The present invention is the the etching step using the insulating film pattern was that the growth of the lower cladding layer, the lower waveguide layer and an upper cladding layer on a substrate according to the manufacturing method of the double waveguide structure is an integrated planar buried semiconductor optical amplifier mode converter flattening the surface so as to grow the the step of patterning a part of the thickness of the upper portion cladding layer, the lower waveguide layer and the lower cladding layer to form a lower waveguide, a planarization layer on the etched portion of the lower clad layer, the lower waveguide layer and an upper clad layer phase and a total space layer on the surface after removing the insulating layer pattern, the upper waveguide layer and a first and a step of growing a cladding layer, said first cladding layer by an etching process using a dielectric pattern, the upper waveguide layer and the spacer layer to a patterned by forming an upper waveguide having a tapered region horizontal, the first of the upper waveguide And a step of growing a second current blocking layer on the exposed first current blocking layer in the portion other than the dielectric pattern below dingcheung, after growing the first current blocking layer on the etched portion of the upper waveguide layer and the spacer layer, after removal of the dielectric pattern formed in the second cladding layer on the entire upper surface, and a step of forming each electrode in the second cladding layer and the substrate.