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This paper presents a simulation model for a large field‐of‐view, wide eye‐box, and high‐resolution ultra‐thin near‐eye display based on a freeform optical lens array. It creatively incorporates a polarization‐based optical folding technique (pancake lens), reducing the thickness of the simulation model to less than 1.4 cm (excluding the display screen). Compared to traditional VR devices, this significantly reduces the volume and weight of the equipment. The parameters of the simulation model are as follows: eye‐box size of 10mm, resolution utilization rate of 50%; the introduction of freeform optics greatly improves the imaging quality of the displayed images. At the same time, the field of view reaches 116° (single eye, vertical direction). [ABSTRACT FROM AUTHOR]

A photonic integrated interference imaging system (PIIIS) is a computational imager based on Michelson interference and photonic integrated circuits (PICs). In this paper, a PIIIS based on a compact sampling lenslet array that can sample the zero spatial frequency through a single lenslet, densely sample the frequency in the azimuth direction through the configuration of a hierarchical multistage lenslet array, and continuously sample the frequency in the radial direction through a Langford sequence is proposed. We introduce the design process of the compact sampling lenslet array in detail and simulate the imaging of the system. The simulation results demonstrate that the lenslet array can effectively improve the imaging quality of a PIIIS. In addition, we design a silicon PIC and a silicon nitride transition PIC that match the compact sampling lenslet array and simulate the imaging of the system under the influence of the on-chip optical loss of PICs (the average interference baseline loss is 15.4 dB at 1550 nm). The results show that on-chip optical loss mainly affects the brightness and contrast of the reconstructed image but has little effect on the structure. [ABSTRACT FROM AUTHOR]

We demonstrate an ultracompact virtual reality (VR) system with thickness of about 1‐cm. In this system, the imaging optics consists of a lenslet array, a deflector array, and a Pancharatnam‐Berry deflector (PBD). We have experimentally demonstrated a polarization interpolation configuration to reduce the system thickness by nearly 50%. [ABSTRACT FROM AUTHOR]

On the demand of low-cost, lightweight, miniaturized, and integrated optical systems, precision lenslet arrays are widely used. Diamond turning is often used to fabricate lenslet arrays directly or molds that are used to mold lenslet arrays. In this paper, mainly by real-time monitoring position following error for slow tool servo, different fabrication parameters are quantitatively studied and optimized for actual fabrication, then by actual fabrication validation, uniform and high-fidelity surface topography across the actual whole lenslet array is achieved. The evaluated fabrication parameters include sampling strategy, inverse time feed, arc-length, etc. The study provides a quick, effective, and detailed reference for both convex and concave lenslet array cutting parameter selection. At the end, a smooth zonal machining strategy toolpath is demonstrated for fabricating concave lenslet arrays. [ABSTRACT FROM AUTHOR]

A photonic integrated interference imaging system (PIIIS) is a computational imager based on Michelson interference and photonic integrated circuits (PICs). In this paper, a PIIIS based on a compact sampling lenslet array that can sample the zero spatial frequency through a single lenslet, densely sample the frequency in the azimuth direction through the configuration of a hierarchical multistage lenslet array, and continuously sample the frequency in the radial direction through a Langford sequence is proposed. We introduce the design process of the compact sampling lenslet array in detail and simulate the imaging of the system. The simulation results demonstrate that the lenslet array can effectively improve the imaging quality of a PIIIS. In addition, we design a silicon PIC and a silicon nitride transition PIC that match the compact sampling lenslet array and simulate the imaging of the system under the influence of the on-chip optical loss of PICs (the average interference baseline loss is 15.4 dB at 1550 nm). The results show that on-chip optical loss mainly affects the brightness and contrast of the reconstructed image but has little effect on the structure.

In the future, various types and parameters of display devices and lenslet arrays will be commercially available. Different display devices can be matched by cutting and expanding elemental images, while different lenses require changing the pixel mapping structure individually for each pixel, which involves complex calculations. A simple pseudoscopic-to-orthoscopic conversion for lenslet arrays with different apertures in real and virtual fields has meaningful practical implications. To this end, orthoscopic integral imaging for different lenslet arrays in real and virtual fields is proposed herein. The tilt-shift photography technique is used to generate a wider view image array, which is cropped to form the orthoscopic elemental image arrays required for lenslet arrays of various shapes, considering their specific structures and shapes. The approach expands the viewing angle without the need to change the system parameters or recalculate the elemental image relative to the viewer's position, enabling multiple individuals to view the three-dimensional (3D) images from different angles simultaneously. It does not require additional devices or depth information. The repositioning of the original camera array enables various display modes, such as real images, virtual images, and co-displays, which enhance the 3D display effect. The experimental results demonstrate that the proposed method can generate 3D images with correct depth relationships and large viewing angles, through subjective and quantitative comparison of the parallax. • The pseudoscopic problem in viewing 3D images effectively addressed. • A flexible method for generating orthoscopic integral images proposed. • Method applicable for different lenslet arrays in real and virtual fields. • Real, virtual, and co-displayed 3D images obtained. • Simulations and optical experiments confirmed method efficacy. [ABSTRACT FROM AUTHOR]

