This PDF file contains the front matter associated with SPIE Proceedings Volume 11306, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

We previously demonstrated the recording of transmission volume holographic optical elements (TVHOE) in our holographic wave front printer setup. The setup is based on two phase-only reflective spatial light modulators (SLMs), which provide the individual recording wave fronts in an adaptive fashion. Recently, we extended the optical system of our holographic wave front printer, so that reflection volume holographic optical elements (RVHOE) can be fabricated. To this end, the optical system, which guides the recording wave fronts from the SLMs to the holographic film, has been duplicated on either side of the film. The SLMs are located in opposite half-spaces relative to the holographic film. The film is placed in the confocal plane of the two optical systems for wave front relay, which face in opposite directions. Consequently, arbitrary recording wave fronts generated at the SLMs are superimposed in the holographic film and produce a reflection hologram structure. Adjacently recording many sub-holograms allows for fabrication of large RVHOEs. In this publication, we report on the working principle of our holographic wave front printing approach. We present our wave front printer laboratory setup along with insights on setup alignment strategies. We demonstrate the functionality of our setup; we successfully produced holographic micro-mirror arrays with short focal length in an off-axis configuration of excellent optical quality.

Several holographic and other interferometry-based techniques have recently grown in commercial interest and feasibility, in part thanks to advancements in new laser technology that is capable of meeting the demanding optical performance requirements in these techniques. White-light analog holography is now capable of generating ultra-realistic true-color replicas of 3D objects that can be used to record and display museum artefacts. Laser-based holographic techniques have recently also drawn a lot of attention for its use in the production of holographic optical elements (HOEs) used for image projection in virtual reality (VR) and augmented reality (AR) devices. Other interferometry-based techniques, such as laser doppler velocimetry (LDV) and laser ultrasonics (LUS) are also increasingly being introduced as on-line process control tools in production environments, for example for OLED display manufacturing.

All of these holographic and interferometric techniques require single-frequency or single-longitudinal-mode (SLM) lasers in the visible spectrum with long coherence length, excellent wavelength stability and precision, as well as high, stable output powers.

As the applications of these techniques are transitioning from laboratory settings to production-scale environments the demands on performance reliability and stability over long time periods and variable environmental conditions are increasing.

Here we present how combining a robust optical assembly technology with advanced procedures for laser optimization and performance verification enables manufacturing of high power SLM lasers that deliver robust spectral performance over long time periods and in varying environmental conditions. We will demonstrate a novel automated SLM test procedure that ensures stable single-frequency performance and show wavelength stability over large temperature cycles.

In recent years, tele-communication using video calling functions of, e.g., PCs and smartphones has been used in various situations, such as conversations in personal life and online meetings at work. Aiming at the enhancement of the sense of presence in video telecommunication systems, a holographic off-axis mirror, which is a see-through off-axis reflector fabricated as a holographic optical element (HOE), is utilized as an upright screen for a virtual- image display and a face image capture with eye-contact. Since the chromatic dispersion of the HOE causes image blur, we previously proposed a optical dispersion compensation technique for this system. In this paper, we extend the dispersion-compensation technique to full-color virtual-imaging systems with a holographic off-axis mirror exposed by red, green, and blue lasers. We demonstrate the proof of concept system experimentally using an A4-sized full-color holographic off-axis mirror. We also apply the same concept to the off-axis image capturing system using a full-color holographic mirror, which is also experimentally demonstrated. The proposed full-color virtual-image display and camera system will enable more attractive visual telecommunication systems, such as video phone or online conference.

