Patent ID: 7583719

Claim:
A complex-coupled distributed feedback (DFB) semiconductor laser device comprising: a) a semiconductor substrate; b) a radiation cavity formed on the semiconductor substrate; c) an active region formed in the radiation cavity, comprising (1) a plurality of quantum-well layers of bandgap energy E q1 , adjoined with symmetric barrier layers of bandgap energy E b1 wherein E b1 >E q1 , and (2) two quantum-well layers of bandgap energy E q2 , adjoined with a barrier layer of bandgap energy E b2 in between the two quantum-well layers, and adjoined with two outside barrier layers of bandgap energy E b1 wherein E b2 >E b1 >E q1 ≧E q2 ; d) a complex-coupled grating having corrugations along the optical axis formed by periodically etching grooves through the active region, the groove etching being stopped in the barrier layer of bandgap energy E b2 , and the grating period comprising a high corrugation section and a low corrugation section, wherein a plurality of the quantum-well layers are etched away from the low corrugation section, wherein the radiation cavity comprises two sections: a front cavity section of length L f in which the complex-coupled grating has Bragg wavelength λ Bf , and a back cavity section of length L b in which the complex-coupled grating has Bragg wavelength λ Bb which is larger than λ Bf , lasing feedback being provided mainly by the front cavity section to give a main lasing mode at the longer wavelength side of the Bragg stop band of the complex-coupled grating in the front cavity section, and wherein the front and back cavity sections have the following lengths L f and L b , and Bragg wavelengths λ Bf and λ Bb : 0.1<L b /(L f +L b )<0.3 and 0<.λ Bb −.λ Bf <3 nm; e) a semiconductor layer regrown in the etched grooves, having bandgap energy E b2 ; and f) contact means facilitating flowing an electrical current through the semiconductor laser device.