On the demand of low-cost, lightweight, miniaturized, and integrated optical systems, precision lenslet arrays are widely used. Diamond turning is often used to fabricate lenslet arrays directly or molds that are used to mold lenslet arrays. In this paper, mainly by real-time monitoring position following error for slow tool servo, different fabrication parameters are quantitatively studied and optimized for actual fabrication, then by actual fabrication validation, uniform and high-fidelity surface topography across the actual whole lenslet array is achieved. The evaluated fabrication parameters include sampling strategy, inverse time feed, arc-length, etc. The study provides a quick, effective, and detailed reference for both convex and concave lenslet array cutting parameter selection. At the end, a smooth zonal machining strategy toolpath is demonstrated for fabricating concave lenslet arrays.

Integral imaging has been considered as the most applicable technology of true 3D display in the near future. In this paper, we propose the method to achieve full parallax and large-screen integral imaging display based on mini LED. Compared to the existing integral imaging systems based on the LED, the proposed method can present both horizontal and vertical parallaxes. We explore the optical parameter matching method between mini LED display unit and lenslet unit and design three different shapes of lenslet arrays. The imaging performance of lenslet arrays of circular-shape, square-shape, and hexagonal-shape is analyzed. The method of window interception is proposed to generate elemental images for the lenslet arrays with different apertures and arranging structures. The experimental results show that the true 3D display with full parallax and screen scalability has been realized using the proposed method and the display effect of lenslet array with hexagonal-shape is the best according to the evaluation of both subjective and objective merits.

High-resolution light distributions are lately in demand for vehicle headlamp systems as an innovative lighting approach. This lighting approach can realize functionalities, such as precise glare avoidance and on-road projection, which are useful for improving traffic comfort and safety. For achieving the required high-resolution light distribution, area-based projection technologies, such as DMD, LCD, and LCoS, are considered to be integrated into such headlamps. These projection devices demand rectangular illumination areas with specific light distributions to fulfill the requirements for illumination efficiency and performance in headlamp systems. Lenslet arrays, based on the principle of Köhler illumination, can effectively homogenize the light and shape it into rectangular shapes simultaneously. Such components are widely used in projection applications. However, they also show functional potentialities to be applied in high-resolution headlamps. This paper explains the design principles and methods of lenslet arrays for beam pre-shaping in headlamp systems. It validates the homogenization using a self-designed and manufactured lenslet array in a demonstrator in the first place. Afterward, this paper introduces two new methods for the centralized beam shaping required by some headlamps. These methods are validated by optical simulations. [ABSTRACT FROM AUTHOR]

High-resolution light distributions are lately in demand for vehicle headlamp systems as an innovative lighting approach. This lighting approach can realize functionalities, such as precise glare avoidance and on-road projection, which are useful for improving traffic comfort and safety. For achieving the required high-resolution light distribution, area-based projection technologies, such as DMD, LCD, and LCoS, are considered to be integrated into such headlamps. These projection devices demand rectangular illumination areas with specific light distributions to fulfill the requirements for illumination efficiency and performance in headlamp systems. Lenslet arrays, based on the principle of Köhler illumination, can effectively homogenize the light and shape it into rectangular shapes simultaneously. Such components are widely used in projection applications. However, they also show functional potentialities to be applied in high-resolution headlamps. This paper explains the design principles and methods of lenslet arrays for beam pre-shaping in headlamp systems. It validates the homogenization using a self-designed and manufactured lenslet array in a demonstrator in the first place. Afterward, this paper introduces two new methods for the centralized beam shaping required by some headlamps. These methods are validated by optical simulations.

