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Aberration-corrected holographic gratings are widely used in spectral instruments. They allow to achieve high resolution and uniformly distributed diffraction efficiency as well as to combine several functions in a single optical element. However, their performance is limited. In particular, when the optical system has a large aperture the hologram replay conditions vary significantly across its’ surface. Due to this variation the hologram aberration properties and its efficiency change locally thus leading to decrease of the resolution and efficiency of the entire system. In the present research we consider a composite volume phase holographic optical element used as a disperser in a spectrograph design. Such an optical element represent a hologram recorded by stitching of several elementary fields or zones. The refraction index modulation depth, the fringes tilt and the hologram spatial frequency may vary locally in each of the elementary fields to match the changing reconstruction conditions. This approach allows to implement a better aberrations correction and to maximize the overall diffraction efficiency. We demonstrate an exemplary spectrograph design with a composite hologram for the visible range of 400-800 nm. It is shown, that in the design as fast as f/2.1 the maximum aberrations can be decreased by factor of 1.19 and 2 in the X and Y directions, respectively, while the average diffraction efficiency increases by 15.6% at shorter wavelenghts. We continue the study by investigation of the composite hologram technological feasibility and demonstrate that it can be recorded with a standard precision of the moving sources positioning, achievable stroke of the auxiliary deformable mirror and reasonably high accuracy of the photosensitive layer’s parameters.

The fabrication of an analog holographic wavefront sensor, capable of detecting the low order defocus aberration, was achieved in an acrylamide-based photopolymer. While other implementations of holographic wavefront sensors have been carried out digitally, this process utilises a recording setup consisting only of conventional refractive elements so the cost and complexity of holographic optical element (HOE) production could be much reduced. A pair of diffraction spots, corresponding to a maximum and minimum amount of defocus, were spatially separated in the detector plane by multiplexing two HOEs with different carrier spatial frequencies. For each wavefront with a known aberration that was introduced during playback of the hologram, the resulting intensity ratio was measured in the expected pair of diffracted spots. A number of HOEs were produced with the diffraction efficiency of the multiplexed elements equalized, for a range of diffraction efficiency strengths, some as low as

Most of waveguide implementation for HUD or augmented reality combiner are flat pieces of glass because the image propagation does not suffer from any aberration when traveling along their length. However, this type of combiner does integrate seamlessly in front of the viewer eyes and a curved optics would be much more appealing. Using holographic optical elements, we demonstrated that it is possible to correct the aberrations induced by the curved surfaces of the waveguide, and display a aberration-free image to the viewer. This correction applies for different waveguide geometries (1D or 2D curvature) as well as different pupil expansions (1D or 2D expansion). A Zemax model is presented along a curved waveguide demonstrator.

We propose a volume holographic optical element (VHOE) used as an objective turret in a lensless digital holographic microscope. It also served as a reference wave guide to reduce the volume of the system. For further optimization of resolution performance, it used a spherical wave in the object light of the VHOE, which served as the reference light of the microscope. Another sheared spherical wave was used to illuminate the sample. The optimized VHOE increased the spatial resolution of the record signal effectively. Furthermore, the change of spherical wave distance leads to the change of imaging magnification.

Optical measurement techniques are of immense importance for research in engineering, industrial production and biomedical applications. In this paper, an experimental study to measure temperature, temperature distribution, and temperature fluctuations in diffusion flames has been conducted using a volume phase holographic grating (VPHG) based digital holographic interferometric (DHI) system. VPHG made on Dichromated gelatin provides high diffraction efficiency and minimizes stray light and coherent speckle noise. The results obtained from VPHG based DHI system show a good agreement with temperature measured by thermocouple. The proposed system is compact, robust, requires lesser number of optical components, simple to align and easy to implementation.

Near-eye displays (NEDs) for augmented and virtual reality (AR/VR) are spotlighted because they have a possibility to provide much more immersive experiences never possible before. With the virtue of recent progress in sensors, optics, and computer science, several commercial products are already available, and the consumer market is expanding rapidly. However, there are several challenging issues for AR and VR NEDs to become closer to our lives. Here, we will explore these issues and important topics for AR and VR, and introduce some of the ideas to overcome them: diffractive optical elements (DOEs), retinal projection displays, and 3D display with focus cues. First, unlike VR with a simple optical system, AR that needs to merge an artificial image with an outer scene requires additional optics. The diffractive elements have the merit of being thin and transparent, suitable for the image combiner. Among them, holographic optical elements (HOEs) have great potential as they can record the desired volume grating from the simple lens to the complex wavefront using light interference. Second, in order to wear the NEDs for a long time, it must deal with the visual fatigue as well as the form factor. Retinal projection display can effectively prevent the vergence-accommodation conflict problem even with a simple optical design. In the retinal projection display, the light rays from the display are adjusted to converge into a small point using a lens. It ensures a wide depth range in which the images are clearly visible. Furthermore, it is possible to provide observers with accurate focus cues for the alleviation of visual fatigue via multi-layer displays and holographic displays. Recently, we conceived tomographic NED that can reproduce dense focal planes. We confirm that this system provides quasi-continuous focus cues, semi-original contrast, and considerable depth of field. The experimental results of our prototypes are explained. We also explain the recent activities of using deep learning in holographic NED system.

