Viewing-angle and viewing-resolution enhanced integral imaging based on time-multiplexed lens stitching

Naked-eye light field display technology based on mini/micro light emitting diode panels: a systematic review and meta-analysis

The light field display technology based on panel light modulation has obvious industrial advantages. However, light field displays still causes discomfort for users in practical applications, due to issues such as angle of view, number of viewpoints, and crosstalk, etc. As a new type of high performance 2D display technology, mini/micro light emitting diode (MLED) has the potential to provide higher quality 3D display effects, but it may also bring new technological challenges. This paper provides a detailed investigation of technical principles and the latest research progress in light field display technology based on panel light modulation, and analyzes the industrial and academic research difficulties, which are brought about by the combination of MLED and naked-eye light field display. This paper is the first to complete a technical review specifically focused on MLED and naked-eye light field display, which is expected to accelerate the technological development and application process of naked-eye light field display based on MLED panels.

Floating depth and viewing angle enhanced integral imaging display system based on a transmissive mirror device

We propose a floating depth and viewing angle-enhanced integral imaging (InIm) display system based on a transmissive mirror device (TMD). The system consists of a 2D display, a micro-lens array (MLA), and a TMD. The light emitted by the proposed InIm display system is reconstructed into a floating 3D image by the TMD, and the floating 3D image has a greater floating depth than the conventional InIm display without sacrificing resolution. The issue of mutual restriction between the floating depth and resolution of the 3D image is solved. The positions of the MLA and the 2D display are reversed through the TMD imaging, which results in an improved viewing range and an improved viewing angle of the floating 3D images. The system expands the floating depth and viewing angle simultaneously without sacrificing resolution. The experimental results prove the feasibility of the proposed system.

Smooth motion parallax method for 3D light-field displays with a narrow pitch based on optimizing the light beam divergence angle

The three-dimensional (3D) light field display (LFD) with dense views can provide smooth motion parallax for the human eye. Increasing the number of views will widen the lens pitch, however, resulting in a decrease in view resolution. In this paper, an approach to smooth motion parallax based on optimizing the divergence angle of the light beam (DALB) for 3D LFD with narrow pitch is proposed. DALB is controlled by lens design. A views-fitting optimization algorithm is established based on a mathematical model between DALB and view distribution. Subsequently, the lens is reversely designed based on the optimization results. A co-designed convolutional neural network (CNN) is used to implement the algorithm. The optical experiment shows that a smooth motion parallax 3D image is achievable through the proposed method.

Integral imaging three-dimensional display system with anisotropic backlight for the elimination of voxel aliasing and separation

Compared with conventional scattered backlight systems, integral imaging (InIm) display system with collimated backlight can reduce the voxel size, but apparent voxel separation and severe graininess still exist in reconstructed 3D images. In this paper, an InIm 3D display system with anisotropic backlight control of sub-pixels was proposed to resolve both voxel aliasing and voxel separation simultaneously. It consists of an anisotropic backlight unit (ABU), a transmissive liquid crystal panel (LCP), and a lens array. The ABU with specific horizontal and vertical divergence angles was proposed and designed. Within the depth of field, the light rays emitted from sub-pixels are controlled precisely by the ABU to minimize the voxel size as well as stitch adjacent voxels seamlessly, thus improving the 3D image quality effectively. In the experiment, the prototype of our proposed ABU-type InIm system was developed, and the spatial frequency was nearly two times of conventional scattered backlight InIm system. Additionally, the proposed system eliminated the voxel separation which usually occurs in collimated backlight InIm system. As a result, voxels reconstructed by our proposed system were stitched in space without aliasing and separation, thereby greatly enhancing the 3D resolution and image quality.

