Optics and Lasers in Engineering最新文献

It is important to evaluate the reliability of the key silicon-based structures such as Through silicon vias (TSV) and Micro-electromechanical Systems (MEMS). The thermo-mechanical stress of TSV and the bonding stress of MEMS are quantitatively determined in this paper based on real-time phase shifting using a polarization camera. The polarizated images based on finite element simulation are reconstructed by stress-optic law and Mueller matrix multiplication for experimental verification. A economical infrared polariscope without rotation of optical elements is developed to provide a rapid measurement of stress in silicon-based structures. The error correction algorithm for the low extinction ratio in infrared polariscope is used for measurement of stress. Experimental results indicate that the infrared photoelastic system enables measurement of stress in TSV and MEMS.

In the measurement of the wheel tread in rail vehicles, line laser vision measurement technology has a good application prospect. However, the intensity and location of the ambient light will constantly change in the actual application scenarios. Traditional laser stripe segmentation algorithms often fail to produce accurate results, leading to decreased measurement precision in wheel tread. To solve the problem, a segmentation algorithm for laser stripes was proposed. Firstly, the SSR algorithm and frame subtraction were utilized to remove the background noise. Then, the OTSU method was used for the preliminary segmentation. After that, smoothing Images and reducing noise were performed with geometric mean filtering and morphological closing. Finally, the segmentation function which was based on the gray scale distribution characteristics of each region of the image was established to achieve the accurate segmentation of laser stripes. Laser stripe segmentation experiments, laser stripe segmentation comparison experiments, and wheel tread geometry extraction experiments were designed and conducted under the ambient light interference. The experimental results show that the segmentation success rate of the proposed algorithm is not <90.625 %. The proposed algorithm has a superior segmentation effect compared to other algorithms. The proposed algorithm can improve the measurement accuracy. For flange height measurement, the mean error decreased from 0.298 mm to 0.161 mm, and the standard deviation decreased from 0.600 to 0.548. For flange width measurement, the mean error remained constant at 0.200 mm, and the standard deviation decreased from 0.681 to 0.536. Under the condition that the ambient light intensity is in the range of 37lux∼1050 lx and the laser power is not <50mW, the proposed algorithm can better realize the adaptive segmentation of laser stripes.

Endoscope plays a crucial role in advancing minimally invasive surgeries. Ultra-compact, agile fiber endoscopes have gained significant popularity as an alternative to traditional bulk imaging systems. They have multiple advantages, such as large field of view, long depth of field and short rigid tip length. However, these systems exhibit honeycomb-like fixed patterns (HFP) and color bias in the output images, which can be attributed to the spacing and cladding around each fiber as well as the physical structure and low light conditions. To address these issues, we propose a fiber endoscope image restoration method based on generative adversarial network (GAN) named Endoir. The generator of Endoir employs a U-Net architecture that incorporates multi-scale skip connections between the encoder and decoder. It can incorporate low-level details with high-level semantics from feature maps in different scales and reduce the number of network parameters to improve the computation efficiency. We generate a synthetic dataset by simulating the fiber endoscope image scheme using an ordinary image dataset as a basis. This approach allows us to obtain a sufficient number of image pairs with more realistic usage scenarios. Our solution not only outperforms previous methods in terms of effectively removing the HFP but also provides the capability to correct color bias. The experiment results show that our method achieves superior accuracy in removing HFP and correcting color bias compared to existing approaches.

The time-resolved correlation technique is a standard approach for examining the intricate microscopic dynamics within polymeric materials. Nonetheless, its traditional application falls short in providing the real-time tracking capabilities required for monitoring the dynamic progression effectively. In this study, we propose adaptive time resolved correlation technique to observe the progression of microscopic dynamics during epoxy resin curing. By employing an adaptive processing method with a scheme for baseline auto-determination and the shortest delay time adjustment, the acquisition of intensity autocorrelation function is adjusted to accommodate the evolving dynamics of the system. Then the function can be well fitted to a standard model, which can reveal the system dynamics influenced by non-equilibrium factors such as internal stress relaxation and the cross-linking network. It is believed that the adaptive time resolved correlation technique effectively characterizes the progression of microscopic dynamics and holds potential as an online monitoring technique.

Underwater wireless optical communication (UWOC) is adversely affected by the scattering of impurity particles and turbulence in seawater channels, causing signal quality degradation over long distances. Owing to their physical properties, Bessel beams exhibit anti-interference capabilities in complex seawater environment, highlighting their significant potential for underwater communication. Addressing the issues of high-speed modulation of Bessel beams and their limited non-diffracting range for underwater communication, this paper proposes a UWOC system using Bessel beams and an acousto-optic modulator (AOM). The modulation speed is enhanced by adjusting the beam's focal distance to achieve a transmission rate of at least 20 Mbps. A telescope system was designed to extend the non-diffracting distance of the Bessel beam to 30 m. Experiments were conducted to compare and analyze the changes in the characteristics of the Bessel and Gaussian beam spots under different conditions of chlorophyll solution and temperature. It was confirmed that Bessel beams in this system exhibit superior turbulence and scattering resistance compared to Gaussian beams. Moreover, an in-depth analysis was conducted on how chlorophyll solutions and thermal gradients affect the signal characteristics of Bessel beams. The results show that at the same chlorophyll concentration, the bit error rate increases linearly with the signal rate; under the same thermal gradient, they are inversely proportional. This system validates the feasibility of using Bessel beams in underwater communication, exploiting their potential and offering a new direction for the development of UWOC systems.