The resolution of images is increasing year by year. High-definition images have a large amount of data so that high calculation cost is required for image processing. For example, when original data is restored from non-clear high-definition two dimensional coded images, it is necessary to improve the image quality. A volume holographic optical element works as a multiple lens for each pixel in an image so that spreading pixel patterns can be individually focused. Then, each pixel becomes clear and original data can be easily restored. However, it is difficult to analytically express the function of volume holographic optical elements. In our previous study, reconstructed images from a volume hologram, in which some data pages were recorded in multiple, were expressed by analytic function. The analytic function was called pixel amplitude function. In this study, the pixel amplitude function is used for an input image to a volume holographic optical element. Then, output image is analytically expressed.

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.

Various technologies to realize the augmented reality (AR) devices have been proposed. Holographic optical element (HOE) is among the most appealing optical components for the optical combiner of AR devices. With the compact size and bendable material, HOE can be applied to AR systems with various form factors. Since HOE has high angular selectivity, the light from the real scene remains nearly intact, making HOE the most promising technology for see-through AR displays. However, several issues of HOE still remain to be resolved, such as narrow field of view or eye box, and severe aberration. In this invited paper, we present the basic characteristics and issues of HOE and introduce how we can resolve the issues.

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..

Holographic optical elements (HOEs) are very interesting optical devices based on the holography technique and have been spotlighted in the augmented reality (AR) application recently. The HOEs have optically see-through property due to their high angular-selectivity, which has an extensive potential to be employed as an image combiner for the AR devices. Various optical functions, such as reflection, lens and diffusing, can be implemented with thin-layer HOEs. This advantage can replace the conventional bulky optics with HOEs for a compact form factor. In addition, multi-functionality can be realized with multiplexed recording, and optical mass production is possible, which is especially useful for AR display systems.

We have investigated the azimuthal orientation behavior of blue phase (BPI) lattice reoriented from the electrically unwound homeotropic state, and it was found that the azimuthal angle changes to align the [001] axis parallel to the easy axis on a unidirectionally orienting surface upon an electric filed treatment. By combining this effect with the Pancharatnam-Berry effect, we designed and demonstrated various holographic optical elements (HOEs) such as deflector, lens, and hologram by appropriately designing the distribution of lattice orientations. In contrast to cholesteric liquid crystals that show diminished circular polarization selectivity upon largely oblique incidence, we demonstrate that the BP-based HOEs maintain the circular polarization selectivity even for oblique light incidence, owing to the three-dimensional helical structure of the BP.

Recent developments in ultra-high-definition (UHD) displays have a major impact on holographic displays as well as conventional display systems. A spatial light modulator (SLM) can reproduce hologram data through wavefront modulation of the incident light, and a holographic printer can record a high-quality hologram by sequentially recording a number of holograms reproduced by the SLM on a holographic material. As UHD (4K) resolution SLMs have been popularized, higher quality holograms can be reproduced compared to previous 2K resolution SLMs. When applied to the holographic printer, it is possible to manufacture holographic optical elements (HOEs) having a multifunctioning property and a wide field of view. In this paper, we introduce the holographic printer system using an amplitude UHD SLM and its applications. The holographic printer consists of optical systems to generate high-quality hologram from UHD SLM and mechanical systems to record the hologram on holographic material. The details of the total system are introduced. Furthermore, we introduce a holographic near-eye display system using UHD SLM and an image combiner HOE which is manufactured by the holographic printer.

The eye-box expansion method using the merging of waveguide and HOE (holographic optical element) is presented. Using the waveguide with the refractive index of 1.7, the wide FoV (field of view) that is up to 60° is achieved. Full color and wide FoV are obtained using 2 waveguides. Projection optical system based on Scheimpflug principle is proposed and designed to compensate large-scale off-axis HOE aberrations. In order to enhance image quality, the projection system is precisely simulated and the grating pitch and alignment are calculated to increase the eye-box and uniformity.

We propose a holographic augmented reality (AR) display by using a cylindrical holographic optical element (HOE). The cylindrical HOE is used as a wavelength-selective reflective screen. A three-dimensional (3D) object is not reconstructed on the cylindrical HOE directly, but behind it as a virtual image. Thus, it becomes possible to superimpose the 3D reconstructed image with a real-existent 3D object without physical contact: augmented reality can be achieved. Moreover, in our method, the shape of the HOE is not planar but cylindrical. Thanks to its shape, the viewing zone of our method becomes much wider than that of planar hologram, where the viewing zone is fundamentally limited to only the forward region of the planar hologram. In our method, information of the 3D object to be reconstructed is coded into a conventional planar hologram such as a spatial light modulator (SLM). Then, the wavefront modulated by the planar hologram enters the cylindrical HOE. Because the cylindrical HOE reflects the incident wavefront with a very wide diverging angle, viewers can observe the 3D object from a very wide horizontal range. For this purpose, our method utilizes the reflection on the cylindrical surface. Thus, holograms for modulating the wavefronts have to be designed considering the reflection on the cylindrical HOE properly. In our method, wavefront propagation via the cylindrical HOE is calculated based on the geometric optics. To verify our method, we performed optical experiments, and our holographic AR display was successfully demonstrated.

