Search

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We propose a holographic near‐eye display system incorporating holographic optical elements. In our design, a holographic optical element is used to replace the traditional eyepiece as a combiner for holographic near‐eye display, a tilted‐plane diffraction propagation algorithm is used to optimize the holograms, and finally an Augmented Reality near‐eye display based on the holographic optical element is realized, and the wearing scheme is demonstrated. [ABSTRACT FROM AUTHOR]

We have developed a novel 360‐degree transparent light field display with 120 viewpoints for fully volumetric 3D video experience. It was achieved by a rotating cylindrical transparent highly‐directional holographic screen and a high‐frame‐rate projector. It enables multiple people to simultaneously view bright and occlusion‐capable volumetric images from any direction. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Epidemics are severe around the world, and people must wear face masks and authenticate in and out of public places to reduce the risk of virus transmission. However, wearing a face mask cannot detect facial features and affect the accuracy of the recognition system, so limitations need to be overcome. Considering that identity recognition does not rely solely on facial information, we use KINECT to get a wider range of skeleton information for judgment. At the same time, it is proposed to replace the diffractive optical elements of the KINECT sensor with a holographic optical element. The problem of uneven intensity and distortion of the light field can be improved to improve the accuracy of skeleton detection. Next, clear scattering information and images are provided to MTCNN and FaceNet models for whole-body imaging identification and pre-training. Besides, we only keep the skeleton features to represent the standing posture and ignore the difference in appearance, which can reduce the changing appearance features. The experimental results show that the proposed method and model with the improved KINECT can solve the problem that is difficult to identify with the mask, and its accuracy is 99.5%. [ABSTRACT FROM AUTHOR]

We propose a holographic printing–recording technology for near-eye display through volume holographic grating analysis in hologram recording and reconstruction. Most near-eye displays are designed based on waveguide-type and analog holographic optical elements, resulting in disruption of the uniformity of the image because of the difference between the initial recording conditions and the source image. This problem can be addressed using holographic printing technology to modulate different diffraction efficiencies for each holographic element. This study uses a digital HOE screen that can fabricate and reconstruct augmented reality images of 1.17”, 1.76”, and 2.35” in a field of view of 28.07°, 41.11°, and 53.13°, respectively, at a distance of 53.33 mm from the eye. Moreover, augmented images are realized with higher diffraction efficiency than conventional methods, simplifying the design and facilitating mass production of uniformed products using digital holographic printing technology.

A method for dual‐view holographic display based on Bragg mismatched reconstruction of holographic optical element (HOE) is proposed. Under the Bragg mismatched condition, the reconstructed images are guided into two separated viewing zones to realize dual‐view holographic display. Meanwhile, the viewing angle of each perspective is increased to 11.2°, which is almost 2.5 times as large as the traditional holographic display system. The design process of HOE is simple only by interference of plane reference wave and converging spherical signal wave, which has high practicability. Furthermore, the HOE can mix the virtual 3D image with real‐world scenes, which could implement augmented reality (AR) display. Experiments validate that the proposed system can achieve dual‐view holographic AR three‐dimensional (3D) display with accommodation effect. [ABSTRACT FROM AUTHOR]

Limited by the low space-bandwidth product of the spatial light modulator (SLM), it is difficult to realize multiview holographic three-dimensional (3D) display. To conquer the problem, a method based on the holographic optical element (HOE), which is regarded as a controlled light element, is proposed in the study. The SLM is employed to upload the synthetic phase-only hologram generated by the angular spectrum diffraction theory. Digital grating is introduced in the generation process of the hologram to achieve the splicing of the reconstructions and adjust the position of the reconstructions. The HOE fabricated by the computer-generated hologram printing can redirect the reconstructed images of multiview into multiple viewing zones. Thus, the modulation function of the HOE should be well-designed to avoid crosstalk between perspectives. The experimental results show that the proposed system can achieve multiview holographic augmented reality (AR) 3D display without crosstalk. The resolution of each perspective is 4K, which is higher than that of the existing multiview 3D display system. [ABSTRACT FROM AUTHOR]

