In view of the fact that the current research of detection technology for large-size grating surface defect was very little, this paper builds a set of grating defect detection device based on the principle of darkfield imaging. The scheme includes three subsystems: displacement system, monochrome light illumination system and image acquisition system. When the displacement system drives the motion stage to move, the monochromatic light illumination system and the image acquisition system jointly complete the acquisition of the grating surface images. In this study, the surface of the diffraction grating with 170×170mm2 was detected for defects, and the statistical data of different defects is given. Experimental results show that, the device meets the needs of defect detection and evaluation on large-size grating surfaces and the mechanical structure is simple and compact, which has the great potential for large-scale detection.
Higher requirements have been put forward for the performance of two-dimensional (2D) gratings, such as polarization independence, high efficiency, wide broadband and so forth. In this letter, we employ the characteristic of diffraction in the grating and propose a 2×2 2D silver cylindrical array grating under normal incidence with excellent polarization independent high diffraction efficiency (DE) over communication band for beam splitting. The simulation and optimization of the DE are based on rigorous coupled wave analysis (RCWA) and simulated annealing (SA) algorithm, respectively. Under the optimal structural parameters, the highest DE of (±1, 0) orders and (0, ±1) orders can achieve over 24% at 1550nm in both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. Within moderate manufacture tolerance, the final discrete rotationally symmetric 2D periodic surface pattern has been fabricated by the holographic exposure technology, wet chemical development process and Electron Beam Evaporation. The measurement results of fabricated grating fully verify the correctness and accuracy of the calculation. Therefore, this 2D grating has considerable application potentials in optical communication, displacement measurement and semiconductor manufacturing.
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