In this paper, an advanced ray-tracing model for simulating holographic optical element is programmed and demonstrated in Zemax OpticStudio. The model integrates the physical properties of the hologram, such as diffraction direction and efficiency based on incident rays’ wave vector and polarization state, into the standard ray-tracing model. Two different algorithms are implemented and tested. The model also accounts for hologram emulsion shrinkage and refractive index shift. The utility of this new model is demonstrated with a case study of a multi-color holographic imaging system, where the structures of multi-color holograms are built with different methods and the full-color image simulation is performed. Results of different methods are compared and discussed.

Staphylococcus aureus (S. aureus) is a round-shaped, aggressive human pathogen that can grow either by fermentation or by utilizing an elective terminal electron acceptor without oxygen. These bacteria can spread from an infected person to others, and it can enter into the body via the bloodstream and can infect body parts and organs. To avoid spreading infections and life-threatening diseases, a rapid, non-invasive, non-contact expeditious detection system is required. In this paper, a holographic optical element based digital holographic interferometric (DHI) system has been demonstrated for the label-free imaging of S. aureus bacteria. A comparison has been made in the proposed holographic optical element based DHI system and the conventional off-axis Mach–Zehnder configuration based DHI system. The proposed DHI system is an economical, efficient and easy-to-operate interferometric system, and significantly improves the signalto- noise ratio of recorded digital holograms without any spatial filtering.

A dual-wavelength circular scanner with collinear transmit and receive axes has been developed for use in the SEAHAWK bathymetric lidar. The scanner optics consist of an achromatic prism pair located concentrically within a 11.3” diameter dual-zone holographic optical element (HOE). This scanner achieves coaligned green and infrared beams at a 20° off- nadir scan angle when using a 50W dual-wavelength laser (30W @ 532 nm and 20W @1064 nm) as the transmitter. The main engineering challenges in achieving the design were minimizing the optical pointing error between the four optical axes (two transmit and two receive) and developing a rugged prism pair design sufficient to withstand the high laser power. The design proved sensitive to fabrication and alignment errors so success depended on analyzing optical and mechanical tolerances, acknowledging fabrication limitations, measuring critical optical components, tailoring the design to the as- built components, and utilizing a custom alignment fixture featuring a digital autocollimator. Final measurements of the deployed scanner indicate its optical pointing error has a cone half angle error of less than 0.06° (1 mrad).

We proposed a three-dimensional (3D) holographic waveguide-type augmented reality (AR) system based on integral imaging using the mirror array. As same with the conventional holographic waveguide, two holographic optical element (HOE) films are utilized as in- and out-couplers, that are located at the input and output parts of the waveguide. The main role of the in-coupler HOE is that reflecting the light beams come from the micro display into the waveguide, and out-coupler reflects the transmitted light beams through the waveguide to the observer eye. On the basic of the main advantages of conventional holographic waveguide structure such as the light-weight and thin-size, the proposed system has an additional critical advantage that the observer can see the realistic 3D visualizations reconstructed by the outcoupler HOE-mirror array (HOE-MA), instead of simple two-dimensional images, with the real-world scenes at same time. In the experiment, the AR feature has been successfully verified that the real-world scene and reconstructed virtual 3D image were observed simultaneously.

Augmented reality (AR) technology is a hot topic research field in recent years. It combines the real world scene and virtual 2D or 3D images. We propose two AR 3D display systems based on integral imaging (II) by using a micro-lens array holographic optical elements (HOE). In the first AR display system, we realize a dual-view-zone 3D display based on angle multiplexing technology. In recording process, two parallel beams with different incident angles illuminate a micro lens array (MLA) to form two sets of inclined spherical wave arrays, and another parallel beam illuminates the opposite side of the photopolymer. After exposure, the MLA-HOE is fabricated. In reconstruction process, only the Bragg matched light can be diffracted, while the Bragg mismatch light transmits through the HOE directly. Thus, when a projector beam satisfies the Bragg match condition, two inclined spherical wave arrays with the different diffraction directions will be rebuilt to realize the dual-view-zone AR 3D display. In the second AR display system, we improve the resolution of the AR 3D display by using a lenticular lens array HOE. In this system, we use a divergent light as the reference beam to simplify the display system and enlarge the display size of the HOE. The AR 3D display system has enhanced resolution and is compact.

