Patent ID: 7564883

Claim:
An optical semiconductor device comprising: a lower clad layer formed over a semiconductor substrate; an optical waveguide layer formed over the lower clad layer and including an active layer for recombining carriers; an upper clad layer formed on the optical waveguide layer; and a contact layer formed on the upper clad layer, the upper clad layer having a mesa stripe configuration including a first mesa portion which is in contact with the contact layer and has a first width and a second mesa portion which is in contact with the first mesa portion and the optical waveguide layer and has a second width larger than the first width and smaller than a width of the optical waveguide layer, a width of the first mesa portion at a contact between the first mesa portion and the second mesa portion and a width of the second mesa portion at the contact being different from each other, the first width, the second width and a thickness of the second mesa portion being set not to cause an oscillation of higher-order transverse mode.