True Colour holography is enjoying a resurgence through the commercialization of both new materials and Diode lasers which combine to produce an interesting number of commercial opportunities. This paper points out an unusual colour shifting on Bayfol HX photopolymer primarily. Later, Geola GP3C photopolymer is also tested for the colour shifting property. Two different images are recorded on silver halide material using two different wavelengths 660nm and 532nn to generate bright silver halide masters. The Bayfol photopolymer was then used to copy the images from the masters which were index matched. An unusual colour shift in photopolymer material, from green to red, using a single-wavelength laser (532nm in this case) to combine different holograms recorded with different reference angles was noted, which means it is possible to reconstruct a hologram, or information, from another pre-recorded object, apparently reconstructing at another wavelength to that of the original. It was possible to capture two different images(information) index matched and placed at 180⁰ to each other at two different wavelengths by using only one laser in reflection mode geometry. This paper summarises how this effect is caused and under what circumstances this occurs.

In the context of highly automated and autonomous driving growing market interest arises with respect to technologies enabling new use cases relying on the front, side and back windows of the car to serve as projection screens for display systems. Holographic diffusers represent a promising approach for the realization of transparent projection screens. We pursue the development of holographic diffusers composed of individual holographic micro-mirrors based on recording in our holographic wave front printer. This recording method allows for the realization of large-area holographic structures with non-conventional diffraction characteristics. We recorded a Holographic Convex Micro-Mirror Array (HCMMA) for red and green target wavelengths via spatial frequency multiplexing. We report on the fundamental properties of HCMMAs and depict the relevant recording procedure. We demonstrate the fitness of the HCMMA to serve as a transparent diffuser screen in conjunction with a LED projector and discuss potential for further improvement of our structures.

In this paper, we analyse the capabilities of the digital holographic approach for evaluation of the refractive index distribution appearing in semiconductor materials due to external optical excitation. The study is based on a modified transmission Mach-Zehnder holographic microscope operating in the near-infrared spectral range. Practical considerations for holographic characterization of semiconductor samples are discussed. Experimentally measured data are compared with simulations as well as approaches to interpretation of the retrieved data are covered.

Depth extraction and recovery from the recorded image have been studied and applied in many fields such as biology, robotics, and computer vision. In some researches, the aperture in the imaging system is coded as a particular function in order to distinguish relative distances from the focal plane or recognize sampled points from the recorded image and the image captured through this coded aperture is useful to retrieve blurred images or acquire depth maps. These studies are associated with the shape of point spread function (PSF). In some approaches, diffraction-based engineered PSFs such as double-helix and cubic phase are applied to extract the depth information. In this paper, we propose a depth measurement method based on the optical analysis of the pupil function. It is well known that the PSF is represented as a Fourier transform of the product of pupil function and spherical phase in a coherent imaging system. Also, it is possible to estimate the intensity of the PSF corresponding to the distance of the object in an incoherent imaging system. Then the depth information is extracted from a snapshot image by inverse transform of the image.

Three-dimensional particle tracking and localization has various applications in biology and medicine, where it may be used to analyze contrast agents, or in flow analysis, e.g. for localizing dust particles in a gas stream or to analyze turbulence in a flow. Moreover, particle localization finds applications in IT-security, where a random arrangement of particles in a transparent environment may represent a Physically Unclonable Function (PUF), which is interesting for individual labeling of high value goods.

In conventional systems, such as bright field microscopy, a three-dimensional representation of particles is rather difficult, as it is challenging to acquire depth information about the sample. Quantitative phase imaging techniques provide phase and amplitude and thus in-depth information. Furthermore, they offer single shot measurements while providing images from multiple focal planes. Concerning the stability, which is an important aspect in localizing particles of diffraction limited size, common-path digital holographic microscopy is a reliable tool in particular in combination with a self-referencing system.

In this article, we show a common-path digital holographic microscope for particle localization. Firstly, the setup is characterized with a test chart in order to evaluate lateral and axial resolution properties. Afterwards a sample with particles distributed in a three-dimensional medium is analyzed. For reconstruction of the holograms, we use the angular spectrum method, numerical phase unwrapping as well as Zernike polynomials for aberration correction. All in all, the system is able to achieve stable particle localization in 3D with lateral resolution in the sub-micrometer range and an axial sensitivity of at least 100 nm.

