| CPC G02B 27/0172 (2013.01) [G02B 6/0016 (2013.01); G02B 6/124 (2013.01); G02B 27/0101 (2013.01); G02B 6/0026 (2013.01); G02B 6/34 (2013.01)] | 20 Claims |
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1. A grating structure, comprising a plurality of grating lines arranged in a plane, the plurality of grating lines being arranged with a period of T along a first direction in the plane and extending along a second direction perpendicular to the first direction, wherein,
each of at least part of the plurality of grating lines has a cross-sectional profile with a narrow top and a wide bottom in a cross section perpendicular to the second direction, the cross-sectional profile comprises six feature points being in sequence along the first direction, which are a first feature point, a second feature point, a third feature point, a fourth feature point, a fifth feature point and a sixth feature point, and the feature points are maximum-curvature points of the cross-sectional profile; and
in a coordinate system with the first feature point as an origin, the first direction as a first coordinate axis L, and a direction perpendicular to the plane as a second coordinate axis H, the first feature point, the second feature point, the third feature point, the fourth feature point, the fifth feature point, and the sixth feature point respectively have coordinates (0, 0), (L2, H2), (L3, H3), (L4, H4), (L5, H5) and (L6, 0), and satisfy following relationships, so that both diffraction efficiency and uniformity are well-maintained:
Hdrop=min(H4,H5)−max(H3,H2)>50 nm;
0.1<(L5−L4)/(L3−L2);
L3>0.34T; and
0.05T<L5−L4<0.32T.
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