The novel design for the compact augmented reality (AR) glasses that utilize holographic optical element (HOE) as a combiner is presented. The wide field of view (FoV) that is larger than 90°, full color and high contrast ratio (CR) are achieved based on the single layer HOE, which has the thickness of 25 μm. In order to implement compactness of AR glasses using HOE combiner, the combination of optical lenses is proposed. In this design, a chromatic aberration and astigmatism, which are caused by highly off-axis projection of the image onto HOE, and the precise wavefront reproduction that maximize the efficiency of the HOE are taken into account simultaneously. The geometrical image distortion is corrected by implementation of image pre-distortion algorithm. The interpupillary distance (IPD) adjustment is applied to compensate small eye box. Based on the design, wearable prototype is introduced. Through the experiments both on benchtop and prototype, at the distance of 2 m, large image with diagonal of 150 inches is displayed.

A Head-mounted displays (HMD) for augmented reality (AR) are researched to use work support. However, it has a fatigue problem occurred by the difference of focal length between the working space and displayed image. The technique of displaying holography using an electronic device called electro-holography are expected to solve the problem, because it is possible to display images at a free depth depending on the working position. So that, holographic HMDs for AR have been studied. But, since it is consisting optical components such as lenses, a mirror and a half mirror, the size and weight of the devise become large and heavy. On the other hand, holographic optical elements (HOE) is possible to produce functions of lens, beam splitter and diffraction grating. Also, it is possible to consolidate the functions of lenses and half mirrors into HOE. In this paper, we purpose near-eye holographic display device using HOE (Egarim-PBS made by Egarim Co., Ltd.). The Egarim-PBS is consolidated the functions of lenses, half mirrors, and optical waveguide, which are all optical components to construct the holographic HMD. So that, we can perform a simpler optical structure which is only consists of an Egarim-PBS and electronic devices. Our proposed concept was proven by experimentally. The proposed system has a potential to make holographic HMD became smaller and lighter than a conventional holographic HMD.

Head-up displays offer ease-of-use and safety advantages over traditional head-down displays when implemented in aircraft and vehicles. Unfortunately, in the traditional head-up display projection method, the size of the image is limited by the size of the projection optics. In many vehicular systems, the size requirements for a large field of view head-up display exceed the space available to allocate for these projection optics. Thus, an alternative approach is needed to present a large field of view image to the user. By using holographic optical elements affixed to waveguides, it becomes possible to reduce the size of the projection system, while producing a comparatively large image. Additionally, modulating the diffraction efficiency of some of the holograms in the system presents an expanded viewing eyebox to the viewer. This presentation will discuss our work to demonstrate a magnified far-field image with an in-line two-dimensional eyebox expansion. It will explore recording geometries and configurations and will conclude by discussing challenges for future implementation.

Head-up displays offer ease-of-use and safety advantages over traditional head-down displays when implemented in aircraft and vehicles. Unfortunately, in the traditional head-up display projection method, the size of the image is limited by the size of the projection optics. In many vehicular systems, the size requirements for a large field of view head-up display exceed the space available to allocate for these projection optics. Thus, an alternative approach is needed to present a large field of view image to the user. By using holographic optical elements affixed to waveguides, it becomes possible to reduce the size of the projection system, while producing a comparatively large image. Additionally, modulating the diffraction efficiency of some of the holograms in the system presents an expanded viewing eyebox to the viewer. This presentation will discuss our work to demonstrate a magnified far-field image with an in-line two-dimensional eyebox expansion. It will explore recording geometries and configurations and will conclude by discussing challenges for future implementation.

Publisher’s Note: This manuscript, originally published on 5 November 2018, has been withdrawn by the publisher for editorial reasons.

Publisher’s Note: This manuscript, originally published on 2 November 2018, has been withdrawn by the publisher for editorial reasons.

Holography can offer unique solutions to the specific problems faced by automotive optical systems. Frequently, when possibilities have been exhausted using refractive and refractive designs, diffraction can come to the rescue by opening a new dimension to explore. Holographic optical elements (HOEs), for example, are thin film optics that can advantageously replace lenses, prisms, or mirrors. Head up display (HUD) and LIDAR for autonomous vehicles are two of the systems where our group have used HOEs to provide original answers to the limitations of classical optic. With HUD, HOEs address the problems of the limited field of view, and small eye box usually found in projection systems. Our approach is to recycle the light multiple times inside a waveguide so the combiner can be as large as the entire windshield. In this system, a hologram is used to inject a small image at one end of a waveguide, and another hologram is used to extract the image several times, providing an expanded eye box. In the case of LIDAR systems, non-mechanical beam scanning based on diffractive spatial light modulator (SLM), are only able to achieve an angular range of few degrees. We used multiplexed volume holograms (VH) to amplify the initial diffraction angle from the SLM to achieve up to 4π steradian coverage in a compact form factor.

