Optical device

An optical device having a central region and a first-type region surrounding the central region, wherein the first-type region comprises a first sub-region and a second sub-region between the central region and the first sub-region, and the optical device comprises:

• a substrate;
• and
• a meta-structure disposed on the substrate, wherein the meta-structure comprises:
• a plurality of first pillars in the first sub-region;
• and
• a plurality of second pillars in the second sub-region,
• wherein in a cross-sectional view of the optical device along a radial direction of the optical device, adjacent two of the first pillars have a first pitch, adjacent two of the second pillars have a second pitch, and the second pitch is greater than the first pitch,
• wherein the optical device further has a second-type region between the central region and the first-type region, and the second-type region comprises third sub-regions, and the meta-structure further comprises:
• a plurality of third pillars in each of the third sub-regions,
• wherein in the cross-sectional view of the optical device along the radial direction of the optical device, a top of each of the third pillars is lower than a top of each of the first pillars and each of the second pillars.