Optical Review最新文献

By encoding object information (object phase, surface height, spectrum) into the polarization state, we can use polarization cameras to image other dimensions of the light field while viewing dynamic scenes. We discuss three recent examples of such video polarization encoding, allowing for quantitative imaging of transparent micro-organisms, for measurement of dynamic surface shape, and for compact spectral imaging.

Yellow glasses for nighttime driving are marketed as tools that can reduce headlight glare and improve visibility by cutting blue light. However, only few empirical evidences support these benefits. The present study was aimed to assess the effect of yellow lenses on reducing disability from peripheral glare caused by headlights and improving contrast sensitivity. On evaluating contrast sensitivity, the participants wore three types of lenses: clear (with 95% luminance transmission), gray (with 79% luminance transmission), and yellow (with 77% luminance transmission). The glare source was induced using low-beam headlights from oncoming vehicles positioned at a distance of 40 m. The results revealed that wearing gray and yellow lenses at night significantly reduced contrast sensitivity, while wearing yellow lenses under glare conditions slightly improved contrast sensitivity. Despite this slight improvement, the use of yellow lenses at night is not advisable, as the overall disadvantages surpass their benefits. These findings raise questions about the claimed benefits of yellow lenses for nighttime driving and highlight the need for further research to validate the effect of nighttime glasses.

The temporal Talbot effect (TTE) embodies the phenomenon of discrete Fourier transform (DFT). However, in an ideal temporal Talbot system, an infinitely long pulse train is required as input, which hinders the application of this property in optical computation of DFT. In this paper, we investigate the phenomenon of DFT in the TTE with input pulse trains of finite duration, aiming to apply it to optical computation of DFT. It is found that precise DFT coefficients can be extracted from the output signal of a system with an input pulse train of finite duration, subject to a specific condition on the pulse train’s duration. A significant advantage of the system employing an input pulse train of finite duration is that the resulting output signal becomes band-limited. This crucially implies that an optical receiver with a limited bandwidth can be utilized to obtain a distortionless signal. We provide a concise and rigorous theoretical framework on the TTE-based DFT system, which fully explains the underlying mechanism for perfect DFT calculation and is consistent with simulation results. Furthermore, we have determined that the single-cycle DFT calculation, using an input pulse train of one period, is feasible. The performance of the single-cycle DFT has been systematically evaluated under various non-ideal conditions, such as sampling time jitter and limited detection bandwidth. This research establishes a foundation for future applications of TTE in optical DFT computation, as it removes the requirement of inputting infinitely long pulse trains.

Near-infrared spectroscopy and imaging using scattered light potentially evaluate the structural properties of the medium, like the average particle size, based on a relation between its structure and light scattering. A qualitative understanding of light scattering is crucial for developing optical imaging techniques. The scattering properties of dense colloidal suspensions have been extensively investigated using the electromagnetic theory (EMT). The colloidal suspensions are widely used in liquid tissue phantoms for optical imaging techniques and are encountered in various fields, such as the food and chemical industries. The interference between electric fields scattered by colloidal particles significantly influences the scattering properties, so-called the interference effects. Despite many efforts since the 1980s, a complete understanding of the interference effects has still not been achieved. The main reason is the complicated dependence of the interference on the optical wavelength, particle size, and so on. This paper briefly reviews numerical and theoretical studies of the interference effect based on the dependent scattering theory, one of the EMTs, and model equations.

With growing demands for higher image quality in the fields of film, video post-production, image restoration, art creation, and computer vision, color transfer between images has become an important research area. Based on previous research on color transfer techniques, this paper proposes a color transfer method for images based on saliency features, aiming at automatic color migration between them. Transferring colors based on the saliency features of the input image can avoid the problem of unnatural color of the output image due to mixing of colors from different regions. First, the local variances of both the original and reference images are calculated, serving as a temporary saliency feature map. This is followed by obtaining a refined saliency feature map after undergoing processes such as minimization filtering, binarization, expansion, and iteration. Subsequently, color is transferred between the saliency and non-saliency regions of the original and reference images. To avoid the generation of pseudo-contours, the image is then refined using base projection. Finally, an output image is obtained by fusing the base-projected image with the outcome from Reinhard’s method, ensuring the output retains its naturalness and consistency. We conducted experiments with different types of images such as natural landscapes, buildings, and art paintings. The experimental results show that the method proposed in this paper not only retains the intricacies of the original image but also offers fuller and more realistic color renditions.

