in the optical integrated devices with ridge waveguide structure based on the conventional technology , there occur such troubles as generation of a recess in a bj section to easily cause a crystal defect due to the mass transport phenomenon of inp when a butt joint is grown , lowering of reliability of the devices , and lowering in a yield in fabrication of devices . in the present invention , a protection layer made of ingaasp is provided on the bj section . the layer has high etching selectivity for the inp cladding layer and remains on the bj section even after mesa etching .