A multi-wavelength holographic grating using photopolymer is presented for a holographic solar concentrator system. Currently, volume holographic optical elements (HOEs) have been proposed for application in solar concentrators due to their advantages, such as lightweight, selective wavelength, and passive tracking. However, their efficiency depends on the central wavelength, which is determined by both the recording material and the recording angle. In this work, a transmission holographic grating with multiple wavelengths is proposed to enhance the performance of holographic solar concentrator systems. The diffraction efficiency and spectral range are significant factors in determining the concentrated efficiency of solar energy. The optimal efficiency of transmission grating is derived based on the optical characteristics of the photopolymer and the wavelength selectivity is then analyzed to compare the concentrated efficiency. The experimental results indicate that the dichromatic transmission grating with an average diffraction efficiency of 70 % and a wavelength band of 278 nm has a concentrated efficiency of 48.7 %. Compared to monochromatic and trichromatic holographic grating, dichromatic grating can concentrate more energy with a wider spectral band. [ABSTRACT FROM AUTHOR]

• Head-up display systems with ultra-simplified structure and low cost are designed and fabricated. • Head-up display system uses a freeform holographic optical element as the optical combiner (OC). • Head-up display system comprises only the optical combiner (OC) and the picture generating unit (PGU). • Feasible display performance and optical see-through viewing are achieved. • The proposed head-up display systems can be applicable for the fields of vehicle, exhibition, entertainment, etc. Head-up display (HUD) systems play an important role in the fields of navigation prompts in aircraft/vehicle, entertainment display, exhibition, etc., In this paper, we propose the design and fabrication of novel ultra-simplified and low-cost HUD systems that only comprise the picture generating unit (PGU) and the optical combiner (OC), where OC is a holographic optical element (HOE) fabricated using freeform wave. OC possesses an equivalent degrees of design freedom compared with optical freeform surface, and it simultaneously performs the optical functions of correcting the off-axis system aberrations and combining the see-through beams. Based on the proposed structure, an off-axis reflective HUD system prototype is designed and fabricated. In addition, a HUD system with a simplified structure applied for the vehicle fields is designed. The proposed ultra-simplified system structure opens a new gateway for developing the next generation HUD systems as well as other AR displays systems in the fields of industry, entertainment, exhibition, vehicle, etc. [ABSTRACT FROM AUTHOR]

• We propose a design method to expand the eyebox size of lensless holographic near-eye-display (NED) system benefiting from the passive eyebox replication technique with the combinational use of the horizontally separated high-order diffractions of the SLM and holographic optical element (HOE) combiner. • When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term under spherical wave illumination. • The proposed prototype system not only replicates the base eyebox size, also increases sufficient field of view (FOV) due to the benefit of the spherical divergence wave illumination of the SLM, breaking the trade-off relationship between the FOV and eyebox. We expand the eyebox size of a lensless holographic near-eye-display (NED) using passive eyebox replication technique that incorporates a spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox size is replicated in the horizontal direction by using the horizontal high-order diffractions of an SLM under spherical wave illumination and a multiplexed HOE combiner. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. The astigmatism introduced during HOE fabrication is counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The prototype system shows simple and effective, distortion-free eyebox expansion of a wide-angle, lensless, holographic NED. [ABSTRACT FROM AUTHOR]

We present a novel design of the lightguide type optical see-through Maxwellian near-eye display. The proposed display reconfigures vertically long input images to horizontally long output images for wide horizontal viewing-angle. The reconfiguration of the input images is optically performed by using folding holographic optical elements and different numbers of total internal reflections within the lightguide. The upper and lower parts of the in-coupled image undergo different numbers of total internal reflections, being separated into two images. After the separation, the upper part is additionally diffracted by the folding holographic optical element to the side of the lower part. Finally, the horizontally tiled upper and lower parts are out-coupled towards the eye by corresponding holographic optical elements. The optical power of the output couplers converges the output image to a focal spot on the eye pupil so that users experience all-in-focus images. In the optical experiment, the wavelength difference between the display and the holographic optical element recording system was pre-compensated by adjusting the recording angle. Our prototype successfully demonstrates horizontal tiling of the upper and lower parts of the input images, showing a two-times larger output horizontal field of view than the input.

