Provided is an optical device having an edge effect with improved phase shift and propagation loss of light without decreasing the dynamic characteristics of the optical device. The optical device includes a first semiconductor layer which is doped with a first type of conductive impurities, and has a recessed groove in an upper portion thereof; a gate insulating layer covering the groove and a portion of the first semiconductor layer; and a second semiconductor layer which covers an upper surface of the gate insulating layer and is doped with a second type of conductive impurities opposite to the first type of conductive impurities.