Patent ID: 8451872

Claim:
A wavelength tunable laser comprising: a semiconductor substrate; an optical output port; a wavelength tunable filter disposed over the semiconductor substrate and including a first waveguide and a second waveguide, the first and second waveguides being aligned parallel at least partially in an in-plane direction of the semiconductor substrate as a co-directional coupler, and one end of the first waveguide being coupled with the optical output port; a gain region disposed over the semiconductor substrate and including a third waveguide coupled with the second waveguide; a reflector with a first grating structure disposed over the semiconductor substrate and including a fourth waveguide coupled with the third waveguide; and a phase adjustment region disposed over the semiconductor substrate and including a fifth waveguide coupled between the second waveguide and the third waveguide, wherein the second waveguide has a second curved portion in the vicinity of the one end of the first waveguide, and the second waveguide is directed away from the first waveguide, and wherein the first waveguide has a first curved portion in the vicinity where the second waveguide is coupled with the fifth waveguide.