We present a novel design of the lightguide type optical see-through Maxwellian near-eye display. The proposed display reconfigures vertically long input images to horizontally long output images for wide horizontal viewing-angle. The reconfiguration of the input images is optically performed by using folding holographic optical elements and different numbers of total internal reflections within the lightguide. The upper and lower parts of the in-coupled image undergo different numbers of total internal reflections, being separated into two images. After the separation, the upper part is additionally diffracted by the folding holographic optical element to the side of the lower part. Finally, the horizontally tiled upper and lower parts are out-coupled towards the eye by corresponding holographic optical elements. The optical power of the output couplers converges the output image to a focal spot on the eye pupil so that users experience all-in-focus images. In the optical experiment, the wavelength difference between the display and the holographic optical element recording system was pre-compensated by adjusting the recording angle. Our prototype successfully demonstrates horizontal tiling of the upper and lower parts of the input images, showing a two-times larger output horizontal field of view than the input. [ABSTRACT FROM AUTHOR]

Continual improvements to holographic recording materials make the development of volume holographic optical elements increasingly more attainable for applications where highly efficient, lightweight diffractive optical elements can replace conventional optics. A fast-curing, water resistant photosensitive sol–gel capable of volume holographic recording has recently drawn attention for its extreme environmental and physical robustness, in particular its water/moisture and scratch resistance. However, to date, the refractive index modulation has been limited. While water-resistant properties are invaluable in the face of the weathering which many practical systems for outdoor applications will endure, high refractive index modulation is also important in order to facilitate high diffraction efficiency holograms recorded in relatively thin layers. Lower grating thickness ensures a large angular and wavelength range of operation-properties that are critical for many applications of holographic optical elements such as solar light harvesting, optical displays and illumination management. For any application where low-cost mass production is envisaged, sensitivity/writing speed is also a crucial factor. In this research, we studied the recording properties of these water-resistant photosensitive sol–gel layers at two different recording wavelengths (532 and 476 nm) and investigated methods for improving these properties. We report more than two-fold improvement of the refractive index modulation from 1.4 × 10 − 3 to 3.3 × 10 − 3 in layers of thickness ranging from 40–100 μm and more than an order of magnitude increase in photosensitivity/recording speed through better matching between recording wavelength and layer absorption, chemical alterations and thermal post-processing techniques. [ABSTRACT FROM AUTHOR]

• Retinal projection display with realistic accommodation cue is proposed. • The proposed system consists of three modules: human eye accommodation response detection module, refocused image generation and matching module, retinal projection display module. • Our method can retain the characteristics of high resolution and free focusing while adding the accommodation cue. Although retinal projection displays have the feature of being always in focus and no loss of image resolution, the lack of accommodation cue makes it difficult to perceive the depth correctly. In this paper, we proposed a retinal projection display system with realistic accommodation cue. The proposed system adds an optometric device to the conventional holographic optical element (HOE)-based retinal projection display. The optometric device detects the accommodation response of the human eyes to observe a real scene at different distances. According to the focused depth of the human eye, refocused images containing realistic focusing and defocusing information are generated through the light field refocusing technology. By establishing a focus depth-lookup table, the refocused images matching with the focused depth of human eye was presented to the human eye, so as to restore the retinal projection display with realistic accommodation cue. A proof-of-concept prototype based on the proposed structure was developed, and the experimental results presented retinal projection displays with realistic accommodation cue at a depth between 250 mm and 400 mm. The proposed system retains the characteristics of high resolution and free focusing while adding the accommodation cue. The developed prototype has great competitiveness in near-eye displays. [ABSTRACT FROM AUTHOR]

Featured Application: Development of holographic optical elements with controlled diffraction efficiency and improved environmental stability in water-resistant photopolymerisable hybrid sol-gel material. Photopolymerisable glasses are holographic recording materials which provide good recording capability, improved dimensional stability, and negligible shrinkage. Recently, a novel photopolymerisable hybrid sol-gel (PHSG) for holographic recording of volume gratings has been reported. The PHSG has significantly improved gelation time and high water resistance, both of which make it an attractive material for mass production of holographic optical elements (HOEs) with no sensitivity to ambient humidity. In order to achieve full control over the performance of the material and further improve its properties, a study of grating formation under holographic patterning is essential. This paper reports characterisation of the grating recording in PHSG. The approach is based on the analysis of grating parameters during exposure and post-recording dark processes. The obtained results suggest that photopolymerisation of the methacrylate groups is the main contributor to the creation of refractive index modulation during exposure. During the dark process, the enhancement of the refractive index modulation is observed, probably due to further polycondensation. The observations made facilitate controlled and predictable diffraction efficiency of gratings recorded on the PHSG, thereby furthering the prospect of the development of HOEs with customisable specification. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By presenting always-in-focus virtual images, Maxwellian near-eye displays can remove the vergence accommodation conflict, which causes eye fatigue or dizziness. Described in this paper are an implementation process and observations of virtual images of the optical-see-through Maxwellian near-eye display prototype made with a three-dimensional printer.

