An optical device includes an active layer disposed over a semiconductor substrate, a diffraction grating disposed over the active layer, a clad layer partly disposed over the diffraction grating, at least one first burying material layer disposed beside side surfaces of end portions of the clad layer over the diffraction grating, and at least one second burying material layer disposed beside side surfaces of a center portion of the clad layer over the diffraction grating. A refractive index of the at least one first burying material layer is different from a refractive index of the at least are second burying material layer.