multiple cameras with one-dimensional configuration, the multi-functional smart motor and controller, and the computer-based integration between the cameras and smart motor. After the user inputs the main parameters such as the number of perspectives and distance/rotation between each neighboring perspectives, the multiple cameras capture the high-resolution perspectives of the real object automatically, by shifting and rotating on the smart motor-driven stage, and the captured images are utilized for the hogel generation of the holographic stereogram printing system. Finally, the natural-view holographic three-dimensional visualization of the real-object is outputted on the holographic material through the holographic stereogram printing system. The proposed method verified through the optical experiment, and the experimental results confirmed that the proposed onedimensional moving camera array-based light field image system can be an effective way to acquire the light field images for holographic stereogram printing.

In this paper, a fast and efficient multiple wavefront recording planes method with parallel processing is proposed for enhancing the image quality and generation speed of point cloud-based holograms. The proposed method gives an optimized fixed active area to generate depth-related multiple WRPs to improve the calculation speed and enhance the color uniformity of full-color hologram. In other to parallel processing the ray tracing intermediate plane is created. This method is more effective when the number of depths is smaller, such as the RGB-D image.

Imaging with partial apertures is suitable for applications where compact, light-weight, and cost-effective optical systems are desired. The feasibility of a partial aperture imaging system (PAIS) with a single annular coded-phase aperture was first studied for future space and ground-based telescopic systems. The concept of PAIS is based on the interferenceless coded aperture correlation holography (I-COACH) technique. Since I-COACH is an incoherent and interferenceless technique, it is compatible with telescopic applications. Although, in PAIS, only a small fraction of light is modulated by the coded aperture the image resolution of PAIS is similar to that of full-aperture imaging systems. In this study, the design and the reconstruction technique of PAIS are modified to provide higher image quality with improved resolution, lower noise, and higher visibility. The upgraded design makes use of sparse-response holograms and a nonlinear reconstruction. Far-field imaging usually suffers from lower power signals at the sensor plane, causing a lower signal-to-noise ratio (SNR) and degradation in the image quality. To improve the SNR, it is crucial to use a power-efficient system, with higher signal intensity per camera pixel. This goal can be achieved by accumulating all the incoming power to a small sensor area, and distributing the light between several randomly distributed dots on the sensor, instead of inefficiently spreading the light over the entire camera plane. The results of the modified PAIS (M-PAIS) are reconstructed by a nonlinear correlation to provide well-resolved images which are compared with full aperture direct imaging results.

We present our first results on the recording of pixelated holograms. This specific recording process is dedicated to an unconventional approach of smart glass design. Due to the use on integrated photonics, this concept requires to adjust locally the properties of out-coupling holographic elements with specific angular distribution. We analyze here a simple Lippmann recording configuration that focus on the material behavior regarding the pixelated process. We demonstrate our ability to record distribution of holographic elements, few micrometers in size, and compare our experimental results to first elements of simulation.

The improvement of holographic waveguide-type two-dimensional/three-dimensional (2D/3D) convertible augmentedreality (AR) display system using the liquid-crystalline polymer microlens array (LCP-MA) with electro-switching polarizer is proposed. The LCP-MA has the properties such as a small focal ratio, high fill factor, low driving voltage, and fast switching speed, which utilizes a well-aligned reactive mesogen on the imprinted reverse shape of the lens and a polarization switching layer. In the case of the holographic waveguide, two holographic optical elements (HOE) films are located at the input and output parts of the waveguide. These two HOEs have functions like mirror and magnifiers. Therefore, it reflects the transmitted light beams through the waveguide to the observer's eye as the reconstructed images. The proposed system has some common features like holographic AR display’s lightweight, thin size, and the observer can see the 2D/3D convertible images according to the direction of the electro-switching polarizer, with the real-world scenes at the same time. In the experiment, the AR system has been successfully verified that the real-world scene and reconstructed 2D/3D images were observed simultaneously.