Waveguide-based near-eye display with dual-channel exit pupil expander

We propose a waveguide-based near-eye display featuring a dual-channel exit pupil expander, which is composed of an in-coupler, relay gratings, and an out-coupler. Unlike the conventional waveguide-based near-eye displays, whose field of views are usually non-split or partially split, our dual-channel exit pupil expander is able to evenly split the field of view into two halves. The greatest benefit of doing so is that the upper limit of field of view could be significantly increased. The design rules for all components, including the microdisplay, collimating lens, waveguide and gratings, have been studied. The refractive index and dimension of waveguide are identified as two factors that limit the field of view. In what follows, its key specifications are recapitulated. Field of view is 70° (diagonal), eye relief is 15 mm, exit pupil is 20 × 9 mm², modulation transfer function is above 0.591 at 30 cycle/degree, contrast ratio is 13, and distortion is 1.38%.     

Near‐to‐eye display with diffractive exit pupil expander having chevron design

Abstract— Near‐to‐eye displays (NEDs) provide a unique way to perceive a larger image than the device itself. The user acceptance of commercially available NEDs has not been high partly because of reported physiological symptoms. Devices also tend to be thick and heavy, and therefore uncomfortable to wear. To overcome these shortcomings and to make a very usable device, a new approach was needed. By using very thin plastic light guides with diffractive structures on the surfaces, many of the known obstacles can be notably reduced. These exit pupil expanders (EPEs) enable a light and thin design for see‐through NEDs. The so‐called chevron EPE was designed to further improve the design and usability aspects of NEDs. The diffractive EPE has typically one incoupling grating area that delivers light into the light guide symmetrically towards the left and right eyes. By using slanted or overhanging gratings, the incoupling is very asymmetric. If the incoupling area is divided into two parts, each having opposite slanting angles, the EPE plate can be cut in half, and the left and right parts can be separated. The plates can be further tilted to a chevron shape following more closely the human face and mimicking the conventional eyeglass design. The reflection of the light from the tilted plate is directed out from the image‐forming optics, and therefore the contrast is improved. The privacy of the usage is improved because at the output the secondary beams are harder to observe. Because the device is brought closer to face, it enables better weight balance. The chevron geometry partially prevents the ambient light from the sides to enter the diffractive structures, and thus the unwanted reflections are also reduced. Furthermore, the half‐size of the chevron EPE parts from the undivided EPE results in a better production yield.     

Wide field of view compressive light field display using a multilayer architecture and tracked viewers

In this paper, we discuss an intuitive extension to compressive multilayer light field displays that greatly extends their field of view and depth of field. Rather than optimizing these displays to create a moderately narrow field of view at the center of the display, we constrain optimization to create narrow view cones that are directed to a few viewers' eyes, allowing the available display bandwidth to be utilized more efficiently. These narrow view cones follow the viewers, creating a wide apparent field of view. Imagery is also recalculated for the viewers' exact eye positions, creating a greater depth of field. The view cones can be scaled to match the positional error and latency of the tracking system. Using more efficient optimization and commodity tracking hardware and software, we demonstrate a real‐time, glasses‐free 3D display that offers a 100° × 40° field of view.     

Holographic waveguide display with large field of view based on volume holographic grating

The field of view (FOV) of waveguide display systems based on volume holographic grating (VHG) is primarily constrained by the diffraction response bandwidth, which is currently insufficient to meet the need for AR immersive displays. Through the composite diffraction response bandwidths, red-responsive and green-responsive double-layer VHG structures are proposed to expand the FOV under varied image sources. The influence of several input spectral bandwidths on FOV improvement is also considered, and OLED micro-display and LCOS micro-display are selected as image sources. As a consequence, the horizontal FOV of the red-responsive double-layer VHG waveguide based on the LCOS micro-display is 19.5°, and that of the green-responsive double-layer VHG waveguide based on the OLED micro-display is 33.4°. Through the simulation and experiment, we effectively illustrate the effect of the double-layer VHG and the input spectral bandwidth on the FOV.     

Wide‐view augmented reality display with diffractive cholesteric liquid crystal lens array

A novel augmented reality display is proposed to achieve a field of view of 100°, while maintaining a good form factor with a glass‐thin waveguide combiner. The out‐coupler consists of an array of off‐axis diffractive lenslets with extremely low f‐number. A breadboard system is built and its performance characterized, combined with analysis and discussion of further improvement.     

Influence of the monocular near‐to‐eye display position on the visual system during dual‐task performance

Abstract— In this research project, the influence of different monocular near‐to‐eye display (NED) positions on user comfort has been investigated. In total, 43 subjects participated in tests; 22 used above and 21 below NED positions during dual‐task performance for 40 minutes. SSQ and VSQ questionnaires were used to compare the eyestrain and other sickness symptoms before and after the task performance for both display positions. According to the subjective test results, the NED position above the eye causes more symptoms than the position below the eye.     

Image formation modeling and analysis of near‐eye light field displays

Near‐eye light field displays based on integral imaging through a microlens array provide attractive features like ultra‐compact volume and freedom of the vergence‐accommodation conflict to head‐mounted displays with virtual or augmented reality functions. To enable optimal design and analysis of such systems, it is desirable to have a physical model that incorporates all factors that affect the image formation, including diffraction, aberration, defocusing, and pixel size. Therefore, in this study, using the fundamental Huygens‐Fresnel principle and the Arizona eye model with adjustable accommodation, we develop an image formation model that can numerically calculate the retinal light field image with near‐perfect accuracy, and experimentally verify it with a prototype system. Next, based on this model, the visual resolution is analyzed for different field of views (FOVs). As a result, a rapid resolution decay with respect to FOV caused by off‐axis aberration is demonstrated. Finally, resolution variations as a function of image depth are analyzed based on systems with different central depth planes. Significantly, the resolution decay is revealed to plateau when the image depth is large enough, which is different from real‐image type light field displays.     