The field of polarization detection is currently important, ensuring lossless detection of polarized light while maintaining a high level of integration presents a challenge. The current research consensus is to establish bionic multilayer structure to solve these problems, but current bionic multilayer research still has the problems of not realizing graphical detection and not stable enough. Building upon existing research in polarization detection structures, this paper proposes a novel Multilayer Al grid Metasurface Bionic Layer /Graphene Stack Polarization Detector (MAGD) to solve the problem. Inspired by the compound eye of insects, the MAGD utilizes a three-layered polarimetric sensing structure. This structure combines graphene and Al grid to form biomimetic structure to achieve simultaneous measurement of the multi-angular components of incident light at a single spatial point. Graphene is combined with quantum dots to improve photoelectric efficiency, and Al grid metasurface bionic layer are optimized to achieve multi-layer polarization sensitivity to mimic the insect compound eye structure. Furthermore, by combining the detection from multiple points, the MAGD can be used for graphical detection. This design offers a promising avenue for achieving more advanced polarization detection capabilities in the future and holds the potential for significantly improved performance compared to existing systems.

Clinical diagnosis increasingly relies on obtaining visualization images through optical coherence tomography (OCT) endoscopes with small-volume, large focusing depth, and high-resolution performance without damaging fragile tissues and organs. However, the mutual constraints of the depth of focus (DOF) and the lateral resolution currently limit the comprehensive imaging performance and widespread application of optical endoscopic probes. To overcome the inherent DOF-resolution tradeoff, a low-cost, ultra-thin fiber-optic endoscopic OCT probe with extended Bessel-like focus has been proposed and demonstrated. The waist diameter of the illumination beam is expanded by a large-diameter no core fiber (∼250 μm) and a fiber microsphere (∼600 μm). The sizable fiber axicon ground on the microsphere provides an opportunity to generate quasi-Bessel beam with a full width at half maxima (FWHM) diameter of the quasi-invariant focused spot-size of about 1.67 μm over the DOF range of 534 μm. The imaging performance and the vast potential for diverse applications of the fiber axicon-based OCT probe were validated by imaging of multiple samples. The low-cost, miniaturization, and ultrahigh imaging performance fiber-optic axicon probe are very attractive for OCT imaging in biomedical, clinical diagnosis, and intervention applications.

In the simplification, a light field is a four-dimensional (4D) function, and light field reconstruction aims to recover this 4D function from a three-dimensional (3D) focal stack, so it is a seriously ill-posed reconstruction problem from incomplete projection data. Based on the known 3D data of the focal stack in the frequency domain, we introduce a 3D assumption for the light field and derive an analytical reconstruction formula of the light field with an infinite depth range ρ. Subsequently, we establish the filtered back projection (FBP) algorithm to reconstruct the light field from the focal stack. Under certain assumptions concerning the light field and window functions, we prove the convergence of our proposed method at any continuous point. Since in actual data sampling scenarios, the light field is reconstructed only by a small number of focal stacks, a deconvolution algorithm is introduced based on the FBP algorithm to further enhance quality, which is called the filtered back projection-deconvolution (FBP-D) method. Our experimental results demonstrate the superiority of the proposed algorithm compared to the FBP method and other existing methods. Notably, the algorithm exhibits enhanced performance when employing a smooth boundary window and a larger depth range ρ.

Digital holographic microscopy (DHM) is emerged as a promising quantitative phase-contrast imaging tool for full complex wavefront reconstruction of micron-sized bio-samples. The technique covers the dynamics investigation ranging in scales from sub-cellular to tissue and from milliseconds to hours. Recent advances of DHM lie in the configuration and numerical development of the method and making it more feasible for the users without optical expertise. In this paper, we aim to propose a low-cost and portable add-on module for DHM, which can be mounted on either the ocular or camera port of a conventional microscope and easily turn it to a multi-modal bright-field and DHM imaging tool. The module works based on the off-axis, common-path geometry using a single Fresnel biprism in the detection path of the microscope. This configuration enables a compact and cost-effective solution for point of care applications and in field measurements. The feasibility and efficiency of the device have been confirmed through several morphological investigations on biological specimens and the sub-nanometer phase stability enables the measurement of cell dynamics and phenotypic changes such as motility, growth, differentiation and membrane oscillations.

In pupil detection within the visible light spectrum, intensity information serves as a carrier for capturing the reflective characteristics of images. When the reflectance of the pupil and its adjacent iris is similar, effectively distinguishing between them becomes challenging. Polarization provides additional information sensitive to the physical and chemical properties of objects, aiding in overcoming this problem. In the polarimetric pupil detection method, the transmission process of polarized light in the human eye model is theoretically analyzed. Arbitrary orthogonal polarization channels are utilized instead of intensity to describe the collected image, facilitating the extraction of polarization information corresponding to each channel. Experimental validation of the proposed method was conducted using active polarization illumination imaging experiments. The experimental results verify that the polarimetric pupil detection method could not only suppress the scatter noise but also be capable of obtaining a combination of intensity and polarization information. Moreover, exploiting the distinctions in depolarization characteristics among biological tissues can substantially improve their contrast.The research findings presented in this article provide insights into enhancing imaging methods for existing pupil detection schemes.