| CPC G02B 1/06 (2013.01) [B32B 3/20 (2013.01); G02B 2207/101 (2013.01); G02B 2207/109 (2013.01); G02F 1/13398 (2021.01)] | 15 Claims |

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1. A flat optical device, comprising:
a substrate, the substrate having a first arrangement of a first plurality of pillars formed thereon, the first arrangement of the first plurality of pillars comprising:
pillars having a height h and a lateral distance d;
a gap g corresponding to a distance between adjacent pillars of the first plurality of pillars, and
a silica-containing aerogel material having an absorption coefficient less than 0.001 only disposed in each gap g; and
a first encapsulation layer disposed on the first arrangement of the first plurality of pillars, the first encapsulation layer is disposed on a top surface of each pillar of the first plurality of pillars and on the silica-containing aerogel material disposed in each gap g, the first encapsulation layer having a refractive index of about 1.0 to about 1.5.
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