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Silicon nitride photonics is on the rise owing to the broadband nature of the material, allowing applications of biophotonics, tele/datacom, optical signal processing and sensing, from visible, through near to mid-infrared wavelengths. In this paper, a review of the state of the art of silicon nitride strip waveguide platforms is provided, alongside the experimental results on the development of a versatile 300 nm guiding film height silicon nitride platform.

Background The vision-based method of Digital Gradient Sensing (DGS) for performing full-field measurement of mechanical fields is currently limited to planar solids. Objective In this work, a methodology to overcome this limitation in order to study 3-D phase objects (transparent solids) using transmission-mode DGS is described. Methods The proposed approach employs the concept of refractive index matching of the solid body under investigation with its liquid surroundings. By placing the 3-D phase object of interest in a refractive index matching fluid environment of a flat-faced tank, refraction effects at the solid–fluid boundary can be eliminated. Results This idea is demonstrated by visualizing and quantifying stress gradients in a PMMA cylinder subjected to a non-uniform stress field due to a concentrated force acting on one of its circular faces. The measurements are successfully compared with the analytical solutions based on Boussinesq equations. Conclusions The proposed method enables investigation of mechanical fields in 3-D transparent solids by exploiting stress-optical effects in phase objects.

One representative of state-of-the-art full-field optical metrology techniques is fringe-pattern-based methods, where the measurand is encoded in the phase distribution of the recorded spatially-periodic intensity pattern. The phase demodulation process comprises a crucial part of a measurement defining the overall achieved accuracy, and its algorithm imposes one of the main information throughput limitations of the entire experimental unit. In this paper, we propose a novel solution that increases the phase space–bandwidth product (SBP) of the optical system in a purely numerical way. It is based on deep learning and a convolutional neural network called DeepQuadrature. It takes two images as the input data: the prefiltered fringe pattern (denoised and detrended by variational image decomposition, for example) and the local orientation map (modulo 2 π ). The network’s output is the quadrature function (input fringe pattern shifted in phase by π /2). The phase distribution is finally calculated via the arctangent function of input and output fringe patterns. The working principle is somewhat motivated by the state of the art in high SBP classical phase estimation, called Hilbert spiral transform, however, with novel adaptive spectral features promoting DeepQuadrature as a versatile and universally applicable method. Phase decoding results for widespread simulated and experimental (testing technical and biological objects) fringe data compare favorably with classical algorithms: learning-free variational Hilbert quantitative phase imaging and the reference multi-frame method. DeepQuadrature thus opens new possibilities in fringe-based high-content optical metrology and is poised to advance biomedical and technical label-free microscopy.

It is crucial to fully master the mechanical properties of building components for ensuring the safety of infrastructures during service. The laboratory deformation test is an important way to study the mechanical properties of building components. At present, there is still a lack of a combination of high-efficiency, high-accuracy, and low-cost measurement methods for laboratory deformation tests. To address the issue, a method is proposed to measure the deformation of building components by using the structured light technique in this paper. It is applied to the axial tensile test of the dog-bone specimen, and the 3D full-field displacement of the dog-bone specimen is obtained by calculating the established deformation tracking model. The experimental results demonstrate the deformation measurement accuracy is at the millimeter level and can meet the accuracy requirement in the laboratory. Furthermore, the results are consistent with the way of force and the deformation mechanism of the dog-bone specimen. This paper presents a novel method for the deformation measurement, which provides a reliable analysis basis for studying the mechanical properties of building components.

This article presents an application of identification via finite elements model update (FEMU) to experimental fields of a plate with a hole using stereo correlation. The presentation includes the evolution of material properties during a tension test, and a first approach in estimating statistical confidence intervals from a single experimental field. These are accomplished by characterizing the material at different load cases, and by repeating the identification multiple times for random samplings of the full field and for random redistributions of noise.

The uniaxial compressive strength (UCS) test is crucial in determining the strength and stiffness behavior of intact rock and is frequently utilized by industry to determine project site characteristics. A fundamental procedure of UCS testing is strain response measurement. Conventionally, discrete strain measuring devices such as extensometers and/or electric foil strain gauges are used to measure the strain response at the mid-height of a specimen. However, this ultimately limits the ability to capture full-field strain of UCS test specimens. This has led to a gap in knowledge in terms of the complexities of UCS test strain responses caused by factors such as specimen heterogeneity and the influence of platen friction. Within this context, a novel distributed optical strain sensing (DOS) technology has been integrated with UCS testing (DOS-UCS technique). Unlike conventional discrete strain measurement methods, the optical technique captures a distributed strain profile along the length of standard, low-cost single mode optical fiber with a spatial sampling resolution of 0.65 mm. By wrapping an optical strain sensor around a UCS specimen, continuous full-field strain profiles along the length and circumference of UCS specimens can be realized. This paper presents a laboratory investigation that illustrates the potential of this technology to provide an in-depth look into the strain response of heterogeneous nodular limestone during UCS testing.