Digital inline holographic microscopy is a promising cellular object imaging modality. We report on two cost-efficient lens-less experimental set-ups comprising of a standard LED or a semiconductor laser light source with a Raspberry Pi Camera for image acquisition. The microscope parts are 3D-printed yielding a highly compact and portable microimaging solution. Tobacco cells, human red blood cells and polystyrene microspheres are successfully imaged by an open-source reconstruction software. The developed microscopes are cost-efficient (<$200) and yield spatial resolutions of 3.91 μm respectively 1.55 μm. They constitute a flexible tool for science and student and early researcher education that can be tailored to the researchers demand. All employed code is open-source accessible aiming at triggering further developments and sharing between research laboratories, diagnostic labs and science education.

See-through optical components are being intensively studied in applications such as Head-up-displays (HUD) and Head-mounted-displays (HMD). In particular, volume holographic optical elements (vHOE) have received a lot of attention due to their unique optical (angular and spectral selectivity) and mechanical (lightweight and thin) characteristics which make them perfectly suitable for use in integrated optical components like spectacle lenses and car windshields. Bayfol® HX photopolymer films prove themselves as easy to process recording materials for vHOEs. The Bayfol® HX instantly developing holographic photopolymer film provides full color capability and adjustable diffraction efficiency as well as an unprecedented optical clarity when compared to classical volume holographic recording materials like silver halide emulsions (AgX) or dichromated gelatin (DCG). Besides the recording step, no pre- or postprocessing is necessary and easy mass production of vHOEs in a completely dry roll to roll process is possible.

The layout of a typical Bayfol® HX film consists of a light-sensitive photopolymer layer coated onto a transparent substrate and protected on the other side by a cover film. The substrate is particularly beneficial, not only for easy handling of the film during holographic recording, but also for further mechanical processing steps which are required to embed the film into a finished optical component. However for certain applications it is desirable to remove the substrate before or after recording. This will allow the user to make full use of the high flexibility of the photopolymer layer, for example if it comes to curved surfaces that have to be covered. Also more complex stack geometries can be realized in which the photopolymer layer could be embedded in optically well designed cavities or mechanically demanding setups. To facilitate this, we developed Bayfol® HX film grades in which the substrate has a lower adhesion to the photopolymer layer compared to the protective cover film. Therefor the substrate can be removed first in contrast to existing Bayfol® HX film grades which only allow to remove the protective cover film. On the other hand the adhesion of the protective cover film can also be well controlled, so that it can be specifically selected according to the needs of the surface to which the photopolymer layer has to be transferred to. In this paper we demonstrate versatile application processes making use of these transfer grades of Bayfol® HX films with respect to adhesion design, integration in complex stacks and application on curved surfaces.

Holography can be a useful strategy for fostering public engagement in science and technology. Thus, an important application of holography is in education and science communication. The Holography4All program was developed and implemented to involve different types of audiences in holography and to study the applications of holography in science communication. This program involves holography labs, portable holographic darkroom, holograms exhibitions and interactive exhibits and it took place in museums, schools, science centers, libraries, maker spaces and outdoor places. This paper will present types of holograms and all holographic systems used and it will explore all holograms and results obtained.

Holography registers and shows the three-dimensionality of the "real" space, but on a two-dimensional support, and the holographic image can float either before or behind the plane of the hologram.

In holography, the time of the image is the time of the viewer, and so as not to eliminate its peculiarity, this type of image can only be seen and felt, in its total uniqueness, through its direct presence.

We have been developing a series of digital art holograms and lenticulars, exploring the movement inside and outside the holographic space, making the viewer's physical space also part of the holographic space.

Starting from a belief in the human body as an emotional tool, as a messenger of memories, we are been creating a new space for the image whose structure is influenced by the holographic images and by the viewer as performer. In this paper we will develop these ideas by analysing a series of digital art holograms that we have been created, through the artistic installations that were produced.

