An optical device includes a substrate and a first optical waveguide including a mesa. The mesa includes a first lower clad layer portion, a first core layer portion, and a first upper clad layer portion. The first lower clad layer portion, the first core layer portion, and the first upper clad layer portion are disposed in this order from the substrate side. The optical device also includes a first etch stop layer configured to stop etching when the first optical waveguide is formed. The first etch stop layer being laminated over the substrate. The first optical waveguide is laminated on the first etch stop layer.