Wavelength tunable laser and optical filter

A wavelength tunable laser comprising:

• a first gain section having an optical gain and emitting light of a first band;
• a second gain section having an optical gain and emitting light of a second band;
• an optical filter provided at a substrate;
• a first reflection portion and a second reflection portion, each of which reflects the light of the first band;
• and
• a third reflection portion and a fourth reflection portion, each of which reflects the light in the second band, wherein
• the optical filter includes a first region configured to allow the light of the first band to propagate, a second region configured to allow the light of the second band to be propagated, a first ring resonator, and a second ring resonator,
• the first gain section is optically coupled to the first region,
• the second gain section is optically coupled to the second region,
• the first region includes a first waveguide, a second waveguide, and a third waveguide,
• the second region includes a fourth waveguide, a fifth waveguide, and a sixth waveguide,
• each of the first waveguide and the fourth waveguide is optically coupled to the first ring resonator and the second ring resonator,
• each of the second waveguide and the fifth waveguide is optically coupled to the first ring resonator,
• each of the third waveguide and the sixth waveguide is optically coupled to the second ring resonator,
• the first waveguide, the first ring resonator, and the second ring resonator are provided between the first reflection portion and the second reflection portion in a propagating direction of light, and
• the fourth waveguide, the first ring resonator, and the second ring resonator are provided between the third reflection portion and the fourth reflection portion in a propagating direction of light.