Purpose – Full parallax integral 3D display is one of the promising future displays that provide different perspectives according to viewing direction. In this paper, the authors review the recent integral 3D display and image processing techniques for improving the performance, such as viewing resolution, viewing angle, etc.Design/methodology/approach – Firstly, to improve the viewing resolution of 3D images in the integral imaging display with lenslet array, the authors present 3D integral imaging display with focused mode using the time-multiplexed display. Compared with the original integral imaging with focused mode, the authors use the electrical masks and the corresponding elemental image set. In this system, the authors can generate the resolution-improved 3D images with the n×n pixels from each lenslet by using n×n time-multiplexed display. Secondly, a new image processing technique related to the elemental image generation for 3D scenes is presented. With the information provided by the Kinect device, the array of elemental images for an integral imaging display is generated.Findings – From their first work, the authors improved the resolution of 3D images by using the time-multiplexing technique through the demonstration of the 24 inch integral imaging system. Authors’ method can be applied to a practical application. Next, the proposed method with the Kinect device can gain a competitive advantage over other methods for the capture of integral images of big 3D scenes. The main advantage of fusing the Kinect and the integral imaging concepts is the acquisition speed, and the small amount of handled data.Originality / Value – In this paper, the authors review their recent methods related to integral 3D display and image processing technique.Research type – general review.

This paper discusses possible methods for on-chip fluorescent imaging forintegrated bio-sensors. The integration of optical and electro-optical accessories, accordingto suggested methods, can improve the performance of fluorescence imaging. It can boostthe signal to background ratio by a few orders of magnitudes in comparison to conventionaldiscrete setups. The methods that are present in this paper are oriented towards buildingreproducible arrays for high-throughput micro total analysis systems (μTAS). The firstmethod relates to side illumination of the fluorescent material placed into micro-compartments of the lab-on-chip. Its significance is in high utilization of excitation energyfor low concentration of fluorescent material. The utilization of a transparent μLED chip,for the second method, allows the placement of the excitation light sources on the sameoptical axis with emission detector, such that the excitation and emission rays are directedcontroversly. The third method presents a spatial filtering of the excitation background.

Purpose - Full parallax integral 3D display is one of the promising future displays that provide different perspectives according to viewing direction. In this paper, the authors review the recent integral 3D display and image processing techniques for improving the performance, such as viewing resolution, viewing angle, etc. Design/methodology/approach - Firstly, to improve the viewing resolution of 3D images in the integral imaging display with lenslet array, the authors present 3D integral imaging display with focused mode using the time-multiplexed display. Compared with the original integral imaging with focused mode, the authors use the electrical masks and the corresponding elemental image set. In this system, the authors can generate the resolution-improved 3D images with the n×n pixels from each lenslet by using n×n time-multiplexed display. Secondly, a new image processing technique related to the elemental image generation for 3D scenes is presented. With the information provided by the Kinect device, the array of elemental images for an integral imaging display is generated. Findings - From their first work, the authors improved the resolution of 3D images by using the time-multiplexing technique through the demonstration of the 24 inch integral imaging system. Authors' method can be applied to a practical application. Next, the proposed method with the Kinect device can gain a competitive advantage over other methods for the capture of integral images of big 3D scenes. The main advantage of fusing the Kinect and the integral imaging concepts is the acquisition speed, and the small amount of handled data. Originality / Value - In this paper, the authors review their recent methods related to integral 3D display and image processing technique. [ABSTRACT FROM AUTHOR]

Abstract: This work presents the fabrication and test of microlens arrays for Hartmann–Shack wavefront sensor, which were optimized, in terms of geometry, to be applied to the ophthalmic context. The optimization procedure was previously proposed by the authors and comprised the minimization of the wavefront reconstruction error through the use of genetic algorithm. The results indicated that arrays with 10 and 16 suitably located lenses could perform as good as those with a larger number of microlenses (25 or 36) in a rectangular geometry. In the present work, the sequence consisted in fabricating molds in silicon of the optimized array geometries; replicating the molds on polymer; and testing the final arrays on an optical bench, to comparatively assess the performance of the fabricated arrays. In general, final results corroborate with the ones predicted by simulations. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a computational depth conversion method based on the lenslet model to display the orthoscopic 3D images in 3D integral imaging display. The proposed method permits the synthesis of elemental images for the orthoscopic 3D images at any arbitrary position without any restrictions and requires no additional procedure during the depth conversion process. Due to the lenslet model involved in the depth conversion procedure, the proposed method can broaden the flexibility of 3D image reconstruction in the integral imaging display system. We carry out the preliminary experiments to prove the feasibility of the proposed method. The experimental results reveal that the proposed method is an effective depth conversion method that allows the reconstruction of the orthoscopic 3D images at any arbitrary position. [Copyright &y& Elsevier]

