Patent ID: 8121170

Claim:
A gain-coupled distributed feedback (DFB) semiconductor laser device, comprising: a laser cavity including at least first and second laser cavity sections; an active region located in the laser cavity, the active region comprising a plurality of quantum-well layers and barrier layers between the quantum-well layers, the band gap energy of the barrier layers being greater than the band gap energy of the quantum-well layers; and a grating formed by grooves extending at least partially through the active region and spaced along at least a portion of the laser cavity, wherein the grating comprises a first-order grating section in the first cavity section and a second-order grating section in the second cavity section, wherein the second-order grating section is longer than the first-order grating section, wherein at least the second-order grating section has a duty cycle of about 50% such that a lasing wavelength is obtained at a Bragg wavelength of the second-order grating section and such that the second-order grating section has an index coupling coefficient of substantially zero and provides substantially pure gain coupling, and wherein the first-order grating section is configured to reflect the lasing wavelength.