Holographic optical element (HOE) based digital speckle pattern shearing interferometer (DSPSI) is presented. The proposed DSPSI setup consists of volume phase holographic (VPH) grating combined with ground glass (diffuser) to shear the incident wavefronts. The shear of the two wavefronts is controlled by the distance between VPH grating and the ground glass. The sheared wavefronts on the ground glass are imaged on the image detector by an imaging lens. As both interfering wavefronts are of almost equal intensities, the contrast of the digital speckle pattern shear interferometric fringes is optimum. The proposed DSPSI setup is used for the measurement of temperature and temperature distribution in butane diffusion flame under the influence of magnetic field. In DSPSI system for the measurement of temperature in gaseous flames, two speckle interferograms are recorded: one in absence of the flame and another in the presence of the flame. These two recorded speckle interferograms are subtracted to get fringe pattern corresponding to the change in refractive index. The phase information is extracted from the experimentally obtained single fringe pattern by using Riesz transform method. The obtained phase information is used to calculate the change in refractive index and hence the temperature inside the flame under study.

In the present paper we consider an optical design of a head-mounted display with a free-standing holographic image combiner. The optical system works with a 24°×18° field of view and a 6mm pupil providing energy concentration up to 89% for a 20μm-pixel. The combiner represents a volume-phase reflective hologram recorded by two point sources. We demonstrate that the recording and replay angles for the hologram considerably vary across the surface, that causes perturbation and overall decrease of the diffraction efficiency. A revised optical design is presented. It provides a higher hologram efficiency together with a better image quality and decreased decenters of the components. The resultant gain in the median efficiency is factor of 5.3.

Studies to integrate increased sensory capacities of the wearer on head mounted displays are growing fast for applications in augmented, virtual and mixed reality. This paper focuses on the characterisation of the combiner of the UNO augmented reality glasses by GlassUp: a volume holographic optical element, recorded at 532 nm on Bayfol® HX, providing high diffraction efficiency over a narrow bandwidth at the desired angles. Furthermore, there is a negligible impact on the head mounted display frontal lens’s width and on the view of the real world. Studying the volume hologram, we developed a characterisation tool that gave us insight into the patterns inside the polymer and served as quality check for UNO. In particular, we designed a setup that provides Total Angular Characterisation through Optical Spectroscopy (TACOS), acquiring the visible spectral response of VHOEs as transmittance, reflectance or dispersion maps at arbitrary angles. Furthermore, it analyses the patterns through a custom fit based on the Kogelnik model. The early stages volumetric holograms presented undesirable secondary efficiency peaks causing ghosts, impairing both the vision of the real world and the image projected by the optical module. TACOS’ custom fit allowed us to conduct a quantitative analysis on the ghosts. In this work, we present an equilibrium study on all these parameters to find the better condition of projection. Moreover, we studied the impact of the recording parameters on the appearance of ghosts, e.g. tuning exposure, power ratios.

Photopolymer films (Bayfol® HX) have been recently introduced into the market place and prove themselves as easy to process for volume holographic optical element (vHOE) recording. The new Bayfol® HX instant 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 (AgHX) or dichromated gelatin (DCG). Besides the recording step no pre- or post-processing is necessary and easy mass production of vHOEs in a completely dry roll to roll process is possible. Due to the nature of vHOEs, multiplexing recording can be used to superimpose multiple optical functions in a single layer. This enables to merge angular wise precise full color diffractive combiner optics in one layer by spectral multiplexing, like RGB recording in Bayfol® HX film. Further optical sensing functions may be added by additional angular multiplexing. For reflection type vHOE recording the necessity of additional partial reflective layers or using total internal reflection (TIR) in a light guide becomes obsolete. Obviously, these unique properties of vHOEs could significantly simplify the layer structure of immersive displays like in Head-Mounted-Displays (HMD) and Head-Up- Displays (HUD). In this paper we investigate and demonstrate wavelength multiplexing recording in Bayfol® HX film with a specific focus on the design of the optical recording setup and its system and stability margins. Well controlled RGB recording power conditions enable high repeatability over extended operation periods of the RGB efficiency balance of reflective vHOEs.

Augmented reality (AR) technology, which integrates virtual computer-generated information into the real world scene, is believed to be the next-generation human-machine interface. However, most AR products adopt stereoscopic 3D display technique, which causes the accommodation-vergence conflict. To solve this problem, we have proposed two approaches. The first is a multi-planar volumetric display using fast switching polymer-stabilized liquid crystal (PSLC) films. By rapidly switching the films between scattering and transparent states while synchronizing with a high-speed projector, the 2D slices of a 3D volume could be displayed in time sequence. We delved into the research on developing high-performance PSLC films in both normal mode and reverse mode; moreover, we also realized the demonstration of four-depth AR images with correct accommodation cues. For the second approach, we realized a holographic AR display using digital blazed gratings and a 4f system to eliminate zero-order and higher-order noise. With a 4k liquid crystal on silicon device, we achieved a field of view (FOV) of 32 deg. Moreover, we designed a compact waveguidebased holographic 3D display. In the design, there are two holographic optical elements (HOEs), each of which functions as a diffractive grating and a Fresnel lens. Because of the grating effect, holographic 3D image light is coupled into and decoupled out of the waveguide by modifying incident angles. Because of the lens effect, the collimated zero order light is focused at a point, and got filtered out. The optical power of the second HOE also helps enlarge FOV.