True-color light-field display system with large depth-of-field based on joint modulation for size and arrangement of halftone dots

A true-color light-field display system with a large depth-of-field (DOF) is demonstrated. Reducing crosstalk between viewpoints and increasing viewpoint density are the key points to realize light-field display system with large DOF. The aliasing and crosstalk of light beams in the light control unit (LCU) are reduced by adopting collimated backlight and reversely placing the aspheric cylindrical lens array (ACLA). The one-dimensional (1D) light-field encoding of halftone images increases the number of controllable beams within the LCU and improves viewpoint density. The use of 1D light-field encoding leads to a decrease in the color-depth of the light-field display system. The joint modulation for size and arrangement of halftone dots (JMSAHD) is used to increase color-depth. In the experiment, a three-dimensional (3D) model was constructed using halftone images generated by JMSAHD, and a light-field display system with a viewpoint density of 1.45 (i.e. 1.45 viewpoints per degree of view) and a DOF of 50 cm was achieved at a 100 ° viewing angle.

Image edge smoothing method for light-field displays based on joint design of optical structure and elemental images

Image visual quality is of fundamental importance for three-dimensional (3D) light-field displays. The pixels of a light-field display are enlarged after the imaging of the light-field system, increasing the graininess of the image, which leads to a severe decline in the image edge smoothness as well as image quality. In this paper, a joint optimization method is proposed to minimize the "sawtooth edge" phenomenon of reconstructed images in light-field display systems. In the joint optimization scheme, neural networks are used to simultaneously optimize the point spread functions of the optical components and elemental images, and the optical components are designed based on the results. The simulations and experimental data show that a less grainy 3D image is achievable through the proposed joint edge smoothing method.

System to eliminate the graininess of an integral imaging 3D display by using a transmissive mirror device

We propose a system to eliminate the graininess of an integral imaging 3D display by using a transmissive mirror device (TMD). The proposed system consists of a 2D display, a micro-lens array (MLA), and a TMD. The TMD comprises square apertures with mirror-reflective inner wall. The light rays pass through the square aperture to form a diffraction spot, and the diffraction light intensity has a Sinc-function distribution. Therefore, the TMD can be used as an optical low-pass filter. In a certain imaging range, the mainlobe of the Sinc-function distribution is almost unchanged. The TMD has the property of a volumetric optical low-pass filter. It can interpolate the interval between discrete 3D pixels. Therefore, the TMD can be used to eliminate the graininess. The resolution of the 3D image is improved by 2.12 times. The experimental results verify the feasibility of the proposed system.

Portable autostereoscopic display based on multi-directional backlight

A multi-directional backlight autostereoscopic display system with high resolution, low crosstalk, and motion parallax is developed in this paper. The proposed multi-directional backlight system is based on the Bragg mismatched reconstruction of volume holographic optical element (VHOE), and includes a set of light sources which are uniformly arrayed along one direction. Each light source produces its corresponding directional lighting to follow the human eye position detected by an eye tracker. Two scenarios are presented to build the multi-directional backlight system. The prism-type backlight system which guides the incident beam with a prism is relatively simple and easy to implement. The waveguide-type one which employs a transflective film to expand the incident light beam within the waveguide and modulate the intensity of the incident beam, is relatively thin and is applicable to large-area display. Two prototypes are built and the effectiveness of the proposed autostereoscopic display system is verified by the experimental results.

Foveated glasses-free 3D display with ultrawide field of view via a large-scale 2D-metagrating complex

Glasses-free three-dimensional (3D) displays are one of the game-changing technologies that will redefine the display industry in portable electronic devices. However, because of the limited resolution in state-of-the-art display panels, current 3D displays suffer from a critical trade-off among the spatial resolution, angular resolution, and viewing angle. Inspired by the so-called spatially variant resolution imaging found in vertebrate eyes, we propose 3D display with spatially variant information density. Stereoscopic experiences with smooth motion parallax are maintained at the central view, while the viewing angle is enlarged at the periphery view. It is enabled by a large-scale 2D-metagrating complex to manipulate dot/linear/rectangular hybrid shaped views. Furthermore, a video rate full-color 3D display with an unprecedented 160° horizontal viewing angle is demonstrated. With thin and light form factors, the proposed 3D system can be integrated with off-the-shelf purchased flat panels, making it promising for applications in portable electronics.