Limited by the low space-bandwidth product of the spatial light modulator (SLM), it is difficult to realize multiview holographic three-dimensional (3D) display. To conquer the problem, a method based on the holographic optical element (HOE), which is regarded as a controlled light element, is proposed in the study. The SLM is employed to upload the synthetic phase-only hologram generated by the angular spectrum diffraction theory. Digital grating is introduced in the generation process of the hologram to achieve the splicing of the reconstructions and adjust the position of the reconstructions. The HOE fabricated by the computer-generated hologram printing can redirect the reconstructed images of multiview into multiple viewing zones. Thus, the modulation function of the HOE should be well-designed to avoid crosstalk between perspectives. The experimental results show that the proposed system can achieve multiview holographic augmented reality (AR) 3D display without crosstalk. The resolution of each perspective is 4K, which is higher than that of the existing multiview 3D display system.

• A dual-mode optical see-through integral imaging display system which can reconstruct 3D images in both real and virtual display modes simultaneously was proposed. The proposed system greatly extends the depth of field of 3D image. • A dual-mode lens array holographic optical element was proposed and specially designed by using two sets of lens arrays, and it featured as a lens array with positive focal length and negative focal length under the illumination of different probe beams. • On the one hand, the focal length of the lens array is increased from 2 mm to 14mm through the combination of two sets of lens arrays, and the depth of field can be improved. On the other hand, two central depth planes are generated simultaneously, and each central depth plane corresponds to a depth of field. These solutions increase the depth of field of the proposed system from 24.5mm to 190mm. Conventional optical see-through integral imaging display system using holographic optical element (HOE) is actually in focused display mode whose central depth plane (CDP) is very close to the HOE plane, and the depth of field (DOF) of the system is limited to several centimeters around the HOE plane. In this paper, we proposed a dual-mode optical see-through integral imaging display system to reconstruct 3D images in both real and virtual display modes simultaneously and greatly extend the DOF. A dual-mode lens array HOE (DM-LAHOE) was specially designed by using two sets of lens arrays, and it featured as a lens array with positive focal length and negative focal length under the illumination of different probe beams. The designed DM-LAHOE can generate two CDPs away from the HOE plane. Hence, the real mode and virtual mode of the integral imaging display can be achieved simultaneously, and the DOF of the system was greatly improved by increasing the focal length of the recorded lens array and the number of CDPs. In the experiment, the DM-LAHOE with large focal lengths of ±14mm was fabricated, and the DOF of the proposed system was increased from 24.5mm to 190mm. The proposed dual-mode optical see-through integral imaging display system is expected to be applied in the fields of augmented reality display, vehicle display, window display, etc. [ABSTRACT FROM AUTHOR]

Abstract In this contribution, we investigate hybrid single vision spectacle lenses (SVSLs) consisting of holographic optical elements (HOEs) embedded into a refractive lens. We evaluate the performance of two examples of hybrid SVSLs in terms of their distributions of spherical error (SPH error), astigmatic error (AST error) and transverse chromatic error (CE) over the lens surface, simulating the optical performance for the patient’s rotating eye. We find that, particularly for high prescription values, hybrid SVSLs outperform their purely refractive counterparts in terms of CE with the additional benefit of reducing the lens thickness. As such, we show that hybrid refractive, holographic designs can be a viable alternative to purely refractive SVSLs for high prescription SVSLs.

Holographic optical elements (HOEs) have been used as important tools for implementing augmented reality (AR) and see-through displays because they are transparent and thin. Moreover, as HOEs usually come in the shape of a thin film, they can be bent, used for coating, or attached to curved surfaces. While they can be used to implement curved AR displays, however, the applications of the curved HOE have not been sufficiently studied. In this paper, an analysis method for curved/bent HOEs using the coupled-wave theory and the numerical ray tracing method is introduced. Using this method, the influence of the surface curvature on the optical characteristics of HOEs, including the aberration and diffraction efficiency, was analyzed. Also presented herein is a method of designing the optimal curvature that can reduce the aberration. Curved HOEs can be applied to see-through displays such as head-mounted displays (HMDs), head-up displays (HUDs), or transparent screens. They can be used to expand the field of view (FOV) and to reduce the form factor. The proposed analysis method provides a useful guideline for designing practical curved see-through displays.