Abstract: This paper describes a novel depth extraction method for 3D objects using the windowing technique in computational integral imaging with a lenslet array. The proposed method includes pickup through a lenslet array with a snapshot, introduction of slice image pairs obtained from the windowing technique, and extraction of depth information using block matching between the slice image pairs. Also, this paper presents a theory of how the windowing technique works for depth extraction and an analysis of how it enables us to have a depth image from low-resolution elemental images. A preliminary optical experiment indicates that the proposed method provides a substantial improvement on the depth extraction technique in computational integral imaging with a lenslet array. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional (3D) image correlator using a fast computational integral imaging reconstruction (CIIR) method based on a pixel-to-pixel mapping is proposed. In order to implement the fast CIIR method, we replace the magnification process in the conventional CIIR by a pixel-to-pixel mapping. The proposed fast CIIR method reconstructs two sorts of plane images; a plane image whose quality is sufficient, and a dot pattern plane image insufficient to view. This property is very useful to enhance the performance of a CIIR-based image correlator. Thus, we apply the fast CIIR method to a CIIR-based image correlator. To show the feasibility of the proposed method, some preliminary experiments on both pattern correlation and computational cost are carried out, and the results are presented. Our experimental results indicate that the proposed image correlator is superior to the previous method in terms of both correlation performance and complexity. [Copyright &y& Elsevier]

Abstract: A Shack-Hartmann wavefront sensor (SHWS) uses a lenslet array to sample incoming wavefront onto a CCD. By comparing the focal spots images of the sample and a reference, wavefront profile is reconstructed and therefore the sample shape is revealed. Various factors affect the performance of SHWS. In order to study how and to which extend does each factor affect the reconstruction result, we established a simulation platform in MATLAB. Detailed properties, especially the configuration of the lenslet array related issues, were analyzed through this system-oriented platform, and by doing so we obtained some guidance in surface measurement experiment. [Copyright &y& Elsevier]

Abstract: In this work we propose to optimize the microlens-array geometry for a Hartmann–Shack wavefront sensor. The optimization makes possible that regular microlens arrays with a larger number of microlenses are replaced by arrays with fewer microlenses located at optimal sampling positions, with no increase in the reconstruction error. The goal is to propose a straightforward and widely accessible numerical method to calculate an optimized microlens array for a known aberration statistics. The optimization comprises the minimization of the wavefront reconstruction error and/or the number of necessary microlenses in the array. We numerically generate, sample and reconstruct the wavefront, and use a genetic algorithm to discover the optimal array geometry. Within an ophthalmological context, as a case study, we demonstrate that an array with only 10 suitably located microlenses can be used to produce reconstruction errors as small as those of a 36-microlens regular array. The same optimization procedure can be employed for any application where the wavefront statistics is known. [Copyright &y& Elsevier]

Abstract: In this paper, we propose an enhanced computational integral imaging system by both eliminating the occlusion in the elemental images recorded from the partially occluded 3D object and recovering the entire elemental images of the 3D object. In the proposed system, we first obtain the elemental images for partially occluded object using computational integral imaging system and it is transformed to sub-images. Then we eliminate the occlusion within the sub-images by use of an occlusion removal technique. To compensate the removed part from occlusion-removed sub-images, we use a recursive application of PCA reconstruction and error compensation. Finally, we generate the entire elemental images without a loss from the newly reconstructed sub-images and perform the process of object recognition. To show the usefulness of the proposed system, we carry out the computational experiments for face recognition and its results are presented. Our experimental results show that the proposed system might improve the recognition performance dramatically. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a novel computational integral imaging reconstruction (CIIR) method to improve the visual quality of the reconstructed images using a pixel-to-pixel mapping and an interpolation technique. Since an elemental image is magnified inversely through the corresponding pinhole and mapped on the reconstruction output plane based on pinhole-array model in the conventional CIIR method, the visual quality of reconstructed output image (ROI) degrades due to the interference problem between adjacent pixels during the superposition of the magnified elemental images. To avoid this problem, the proposed CIIR method generates dot-pattern ROIs using a pixel-to-pixel mapping and substitutes interpolated values for the empty pixels within the dot-pattern ROIs using an interpolation technique. The interpolated ROIs provides a much improved visual quality compared with the conventional method because of the exact regeneration of pixel positions sampled in the pickup process without interference between pixels. Moreover, it can enable us to reduce a computational cost by eliminating the magnification process used in the conventional CIIR. To confirm the feasibility of the proposed system, some experiments are carried out and the results are presented. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a method that controls the depth of the three-dimensional (3D) object existing over the depth-of-focus in integral imaging. The depth control method is performed only in a computer by synthesizing the intermediate sub-images between original sub-images obtained by transforming the captured elemental images. In the reconstruction process, we can obtain reconstructed 3D images with the better image quality within depth-of-focus than that reconstructed over the depth-of-focus. To demonstrate the feasibility of our method, optical and computational experiments are carried out and its results are presented. [Copyright &y& Elsevier]