Optical Review最新文献

In this paper, we revealed that the pseudo-3D perception of a 2D aerial image is increased by reducing the luminance and contrast of the background pattern, and by adding image movement that changes the shape and shading of the aerial image. In recent years, aerial images are used in our daily lives as entertainment, aerial touch panels etc. Most of them are 2D aerial images, but we sometimes perceive the depth of them as 3D objects. In this paper, we call this phenomenon pseudo-3D perception. However, it is not revealed what factors affect the pseudo-3D perception of 2D aerial images. Therefore, we evaluated what factors affect it. Especially, we evaluated how the luminance and contrast of the background pattern of the aerial image and the depth position of the aerial image relative to the background affect the pseudo-3D perception of the 2D aerial image. In addition, we evaluated how adding movement to the 2D aerial image affects the pseudo-3D perception of the 2D aerial image.

Two technologies for improving image gaps and narrow viewing angle were applied to a space-saving compact aerial display with striped retro-reflector on a LED panel. The aerial image gaps created by the striped retro-reflector structure was smoothed by scrolling the images perpendicular to the stripe direction. The narrow viewing angle inherent to the compact aerial display was successfully improved by increasing the width of the striped retro-reflector, verified by both theoretical calculation and measurement. These improvements in the space-saving compact aerial display would greatly expand its applications, such as digital signage and touchless interface.

Terahertz imaging technology has been widely used in security inspections due to its ability to detect various concealed hazardous materials and the advantage of being harmless to the human body. However, limited by the terahertz imaging system, it is challenging to detect concealed objects due to hard samples and imbalanced categories caused by terahertz image quality. To solve these issues, we propose a hybrid network with difficult–easy learning (DEL) for concealed object detection in the imbalanced activated terahertz image dataset. Based on the one-stage framework YOLOv5m, a path aggregation hybrid structure (PAHS) is proposed to improve the performance of the proposed network while maintaining real-time detection. Specifically, PAHS with transformer block (TB) and a fine-tuned global context attention (GCA) are designed to fully exploit and fuse the multi-scale information by path aggregation, which improves the detection accuracy of low contrast and noise-interfered objects. To solve the problem of imbalanced categories in the activated terahertz dataset, a DELoss is developed to guide the network classification. Moreover, EIOU is adopted to boost the network training, and a modified B-Ocl loss is used to discriminate the positive and negative samples. Experiments are conducted on a public imbalanced activate terahertz image dataset. The experimental results illustrate that the proposed network achieves competitive performance compared with recently reported state-of-the-art detection methods. Moreover, the proposed method improves the balanced detection ability of different categories.

This study aimed to explore the effectiveness of yellow glasses in reducing discomfort glare caused by white light-emitting diode headlights during night-time driving. The 30 visually normal participants were categorized into two age groups: 15 younger adults (mean age = 21.0 ± 1.6 years) and 15 older adults (mean age = 71.0 ± 1.6 years). Participants, simulating a driving position, assessed discomfort glare from glare sources (high- and low-beam headlights of oncoming vehicles) located 40 m away using the de Boer scale. Yellow glasses meeting night driving standards were found to have no significant impact on discomfort glare compared to neutral density filters with identical luminous transmittance, across all age groups. These findings imply that the ability of yellow glasses to partially block blue light, prevalent in white light-emitting diode headlights, does not alleviate discomfort glare. In conclusion, yellow glasses with a luminous transmittance of 75% or higher, meeting night driving standards, do not reduce discomfort glare caused by white LED headlights, regardless of the age group of the driver.

The large thermal conductivity of phosphor materials is crucial for laser lighting. Since the laser beam for pumping is focused on a small spot size (usually less than 1 mm²), heat generation is unavoidable at this point. Composite ceramic phosphors for cool-white laser lighting, the correlated color temperature of which is around 5000 K, produced by mixing of yellow photoluminescent light from Y₃A₅O₁₂:Ce (YAG:Ce) with unutilized pumping blue light, were well studied. However, composite ceramic phosphors for warm-white around 3000 K are not as researched; this is because the difficulties in sintering nitride phosphors which are useful as red or orange phosphors. We have proposed improved ternary composite ceramic phosphors for warm-white laser lighting. The ceramic phosphors utilize a red phosphor: ((Ba,Sr)₂Si₅N₈:Eu), a yellow phosphor: (YAG:Ce), and a thermal conducting matrix: (Al₂O₃). There are two types of composite ceramics: Type A with higher emission efficiency, and Type B more effective for warm light. These composite ceramic phosphors have higher saturation input laser power than our previous one, in which Sr₂Si₅N₈ was utilized as a red phosphor. The improved ceramic phosphors (Type A) do not have a saturation peak of at least up to 16 W (power density:20 W/mm²) pumping laser power, but our previous one had a saturation peak at 6 W (power density:7.6 W/mm²). We recently got a good sample, the correlated color temperature of which is 3422 K, output efficiency is 177 lm/W, and general color rendering index (Ra) is 65. The improved ternary composite ceramic phosphors are extremely useful for warm-white laser lighting.

We conducted sensory test for visibility of blur-added and color-changed virtual characters and analyzed it to investigate the way to improve the user’s visibility for AR display. We added blur to the virtual characters (blur-added AR) and changed color of virtual characters (color-changed AR). The results show that blur-added AR and color-changed AR are effective to improve the user’s visibility for AR display and there is a tendency that blur-added AR is more preferred than color-changed AR.