Patent ID: 7633986

Claim:
A distributed feedback laser diode comprising a phase-shifting portion within diffraction gratings, wherein the magnitude of a phase shift caused by the phase-shifting portion is 8Λ/40 to 9Λ/40, Λ representing twice the pitch of the diffraction gratings, and wherein the magnitude of the phase shift equals the width of the phase-shifting portion along the direction of oscillation of the diffraction gratings, wherein the distributed feedback laser diode has a coupling coefficient between 2.5 and 3.5, and wherein a main mode stands on a shorter wavelength side of a center of a stop band when injected current is at a level of a threshold current, and the main mode is shifted to the center of the stop band and the submode is suppressed from growing when injected current is at a level of an operating current, such that the distributed feedback laser diode achieves single mode operation when injected with an electric current that is higher than an electric current for normal operation.