a lower cladding layer comprising InAlAs disposed on a substrate;

a ridge including an optical waveguide layer, a quantum dot active layer, an upper cladding layer comprising InAlAs, and an ohmic contact layer, which are sequentially stacked on the lower cladding layer, and having a predetermined width, which is obtained by performing a channel etching process on both sides of the ridge, wherein the ridge also includes a portion of the lower cladding layer;

an oxide layer formed by oxidizing surfaces of the upper and lower cladding layer to control an effective width of the ridge;

a dielectric layer disposed on left and right channels of the ridge;

an upper electrode layer disposed on the entire surface of the resultant structure to enclose the ridge and the dielectric layer; and

a lower electrode layer disposed on a bottom surface of the substrate,

wherein the upper and lower cladding layers have a faster oxidation rate than that of the optical waveguide layer and active layer so that the formation of the oxide layer substantially changes the effective width of the ridge without substantially changing the predetermined width of the active layer or the optical waveguide layer.