Three-dimensional/two-dimensional convertible projection screen using see-through integral imaging based on holographic optical element

Compact full-color augmented reality near-eye display using freeform optics and a holographic optical combiner

We develop a compact full-color augmented reality near-eye display system with a multicolor holographic optical combiner and a freeform relay system. The digital image is produced by a full-color micro organic light-emitting diode (Micro-OLED) display module. The freeform relay system includes four freeform optics and a holographic optical mirror, which are employed to correct both the monochromatic and chromatic aberrations caused by the holographic optical combiner. The two multicolor holographic mirrors have a three-layer laminated structure and are delicately fabricated to yield an improved diffractive efficiency and a reduced efficiency difference for red, green, and blue colors. The high degrees of freedom of freeform optics, and the thin and light nature of the holographic optical combiner yield a compact form factor near-eye display system with a diagonal field of view (FOV) of 20° and the eye-box of 5 mm × 5 mm. Two prototypes are built to demonstrate the feasibility of the proposed display system.

Distortion-Corrected Integral Imaging 3D Display System Based on Lens Array Holographic Optical Element

We propose a distortion-corrected integral imaging (II) 3D display system based on lens array holographic optical element (LAHOE). The LAHOE is used as a projection screen. The projection beam of the LAHOE is parallel light. Hence, the projection system consists of a spatial light modulator, a reverse projection lens, a relay optical element, and a telecentric lens. The acquired 3D data and the reconstructed 3D image of II are symmetrically related to each other. Therefore, there is lens distortion in the projection system. To avoid affecting the viewing experience of the viewers, the elemental image array (EIA) is projected obliquely on the LAHOE, causing the lateral distortion of the EIA. There is a position deviation in the projection system, so the projected EIA has geometric deformation. Due to the distortion of the EIA, it is difficult to precisely align the projected EIA and LAHOE, which results in serious flip of the reconstructed 3D images. The distortion of the EIA affects the asymmetry of the 3D image reconstruction. Lens distortion can be solved by the distortion compensation method. Lateral and the geometric deformation can be solved by the perspective transformations in computer graphics. After correction, the undistorted EIA is projected, and the projected EIA on the LAHOE has little distortion. In the process of 3D image reconstruction, the causes of asymmetry affecting 3D image reconstruction are analyzed, and the issues that generate these asymmetric factors are addressed. Experimental results indicate that a better 3D display effect is achieved.

Waveguide-type see-through dual focus near-eye display with a polarization grating

Waveguide-type near-eye displays have useful properties such as compact form factor, lightweight and see-through capability. Conventional systems, however, support only a single image plane fixed at a certain distance, which may induce eye fatigue due to the vergence-accommodation conflict. In this paper, we propose a waveguide-type near-eye display with two image planes using a polarization grating. Two images with orthogonal polarizations propagate within the waveguide with different total internal reflection angles and form virtual images at different distances. The use of the polarization grating and two pairs of holographic optical elements enables dual image plane formation by a single waveguide with high transparency for the real scene. Optical experiments confirm the principle of the proposed optical system.

Optical See-through 2D/3D Compatible Display Using Variable-Focus Lens and Multiplexed Holographic Optical Elements

An optical see-through two-dimensional (2D)/three-dimensional (3D) compatible display using variable-focus lens and multiplexed holographic optical elements (MHOE) is presented. It mainly consists of a MHOE, a variable-focus lens and a projection display device. The customized MHOE, by using the angular multiplexing technology of volumetric holographic grating, records the scattering wavefront and spherical wavefront array required for 2D/3D compatible display. In particular, we proposed a feasible method to switch the 2D and 3D display modes by using a variable-focus lens in the reconstruction process. The proposed system solves the problem of bulky volume, and makes the MHOE more efficient to use. Based on the requirements of 2D and 3D displays, we calculated the liquid pumping volume of the variable-focus lens under two kinds of diopters.

Pre-compensation method for optimizing recording process of holographic optical element lenses with spherical wave reconstruction

We propose a pre-compensated recording process of holographic optical element (HOE) lenses, where both of reference and signal waves have spherical wavefronts, for solving a wavelength mismatch problem between the recording and displaying process. Based on a localized approximation for aperiodic volume gratings, the wavelength mismatch and shrinkage effects are pre-compensated by optimizing the recording setup of HOE lenses, so that the Bragg condition of each local grating is satisfied. In order to realize the practical implementations of recording setup, complicated wavefronts to be required for the wavelength and shrinkage compensation are approximated into spherical waves. The simulation results using the volume hologram models of OpticStudio verify that the undesirable focal shift and color breakup problems in the HOE lens due to the wavelength mismatch are compensated. Displaying experiments using a full-color HOE lens with the field of view of 30° are presented, where the maximum wavelength mismatch between the recording and displaying process is 17 nm.