Holograms are a promising technology for realizing a natural three-dimensional display. While the holographic pattern records both the phase and intensity information of an object, the spatial light modulator, which is a device for reproducing it, is capable of modulating either phase or amplitude. Therefore, in order to realize a perfect holographic image, a complex hologram must be converted into a phase-only hologram. Currently, SLM resolution is 4k or less, but resolution needs to be increased to achieve better quality holograms. This will increase the computational complexity of the Fourier transform, which is needed for each iterate. Therefore, a way to create a phase-only-hologram with a minimum number of iterations is needed. It is known that in the iterative method, the initial predicted value greatly affects the result. In this study, we propose a method to make initial guess to obtain more accurate phase only hologram with fewer iteration times. To obtain the initial guess, the desired image was divided into several parts, and the phaseonly hologram corresponding to each was obtained and added again. We used hybrid-input-output iteration to maximize the effect of pre-iterated guess. When iterates the same number of times, the peak signal-to-noise ratio (PSNR) value obtained by using proposed pre-iterated guess was higher than using the random initial guess. In other words, the desired PSNR value can be reached with a smaller number of iterations by using proposed method. After 15 iterations, proposed initial guess have ~0.3dB higher PSNR value, which means one or two times of reduced iterations.

We previously proposed a bimodal incoherent digital holography system to implement both three-dimensional and infinite depth-of-field (DOF) imaging. In this paper, we reveal the basic operation of our system in detail to control its imaging properties such as transverse magnification and DOF. We numerically evaluated the effect of rotational shear on these imaging properties, and the results indicate that it is possible to control both properties by simply changing the rotation angle of a light instead of replacing an imaging lens.

Beam shaping techniques with diffractive optical elements have garnered considerable attention for laser material processing and microscopy because of their high efficiency of light utilization. Particularly, the design of top-hat beams with several shapes including circular and rectangular is required to facilitate a high-throughput system for line scanning and surface peeling applications. In this study, we propose a diffractive beam shaping method for the generation of a tophat beam with arbitrary shapes under tight focusing conditions. We implemented the iterative Fourier-transform algorithm (IFTA) with an error function in the form of a Gaussian distribution in the input laser beam to calculate an optimized phase distribution for generating a top-hat beam with arbitrary shape. This phase distribution was generated with a phase-only spatial light modulator and relayed with an optical system to the pupil of an objective lens with a numerical aperture of 0.75. The point spread function under the focal spot was observed with a microscopic imaging system placed opposite to the beam focusing optics. We experimentally demonstrate that the size of the focused top-hat beam is twice the size of the airy disk under tight focusing conditions. Further, we measure the profile of the generated beams. The proposed method with a spatial light modulator offers an adaptive control on the uniformity of the generated distribution, which fluctuates according to the effect of slightly different laser conditions on the diameter and profile of the input beam.

To measure object wave in digital holography, the phase-shifting technique is popular by changing the phase of the reference wave. A piezo actuator (PZT) is usually used as a device to shift the phase. In a case to obtain the phase information of color object with multiple wavelengths, four-step phase-shifting algorithm with quarter wavelength shift is not convenient since the amount of the phase shift is difference according to each wavelength. In this paper, the generalized four-step phase-shifting method is proposed and experimentally verified to obtain color digital hologram using an image sensor with a Bayer pattern for capturing interference pattern shifted phase by one PZT.

Recently the technology of hologram receives a lot of interest owing to its advantages and many researches on hologram recordings have been actively studied. In some studies, digital hologram printing methods have lots of applications because of the ability to record large area hologram based on the technique of holographic stereogram. The holographic stereogram printing method records the hologram composed of hogels which are the unit of the hologram recorded at once. This method has advantages in flexibility of the size since it records the hologram hogel by hogel. In addition, the hologram printer records not only wavefront of real objects captured by charge coupled device (CCD) but also hologram patterns of virtual objects calculated by computer-generated hologram (CGH) algorithm. In previous systems, it is difficult to implement the hologram in high resolution because of the low numerical aperture of hogels. In this paper, we suggest the method of recording high-resolution hologram using binary wavefront pattern and discuss the optical modulation properties of the printed binary pattern.