Continual improvements to holographic recording materials make the development of volume holographic optical elements increasingly more attainable for applications where highly efficient, lightweight diffractive optical elements can replace conventional optics. A fast-curing, water resistant photosensitive sol–gel capable of volume holographic recording has recently drawn attention for its extreme environmental and physical robustness, in particular its water/moisture and scratch resistance. However, to date, the refractive index modulation has been limited. While water-resistant properties are invaluable in the face of the weathering which many practical systems for outdoor applications will endure, high refractive index modulation is also important in order to facilitate high diffraction efficiency holograms recorded in relatively thin layers. Lower grating thickness ensures a large angular and wavelength range of operation-properties that are critical for many applications of holographic optical elements such as solar light harvesting, optical displays and illumination management. For any application where low-cost mass production is envisaged, sensitivity/writing speed is also a crucial factor. In this research, we studied the recording properties of these water-resistant photosensitive sol–gel layers at two different recording wavelengths (532 and 476 nm) and investigated methods for improving these properties. We report more than two-fold improvement of the refractive index modulation from 1.4×10−3 to 3.3×10−3 in layers of thickness ranging from 40–100 μm and more than an order of magnitude increase in photosensitivity/recording speed through better matching between recording wavelength and layer absorption, chemical alterations and thermal post-processing techniques.

Modern Pepper's ghost—“floating hologram”—systems generally use transparent screens called half mirrors or foils. this system must have the same screen size as the image size in order to display a large-sized image. Further, depth of the image can only be obtained from the distance between the screen and the display panel. These limitations can be overcome using holographic optical elements (HOE). HOE is made by recording as a refractive force of the lens with holographic material. In this study, the numerical values of the reconstructed images were theoretically analyzed through optical ray tracing, and the theoretical design of the reconstructed image size and depth plane was numerically measured and experimentally verified.

We propose a novel design to implement eyeglasses‐style Maxwellian‐view near‐eye display for augmented reality. In our design, holographic optical element is fabricated and used as an off‐axis lens array to expand the eyebox for near‐eye display. A prototype with eyeglasses‐style compact form factor was successfully developed using a micro projector module as the display source and the prototype is successfully to achieve 60° wide field‐of‐view (FOV) and 10mm×10mm eyebox. [ABSTRACT FROM AUTHOR]

Photopolymerisable glasses are holographic recording materials which provide good recording capability, improved dimensional stability, and negligible shrinkage. Recently, a novel photopolymerisable hybrid sol-gel (PHSG) for holographic recording of volume gratings has been reported. The PHSG has significantly improved gelation time and high water resistance, both of which make it an attractive material for mass production of holographic optical elements (HOEs) with no sensitivity to ambient humidity. In order to achieve full control over the performance of the material and further improve its properties, a study of grating formation under holographic patterning is essential. This paper reports characterisation of the grating recording in PHSG. The approach is based on the analysis of grating parameters during exposure and post-recording dark processes. The obtained results suggest that photopolymerisation of the methacrylate groups is the main contributor to the creation of refractive index modulation during exposure. During the dark process, the enhancement of the refractive index modulation is observed, probably due to further polycondensation. The observations made facilitate controlled and predictable diffraction efficiency of gratings recorded on the PHSG, thereby furthering the prospect of the development of HOEs with customisable specification.

Light field 3D displays require a precise alignment between the display source and the micromirror-array screen for error free 3D visualization. Hence, calibrating the system using an external camera becomes necessary, before displaying any 3D contents. The inter-dependency of the intrinsic and extrinsic parameters of display-source, calibration-camera, and micromirror-array screen, makes the calibration process very complex and error-prone. Thus, several assumptions are made with regard to the display setup, in order to simplify the calibration. A fully automatic calibration method based on several such assumptions was reported by us earlier. Here, in this paper, we report a method that uses no such assumptions, but yields a better calibration. The proposed method adapts an optical solution where the micromirror-array screen is fabricated as a computer generated hologram with a tiny diffuser engraved at one corner of each elemental micromirror in the array. The calibration algorithm uses these diffusing areas as markers to determine the relation between the pixels of display source and the mirrors in the micromirror-array screen. Calibration results show that virtually reconstructed 3D scenes align well with the real world contents, and are free from any distortion. This method also eliminates the position dependency of display source, calibration-camera, and mirror-array screen during calibration, which enables easy setup of the display system. [ABSTRACT FROM AUTHOR]