One problem common to imaging techniques based on coherent light is speckle noise. This phenomenon is caused mostly by random interference of light scattered by rough surfaces. Speckle noise can be avoided by using advanced holographic imaging techniques such as optical scanning holography. A more widely known method is to capture several holograms of the same object and to perform an averaging operation so that the signal to noise ratio can be improved. Several digital filters were also proposed to reduce noise in the numerical reconstruction plane of holograms, even though they usually require finding a compromise between noise reduction and edge preservation. In this study, we used a digital filter based on compressive sensing algorithm. This approach enables to obtain results equivalent to the average of multiple holograms, but only a single hologram is needed. Filters for speckle reduction are applied on numerical reconstructions of hologram, and not on the hologram itself. Then, optical reconstruction cannot be performed. We propose a method based on direct-binary search (DBS) algorithm to generate binary holograms that can be reconstructed optically after application of a speckle reduction filter. Since the optimization procedure of the DBS algorithm is performed in the image plane, speckle reduction techniques can be applied on the complex hologram and used as a reference to obtain a binary pattern where the speckle noise generated during the recording of the hologram has been filtered.

Phoropters are the most common instrument used to detect refractive errors. During a refractive exam, lenses are flipped in front of the patient who looks at the eye chart and tries to read the symbols. The procedure is fully dependent on the cooperation of the patient to read the eye chart, provides only a subjective measurement of visual acuity, and can at best provide a rough estimate of the patient’s vision. Phoropters are difficult to use for mass screenings requiring a skilled examiner, and it is hard to screen young children and the elderly etc. We have developed a simplified, lightweight automatic phoropter that can measure the optical error of the eye objectively without requiring the patient’s input. The automatic holographic adaptive phoropter is based on a Shack-Hartmann wave front sensor and three computercontrolled fluidic lenses. The fluidic lens system is designed to be able to provide power and astigmatic corrections over a large range of corrections without the need for verbal feedback from the patient in less than 20 seconds.

We created a record of an optical field formed due to interference of a spherical divergent reference wave and signal plane wave in a self-developing photopolymer film using a He-Ne laser and Mach-Zehnder-like interferometric set-up. Due to Bragg reflections the recorded volume holographic grating acts as holographic lens and transforms the reference divergent wave onto a near-collimated one. After successful recording the diffraction efficiency of the lens is found to be 84% at Bragg angle. The lens is used to modify the radiation pattern of a commercially available red emitting LED. The effect of the holographic lens on the LED’s radiation pattern is investigated by far-field measurement of intensity pattern as function of angle for LED without the lens and with applied holographic lens.

We propose the coherent backlight unit (BLU) using Holographic Optical Element (HOE) for full-color flat-panel holographic display. The HOE BLU consists of two reflective type HOEs that change the optical beam path and shape by diffraction. The diverging incident beam is transformed to the collimated beam which has a very small diffraction angle (7.5°) by HOE 1 (H1) in order to illuminate the whole display. This collimated beam is converged to a point at a distance from the glass substrate by HOE 2 (H2). As a result, the diverging incident beam is converted to a point light by H1 and H2. When the high resolution Spatial Light Modulator (SLM) displaying Computer Generated Hologram (CGH) is illuminated by HOE BLU, the hologram image is displayed at a view point near focal point. Practically, we fabricated the full color HOE BLU for 5.5" flat panel holographic display by using the proposed design. At least 5.5" size of HOE is required to illuminate the whole panel. For this reason, we recorded 150 mm x 90 mm size HOE on the 10 mm thickness glass substrate. This HOE BLU exhibits a total efficiency of 8.0% at Red (660 nm), 7.7% at Green (532 nm), 3.2% at Blue (460 nm) using optimized recording conditions for each wavelength. Finally, a bright full color hologram image was achieved.

We discuss on the recent state of the augmented reality (AR) display technology. In order to realize AR, various seethrough three-dimensional (3D) display techniques have been reported. We describe the AR display with 3D functionality such as light-field display and holography. See-through light-field display can be categorized by the optical elements which are used for see-through property: optical elements controlling path of the light-fields and those generating see-through light-field. Holographic display can be also a good candidate for AR display because it can reconstruct wavefront information and provide realistic virtual information. We introduce the see-through holographic display using various optical techniques.

The optical scheme of holographic printer for obtaining of holographic stereograms with an increasing field of view is proposed. Conventional holographic printers allow obtaining holographic stereograms with the field of view up to 90°. Proposed scheme allows increasing field of view up to 120°. The optical scheme is based on a diffuser and a diffraction optical element, the high-aperture diffractive lens. The experience of using the composite holographic lens and the amplitude diffractive lens based on a binary Fresnel zone plate as a high-aperture diffractive lens is described. Samples of high-aperture diffractive lens with f-number f/0.3 are obtained and investigated. Samples of holographic stereograms are obtained using samples of high-aperture diffractive lens.