2D/3D mixed display based on integral imaging and a switchable diffuser element

In this paper, we present a 2D/3D mixed system with high image quality based on integral imaging and a switchable diffuser element. The proposed system comprises a liquid crystal display screen, lens array, switchable diffuser element and projector. The switchable diffuser element can be controlled to present 2D/3D mixed images or 2D and 3D images independently, and can reduce the Moire fringe and black grid. In addition to the improved display quality, the proposed system has advantages of a simple structure and is low cost, which contribute to the portability and practicability.

See-through optical combiner for augmented reality head-mounted display: index-matched anisotropic crystal lens

A novel see-through optical device to combine the real world and the virtual image is proposed which is called an index-matched anisotropic crystal lens (IMACL). The convex lens made of anisotropic crystal is enveloped with the isotropic material having same refractive index with the extraordinary refractive index of the anisotropic crystal. This optical device functions as the transparent glass or lens according to the polarization state of the incident light. With the novel optical property, IMACL can be utilized in the see-through near eye display, or head-mounted display for augmented reality. The optical property of the proposed optical device is analyzed and aberration by the anisotropic property of the index-matched anisotropic crystal lens is described with the simulation. The concept of the head-mounted display using IMACL is introduced and various optical performances such as field of view, form factor and transmittance are analyzed. The prototype is implemented to verify the proposed system and experimental results show the mixture between the virtual image and real world scene.

Projection-type integral imaging system using a three-dimensional screen composed of a lens array and a retroreflector film

We propose an improved projection-type integral imaging system using a three-dimensional (3D) screen consisting of a lens array and a retroreflector film in this paper. The projection-type integral imaging system suffers from the disadvantage of low-visibility images because of the inherently small exit pupil size of the projector. In order to resolve this problem, we adopt a 3D screen to avoid the demerits of a diffuser screen, such as off-screen image blur and loss of parallax. To determine the appropriate configuration of the 3D screen in the system, a simulation based on a ray transfer matrix analysis method was performed. The results show that the 3D screen should be located near the central depth plane of the integral imaging system, which leads to the conclusion that only the real mode is available for the proposed system. Experiments to verify this configuration and the feasibility of the proposed system were conducted using a system constructed with a real mode integral imaging system including a convex mirror array, which can fundamentally eliminate the pseudoscopic problem.

See-through multi-projection three-dimensional display using transparent anisotropic diffuser

We propose a see-through multi-projection three-dimensional (3D) display using a transparent anisotropic diffuser. By immersing a metal-coated anisotropic diffuser into index matching oil which has the same refractive index of anisotropic diffuser, a transparent anisotropic diffuser is implemented. The reflectance of the transparent anisotropic diffuser is analyzed with the transfer matrix. Two multi-projection methods are proposed based on reflection type integral imaging and multi-view method. Especially, the reflection type multi-view-based system is realized with a curved anisotropic diffuser. High resolution see-through 3D display can be realized with the proposed methods. They can be used in various applications with the two multi-projection methods. In order to show the augmented reality features, real objects and virtual 3D images are presented at the same time in the experimental setup.

Holographic display for see-through augmented reality using mirror-lens holographic optical element

A holographic display system for realizing a three-dimensional optical see-through augmented reality (AR) is proposed. A multi-functional holographic optical element (HOE), which simultaneously performs the optical functions of a mirror and a lens, is adopted in the system. In the proposed method, a mirror that is used to guide the light source into a reflection type spatial light modulator (SLM) and a lens that functions as Fourier transforming optics are recorded on a single holographic recording material by utilizing an angular multiplexing technique of volume hologram. The HOE is transparent and performs the optical functions just for Bragg matched condition. Therefore, the real-world scenes that are usually distorted by a Fourier lens or an SLM in the conventional holographic display can be observed without visual disturbance by using the proposed mirror-lens HOE (MLHOE). Furthermore, to achieve an optimized optical recording condition of the MLHOE, the optical characteristics of the holographic material are measured. The proposed holographic AR display system is verified experimentally.

Recent progress in see-through three-dimensional displays using holographic optical elements [Invited]

The principles and characteristics of see-through 3D displays are presented. We especially focus on the integral-imaging display system using a holographic optical element (IDHOE), which is able to display 3D images and satisfy the see-through property at the same time. The technique has the advantage of the high transparency and capability of displaying autostereoscopic 3D images. We have analyzed optical properties of IDHOE for both recording and displaying stages. Furthermore, various studies of new applications and system improvements for IDHOE are introduced. Thanks to the characteristics of holographic volume grating, it is possible to implement a full-color lens-array holographic optical element and conjugated reconstruction as well as 2D/3D convertible IDHOE. Studies on the improvements of viewing characteristics including a viewing angle, fill factor, and resolution are also presented. Lastly, essential issues and their possible solutions are discussed as future work.