3D light-field display with an increased viewing angle and optimized viewpoint distribution based on a ladder compound lenticular lens unit

Three-dimensional (3D) light-field displays (LFDs) suffer from a narrow viewing angle, limited depth range, and low spatial information capacity, which limit their diversified application. Because the number of pixels used to construct 3D spatial information is limited, increasing the viewing angle reduces the viewpoint density, which degrades the 3D performance. A solution based on a holographic functional screen (HFS) and a ladder-compound lenticular lens unit (LC-LLU) is proposed to increase the viewing angle while optimizing the viewpoint utilization. The LC-LLU and HFS are used to create 160 non-uniformly distributed viewpoints with low crosstalk, which increases the viewpoint density in the middle viewing zone and provides clear monocular depth cues. The corresponding coding method is presented as well. The optimized compound lenticular lens array can balance between suppressing aberration and improving displayed quality. The simulations and experiments show that the proposed 3D LFD can present natural 3D images with the right perception and occlusion relationship within a 65° viewing angle.

Use of multiple light sources to enhance the resolution of point light source displays

The point light sources (PLSs) of integral imaging displays have a wide depth range; however, the resolution is very low. We developed resolution-enhanced PLS displays using multiple light sources that create extra PLSs in the PLS plane. Given aberrations in the lens arrays, the PLSs initially appeared on planes and at distances that differed from the theoretical values. We thus determined the distances between adjacent light sources that compensated for the aberrations. Experimentally, our method enhanced the resolution fourfold compared to that of a conventional PLS display in both vertical and horizontal directions. Our approach allows facile compensation of lens array aberrations and is applicable to 3D displays.

Highly Reflective Thin-Film Optimization for Full-Angle Micro-LEDs

Displays composed of micro-light-emitting diodes (micro-LEDs) are regarded as promising next-generation self-luminous screens and have advantages such as high contrast, high brightness, and high color purity. The luminescence of such a display is similar to that of a Lambertian light source. However, owing to reduction in the light source area, traditional secondary optical lenses are not suitable for adjusting the light field types of micro-LEDs and cause problems that limit the application areas. This study presents the primary optical designs of dielectric and metal films to form highly reflective thin-film coatings with low absorption on the light-emitting surfaces of micro-LEDs to optimize light distribution and achieve full-angle utilization. Based on experimental results with the prototype, that have kept low voltage variation rates, low optical losses characteristics, and obtain the full width at half maximum (FWHM) of the light distribution is enhanced to 165° and while the center intensity is reduced to 63% of the original value. Hence, a full-angle micro-LEDs with a highly reflective thin-film coating are realized in this work. Full-angle micro-LEDs offer advantages when applied to commercial advertising displays or plane light source modules that require wide viewing angles.

Space-division-multiplexed catadioptric integrated backlight and symmetrical triplet-compound lenticular array based on ORM criterion for 90-degree viewing angle and low-crosstalk directional backlight 3D light-field display

A novel optical reverse mapping (ORM) method and an ORM criterion are proposed to evaluate the relevance between the directional backlight (DB) 3D light-field display system aberration and the crosstalk. Based on the ORM criterion, the space-division-multiplexed catadioptric integrated backlight (SCIB) and symmetrical triplet-compound lenticular array (triplet LA) are designed. The SCIB is composed of hybrid Fresnel integrated backlight unit (hybrid Fresnel unit) and space-division-multiplexed microprism unit (microprism unit). The hybrid Fresnel unit is used to provide the directional light, and the divergence angle is 2.4-degrees. The average uniformity of 83.02% is achieved. The microprism unit is used to modulate the directional light distribution into three predetermined directions to establish a 90-degree viewing area. Combined with SCIB, the triplet LA is used to suppress the aberrations and reduce the crosstalk. In the experiment, a DB 3D light-field display system based on SCIB and triplet LA is set up. The displayed light-field 3D image can be observed in a 90-degree viewing angle. Compared to the conventional DB 3D display system, the light-field 3D image is aberration-suppressed, and the SSIM values are improved from 0.8462 to 0.9618. Meanwhile, the crosstalk measurement results show that the average crosstalk is 3.49%. The minimum crosstalk is 2.31% and the maximum crosstalk is 4.52%. The crosstalk values in 90-degree are lower than 5%.