大视场双目立体视觉的摄像机标定

针对大视场视觉测量应用,在分析摄像机成像模型的基础上,设计制作了可自由转动的十字靶标,实现了大视场双目视觉摄像机的精确标定。将十字靶标在测量空间内多次均匀摆放,两摄像机同步拍摄多幅靶标图像。由本质矩阵得到摄像机参数的初始值,采用自检校光束法平差得到摄像机参数的最优解。该方法不要求特征点共面,仅需要知道特征点之间的物理距离,降低了靶标制作难度。采用TN3DOMS．S进行了实测,在1500mm×1500mm的测量范围内测试标准标杆,误差均方值为0．06mm。     

Development of a volumetric projection technique for the digital evaluation of field of view

Current regulations for field of view requirements in road vehicles are defined by 2D areas projected on the ground plane. This paper discusses the development of a new software-based volumetric field of view projection tool and its implementation within an existing digital human modelling system. In addition, the exploitation of this new tool is highlighted through its use in a UK Department for Transport funded research project exploring the current concerns with driver vision. Focusing specifically on rearwards visibility in small and medium passenger vehicles, the volumetric approach is shown to provide a number of distinct advantages. The ability to explore multiple projections of both direct vision (through windows) and indirect vision (through mirrors) provides a greater understanding of the field of view environment afforded to the driver whilst still maintaining compatibility with the 2D projections of the regulatory standards.

Practitioner Summary: Field of view requirements for drivers of road vehicles are defined by simplified 2D areas projected onto the ground plane. However, driver vision is a complex 3D problem. This paper presents the development of a new software-based 3D volumetric projection technique and its implementation in the evaluation of driver vision in small- and medium-sized passenger vehicles.     

基于大视场星敏感器的目标识别技术

天基目标探测技术已成为当今空间研究领域的前沿性技术.深空目标由于距离较远,在探测器上为点目标成像,很难通过外形特征将其与恒星、行星等虚假目标区分.大视场星敏感器由于自带导航星库,能有效地将虚假目标中恒星剔除.依据真假目标在赤经坐标系下运动规律的不同,结合星敏感器的姿态矩阵,可将真正的目标从复杂的星空背景中准确地识别出来,从而达到安全防护目的.仿真结果验证了该方法的有效性.     

Design of a low‐cost 1‐20 GHz magnetic near‐field probe with FR‐4 printed circuit board

An ultra‐wideband magnetic near‐field probe based on a conventional low‐cost four layers of FR‐4 printed circuit board is proposed in this article. It can be used to measure the magnetic near‐field strength from RF magnetic sources or electronic devices for EMI conformance test. The operating frequency of the probe is from 1 GHz up to 20 GHz. The probe is constructed based on a coplanar waveguide and stripline with a short‐end loop. The probe dimension is 10 mm × 25 mm × 0.6 mm. The prototype probe is electric field‐shield structure and has a very high unwanted electric field suppression ratio about 17.7 dB. The probe calibration factor from the simulation agrees well with the calibration factor computed from the measurement. The average probe factor is 38.8 dBS/m and probe sensitivity is 47.4 dB μ A/m.     

Precise evaluation of LCD gray‐to‐gray response time based on a reference pattern synchronous measurement using high speed charge‐coupled device camera

A reference pattern method based on synchronous measurement for evaluating the response time of liquid crystal display was proposed to overcome the shortcomings of the unsmooth response curve induced by the backlight modulation. The feasibility of the method is verified by measurement using a high speed charge‐coupled device camera. The measured gray‐to‐gray response time results are compared with those obtained from standard measurement approach. The results indicate that the proposed method improves the accuracy and repeatability of the response time measurement.     

Ridge extraction of a smooth 2-manifold surface based on vector field

This paper presents a general scheme to compute ridges on a smooth 2-manifold surface from the standpoint of a vector field. A ridge field is introduced. Starting with an initial ridge, which may or may not be umbilical, a ridge line is then traced by calculating an associated integral curve of this field in conjunction with a new projection procedure to prevent it from diverging. This projection is the first that can optimize a ridge guess to lie on a ridge line uniquely and accurately. In order to follow this scheme, we not only develop practical ridge formulae but also address their corresponding computational procedures for an analytical surface patch, especially for an implicit surface. In contrast to other existing methods, our new approach is mathematically sound and characterized by considering the full geometric structures and topological patterns of ridges on a generic smooth surface. The resulting ridges are accurate in the numerical sense and meet the requirement of high accuracy with complete topology. Although the objective of this paper is to develop a mathematically sound framework for ridges on a smooth surface, we give a comprehensive review of relevant works on both meshes and smooth surfaces for readers.     

差动变压器式大量程精密角位移传感器的设计

设计了一种基于差动变压器原理的大量程精密角位移传感器。阐述了差动变压器式角位移传感器的工作原理,指出了传统传感器的不足。通过衔接法,既扩大了传感器的量程,又提高了传感器的精度。最大量程为±145°,精度可达1%。同时,采用多种温度补偿措施,改善了传感器的工作特性。