An optical device is provided. The optical device includes a substrate, a first optical layer; a high k layer, and a second optical layer. The first optical layer is disposed on the substrate. The first optical layer comprises a top surface, a first sidewall, and a second sidewall opposite thereto. The high k layer is disposed on the top surface of the first optical layer. The second optical layer is disposed on the high k layer. The second optical layer includes a top surface, a third sidewall, and a fourth sidewall opposite thereto. The first sidewall of the first optical layer is misaligned with the third sidewall of the second optical layer. The second sidewall of the first optical layer is coplanar with the fourth sidewall of the second optical layer.