Optical Review最新文献

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.

This study aimed to explore the impact of three wavelength-cut (TWC) lenses, which allowed 75% luminance transmittance while blocking wavelengths < 420 nm, approximately 460 nm, and approximately 585 nm, on visual function and color perception, and aging interaction effect. This single-center study enrolled 30 participants into two groups including 15 young participants (age 21.4 ± 1.3 years) and 15 older participants (age 71.7 ± 1.7 years). We used TWC lenses and a neutral density (ND) filter to assess the wavelength-cut effects on visual acuity, contrast sensitivity, and cone contrast sensitivity. Visual acuity and contrast sensitivity were assessed under photopic (luminance 85–100 cd/m²) and mesopic conditions (luminance 0.8 cd/m²). Significant interactions between age and lens conditions were observed for contrast sensitivity under photopic conditions (Bonferroni corrected α = 0.025, F_(1,28) = 7.98, P = 0.01, η² = 0.003), suggesting that contrast sensitivity to white and black gratings is better with TWC lenses (75%) than with the ND filter in young participants (F_(1,28) = 7.25, P = 0.01, η² = 0.206). However, the lens condition did not affect visual acuity and had only a minimal effect on cone contrast sensitivity for each cone type. In conclusion, TWC lenses, despite their nearly colorless and transparent appearance, can selectively block specific wavelengths to improve contrast sensitivity, while minimally affecting color perception. However, since the effect size of these interactions is very small, the impact is limited, therefore glasses should be prescribed with caution for young individuals.

A special type of semi non-classical states namely semi squeezed states is introduced. Some non-classical properties of these states are analyzed. Especially photon number distribution, quantum quantifier skew information, second-order correlation function and amplitude square squeezing are studied. Also, our discussion is extended to include the quasi-probability distribution functions (Q-functions). Finally, Pegg-Barnett phase is considered.

Face recognition, a biometric technology that analyzes facial features to authenticate individuals’ identities, has various applications and implications across different fields. However, the advancement of technologies such as the Internet of Things has posed challenges for face recognition systems in terms of size, weight, cost, and privacy issues. In response to these challenges, some scholars have suggested a mask-based lensless face recognition system that captures facial images through a mask, eliminating the need for lenses. Nevertheless, the performance of lensless face recognition systems is limited by mask-based imaging, resulting in suboptimal results. To address this limitation, we propose a novel mask-based lensless face recognition system based on the Dual-Prior Face Restoration (DPFR) model. This model utilizes a dual-prior generator to create distinct facial priors that aid the Generative Adversarial Network (GAN) blocks in reconstructing both the global face structure and local face details. Extensive experiments have been carried out on the FlatCam Face Dataset (FCFD) captured using a lens camera and Flatcam lensless camera. The enhanced accuracy, precision, and True Accept Rate (TAR) performance metrics validate the effectiveness of the proposed mask-based lensless face recognition system.

Aquatic display, which forms a floating image in water without a screen, used in behavioral experiments of aquatic organisms as optical stimuli, and accurately determining the imaging position in the water is important for aquatic display. We derive a formula for the imaging distance of an aquatic image by an aquatic display, including both the thickness and refractive index of the water tank by using paraxial approximation. To examine the accuracy of the derived theoretical formula, the imaging distances are estimated at various imaging distances. Our theoretical formula is measured to have 4% error by comparing with experimental results.

In this paper, we propose and experimentally demonstrate an artificial intelligence (AI)-enabled efficient modulation classification technique for underwater optical wireless communication (UOWC) systems. Specifically, time-domain waveform histograms are adopted as classification features, where three modulation formats including direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM) and pulse amplitude modulation (PAM) are considered. Moreover, AI algorithms such as decision trees (DT), k-nearest neighbors (k-NN), support vector machines (SVM) and convolutional neural networks (CNN) are utilized to realize efficient modulation classification based on the obtained waveform histogram features. Experimental results demonstrate that all the four algorithms can achieve accuracy surpassing 95% when the received signal-to-noise ratio (SNR) exceeds 6.3 dB. Furthermore, increasing the number of symbols in histograms enhances classification accuracy, whereas altering the number of histogram bins has minimal impact on classification accuracy.

Cylindrical lens is irreplaceable in the field of beam manipulation, which can generate new types of light field by diffraction effect, providing possible tools in micrography, optical micromanipulation and biomedicine field in future. The diffraction light field distributions of the Bessel beam and bottle beam passed though a cylindrical lens are studied in this paper using both experiment and simulation methods. In terms of simulation, Collins formula, combined Huygens Fresnel diffraction integral formula and optical matrix, is used to calculate the diffraction patterns. Specially, the thickness and refractive factors of the lenses in the optical system are introduced into the matrices in this paper, so that the lens is no longer approximated as a thin film, and the bottle beam diffracted by a cylindrical lens is first studied. The simulation and experimental images are broadly consistent for both those two diffraction phenomena.