Disclosed is an optical detector. The optical detector includes: a first dielectric layer; a graphene optical transmission line formed on the first dielectric layer; a graphene optical detector formed on the first dielectric layer and configured to detect light transmitted along the graphene optical transmission line; electric wires formed on the graphene optical detector; metal pads positioned at both ends of the graphene optical detector and connected with the electric wires; and a second dielectric layer formed on the graphene optical transmission line, in which the graphene optical detector detects an intensity of light incident in a horizontal direction with respect to a surface of the graphene optical transmission line.