Chang-Kun Lee

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.

Depth-expression characteristics of multi-projection 3D display systems [invited].

A multi-projection display consists of multiple projection units. Because of the large amount of data, a multi-projection system shows large, high-quality images. According to the projection geometry and the optical configuration, multi-projection systems show different viewing characteristics for generated three-dimensional images. In this paper, we analyzed the various projection geometries of multi-projection systems, and explained the different depth-expression characteristics for each individual projection geometry. We also demonstrated the depth-expression characteristic of an experimental multi-projection system.

Compact three-dimensional head-mounted display system with Savart plate.

We propose three-dimensional (3D) head-mounted display (HMD) providing multi-focal and wearable functions by using polarization-dependent optical path switching in Savart plate. The multi-focal function is implemented as micro display with high pixel density of 1666 pixels per inches is optically duplicated in longitudinal direction according to the polarization state. The combination of micro display, fast switching polarization rotator and Savart plate retains small form factor suitable for wearable function. The optical aberrations of duplicated panels are investigated by ray tracing according to both wavelength and polarization state. Astigmatism and lateral chromatic aberration of extraordinary wave are compensated by modification of the Savart plate and sub-pixel shifting method, respectively. To verify the feasibility of the proposed system, a prototype of the HMD module for monocular eye is implemented. The module has the compact size of 40 mm by 90 mm by 40 mm and the weight of 131 g with wearable function. The micro display and polarization rotator are synchronized in real-time as 30 Hz and two focal planes are formed at 640 and 900 mm away from eye box, respectively. In experiments, the prototype also provides augmented reality function by combining the optically duplicated panels with a beam splitter. The multi-focal function of the optically duplicated panels without astigmatism and color dispersion compensation is verified. When light field optimization for two additive layers is performed, perspective images are observed, and the integration of real world scene and high quality 3D images is confirmed.

Crosstalk-Reduced Dual-Mode Mobile 3D Display

We propose a novel crosstalk-reduced mobile 3D display system providing high quality 3D images both in portrait mode and landscape mode. We analyze a conventional commercial mobile 3D display system with simulations and experiments. Then we propose a crosstalk-reduced mobile 3D display system. We design a micro lens array film and propose a mapping algorithm for the system. To reduce crosstalk, we adopt the mobile phone with a diamond pentile display panel. We build a demonstration with a parallax barrier film and diamond pentile display. This newly implemented system provides 3D images with a similar quality in both portrait mode and landscape mode. The crosstalk of implemented system is 8.3% in portrait mode and 9.2% in landscape mode.

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.

Viewing zone duplication of multi-projection 3D display system using uniaxial crystal.

We propose a novel multiplexing technique for increasing the viewing zone of a multi-view based multi-projection 3D display system by employing double refraction in uniaxial crystal. When linearly polarized images from projector pass through the uniaxial crystal, two possible optical paths exist according to the polarization states of image. Therefore, the optical paths of the image could be changed, and the viewing zone is shifted in a lateral direction. The polarization modulation of the image from a single projection unit enables us to generate two viewing zones at different positions. For realizing full-color images at each viewing zone, a polarization-based temporal multiplexing technique is adopted with a conventional polarization switching device of liquid crystal (LC) display. Through experiments, a prototype of a ten-view multi-projection 3D display system presenting full-colored view images is implemented by combining five laser scanning projectors, an optically clear calcite (CaCO3) crystal, and an LC polarization rotator. For each time sequence of temporal multiplexing, the luminance distribution of the proposed system is measured and analyzed.

Real-time depth controllable integral imaging pickup and reconstruction method with a light field camera

In this paper, we develop a real-time depth controllable integral imaging system. With a high-frame-rate camera and a focus controllable lens, light fields from various depth ranges can be captured. According to the image plane of the light field camera, the objects in virtual and real space are recorded simultaneously. The captured light field information is converted to the elemental image in real time without pseudoscopic problems. In addition, we derive characteristics and limitations of the light field camera as a 3D broadcasting capturing device with precise geometry optics. With further analysis, the implemented system provides more accurate light fields than existing devices without depth distortion. We adapt an f-number matching method at the capture and display stage to record a more exact light field and solve depth distortion, respectively. The algorithm allows the users to adjust the pixel mapping structure of the reconstructed 3D image in real time. The proposed method presents a possibility of a handheld real-time 3D broadcasting system in a cheaper and more applicable way as compared to the previous methods.

Real-mode depth-fused display with viewer tracking.

A real-mode depth-fused display is proposed by employing an integral imaging method in the depth-fused display system with viewer tracking. By giving depth-fusing effect between a transparent display and a floated planar two-dimensional image generated by the real-mode integral imaging method, a three-dimensional image is generated in front of the display plane unlike conventional depth-fused displays. The viewing angle of the system is expanded with a viewer tracking method. In addition, dynamic vertical and horizontal motion parallax can be given according to the tracked position of the viewer. As the depth-fusing effect is not dependent on the viewing distance, accommodation cue and motion parallax are provided for a wide range of viewing position. We demonstrate the feasibility of our proposed method by experimental system.

Projection-type dual-view three-dimensional display system based on integral imaging

A dual-view display system provides two different images in different directions. Most of them only present two-dimensional images for observers. In this paper, we propose a projection-type dual-view three-dimensional (3D) display system based on integral imaging. To assign directivities to the images, a projection-type display and dual-view screen with lenticular lenses are implemented. The lenticular lenses split the collimated image from the projection device into two different directions. The separated images are integrated by a single lens array in front of the screen, and full-parallax 3D images are observed in two different viewing regions. The visibility of the reconstructed 3D images can be improved by using high-density lenticular lenses and a high numerical aperture lens array. We explain the principle of the proposed method and verify the feasibility of the proposed system with simulations and experimental results.

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.