US Patent 7615791 Semiconductor optical device

A semiconductor optical device comprises a lower cladding layer of a first conductive type, an upper cladding layer of a second conductive type, and an active layer. The lower cladding layer has a first region and a second region. The first region extends in a direction of a predetermined axis, and the second region is located adjacent to the first region. The active layer is provided between the first region of the lower cladding layer and the upper cladding layer. The thickness of the active layer is changed in the direction such that TM mode gain and TE mode gain are substantially equal to each other.