Floating holograms using holographic optical element screens differ from existing systems because they can float 2D images in the air and provide a sense of depth. Until now, the verification of such displays has been conducted only on the system implementation, and only the diffraction efficiency and angle of view of the hologram have been verified. Although such displays can be directly observed with the human eye, the eye's control ability has not been quantitatively verified. In this study, we verified that the focus of the observer coincided with the appropriate depth value determined with experiments. This was achieved by measuring the amount of control reaction from the perspective of the observer on the image of the floating hologram using a holographic optical element (HOE). An autorefractor was used, and we confirmed that an image with a sense of depth can be observed from the interaction of the observer's focus and convergence on the 2D floating image using a HOE. Thus, the realization of content with a sense of depth of 2D projected images using a HOE in terms of human factors was quantitatively verified. [ABSTRACT FROM AUTHOR]

Holographic optical elements (HOEs) have a wide range of applications, including their emerging use in virtual and augmented reality displays, but their design and fabrication have remained largely limited to configurations using simple wavefronts. In this paper, we present a pipeline for the design, optimization, and fabrication of complex, customized HOEs that enhances their imaging performance and enables new applications. In particular, we propose an optimization method for grating vector fields that accounts for the unique selectivity properties of HOEs. We further show how our pipeline can be applied to two distinct HOE fabrication methods. The first uses a pair of freeform refractive elements to manufacture HOEs with high optical quality and precision. The second uses a holographic printer with two wavefront-modulating arms, enabling rapid prototyping. We propose a unified wavefront decomposition framework suitable for both fabrication approaches. To demonstrate the versatility of these methods, we fabricate and characterize a series of specialized HOEs, including an aspheric lens, a head-up display lens, a lens array, and, for the first time, a full-color caustic projection element. [ABSTRACT FROM AUTHOR]

By presenting always-in-focus virtual images, Maxwellian near-eye displays can remove the vergence accommodation conflict, which causes eye fatigue or dizziness. Described in this paper are an implementation process and observations of virtual images of the optical-see-through Maxwellian near-eye display prototype made with a three-dimensional printer. [ABSTRACT FROM AUTHOR]

A see‐through 2D/3D compatible display based on integral imaging is proposed. It consists of a lens‐array holographic optical element (LAHOE) film, a polymer dispersed liquid crystal (PDLC) film and two projectors. The see‐through projection screen is composed of the LAHOE film and the PDLC film. The PDLC film is tightly behind the LAHOE film. With applied voltage, the projection screen works in the transparent display mode. 3D image for Bragg matched image can be presented, and 2D image can also be presented. [ABSTRACT FROM AUTHOR]

This paper presents a wearable display system combined directional scattering holographic waveguide (DSHW) with goggle for augmented reality. DSHW and goggle are used to form a suitable exit pupil and a large field of view with high luminance uniformity, respectively. The results of design and experiments are given in detail. [ABSTRACT FROM AUTHOR]

A 3D/2D switchable display system based on integral imaging is proposed by using a projection screen and a projector. The projection screen consists of a lens array holographic optical element (LAHOE) and a polymer dispersed liquid crystal (PDLC) film. The experimental results prove the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

Phase compensation is a critical step for the optical measuring system using spatial light modulator (SLM). The wavefront distortion from SLM is mainly caused by the phase modulation non-linearity and non-uniformity of SLM’s physical structure and environmental conditions. A phase modulation characteristic calibration and compensation method for liquid crystal on silicon spatial light modulator (LCoS-SLM) with a Twyman-Green interferometer is illustrated in this study. A method using two sequences of phase maps is proposed to calibrate the non-uniformity character over the whole aperture of LCoS-SLM at pixel level. A phase compensation matrix is calculated to correct the actual phase modulation of the LCoS-SLM and ensure that the designed wavefront could be achieved. Compared with previously known compensation methods, the proposed method could obtain the phase modulation characteristic curve of each pixel on the LCoS-SLM, rather than a mono look-up table (LUT) curve or multi-LUT curves corresponding to an array of blocks over the whole aperture of the LCoS-SLM. The experiment results show that the phase compensation precision could reach a peak-valley value of 0.061λ in wavefront and this method can be applied in generating freeform wave front for precise optical performance.

