Patent ID: 7366220

Claim:
A tunable laser, comprising: an optical waveguide alternately including a gain waveguide portion capable of generating a gain and a wavelength controlling waveguide portion capable of controlling the oscillation wavelength by current injection or voltage application without generating a gain in the optical axis direction; and a diffraction grating provided along said optical waveguide over the entire length of said optical waveguide; said diffraction grating including a gain diffraction grating provided at a position corresponding to the gain waveguide portion and a wavelength controlling diffraction grating provided at a position corresponding to the wavelength controlling waveguide; a wavelength controlling region being configured such that the wavelength controlling waveguide portion and the wavelength controlling diffraction grating are included therein; a gain region being configured such that the gain waveguide portion and the gain diffraction grating are included therein; the Bragg wavelength of said wavelength controlling region being longer than that of said gain region in a state in which current injection or voltage application is not performed for the wavelength controlling waveguide portion.