In this paper, a grating defect detection system based on the principle of darkfield imaging is proposed for the surface defect detection of existing large-size gratings, and the corresponding mechanical device is built. The device mainly includes two categories: hardware system and software system, of which the hardware system has lighting module, image acquisition and displacement module, and the software system has target edge reconstruction module and target edge detection module. Through the device, the surface defects of two-dimensional diffraction gratings of different sizes and different process conditions (substrate, mask grating, etching grating and coating grating) are automatically detected, and the statistical data of different types of defects are given. Through the analysis and study of the cause, transmittance and how to avoid different kinds of grating defects, whether it will affect the optical performance of grating use.The experimental results show that the proposed system meets the needs of large-size grating surface defect detection and evaluation in terms of accuracy and accuracy of defect detection, and the mechanical structure of the device is simple and compact, which has the potential of industrial large-scale detection. The device is of great significance for evaluating large-size high-precision grating manufacturing technology.
We treat wideband subwavelength guided-mode resonant gratings with grating-depth dependent duty cycles. By rigorous numerical computations, we visualize Bloch modal evolution while transforming the grating profile from trapezoid to triangle. Parametric optimization is achieved using the coordinate transformation method of Chandezon. With the increase of the profile base angle, the higher mixed resonant modes TM1 , 1 & 2 attract and combine and interact with the modes at both sides, forming wide reflection bands. This modal combination and interaction are the key determinant of broadband reflectivity spectral location and width. The optimized structure exhibits 99% reflectivity across a 613-nm spectral range, spanning a 1438- to 2051-nm wavelength range with a fractional bandwidth of ∼35 % . It is shown that gratings with trapezoidal profiles possess a good tolerance to groove depth variation, thus being easier to fabricate with a diamond-tip than triangular profile-based gratings.
We review guided-mode resonant photonic lattices by addressing their functionalities and potential device applications. The 1D canonical model is rich in properties and conceptually transparent, with all the main conclusions being applicable to 2D metasurfaces and periodic photonic slabs. We explain the operative physical mechanisms grounded in lateral leaky Bloch modes. We summarize the band dynamics of the leaky stopband. With several examples, we demonstrate that Mie scattering is not causative in resonant reflection. Illustrated applications include a wideband reflector at infrared bands as well as resonant reflectors with triangular profiles. We quantify the improved efficiency of a silicon reflector operating in the visible region relative to loss reduction as realizable with sample hydrogenation. A resonant polarizer with record performance is presented.
The fabrication of high-quality large-area thick Al films with a thickness around 10 μm or even more is one of the most important factors to realize high-performance large-size echelle gratings. During the deposition process of large-area Al films, Al film quality generally exhibits a different behavior along the radius (R) direction, which seriously affects the performance of echelle gratings. In this study, for the first time, we investigate the radial-quality uniformity of large-area (R=400 mm) thick (>10 μm) Al films in detail. We not only analyze the radial-quality difference of Al films prepared by the traditional electron-beam evaporation process, but also significantly improve the radial-quality uniformity of large-area thick Al films by using a coevaporation process. By comparing two kinds of film coating processes, we clarify the origin of the radial-quality difference of Al films, and prepare large-area thick Al films with excellent radial-quality uniformity.
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