• A novel technique to extend the field of view and enhance the resolution of an off-axis digital holographic system simultaneously, using a multifunctional holographic optical element is presented. • The main advantages of the proposed digital holographic system include a simple optical setup, Compact size, and Cost-effectiveness due to the use of fewer optical elements. • The system's feasibility demonstrates its ability to increase the field of view and enhance resolution at the same time. • The system's easy-to-set-up experimental configuration and impressive results make it a powerful tool for various optical imaging and empirical research applications. The spatial resolution and field of view (FOV) of the digital holographic system are limited by the finite pixel size of the image sensor. In order to record high-resolution digital holograms of larger objects at a shorter object-to-sensor distance, which is desirable for applications such as display, non-destructive testing, etc., the holographic system must have a larger FOV. We propose a compact off-axis digital holographic setup in which a multifunctional holographic optical element (MHOE) is employed in the path of the object and reference beams to improve the system's resolution simultaneously enhancing the FOV by utilizing the same specifications of the digital sensor. In this configuration, a diffractive optics property of the MHOE enhances the spatial resolution of the optical system. At the same time, the lens function recorded in the same MHOE enables a large imaging area. The experimental results obtained with the proposed configuration are compared to conventional digital holography, where the proposed configuration shows a 423% increase in the FOV. The quality of the reconstructed image with the proposed configuration is measured by calculating the structural similarity index measure (SSIM) value. Experimental results and simulations have verified the feasibility of the proposed system. Furthermore, the proposed system is incredibly compact due to the use of the MHOE. [ABSTRACT FROM AUTHOR]

Light field 3D displays require a precise alignment between the display source and the micromirror-array screen for error free 3D visualization. Hence, calibrating the system using an external camera becomes necessary, before displaying any 3D contents. The inter-dependency of the intrinsic and extrinsic parameters of display-source, calibration-camera, and micromirror-array screen, makes the calibration process very complex and error-prone. Thus, several assumptions are made with regard to the display setup, in order to simplify the calibration. A fully automatic calibration method based on several such assumptions was reported by us earlier. Here, in this paper, we report a method that uses no such assumptions, but yields a better calibration. The proposed method adapts an optical solution where the micromirror-array screen is fabricated as a computer generated hologram with a tiny diffuser engraved at one corner of each elemental micromirror in the array. The calibration algorithm uses these diffusing areas as markers to determine the relation between the pixels of display source and the mirrors in the micromirror-array screen. Calibration results show that virtually reconstructed 3D scenes align well with the real world contents, and are free from any distortion. This method also eliminates the position dependency of display source, calibration-camera, and mirror-array screen during calibration, which enables easy setup of the display system.

Floating holograms using holographic optical element screens differ from existing systems because they can float 2D images in the air and provide a sense of depth. Until now, the verification of such displays has been conducted only on the system implementation, and only the diffraction efficiency and angle of view of the hologram have been verified. Although such displays can be directly observed with the human eye, the eye’s control ability has not been quantitatively verified. In this study, we verified that the focus of the observer coincided with the appropriate depth value determined with experiments. This was achieved by measuring the amount of control reaction from the perspective of the observer on the image of the floating hologram using a holographic optical element (HOE). An autorefractor was used, and we confirmed that an image with a sense of depth can be observed from the interaction of the observer’s focus and convergence on the 2D floating image using a HOE. Thus, the realization of content with a sense of depth of 2D projected images using a HOE in terms of human factors was quantitatively verified.

Holographic sensor based on photopolymer has been much attention due to simple process,low cost,excellent performance,and obvious optical phenomenon. The fringe space recorded in the materials is changed when the environmental condition changes,especially temperature and humidity. It provides wavelength shift of diffraction peak,and the corresponding sensing process can be achieved. Temperature as a significant parameter can directly affect the sensing measurement of holographic sensor. This paper developed a novel N-isopropylacrylamide photopolymer with thermal-sensitivity,and the corresponding novel sensor based on the polymer. The comparison of thermal-sensitive capacity tests indicates an obvious improvement of * wavelength shift in response to the environmental conditions in novel photopolymer system. Temperature and humidity are two significant parameters for the holographic sensing response. The experimental result shows the blue shift of peak wavelength in exponential form at corresponding environmental conditions. In view of the evident experimental phenomenon and low cost,the corresponding experimental setup would be able to make the student understand the development of holographic optical elements and application area. [ABSTRACT FROM AUTHOR]

