Optical Review最新文献

A novel self-powered ultraviolet (UV) photodetector (PD) based on a CuI/MgZnO heterojunction modified by an ultrathin Cu₂O layer has been fabricated by the successive ionic layer adsorption and reaction (SILAR) method. Compared with the CuI/MgZnO self-powered PD, the optimised heterojunction PD (CuI/Cu₂O/MgZnO) exhibits significantly improved self-powered properties. Under 325 nm UV light at an intensity of 450 µW/cm², the CuI/Cu₂O/MgZnO heterojunction PD shows exceptional photoelectric performance, featuring a high photo-to-dark current ratio of 1611, a large responsivity of 48.43 mA/W, and rapid rise and decay times of 261 ms and 890 ms, respectively, without any external power supply. Incorporating the Cu₂O interface layer results in notable enhancements in responsivity and detectivity compared to the heterojunction without the Cu₂O layer. This improvement is attributed to heterojunction interface contact, energy band engineering, and the tunneling effect. The Cu₂O layer expands the depletion zone and promotes charge separation. Due to its thinness, charges can tunnel through the Cu₂O layer from one metal electrode to another. Furthermore, the interfacial Cu₂O layer can alter the valence band offset and the conduction band offset of the p-CuI/n-MgZnO junction, enhancing carrier transport between MgZnO and CuI. These results lay the groundwork for using self-powered MgZnO-based heterojunction photodetectors in light-based devices in the future. They also demonstrate the potential of designing novel heterojunctions to create high-performance self-powered PDs for UV detection.

In the industrial production of steel materials, various complex defects may appear on the steel surface owing to the influence of environmental and other ambient factors. These defects are often accompanied by large amounts of background texture information. Especially, some defects with the low resolution and small size are prone to false alarms and missing detections. Aiming to address the issues of these specific defects, this paper proposes a bidirectional cross-scale feature fusion network combined with non-stridden convolution for steel surface defect detection. First, to improve the model’s inference speed and reduce the number of parameters, a simple yet effective convolution (PConv), the core component of FasterNet, is introduced in the feature extraction module instead of the traditional ResNet operator. Second, the bidirectional crossing (BiC) module is embedded to construct a bidirectional cross-scale feature fusion network (BiCCFM), which provides more accurate localization clues to enhance the feature representation on small targets. Finally, combined with non-stridden convolution, the SPD-Conv module is developed to aggregate the detection performance of small targets in low-resolution images. Comprehensive experimental results on the public NEU-DET dataset validate the effectiveness of the embedded modules and the proposed model. Compared with other state-of-the-art methods, the proposed model achieves the best accuracy (74.2% mAP @ 0.5) while maintaining a relatively small number of parameters.

Background

Two-dimensional mapping based on reflectance measurements is a promising approach for evaluating the characteristics of breast cancer and its response to chemotherapy. However, three-dimensional imaging should enable extraction of more accurate values and distributions of the parameters, potentially increasing the validity of the assessment. Therefore, we have been developing reflectance diffuse optical tomography (RDOT) for three-dimensional imaging of breast cancer using time-domain reflectance measurements.

Methods

We performed RDOT imaging on 64 patients with breast cancer and acquired three-dimensional images of total hemoglobin concentration (tHb) and tissue oxygen saturation (StO₂) at the lesion and a symmetrical area in the normal breast. The correlation between tHb and the skin-to-chest wall distance was investigated to evaluate the effect of the chest wall. We also examined correlations of tHb with tumor depth and tumor thickness. In addition, we measured patients with breast cancer before and after they underwent neoadjuvant chemotherapy and compared the results.

Results

The tHb value increased in both cancerous and normal breasts as the skin-to-chest wall distance decreased. Cancerous breasts showed higher tHb and lower StO₂ than normal breasts. tHb showed a negative correlation with tumor depth and a positive correlation with tumor thickness. Long-term monitoring of lesions during chemotherapy demonstrated that tHb decreased as the tumor size reduced with chemotherapy.

Conclusions

We confirm that the RDOT has potential for a novel examination method with no pain and no radiation exposure; however, the reconstructed image is still affected by chest wall, tumor size, and tumor depth.

With the development of deep learning and structured light streak projection techniques in three-dimensional (3D) imaging, research on the direct reconstruction of 3D shapes from single-streak images has attracted much attention. However, accurately reconstructing 3D shapes is particularly challenging when dealing with objects with specular reflective surfaces. To address this problem, this paper proposes an innovative multi-stage deep learning method that combines the pix2pix adversarial network and a modified version of the DC-HNet architecture. The technique aims to accurately reconstruct 3D shapes from streaked images by eliminating highlights in specular reflection regions through a staged process first. Specifically, the pix2pix adversarial network is first used to eliminate highlights and generate streak images without specular reflections; subsequently, the improved DC-HNet network is further processed to accurately deduce the phase distribution information of the object from the streak images with the elimination of highlights, and then reconstruct the 3D shape. Compared with the traditional self-encoder-based convolutional neural network (CNN) model, the multi-stage approach proposed in this paper significantly improves the accuracy of 3D shape reconstruction by separating the two key steps of highlight elimination and phase derivation and combining them with multi-scale feature enhancement. In this paper, the method’s effectiveness is verified on experimental data, and the results show that the proposed method provides a significant improvement in 3D shape prediction accuracy compared with the existing U-Net network and MultiResUet network. These findings not only demonstrate the innovation and robustness of the proposed method but also show its potential in scientific research and engineering applications.

