US Patent 7366220 Tunable laser

A tunable laser includes an optical waveguide alternately including a gain waveguide portion and a wavelength controlling waveguide portion, and a diffraction grating. The diffraction grating includes a gain diffraction grating and a wavelength controlling diffraction grating. A wavelength controlling region is configured such that the wavelength controlling waveguide portion and the wavelength controlling diffraction grating are included therein. A gain region is configured such that the gain waveguide portion and the gain diffraction grating are included therein. The Bragg wavelength of the wavelength controlling region is longer than that of the gain region in a state in which current injection or voltage application is not performed for the wavelength controlling waveguide portion.