A method for realizing a three-dimensional see-through augmented reality in Fourier holographic display is proposed. A holographic optical element (HOE) with the function of Fourier lens is adopted in the system. The Fourier hologram configuration causes the real scene located behind the lens to be distorted. In the proposed method, since the HOE is transparent and it functions as the lens just for Bragg matched condition, there is not any distortion when people observe the real scene through the lens HOE (LHOE). Furthermore, two optical characteristics of the recording material are measured for confirming the feasibility of using LHOE in the proposed see-through augmented reality holographic display. The results are verified experimentally.

Holographic optical elements (HOEs) play important role in realization of compact and cost effective systems. Use of HOE not only give above mentioned advantages but an HOE can also be used to design and develop unusual system configurations which may not be possible, at all, using the concepts of conventional optics. Present paper describes fabrication of an HOE which contains both, reference and object, beams required for recording an off-axis hologram of phase objects. Illumination of HOE with a collimated beam generates two spatially separated collimated beams which intersect each other in the hologram recording plane. This combined HOE reduces a large number of opto-mechanical components and alignment related issues, generally encountered in off-axis holography. Fabrication of HOE and recording of holograms of phase objects using the HOE is described and experimental results of reconstructed holograms are presented.

Many areas of optical science and technology require fast and accurate measurement of the radiation wavefront shape. Today there are known a lot of wavefront sensor (WFS) techniques, and their number is growing up. The last years have brought a growing interest in several schematics of WFS, employing the holography principles and holographic optical elements (HOE). Some of these devices are just the improved versions of the standard and most popular Shack-Hartman WFS, while other are based on the intrinsic features of HOE. These are, for instance the modal holographic WFS configurations and some others. The paper presents the review of such techniques.

We proposed the 360-degree 3D display system which is composed of a flat panel display, a light control film, and holographic optical element (HOE). The HOE is a diffraction grating which is made by holography technique. HOE lens can be produced on the thin polygonal glass plate. The light control film and HOE lenses are used to control the direction of light from the flat panel display in our system. The size of proposed system depends on the size of the flat panel display is because other parts of proposed system are thin and placed on the screen of the flat panel display. HOE lenses and a light control film are used to control lights from multiple pixels of a flat panel display to multiple viewpoints. To display large 3D images and to increase viewpoints, we divided parallax images into striped images and distributed them on the display for multiple viewpoints. Therefore, observers can see the large 3D image around the system. To verify the effectiveness of the proposed system, we made the experimental system. To verify the effectiveness of the proposed system, we constructed the part of the proposed system. The experimental system is composed of the liquid crystal display (LCD), prototype HOE lenses, and light control films. We confirmed that experimental system can display two images to different viewpoints. This paper describes the configuration of the proposed system, and also describes the experimental result.

In this paper, the design and produce of the wedge-shaped waveguide head-mounted display (HMD) based on reflection holographic optical element (RHOE) are described. A variety of factors were considered when designing, such as loss of efficiency, volume, wide field of view (FOV), and eye box. The thickness of the designed wedge-shaped waveguide can be reduced to two times in comparison with the system that uses the conventional reflective optics in the waveguide. The measured optical efficiency of the monocular HMD using HOE is 34%, with 15° FOV and a large eye box. The results confirm that the designed and fabricated waveguid e can be employed in future commercial HMD. Keywords: Holographic optical element, head mounted display, field of view 1. INTRODUCTION The HMD comes to be an important device along with two technological environment changes, i.e. widespread use of mobile video contents such as digital broadcasts and video download services via cellular phone networks or wireless players and mobile TV devices which weights and sizes are esse ntially determined by the size of those displays [1-3]. It has mainly three advantages beyond a direct-viewing mobile display; hands-free, high privacy nature, and larger screen size. Undoubtedly, the HMD has a huge potential market when used as a mobile display, and in applications for mixed reality, games, and navigation. Therefore, it will need to be more affordable and attractive enough so that users may easily adopt them. The major issues for an HMD de signer are price, performance, and features. Using a waveguide, the physical display, and electronics can be moved to the side and a fully unobstructed view of the world can be achieved, therefore opening up the possibilities to true augmented reality experiences. Various waveguide techniques have existed for some time for see-through HMDs. These techniques include polarized optics, reflective optics, diffraction optics [4, 5], and holographic optics. In comparison with other waveguide HMDs, the holographic waveguide technique has the advantage of having a small volume, low price, and good command of angular and spectral selectivity of optical elements. The requirements for each specific application lead to the HMD design process using a holographic waveguide. The various waveguide structures and designed HOE changed the beam paths through the system. From the existing light path in a waveguide structure, we attempt to determine the ap propriate design for the system by investigating the features of the HOE and the light path, according to the waveguide struct ure. Certainly, to obtain a satisfactory FOV, a variety of factors were considered during the design process, such as the volume and reducing efficiency loss. In this work, the design and proof of the concept of a wide angle holographic waveguide for monocular HMD’s are present. Even though the conventional reflective optics without holographic mirror can make the TIR, the main problem arises due to the limited size of the resulting eye box and the thickness of the waveguide optics.

