Optical Projection System Research Articles

Mapping-based design method for high-quality integral projection system

A general method for designing an integral projection system is proposed, including optical design and digital preprocessing based on the mapping within the projection system. The per-pixel mapping between the sub-images and the integral projection image is generated by incorporating an integral projection imaging model as well as the ray data of all sub-channels. By tracing rays for sparsely sampled field points of the central sub-channel and constructing the mapping between the central sub-channel and other sub-channels, the efficient acquisition of ray data for all sub-channels is achieved. The sub-image preprocessing pipeline is presented to effectively address issues such as overlapping misalignment, optical aberrations, inhomogeneous illumination, and their collective contribution. An integral projection optical system with a field of view (FOV) of 80°, an F-number of 2, and uniform image performance is given as a design example. The ray tracing simulation results and quantitative analysis demonstrate that the proposed system yields distortion-free, uniformly illuminated, and high-quality integral projection images.

Design and optimization of Micro LED vehicle light projection optical system

Design and optimization of Micro LED vehicle light projection optical system

Overall study of solar simulation optical system with large irradiated surface using free-form concentrator to improve uniformity

Large irradiation surface solar simulator often has the problem of low irradiation uniformity. Therefore, a method for designing a large irradiation surface solar simulator with high irradiation uniformity is proposed. According to the law of conservation of energy and the edge-ray principle of non-imaging optics, the free-form surface concentrator is designed and optimized by using the simulated annealing algorithm based on Bessel curve to improve the incident beam uniformity of the integrator. The optical integrator and projection system are also designed and optimized to eliminate aberrations, improve light efficiency, and enlarge the irradiation area. The design is verified using LightTools software and achieves an effective irradiation size of Φ1200mm with an irradiance of a solar constant and an irradiation uniformity of less than 2.0%. This study provides accurate and reliable solar irradiation for laboratory calibration and performance testing of spacecraft payloads.

Applying multi-focus filtering plane in double-step Fresnel diffraction method for enhanced holographic projection region

Computer-generated holography has been anticipated in augmented reality (AR) since it can fully provide multi-depth 3D information to users, but speckle noises are often accompanied as one of the most significant degradation factors. Since complex amplitude encoding can suppress speckle noises, applying double-phase encoding to a lensless holographic projection system using a double-step Fresnel diffraction (DSF) algorithm has been reported to reduce those noises. However, a single filtering focus at a virtual focal plane might significantly reduce the projection region compared to the maximum diffraction bandwidth of the spatial light modulator. In this paper, we applied multiple foci for the focal plane of the DSF method with off-axis phase encoding, which can expand the projection region and is applicable to display multi-depth images with DSF. Numerical analysis conducted for image quality compared with conventional single focus DSF algorithm shows that the speckle performance does not degrade so much as the number of foci increase. We expect the proposed method to be useful for holographic projection optical systems such as AR head-up display.

Design and fabrication method of holographic waveguide near-eye display with 2D eye box expansion.

Augmented reality near-eye display (AR-NED) technology has attracted enormous interests for its widespread potential applications. In this paper, two-dimensional (2D) holographic waveguide integrated simulation design and analysis, holographic optical elements (HOEs) exposure fabrication, prototype performance evaluation and imaging analysis are completed. In the system design, a 2D holographic waveguide AR-NED integrated with a miniature projection optical system is presented to achieve a larger 2D eye box expansion (EBE). A design method for controlling the luminance uniformity of 2D-EPE holographic waveguide by dividing the two thicknesses of HOEs is proposed, which is easy to fabricate. The optical principle and design method of the HOE-based 2D-EBE holographic waveguide are described in detail. In the system fabrication, laser exposure fabrication method of eliminating stray light for HOEs is proposed, and a prototype system is fabricated and demonstrated. The properties of the fabricated HOEs and the prototype are analyzed in detail. The experimental results verified that the 2D-EBE holographic waveguide has a diagonal field of view (FOV) of 45°, an ultra-thin thickness of 1 mm, and an eye box of 16 mm × 13 mm at an eye relief (ERF) of 18 mm, the MTF values of different FOVs at different 2D-EPE positions can be better than 0.2 at 20 lp/mm, and the whole luminance uniformity is 58%.

Versatile volumetric additive manufacturing with 3D ray tracing.

Tomographic volumetric additive manufacturing (VAM) is an optical 3D printing technique where an object is formed by photopolymerizing resin via tomographic projections. Currently, these projections are calculated using the Radon transform from computed tomography but it ignores two fundamental properties of real optical projection systems: finite etendue and non-telecentricity. In this work, we introduce 3D ray tracing as a new method of computing projections in tomographic VAM and demonstrate high fidelity printing in non-telecentric and higher etendue systems, leading to a 3x increase in vertical build volume than the standard Radon method. The method introduced here expands the possible tomographic VAM printing configurations, enabling faster, cheaper, and higher fidelity printing.