We proposed an effective method of digital content generation for the holographic printer using the integral imaging technique. In order to print the three-dimensional (3D) holographic visualizations of the given object, a printed hologram consists of an array of sub-hologram (hogels) should be generated, before the hardware system of the holographic printer is run. There are mainly three parts related to the digital content generation. In the first part, the acquisition of the 3D point cloud object is applied and the second part provided an encoding of directional information extracted from the 3D object. The array of hogel is generated by implementing direction inversed computer-generated integral imaging plus phasemodulation for improvement of the content generation, and displayed on the reflective phase-only spatial light modulator (SLM) then recorded onto holographic material one-by-one in sequence, while motorized X-Y translation stage shifts the holographic material; so, the full-parallax holographic stereogram (HS) is printed on the holographic material and 3D visualization of the object is successfully observed. Numerical simulation and optical reconstructions are verified effective computation and image quality respectively.

We have been developing a magneto-optical (MO) spatial light modulator (SLM) with a narrow pixel pitch which enables reproducing holographic three-dimensional (3D) images with wide-viewing angle. In this study, we investigated a light modulation performance for reproducing holographic 3D image of an MO light modulation device array. The light modulation device array can easily realize a magnetic interference fringe pattern by applying an external magnetic field without a transistor (i.e. without fabricating the real MO-SLM). The pattern, however, is not rewritable. The array was designed with a pitch of 1 × 2 μm. When a reproducing illumination light was incident to the device, a holographic 3D image with wide-viewing angle of 36° in the horizontal direction and 18° in the vertical direction was reproduced. A clear holographic image was observed through an analyzer because the phase of the unnecessary diffracted light, generated by the pixel structure, shifts by 90° from that of the magnetically diffracted component by the MO effect. If the light modulation device array is fabricated on the transistor backplane, any magnetization pattern can be realized by injecting a current. The MO-SLM was shown as an effective device for realizing a holographic display with a wide-viewing angle.

We recorded real time holographic gratings in a photosensitive liquid material. This material is Norland Optical Adhesive (NOA 65®) mixed with yellow eosin dye. The NOA 65® is a clear, colorless, liquid photopolymer that cures when is exposed to ultraviolet light (UV) but when is mixed with yellow eosin becomes sensitive to visible region. To record the gratings we used the interference between two diode laser, obtaining gratings by refraction index changes. We use two different wavelengths, for recording the gratings and its highest diffraction efficient was obtained when the grating was illuminated with a wavelength.

Polarized Digital Holography (PHD) is a fast and efficient tool for analyzing mechanical effects in materials. Especially when the task requires non-invasive techniques that do not damage the material in study, the use of PHD has great perspectives. The most common methods of digital reconstruction use the convolution theory to discretize the Huygens- Fresnel integral. When external stresses are applied to photoelastic materials, the relationship between these stresses and phase differences observed by polarization holography is an intrinsic characteristic of the material called the photoelastic dispersion coefficient. In photoelasticity, this coefficient depends on the wavelength. By using PHD the authors show in the present paper that the photoelastic dispersion coefficient also depends on the wavelength in Holography. A Mach- Zehnder interferometer, modified with the inclusion of linear polarizers, was built to verify this effect in a sample of photoelastic material. In this set-up, two coherent light sources with different wavelengths were used. For the analysis, a digital method was created that correlated the mean stresses differences on the photoelastic material sample and the mean phases differences at each distinct wavelength.

Study of wave propagation with random amplitude and phase, which overlap to form interference, is presented. Where each superimposed wave has independent random amplitude and phases that are monitored by the visibility parameter. This parameter is a function of the spatial correlation distribution of amplitudes and phases of the waves that emerge from the openings. The interference fringes visibility depends on the degree of phase randomness and to a lesser extent wave amplitude.