Background Digital Image Correlation (DIC) is an image-based measurement technique routinely used in experimental mechanics, which provides displacement and strain maps of an observed surface/volume. The metrological performance of DIC has reached its limit which is directly determined by the texture of the imaged surface/volume. Objective This paper proposes a novel DIC strategy, which relies on a virtual image. This image, noiseless and of infinite resolution, is moreover optimized for providing measurements with the best metrological performance. Methods The so-called Virtual DIC retrieves the displacement fields by comparing this virtual image to the experimental images. No interpolation is required and processing optimal textures such as checkerboards is possible. Results Virtual DIC is first applied on synthetic images for comparison purposes with a usual DIC approach. Outstanding metrological performance is observed thanks to the possibility of processing checkerboard patterns. Conclusions The proposed Virtual DIC is twofold: (i) thanks to the use of a closed-form expression, built-in DIC operators are elaborated without recurring to noisy and poorly defined real images. Interpolation is therefore avoided; (ii) it makes possible it to process checkerboard patterns, which offers the best metrological performance.

Background Reliably measuring sharp details in displacement and strain maps returned by full-field measurement techniques remains an open question in the photomechanics community. Objective The primary objective of this study is to improve and fine-tune a deconvolution algorithm in order to limit the blur that obscures the details in displacement and strain maps. Methods Checkerboard patterns are used and processed with a spectral method, namely the Localized Spectrum Analysis (LSA), and the raw maps returned by this technique are deconvolved. The influence of various settings on the quality of the results is studied by using synthetic images deformed through a well-vetted reference displacement field. Results It is shown that linking the size of the analysis window used in LSA on the one hand, and the size of the second derivative kernel employed in the deconvolution algorithm on the other hand, ensures the convergence of the deconvolution algorithm in all cases. This was not the case with the initial version. The ratio between these sizes, which optimizes the metrological performance of LSA followed by deconvolution, is identified. The influence of the sampling density of the checkerboard pattern in the images is also examined. The efficiency of the deconvolution algorithm employed with optimized settings is illustrated with strain maps obtained on two specimens, one in shape memory alloy, and the other in wood. Conclusions It is shown in this study that deconvolution with optimized settings is an effective tool to enhance small and sharp details in strain maps obtained with LSA.

Geotechnical particle image velocimetry (GeoPIV), as a type of digital image correlation (DIC), represents the state-of-the-art methodology for non-contact full-field deformation measurement in geotechnical engineering. Yet, when applying GeoPIV on sand specimens with interests in grain level, the discontinuities detection at grain boundaries remains as a challenge for 2D GeoPIV applications. In order to facilitate the full-field measurement for microscopic study, a method is proposed in this study to realize 2D pixel-level motion calculation using supervised optical flow algorithm with deep networks. Using digital images acquired from direct shear testing, the performance of this approach is demonstrated and compared with the prevailing GeoPIV method. Two series of experiments using small and large displacement modes were conducted, respectively, to demonstrate the method’s ability of revealing greater insights on soil behavior at grain level. To verify its accuracy, performance benchmarking of the approach was also conducted. Besides, a method was proposed to evaluate the errors in experimental images to ensure the accuracy and precision. It was demonstrated that the proposed method can achieve accurate pixel-level motion field calculation using images of common size and that the deformation discontinuities among particles can be clearly presented.

Rapid full-field surface topography measurement for large-scale wafers remains challenging due to limitations in speed, system complexity, and scalability. This work presents a interferometric system based on thin-film interference for high-precision wafer profiling. An optical flat serves as the reference surface, forming a parallel air-gap structure with the wafer under test. A large-aperture collimated beam is introduced via an off-axis parabolic mirror to generate high-contrast interference fringes across the entire field of view. Once the wafer is fully illuminated, topographic information is directly extracted from the fringe pattern. Comparative measurements with a commercial interferometer show relative deviations below 3% in bow and warp, confirming the system’s accuracy and stability. With its simple optical layout, low cost, and robust performance, the proposed method shows strong potential for industrial applications in wafer inspection and online surface monitoring.