An optical device includes: an optical waveguide; and a plurality of diffraction grating layers, provided along the optical waveguide, each including a diffraction grating defined by a discontinuous first semiconductor layer and a second semiconductor layer having a refractive index different from a refractive index of the first semiconductor layer and burying the first semiconductor layer, one diffraction grating layer of the plurality of diffraction grating layers including a third semiconductor layer being continuous with the diffraction grating and made from a material different from materials of the first and the second semiconductor layers.