Infrared scene projection optical system for blackbody micro cavity array

The ground experiment of a spaceborne infrared detection system requires to generate infrared images that simulate infrared characteristics of space targets under laboratory conditions. The infrared images are physically generated by an infrared scene generator and projected to the detection system by an infrared scene projection optical system (IRSPOS). In this paper, a middle-wave IRSPOS (MW-IRSPOS) and a long-wave IRSPOS (LW-IRSPOS) are designed to operate in the cryogenic environment. The IRSPOSs have an operating temperature range of 100–350 K and operating wavebands of 3–5 μm and 8–10 μm, respectively. The thermal deformation of the IRSPOS structures is analyzed, and the IRSPOS structures are optimized to ensure the temperature adaptability. The LW-IRSPOS prototype is fabricated according to the analysis results, and the infrared scene projection experiment is carried out. Experimental results show that the modulation transfer function (MTF) of the LW-IRSPOS is higher than 0.21 at a spatial frequency of 13.5 lp/mm in the cryogenic environment. This LW-IRSPOS has been successfully applied to the ground experiment of a space infrared detection system.

Superfast and large-depth-range sinusoidal fringe generation for multi-dimensional information sensing

Among many multi-dimensional information sensing methods such as structured-light and single-pixel imaging technologies, sinusoidal fringe generation is general and crucial. Current methods of sinusoidal fringe generation force concessions in either the speed or the depth range. To mitigate this trade-off, we have simultaneously achieved both speed breakthrough and depth range enhancement by improving both the optical projection system and binary coding algorithm based on an off-the-shelf projector. Specifically, we propose a multifocal projection system and oblique projection method, which essentially eliminates the existence of a single focal plane in the conventional axisymmetric system and utilizes its anisotropy characteristics to achieve a superior filtering effect. Furthermore, the optimal pulse width modulation technique is introduced to modulate the square binary pattern for eliminating specific harmonics. To the best of our knowledge, the proposed method, for the first time, simultaneously achieved superfast (9524 frames per second) and large-depth-range (560 mm, about three times that of the conventional method) sinusoidal fringe generation with consistently high accuracy. Experimental results demonstrate the superior performance of the proposed method in multi-dimensional information sensing such as 3D, 4D, and [ x , y , z , t ; s (strain)].

Enhancing the design by optimizing MTF performance of MLA with overlapping aperture

In this paper, we introduced a novel microlens array (MLA) design approach with the use of overlapped apertures. The chief ray tracing and paraxial imaging optics are utilised in projection imaging analysis. This work makes MLA structure design requirements more flexible. The proposed design is small and compact. It provides homogeneous illumination over the whole field of view (FOV). In the demonstration, a comparison of the sample 3x3 MLA projector and the proposed 3x3 MLA projector with the same aperture size is illustrated with the help of overlapped apertures. Finally, the proposed MLA projection imaging simulations are accomplished. It substantially outperforms the basic design in terms of FOV and modulation transfer function (MTF). We performed comparative analysis for proposed design with the help of diffraction MTF analysis tool. Our research will aid in the development and exploration of more efficient and advanced compact MLA projection optical systems.

Synchronized Two-Camera Laser Monitor for Studying Combusting Powder Systems

In this paper, we offer a laboratory facility for in situ visualization of the combustion of ultrafine metal powders, which combines laser initiation and simultaneous high-speed recording of images of the flame of a burning material and a surface covered by a flame. Visualization of the surface through the flame is realized using a laser monitor—an optical projection system with brightness amplification. The proposed imaging system makes it possible to get more detailed information about the combustion process, in particular, to study the change in the surface through the flame in the area of laser initiation, and the propagation of heating and combustion waves over the sample, as well as to study the change in the surface reflectance during combustion. To study the area of laser initiation, it is proposed to simultaneously record images of a laser monitor with two cameras. The symmetry of the combustion wave front propagation and the combustion products’ formation during laser initiation of the nanoAl + Fe3O4 thermite mixture was demonstrated. The nature of propagation in the form of a ring is a consequence of the symmetry of the properties of the system under study, at the micro and macro levels.

Design of projection optical system for 3D defect detection on PCB

According to the practical experience of PCB defect detection in semiconductor industry, a projection optical system suitable for structured light detection device is designed by using a DMD chip. In order to realize the lateral projection of structured light stripe and improve the quality of system projection, the design of tilt back group of projection lens is adopted and the projection size is 57×32mm.The simulation results show that the illumination uniformity of the projection system on the measured surface is more than 85%, the fringe contrast is larger than 0.5, and the maximum height of the measuring device is 5mm, which provides a guarantee for practical application of structured light fringe for 3D defect detection on PCB.

Correcting ray distortion in tomographic additive manufacturing.

Light-based additive manufacturing techniques enable a rapid transition from object design to production. In these approaches, a 3D object is typically built by successive polymerization of 2D layers in a photocurable resin. A recently demonstrated technique, however, uses tomographic dose patterning to establish a 3D light dose distribution within a cylindrical glass vial of photoresin. Lensing distortion from the cylindrical vial is currently mitigated by either an index matching bath around the print volume or a cylindrical lens. In this work, we show that these hardware approaches to distortion correction are unnecessary. Instead, we demonstrate how the lensing effect can be computationally corrected by resampling the parallel-beam radon transform into an aberrated geometry. We also demonstrate a more general application of our computational approach by correcting for non-telecentricity inherent in most optical projection systems. We expect that our results will underpin a more simple and flexible class of tomographic 3D printers where deviations from the assumed parallel-beam projection geometry are rectified computationally.

