A semiconductor laser diode is provided, including: an active layer; an upper clad layer formed above the active layer; a first lower clad layer formed below the active layer; a second lower clad layer formed under the first lower clad layer; and a substrate formed under the second lower clad layer, wherein a refractive index of the first lower clad layer is identical with a refractive index of the upper clad layer and is lower than a refractive index of the second lower clad layer.