Aerial images are expected to be actively used in the entertainment field in the future,and various research is being conducted to achieve this. Electro-holography shows promise for displaying high-quality aerial images in the future,but the disadvantage is that the viewing zone, which is the range where the observer can observe the reconstructed image,is narrow. The viewing zone of an electro-holography is determined by the pixel pitch of the display device (e.g.,a liquid crystal display). The smaller the pixel pitch, the larger the viewing zone, so it makes sense that a higher performing display device would be the best way to solve this problem. However, the pixel pitch of the currently used display devices are not sufficiently small, and significant improvements in performance are not likely. In this work, we propose a tabletop optical system utilizing a CGH calculation method based on Fourier transform holographic calculation that expands the viewing zone of an electronic holography regardless of the performance of the display device. The proposed optical system can display an aerial image with a wider viewing zone when the size of the display device is larger, so even a current display device can reproduce an aerial image with a wider viewing zone.

Computer-generated hologram (CGH) can generate an ideal 3D video, but the downside is that the calculation time is huge. Recently, it is becoming more common to use a graphics processing unit (GPU) to enable fast calculation for CGH. Therefore, we have created a system that automatically changes various parameters in the CGH calculation by the GPU, searches for optimal parameters, and performs automatic tuning. In this work, we optimized four parameters-loop unrolling, memory structure, point light source sparsity, and allocation of calculation processing units-and found that the calculation time was 1.8 times faster as a result of the optimization.

Incorporation of copper into a recording material of poly (vinyl alcohol) with Iron (III) Chloride is observed to give improved its characteristics as holographic recording medium. We show preliminary results; transmission gratings were recorded in the photopolymer films using a diode laser (445 nm). Copper-doped films showed good energy sensitivity and gratings recorded in films exhibited a diffraction efficiency of 20% at first order. This material have great advantages such as real-time image development, self-processing and high photosensitivity.

A method for the recording of a rainbow hologram with multiple objects at different depths in a single exposition is presented. The created hologram can be observed under white incoherent light and shows three letters R, O, and X where the R is closest to the observer at surface level and the other two letters are placed at 2mm increments into the hologram. A spatial light modulator containing the information of a binary computer-generated hologram (CGH) of the three letters is illuminated with a 632.8nm HeNe laser. The reconstructed hologram is projected on a photosensitive film and interfered with a plane wave acting as a reference beam for 90s and then developed.

A novel asymmetric public key cryptographic algorithm is proposed by modifying the conventional RSA public key protocol, which can be optically implemented by using the phase-shifting digital holography. The proposed method involves a two-key encryption scheme so that it provides stronger security than the one-key encryption method. Optically, two unknown randomly generated numbers are changed to digital holograms which are used as public keys for asymmetric cryptography. The generated public keys and cipher texts by using them are Fourier transformed digital holograms with 256 gray level quantized intensities which are recorded on CCDs. The original plain text can be decrypted only with correct pairs of public-private keys and the holographic encryption-decryption keys in the proposed algorithm. The proposed optical schematic has an advantage of producing an enhanced asymmetric public key cryptosystem compared to the conventional RSA cryptosystem. The results of computer simulations verify that the proposed method shows the feasibility of application to an asymmetric public key cryptosystem with high security strength.

Digital holography is technique for registering of 2D- and 3D-scenes characteristics: amplitude or phase images of object, roughness, and etc. Numerical reconstruction allows fast images recovery. However high quality optical reconstruction is not so fast due to the hologram transferring to the spatial light modulator (SLM), hologram digital preprocessing, SLM calibration, and etc. In this work we analyzed possibilities of fast processing of the holograms for increasing of quality of optically reconstructed images. Amplitude type holograms were registered and images were optically reconstructed using phase liquid crystal SLM. Various techniques of improvement of reconstruction quality were used.

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.