Wave-optics and spatial frequency analyses of integral imaging three-dimensional display systems

Wave optics is usually thought to be more rigorous than geometrical optics to analyze integral imaging (II) systems. However, most of the previous wave-optics investigations are directed to a certain subsystem or do not sufficiently consider the finite aperture of microlens arrays (MLAs). Therefore, a diffraction-limited model of the entire II system, which consists of pickup, image processing, and reconstruction subsystems, is proposed, and the effects of system parameters on spatial resolution are especially studied. With the help of paraxial scalar diffraction theory, the origin impulse response function of the entire II system is derived; the parameter matching condition with optimum resolution and the wave-optics principle are achieved. Besides, the modulation transfer function is then obtained and Fourier analysis is performed, which indicates that the features of MLA and the display play a critical role in spatial frequency transfer characteristics, greatly affecting the resolution. These studies might be useful for the further research and understanding of II systems, especially for the effective enhancement of resolution.

Large-scale microlens arrays on flexible substrate with improved numerical aperture for curved integral imaging 3D display

Curved integral imaging 3D display could provide enhanced 3D sense of immersion and wider viewing angle, and is gaining increasing interest among discerning users. In this work, large scale microlens arrays (MLAs) on flexible PMMA substrate were achieved based on screen printing method. Meanwhile, an inverted reflowing configuration as well as optimization of UV resin's viscosity and substrate's surface wettability were implemented to improved the numerical aperture (NA) of microlenses. The results showed that the NA values of MLAs could be increased effectively by adopting inverted reflowing manner with appropriate reflowing time. With decreasing the substrate's wettability, the NA values could be increased from 0.036 to 0.096, when the UV resin contact angles increased from 60.1° to 88.7°. For demonstration, the fabricated MLAs was combined to a curved 2D monitor to realize a 31-inch curved integral imaging 3D display system, exhibiting wider viewing angle than flat integral imaging 3D display system.

Enhancing integral imaging performance using time-multiplexed convergent backlight

A method to enhance the performance of an integral imaging system is demonstrated using the time-multiplexed convergent backlight technique. The backlight increases the space bandwidth of the integral imaging system. As a result, the resolution, depth of field, and viewing angle of the integral imaging system are increased simultaneously. The cross-talk noise is also decreased without using any optical barrier. One part of the added space bandwidth comes from the optimized illumination. The other part is converted from the time bandwidth of the system by time-multiplexing. The time-multiplexed convergent backlight modulates the direction of the backlight in time sequence to illuminate the elemental images. Then, the elemental images synthesize the 3D images using a microlens array. An elemental images rendering method using a conjugate pinhole camera and pinhole projector model is designed to dynamically match the illumination direction. The rendering method eliminates the distortion and maximizes the viewing angle and viewing zone. A field programmable gate array (FPGA)-based controller is used to manage and synchronize the time sequence of the backlight and the display devices. Using this technique, high-performance 3D images are realized. Comparison experiments of the integral imaging system using diffused backlight and convergent backlight are performed. The results show the effectiveness of the proposed technique.

Bionic-compound-eye structure for realizing a compact integral imaging 3D display in a cell phone with enhanced performance

A bionic-compound-eye structure (BCES), which is a substitute of a microlens array, is proposed to enhance the performance of integral imaging (II) 3D display systems. Hexagonal ocelli without gaps and barriers are predesigned to obtain a continuous image, high-resolution, and uniform parallax. A curved substrate is designed to enhance the viewing angle. In addition, ocelli are fused with the substrate to form a relief structure, BCES. When they are placed above a normal display, continuous and full-parallax 3D images with 150 µm effective resolution and a 28° horizontal, 22° vertical viewing angle could be achieved, about twice as much as that of normal systems. The weight of the BCES is 31 g, and the thickness of the whole system is 22 mm; thus, the BCES-based II (BCES-II) is very compact. In addition, this structure can be easily integrated into a cell phone or iPad for compact quasi-2D and 3D adjustable display.