Several wavefront printers have been recently proposed. Since the printers can record an arbitrary computer-generated wavefront, they are expected to be useful for fabricating complex mirror arrays used in front projection 3-D screens without using real existing optics. We prototyped two transparent reflective screens using our hologram printer in experiments. These screens could compensate for a spherically distorted reference wave caused by a short projection distance to obtain an ideal reference wave. Owing to the use of the wavefront-printed screen, the 3-D display was simply composed of a normal 2-D projector and a screen without using extra optics. In our binocular system, reflected light rays converged to the left and right eyes of the observer and the crosstalk was less than 8%. In the light field system, the reflected light rays formed a spatially sampled light field and focused a virtual object in a depth range of ±30 mm with a ±13.5- deg viewing angle. By developing wavefront printing technology, a complex optics array may easily be printed by nonprofessionals for optics manufacturing. [ABSTRACT FROM AUTHOR]

The wavefront aberration compensation method of holographic optical element (HOE) for augmented reality system is proposed. The wavefront aberration is detected as a linear combination of Zernike polynomials using a phase shifting interferometry. The aberration of HOE is compensated using a correction wavefront profile with a spatial light modulator. The simulation and experiment verified that the proposed method can effectively improve the aberration of HOE. [ABSTRACT FROM AUTHOR]

Recently, holographic sensor based on polymer has been much noticed due to simple process, low cost, excellent performance, and obvious optical phenomenon. The fringe space recorded inside the materials can he changed when the environmental condition changes, especially temperature and humidity. It brings about wavelength shift of diffraction peak. The corresponding sensing process is achieved during the process. Temperature as a significant parameter can directly affect the sensing measurement of holographic sensor. This paper shows the temperature response characterization of holographic sensor. The peak wavelength of diffraction spectrum presents an intuitive temperature response process. The obvious blue shift of peak wavelength is observed during sensing process. The measuring average refractive index at various temperature and humidity demonstrate the inducement of the blue shift. The experiments provide the significant foundation and responsive parameters for its practical application and analyzing the sensing mechanism. Due to the evident experimental phenomena and low cost, the corresponding experimental setup would he able to make the student understand the development of holographic optical elements and application area. [ABSTRACT FROM AUTHOR]

We introduce a projection-type holographic 3D display in which a digitally designed holographic optical element (DDHOE) fabricated by the wavefront printing technique and digital holographic projection technique were combined. Since this system can achieve a higher degree of freedom of display size and visual angle via see-through DDHOE screen, it will accelerate the adoption of holographic three-dimensional displays in industrial applications, such as digital signage, in-car head-up displays, smart-glasses and head-mounted displays. [ABSTRACT FROM AUTHOR]

Recently, holographic optical element based on polymer has been paid much attention due to its low cost, simple process, excellent performance, and obvious optical phenomenon. The fringe space recorded inside the materials can be changed by the environmental conditions. It brings about wavelength shill of diffraction peak. The corresponding sensing process is achieved during the process. Based on acrylamide systems with polyvinyl alcohol (PVA) binder the novel holographic sensor is formed by solvent evaporation. This holographic sensor is sensitive to the environmental humidity. After osmosis of water molecules into the binder, the intermolecular forces can be changed by bonding with polar molecules and then the swelling process of hinder can he caused. Using fiber spectrometer to measure the diffraction wavelength, the wavelength shill is obvious for the instrument. The quantitative relations between relative humidity and holographic properties can bring about a calibration. [ABSTRACT FROM AUTHOR]

The aberrations of a conventional lens holographic optical element (HOE) are considerable because of the off-axis recording and diffraction nature. A freeform HOE was introduced to alleviate these aberrations. To design and optimize the recording wavefront of a freeform HOE, it is important to figure out the imaging properties of an HOE. We systematically derived a general characterization of the conjugate imaging equation of an elementary HOE recorded by two spherical wavefronts using the scalar diffraction theory. In our design, each patch of a freeform HOE is considered as an elementary HOE. The recording wavefronts of a freeform HOE is designed by determining each elementary HOE through the conjugate imaging equation. The image position predicted by the imaging equation is consistent with that of the finite ray-tracing method. The error when the imaging equation is applied to off-axis object points and different reconstruction wavelengths is eliminated effectively through coordinate transformation. Furthermore, based on this equation, a freeform HOE with 3 × 3 tiling elementary HOEs is designed to eliminate distortion and astigmatism of the HOE imaging system. A holographic printer to fabricate this freeform HOE is recommended. [ABSTRACT FROM AUTHOR]