Phase masks are important optical elements that have been utilized for several decades in a large variety of applications. Recently, we demonstrated a new type of phase masks fabricated by encoding phase profiles into volume Bragg gratings, allowing these holographic elements to be used as phase masks at any wavelength capable of satisfying the Bragg condition of the hologram. Here, we present a new method of true achromatization of this type of phase masks that removes the need for angle tuning and is implemented by combining this holographic phase masks approach with a pair of surface diffraction gratings.

Higher Order Bessel Beams (HOBBs) have many useful applications in optical trapping experiments. The generation of HOBBs is achieved by illuminating an axicon by a Laguerre-Gaussian beam generated by a spiral phase plate. It can also be generated by a Holographic Optical Element (HOE) containing the functions of the Spiral Phase Plate (SPP) and an axicon. However the HOBB’s large focal depth reduces the intensity at each plane. In this paper, we propose a multifunctional Diffractive Optical Element (DOE) containing the functions of a SPP, axicon and a Fresnel Zone Lens (FZL) to generate higher efficiency higher order Bessel-like-beams with a reduced focal depth. The functions of a SPP and a FZL were combined by shifting the location of zones of FZL in a spiral fashion. The resulting element is combined with an axicon by modulo-2π phase addition technique. The final composite element contains the functions of SPP, FZL and axicon. The elements were designed with different topological charges and fabricated using electron beam direct writing. The elements were tested and the generation of a higher order Bessel-like-beams is confirmed. Besides, the elements also generated high quality donut beams at two planes equidistant from the focal plane of the FZL.

Holographic optical element (HOE) have classically been designed using grating theory, logically so, since an HOE is a grating produced on film by two interfering beams of coherent light. This paper describes the development of full color HOE recorded on aspherical substrate using a photopolymer. The reflection HOE was evaluated by measuring the diffraction efficiencies of holographic volume gratings recorded individually at 633 nm, 532 nm, and 473nm wavelengths. The spectral characterization of the HOE, recorded using a combined single beam, and recorded using sequential beam, was carried out. Practical methods for fabrication of high efficiency aspheric HOE by single layer photopolymer were developed.

Thermodynamic principles limit the conversion efficiency of a single bandgap organic photovoltaic (OPV) cell to 33%1 . In order to increase efficiency, multiple OPV devices can be combined to cover a larger spectral range of the incident solar spectrum. The most common way of doing this is to mount multiple bandgap cells in tandem or series. However, stacked multijunction systems have limitations, such as current-matching constraints and optical quality of the OPV layer. A separated arrangement with spectrum splitting is a promising alternative to the stacked tandem approach. In this paper, two organic photovoltaic cells with complementary EQE curves are integrated into a holographic spectrum splitting module. The highest possible conversion efficiency of this two-cell combination is quantified assuming an ideal spectral filter as a reference. A spectrum splitting module is built, consisting of a reflective hologram oriented at an angle to split the incident beam into two spectral bands. The holographic beamsplitting system is assembled and studied under a solar simulator. Power output and conversion efficiency of the holographic spectrum splitting system is evaluated in terms of Improvement over Best Bandgap (IoBB) of the two-cell combination. The combined system has a measured improvement over its best single cell of 12.30% under a solar simulator lamp and a predicted improvement of 16.39% under sunlight.

In this paper, we propose multiple recording process of photopolymer for a full-color multi-view including multiple-view auto-stereoscopic 3D display system based on VHOE (Volume Holographic Optical Element). To overcome the problems such as low resolution, and limited viewing zone of conventional 3D-display without glasses, we designed multiple recording condition of VHOE for multi-view display. It is verified that VHOE may be optically made by angle-multiplexed recording of pre-designed multiple-viewing zone that uniformly is recorded through optimized exposuretime scheduling scheme. Here, VHOE-based backlight system for 4-view stereoscopic display is implemented, in which the output beams that playing a role reference beam from LGP(Light guide plate)t may be sequentially synchronized with the respective stereo images displayed on the LCD panel.

We propose a retinal projection type super multi-view head-mounted display (HMD). The smooth motion parallax provided by the super multi-view technique enables a precise superposition of virtual 3D images on the real scene. Moreover, if a viewer focuses one’s eyes on the displayed 3D image, the stimulus for the accommodation of the human eye is produced naturally. Therefore, although proposed HMD is a monocular HMD, it provides observers with natural 3D images. The proposed HMD consists of an image projection optical system and a holographic optical element (HOE). The HOE is used as a combiner, and also works as a condenser lens to implement the Maxwellian view. Some parallax images are projected onto the HOE, and converged on the pupil, and then projected onto the retina. In order to verify the effectiveness of the proposed HMD, we constructed the prototype HMD. In the prototype HMD, the number of parallax images and the number of convergent points on the pupil is three. The distance between adjacent convergent points is 2 mm. We displayed virtual images at the distance from 20 cm to 200 cm in front of the pupil, and confirmed the accommodation. This paper describes the principle of proposed HMD, and also describes the experimental result.