Optical semiconductor device with diffraction grating

摘要

An optical semiconductor device includes: a waveguide structure including layers grown over a semiconductor substrate, having a width defined by sidewalls formed by etching the layers, and including a wide (WCw), a narrow (WGn), and an intermediate (WGe) portion, formed along a propagation direction; and a diffraction grating formed on the sidewalls of at least one of the wide and narrow portions (WGw, WGn) of the waveguide structure, the diffraction grating having vertical grooves periodically disposed along the propagation direction and defining a wavelength of propagation light. The narrow portion (WGn) is formed in such a manner that a loss of 50 % or more is imparted to a higher order transverse mode. An optical semiconductor device having a vertical diffraction grating is thus provided which can suppress generation of a higher order transverse mode without unduly increasing the device resistance.