We numerically and experimentally developed a cantilever that provided both fast and analog actuation for THz metamaterials (MMs) by properly geometrizing a dimpled tip. Owing to its small size and light mass, the cantilever had a high mechanical resonance at 705 kHz. Cantilever arrays were fabricated with different tip gaps and integrated into a ladder-shaped MM (LS-MM). By changing the tip gap from 0.80 to 0.32 μm, the resonance of the transmittance spectrum changed from 1.235 to 0.795 THz, indicating that the reconfigurable LS-MM was capable of continuously tuning the resonance of the THz wave transmission with the tip gap. Additionally, the dimple served as an anti-stiction structure, providing the cantilever with a fabrication yield of 99.8%. This work shows a practical pathway to high-performance active metamaterials, which holds potential in advanced THz technologies such as 6G communications and fast imaging.

Imaging is a longstanding research topic in optics and photonics and is an important tool for a wide range of scientific and engineering fields. Computational imaging is a powerful framework for designing innovative imaging systems by incorporating signal processing into optics. Conventional approaches involve individually designed optical and signal processing systems, which unnecessarily increased costs. Computational imaging, on the other hand, enhances the imaging performance of optical systems, visualizes invisible targets, and minimizes optical hardware. Digital holography and computer-generated holography are the roots of this field. Recent advances in information science, such as deep learning, and increasing computational power have rapidly driven computational imaging and have resulted in the reinvention these imaging technologies. In this paper, I survey recent research topics in computational imaging, where optical randomness is key. Imaging through scattering media, non-interferometric quantitative phase imaging, and real-time computer-generated holography are representative examples. These recent optical sensing and control technologies will serve as the foundations of next-generation imaging systems in various fields, such as biomedicine, security, and astronomy.

Increasing the sensitivity of image sensors is a major challenge for current imaging technology. Researchers are tackling it because highly sensitive sensors enable objects to be recognized even in dark environments, which is critical for today’s smartphones, wearable devices, and automobiles. Unfortunately, conventional image-sensor architectures use light-absorptive color filters on every pixel, which fundamentally limits the detected light power per pixel. Recent advances in optical metasurfaces have led to the creation of pixelated light-transmissive color splitters with the potential to enhance sensor sensitivity. These metasurfaces can be used instead of color filters to distinguish primary colors, and unlike color filters, they can direct almost all of the incident light to the photodetectors, thereby maximizing the detectable light power. This review focuses on such metasurface-based color splitters enabling high-sensitivity color-image sensors. Their underlying principles are introduced with a focus on dispersion engineering. Then, their capabilities as optical elements are assessed on the basis of our recent findings. Finally, it is discussed how they can be used to create high-sensitivity color-image sensors.

In this paper, a small-world network-based reservoir computing (SWN-RC) is introduced to a micro-electromechanical system (MEMS) mirror-based laser scanner to achieve high-accuracy and low-delay laser trajectory control. The benefits of SWN-RC are confirmed through a comprehensive simulation, comparing it with reservoir computing (RC) based on regular and random networks. Subsequently, the RC control module is designed and implemented on a cost-optimized field-programmable gate array (FPGA). To balance the resource consumption and the processing delay, we use a half-parallel architecture for the large-scale matrix multiplications. In addition, the weight matrices of the RC are expressed by the 12-bit fixed-point data, which sufficiently suppresses the quantization noise. Furthermore, we simplify the activation function as a piecewise linear function and store the values in the read-only memory (ROM), resulting in a 76.6% reduction in ROM utilization. Finally, the SWN-RC, regular-RC, and random-RC control modules are implemented on the FPGA board and experimentally tested in the MEMS mirror-based laser scanner system. To the authors’ knowledge, it is the first reported RC-based MEMS mirror control system implemented on FPGA. In addition, the PID control is also tested as a baseline experiment. The results indicate that the RC control greatly outperforms the PID control with a 57.18% reduction in delay and over a 58.83% reduction in root mean square error (RMSE). Among the RC controls, the SWN-RC exhibits the best performance than the others. The SWN-RC achieves a further 14.03% and 12.42% reduction in RMSE compared to regular-RC and random-RC, respectively.

UV curing hybrid materials via the photo polymerization have significant significance for the lithography fields due to the high resolution. In this work, the UV-curable SiO₂ materials with chelating compound structure are synthesized by photosensitive Sol–Gel approach, which have a wide absorption band at 267 nm. With the UV light irradiation, the chelating compound structure decomposes and the solubility of the film in organic solvent decreases. Based on this premise, the presented material exhibits the ability to fabricating highly ordered SiO₂ microarrays on several substrates through UV photolithography. The SiO₂ micro arrays can be used to as templates to prepare noble metal micro-structures, which own wide potential application prospects in highly ordered SERS substrates with high activity and reproductivity for trace detection.