Resolution-enhanced integral imaging using two micro-lens arrays with different focal lengths for capturing and display

Wide-Viewing-Angle Integral Imaging System with Full-Effective-Pixels Elemental Image Array

There exists a defect of the narrow viewing angle in the conventional integral imaging system. One reason for this is that only partial pixels of each elemental image contribute to the viewing angle and the others cause image flips. In this paper, a wide-viewing-angle integral imaging system with a full-effective-pixels elemental image array (FEP-EIA) was proposed. The correspondence between viewpoints and pixel coordinates within the elemental image array was built up, and effective pixel blocks and pixels leading to flipping images were deduced. Then, a pixel replacement method was proposed to generate the FEP-EIAs, which adapt to different viewing distances. As a result, the viewing angle of the proposed integral imaging system was effectively extended through the replacement of the pixels, which caused the image flips. Experiment results demonstrated that wide viewing angles are available for the proposed integral imaging system regardless of the viewing distances.

Multi-View 3D Integral Imaging Systems Using Projectors and Mobile Devices

Glassless 3D displays using projectors and mobile phones based on integral imaging technology have been developed. Three-dimensional image files are created from the 2D images captured by a conventional camera. Large size 3D images using four HD and Ultra HD 4K projectors are created with a viewing angle of 35 degrees and a large depth. Three-dimensional images are demonstrated using optimized lenticular lenses and mobile smartphones, such as LG and Samsung with resolution 2560 × 1440, and 4K Sony with resolution 3840 × 2160.

Light output enhancement of scintillators by using mixed-scale microstructures

Scintillators play an important role in the field of nuclear radiation detection. However, the light output of the scintillators is often limited by total internal reflection due to the high refractive indices of the scintillators. Furthermore, the light emission from scintillators typically has an approximately Lambertian profile, which is detrimental to the collection of the light. In this paper, we demonstrate a promising method to achieve enhancement of the light output from scintillators through use of mixed-scale microstructures that are composed of a photonic crystal slab and a microlens array. Simulations and experimental results both show significant improvements in the scintillator light output. The X-ray imaging characteristics of scintillators are improved by the application of the mixed-scale microstructures. The results presented here suggest that the application of the proposed mixed-scale microstructures to scintillators will be beneficial in the nuclear radiation detection field.

Performance improvement for compressive light field display based on the depth distribution feature

Compressive light field (CLF) display using multi-layer spatial light modulators (SLMs) is a promising technique for three-dimensional (3D) display. However, conventional CLF display usually uses the reference plane with fixed depth, which does not consider the relationship between the depth distribution of the object and the image quality. To improve the quality of the reconstructed image, we further analyze the relationship between them in the paper. The theoretical analysis reveals that the object with a closer distance to the physical layer has a better reconstruction quality when the SLM layers have the same pixel density. To minimize the deviation between the reconstructed light field and the original light field, we propose a method based on the depth distribution feature to automatically guide the light field optimization without increasing the layered number or the refresh rate. When applied to a different scene, it could detect the dense region of depth information and map them as close to the physical layers as possible by offsetting the depth of the reference plane. Simulation and optical experiments with the CLF display are demonstrated to verify the proposed method. We implement a CLF display that consists of four-layer stacked display panels and the distance between two adjacent layers is 5cm. When the proposed method is applied, the peak signal-to-noise ratio (PSNR) is improved by 2.4dB in simulations and 1.8dB in experiments.

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.

CO2 laser thermal reflow shaped convex glass microlens array after Bessel picosecond laser inscribing and hydrofluoric acid processing

In this paper, a convex micro-glass lens array fabrication process that utilizes ${{\rm CO}_2}$CO₂ laser thermal reflow in the Bessel picosecond laser inscribing and hydrofluoric acid processed micro-glass pillars array is presented. The Bessel picosecond laser permits high tolerance and precise micro-pillar fabrication. In the thermal reshape process, the ${{\rm CO}_2}$CO₂ laser power, relative defocus length, and scanning velocity are three crucial parameters to the microlens array's focal length. By using this method, microlens arrays with focal length ranging from several tens of micrometers to several hundred micrometers can be created. This research provides another way to fabricate convex micro-glass lens arrays with several hundred micrometers focal length in good utility.

Three-dimensional imaging system with both improved lateral resolution and depth of field considering non-uniform system parameters

In this paper, we propose a new 3D passive image sensing and visualization technique to improve lateral resolution and depth of field (DoF) of integral imaging simultaneously. There is a resolution trade-off between lateral resolution and DoF in integral imaging. To overcome this issue, a large aperture and a small aperture can be used to record the elemental images to reduce the diffraction effect and extend the DoF, respectively. Therefore, in this paper, we utilize these two pickup concepts with a non-uniform camera array. To show the feasibility of our proposed method, we implement an optical experiment. For comparison in details, we calculate the peak signal-to-noise ratio (PSNR) as the performance metric.

Diffraction of partially-coherent light beams by microlens arrays

The synthesis method including wave-optics and ray-tracing for the acceleration of the simulation of micro-optical systems has been developed. The effects of the spatial coherence and randomization of microlens array (MLA) parameters have been considered. The method based on coherent states representation for the calculation of the optical efficiency of microlens arrays taking into account the light source polarization has been developed. Numerical simulations of the intensity distributions and spreading angle of a diffracted beam have been carried out.

Fabrication of Large-Scale Microlens Arrays Based on Screen Printing for Integral Imaging 3D Display

The low-cost large-scale fabrication of microlens arrays (MLAs) with precise alignment, great uniformity of focusing, and good converging performance are of great importance for integral imaging 3D display. In this work, a simple and effective method for large-scale polymer microlens arrays using screen printing has been successfully presented. The results show that the MLAs possess high-quality surface morphology and excellent optical performances. Furthermore, the microlens' shape and size, i.e., the diameter, the height, and the distance between two adjacent microlenses of the MLAs can be easily controlled by modifying the reflowing time and the size of open apertures of the screen. MLAs with the neighboring microlenses almost tangent can be achieved under suitable size of open apertures of the screen and reflowing time, which can remarkably reduce the color moiré patterns caused by the stray light between the blank areas of the MLAs in the integral imaging 3D display system, exhibiting much better reconstruction performance.