Patent ID: 7242699

Claim:
A wavelength tunable semiconductor laser device, comprising: a first semiconductor laser portion and a second semiconductor laser portion; a first optical waveguide and a second optical waveguide connected to outputs of said first and second semiconductor laser portions, respectively; and an optical combiner for combining light waves output from said first and second optical waveguides; wherein the oscillation wavelengths of said first and second semiconductor laser portions can be controlled; wherein the oscillation wavelength of said first semiconductor laser portion can be continuously varied between wavelengths λ 1 and λ 2 and between wavelengths λ 3 and λ 4 , where λ 1 <λ 2 <λ 3 <λ 4 ; and wherein the oscillation wavelength of said second semiconductor laser portion can be continuously varied between wavelengths λ 5 and λ 6 that satisfy the relation: λ 5 <λ 2 <λ 3 <λ 6 ; said first semiconductor laser portion includes a first front DBR region, a first gain region, and a first rear DBR region arranged in series; said first optical waveguide, said first front DBR region, said first gain region, and said first rear DBR region are adjacent each other in that order; said second semiconductor laser portion includes a second front DBR region, a second gain region, and a second rear DBR region arranged in series; said second optical waveguide, said second front DBR region, said second gain region, and said second rear DBR region are adjacent each other in that order; and the following equation is satisfied: Lgrt 2−Λ×( 1/10)≦ Lgrt 1+Λ×( N +½)≦ Lgrt 2+Λ×( 1/10), where: Lgrt 1 denotes the distance between a substantially center portion of the one of first rear grating elements closest to said first gain region and a substantially center portion of the one of first front grating elements closest to said first gain region, said first rear grating elements being formed in said first rear DBR region, said first front grating elements being formed in said first front DBR region; Lgrt 2 denotes the distance between a substantially center portion of the one of second rear grating elements closest to said second gain region and a substantially center portion of the one of second front grating elements closest to said second gain region, said second rear grating elements being formed in said second rear DBR region, said second front grating elements being formed in said second front DBR region; Λ denotes the pitch of a first gating and a second grating, said first grating being made up of said first rear grating elements and said first front grating elements formed in said first rear DBR region and said first front DBR region, respectively, said second grating being made up of said second rear grating elements and said second front grating elements formed in said second rear DBR region and said second front DBR region, respectively; and N denotes an integer.