Novel hexagonal form factor for evaluating chromaticity distribution of color speckle using red, green, and blue lasers is proposed. The measured color speckle distribution data were plotted on CIE 1931 chromaticity diagram. Only the small amount of outer rim data was extracted from the whole data of the chromaticity distribution to introduce the novel form factor. Specifically, the highest 1% and the lowest 1% of each of red, green, and blue monochromatic speckle data were picked up to form six outer rim regions. The average chromaticity coordinates of the six regions corresponding to hexagonal apexes are appropriate for evaluating the form factor of the chromaticity distributions, clarifying the distinctive difference between the measured and the calculated color speckle distributions.

A microchannel plates (MCPs) photon-counting detector with a cross-delay line (XDL) is expected for high-quality and wide-field target imaging. However, it is a great challenge for the uniformity of system response as the increasing of effective detection area. In this article, we develop a XDL photon-counting detector with a wide field of 120 mm × 50 mm. Additionally, we investigate the origin of image distortion and propose a partial polynomial correction method to alleviate it. The experimental results show that the drift correction index is improved by around 60% under the proposed method, which confirms that the partial polynomial correction method has general applicability and high efficiency in addressing distortion issues.

3D displays sometimes evoke illusion of perceived rotation angle change. In hollow face illusion, the direction of the 3D face changes according to the observation angle although the 3D face itself is static. Arc 3D display can show simple 3D image that is visible over a wide viewing angle by use of a thin substrate and illumination light. This structure is suitable for various applications such as digital signage or entertainments with illusion. If rotational perception like hollow face illusion would be obtained by simple aerial images like simple illustrations, application zone could be expanded to various field, such as animation or marks. To investigate the addition of rotation perception in 3D image with arc 3D display, we study perceived rotation angle of face-like illustration with inverted concave depth. In this paper, we quantitatively investigate the perceived rotation angle of the face image due to changing observation position and perceived depth position of face-like parts. The perceived rotation of the face image illustration can be achieved although the perceived depth of the face-like parts has various values by subject.

A simple photonic crystal fiber (PCF) arranged in a square geometry with two gold-coated air holes and one material-infiltrated core is proposed. A broadband polarization filter and a temperature sensor can be achieved based on the same simple PCF structure, with a hollow core separately filled with liquid crystal and toluene. The polarization filtering and sensing properties of the proposed PCF were studied using the finite element method (FEM). Numerically results show that variations in the diameter of both the liquid crystal-infiltrated central hole and the cladding air holes have a slight effect on the polarization filter characteristics. The polarization filter can be effectively tuned in terms of the central wavelength, crosstalk, and bandwidth by adjusting the thickness of the gold film. The proposed PCF polarization filter with t = 22.5 nm has achieved a wide bandwidth of 1850 nm across wavelengths ranging from 1.2 to 3.05 μm for a fiber length of 50 μm, achieving a high value of polarization loss ratio (PLR) of 28,717 at λ = 1.31 μm with losses of 1723 dB/cm for y-polarization and 0.06 dB/cm for x-polarization. The y-polarized core mode in this design with t = 10 nm is rapidly attenuated, experiencing losses larger than 1340 dB/cm over wavelengths ranging from 1.9 to 3.0 μm; it also exhibits a bandwidth of 2200 nm with crosstalk greater than 20 dB when using a fiber length of 50 μm at wavelengths above 1.5 μm. Furthermore, a temperature sensor that utilizes toluene as its core material exhibits a consistent average sensitivity of 6.68 nm/°C for y-polarization and can detect temperatures ranging from − 10 to 40 °C. The sensor maintains stable sensitivity within ± 1% fluctuation of the gold film thickness in the sensing range of − 10 to 40 °C.

Mid-air imaging, a visual display technology for augmented reality (AR) that enables multiple people to view images simultaneously without the need for special eyewear, involves the formation of real images in mid-air through various optical elements. This paper presents a novel mid-air imaging optical plate, termed the truncated cylindrical array plate (TCAP). TCAP is composed of transparent cylinders with obliquely truncated ends and mirrors, specifically designed to address issues such as stray light and limited viewing angles in existing mid-air imaging optical elements. We evaluated TCAP through computer simulations and by fabricating a prototype optical element. Ray tracing simulations and stereo matching algorithms demonstrated that mid-air images are symmetrically formed on the side opposite of the light source relative to the TCAP. Furthermore, the simulations indicated that a bright, stray-light-free mid-air image could be achieved within a horizontal viewing angle of approximately (pm , 40 ^circ ). Experimental evaluation using a handcrafted prototype further confirmed the plane symmetry of mid-air image formation, validating its functionality as a mid-air imaging element. The proposed method is advantageous in systems where stray light is problematic, such as mid-air image interaction systems or optical systems utilizing mid-air imaging elements.

Electro-optic (EO) modulators are crucial components to generate high-speed photonic signals in the modern photonic communication system. Here we study the performance of a hybrid EO modulator employing a Si slot waveguide and a BaTiO₃ layer, where the EO effect of BaTiO₃ is stronger than that of widely used LiNbO(_3). We demonstrate that an appropriate design for the slot waveguide, the BaTiO(_3) layer, and doped Si connectors to metal contacts can achieve a low voltage-length product (V_pi L) of 0.16 V cm, a wide modulation bandwidth of 50 GHz, and a small propagation loss of (<1) dB/cm simultaneously. These values indicate efficient use of the proposed modulator in the photonic communication system.