Optical projection system with a telecentric ray path for on-board aviation displays

In this paper, we discuss the design principles of an optical projection system that is compatible with a liquid-crystal display. We describe a procedure for synthesis of a complex optical system using conceptual design and third-order aberration theory. The resulting optical system design has high image quality over the entire field, low distortion, and high telecentricity, enabling liquid-crystal displays to replace cathode-ray tubes in modern on-board aviation displays.

CORRECTION OF PROJECTIVE DEFORMATIONS OF 3D OBJECT, ON THE STAGE OF HOLOGRAM FORMATION

The problems of digital synthesis of holograms associated with a discrete representation of a signal forming a holographic image are analyzed. One of the significant limitations is the technological problems of the formation of holographic structures pointwise due to diffraction limitations of the size of the focused spot of the optical-mechanical builder. This narrows the spectrum of possible spatial frequencies of the pointwise synthesized hologram in comparison with the classical hologram recorded in an analog way, which in turn leads to difficulties in recording holograms with a large depth of 3D image. We discuss a way to overcome this problem by using an optical projection system with the possibility of both transverse and longitudinal image size. Some possibilities of constructing such systems are shown and experimentally confirmed, and some problems of deformation distortions of 3D images arising during their creation are analyzed.

Projection optical system with telecentric beam path for aircraft on-board indicators

Projection optical system with telecentric beam path for aircraft on-board indicators

Оценка влияния тепловых потоков на точность определения размеров изделий оптической проекционной системой

Оценка влияния тепловых потоков на точность определения размеров изделий оптической проекционной системой

Effect of oblique incidence on the optical engine of extinction ratio

The optical engine (OE) is the core component of a projection optical system. The extinction ratio (EO) directly affects imaging contrast. A three-dimensional EO calculation and analysis method, based on traditional EO theory, is proposed to obtain the optimal incidence angle range and solve the problem of ignoring the oblique incidence’s influence on the EO’s existing research process. The method is simulated and verified by LightTools. Results show that, when the incident azimuth half angle is less than4.7∘, and the spatial half angle is less than180∘, the EO is 0.016, distribution is uniform, and the stray light is effectively suppressed.

Design of corneal cross-linking system: with real-time positioning of pupil position

This paper presents a design of a corneal cross-linking instrument with the function of tracking and locating the central position of the pupil in real time. According to the application requirements, based on the principle of uniform light of compound eye lens, the optical projection system of the corneal crosslinking instrument with the diameter of the treatment spot being 9mm and the uniformity being greater than 90% was designed. And put forward a kind of the pupil localization algorithm, the acquisition of the pupil image gray processing and calculate the histogram, according to the characters of histogram adaptively to take out the appropriate threshold binarization, again after the binarization of image contour tracking, get accurate boundary, the outline of the final vote based on the sliding arc length increment method to determine the pupil center and radius. Experimental results show that the corneal cross-linking system designed in this paper can not only accurately project the treatment of light spot, but also accurately track the central position of the pupil of the human eye.

Design and engineering verification of an ultrashort throw ratio projection system with a freeform mirror.

A refractive-reflective combined ultrashort throw ratio projection optical system is designed. We use a freeform mirror to shorten the projection distance and correct distortion, and a plane mirror to turn back the optical path and reduce system volume. The projection system design method combines refractive lens group design and freeform surface mirror design with integrated optimization. The system's throw ratio is 0.11 with a projection distance of 320mm and a 130in. (1 in.=25.4 mm) screen size, which illustrates the advantages of the low throw ratio. The system's maximum distortion is 0.07%. To demonstrate the proposed system's performance, a prototype is developed. Experimental results confirm that the system performs excellently while meeting the design requirements. The system's advantages include low throw ratio, excellent imaging quality, miniaturization, and engineering feasibility.

Dynamic Analysis of a 5-DOF Flexure-Based Nanopositioning Stage

A multibody dynamic model is developed for dynamic analysis of a 5-DOF flexure-based nanopositioning stage in the projection optical system of the semiconductor lithography in this paper. The 5-DOF stage is considered as an assembly of rigid bodies interconnected by elastic flexure hinges. Considering the length effects of flexure hinges, multibody dynamic equations are established according to spatial motions of rigid bodies by using Lagrangian method. The shear effects and the torsional compliances of the commonly used circular flexure hinges are considered to enhance the modeling accuracy. The accuracies of various out-of-plane compliance formulas are also discussed. To verify the developed dynamic model, the finite element analyses (FEA) by using ANSYS and modal hammer experimental tests of the primary flexure-based composition structures and the integral 5-DOF stage are performed. The analytical modal frequencies are well in agreement with FEA and experimental test. The results are significant to analyze and optimize the 5-DOF flexure-based nanopositioning stage.