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In fringe projection profilometry, system calibration is crucial for guaranteeing the measurement accuracies. Its difficulty lies in calibrating projector parameters, especially when the projector lens has distortions, since the projector, unlike a camera, cannot capture images, leading to an obstacle to knowing the correspondences between its pixels and object points. For solving this issue, this paper, exploiting the fact that the fringe phases on a plane board theoretically have a distribution of rational function, proposes an iterative calibration method based on phase measuring. Projecting fringes onto the calibration board and fitting the measured phases with a rational function allow us to determine projector pixels corresponding to the featured points on the calibration board. Using these correspondences, the projector parameters are easy to estimate. Noting that the projector lens distortions may deform the fitted phase map thus inducing errors in the estimates of the projector parameters, this paper suggests an iterative strategy to overcome this problem. By implementing the phase fitting and the parameter estimating alternately, the intrinsic and extrinsic parameters of the projector, as well as its lens distortion coefficients, are determined accurately. For compensating for the effects of the lens distortions on measurement, this paper gives two solutions. The pre-compensation actively curves the fringes in computer when generating them; whereas when using the post-compensation, the lens distortion correction is performed in the data processing stage. Both methods are experimentally verified to be effective in improving the measurement accuracies.We present a numerical investigation on the effect of introducing the second ring of antiresonant tubes on the guiding properties of the negative-curvature fiber. We determine the range of structural parameters for achieving the optimum light guidance in the double-ring geometry. Our study shows that the double-ring negative-curvature fiber can improve the confinement loss by up to four orders of magnitude with considerably better bending and single-mode performance when compared to its single-ring counterpart.PMMA-based fibers are widely studied for strain measurements and show repeatable results for Fiber Bragg Gratings (FBGs) inscribed using 325 nm laser and 248 nm laser. However, there is no available material mechanical behavior characterization of the UV source impact on the fiber properties. find more In this manuscript, fibers are irradiated with high fluence of 325 nm and 248 nm lasers and the fibers properties are investigated using dynamic mechanical analysis and tensile strain for potential use of these fibers past the yield point. It is demonstrated that the UV sources shifted the ultimate tensile strength and changed the strain hardening behavior. Tensile strain measurements show excellent repeatability for gratings inscribed with these two sources with similar sensitivity of 1.305 nm/mɛ for FBG inscribe with 325 nm laser, and 1.345 nm/mɛ for grating written with 248 nm laser in the range 0 to 1.5 % elongation. Furthermore, tests far beyond the yield point (up to 2.8 % elongation) show that grating inscribed with lower UV wavelength exhibit hysteresis. Finally, we demonstrate that 248 nm laser fluence shall be chosen carefully whereas even high 325 nm laser fluence do not critically impact the sensor properties.In this paper, we present a novel approach to spectral stereoscopic imaging. It is based on simultaneous spectral filtration of two light beams with a tunable acousto-optical filter (AOTF) of original design. It does not require large crystals and complicated optical relay systems, because two beams diffract in the same volume of the crystal medium but at different angles. We show that this geometry can be composed of a common-type AO cell and two triangular prisms of the same material. We derive equations, which specify the prism angles ensuring the necessary orientation of beams trajectories inside the crystal medium as well as parallel propagation of input and output beams. Some angles were additionally optimized for aberrations minimization by means of ray-tracing simulation. Experimental testing demonstrates rather high quality of spectral images, which is necessary for stereoscopic reconstruction procedure. The proposed approach makes possible development of spectral stereo-imaging components based on different types of previously developed AOTFs.In this paper, a multi-bit dielectric reflective metasurface is presented for control of electromagnetic (EM) wave scattering and anomalous reflection. The unit cell is designed to act as a 1-, 2-, and 3-bit coding metasurface to attain better control of EM waves. For the 3-bit coding metasurface, the eight digital states have phase responses of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°. The top layer of the proposed metasurface consists of high permittivity material to realize a high Q factor. The proposed multi-bit coding metasurface can reflect the incident EM wave to the desired angle with more than 93% power efficiency. For radar cross section reduction applications, the discrete water cycle algorithm is utilized to obtain an optimal coding matrix for the unit cell arrangement, leading to better diffusion-like scattering, dispersion of the EM wave in all directions, and hence minimal specular reflection. The simulation and experimental results verify that the proposed metasurface is a suitable candidate for control of EM wave scattering and anomalous reflection.Computational imaging with random encoding patterns obtained by scattering of light in complex media has enabled simple imaging systems with compelling performance. Here, we extend this concept to axial reflectivity profiling using spatio-temporal coupling of broadband light in a multimode fiber (MMF) to generate the encoding functions. Interference of light transmitted through the MMF with a sample beam results in path-length-specific patterns that enable computational reconstruction of the axial sample reflectivity profile from a single camera snapshot. Leveraging the versatile nature of MMFs, we demonstrate depth profiling with bandwidth-limited axial resolution of 13.4 µm over a scalable sensing range reaching well beyond one centimeter.
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