Patent ID: 8311071

Claim:
A wavelength tunable laser, comprising: a DFB portion including a first optical waveguide provided with a first grating; a DBR portion including a second optical waveguide that is optically coupled to the first optical waveguide and is provided with a plurality of second gratings and a plurality of third gratings arranged between the second gratings in the second optical waveguide; and a phase shift portion including a third optical waveguide that is optically coupled to the first and second optical waveguides, the third optical waveguide being adjacent to the second optical waveguide at an interface therebetween, wherein each of the second gratings has a grating formation area in which a grating is formed, and a grating shift area, the grating phase shift area shifting the phase of the grating adjacent thereto in the second grating, the second gratings are periodically arranged from a start position in a waveguide direction, the start position being at a distance from the interface, each of the grating formation areas in the second gratings substantially has a same length, the second grating has a first length in the waveguide direction, and the length of the grating shift area is a half or quarter of a period of the grating of the second grating, and wherein each of the third gratings has a grating formation area in which a grating is formed, and a grating phase shift area, the grating phase shift area shifting the phase of the grating adjacent thereto in the third grating, and wherein the third grating has a second length in the waveguide direction, the second length being different from the first length.