Abstract: A distributed feedback semiconductor laser structure of the type having a guidance zone providing lateral guidance by refractive index variation, including a phase-shifting diffraction grating extending between two end regions along a light propagation direction, for obtaining coupling within the structure between light propagating in one direction and light propagating in the opposite direction. The diffraction grating is adapted to implement coupling of varying amplitude along the structure between said end regions, and the width of said guidance zone varies such that the phase shift induced by said variation in width compensates for the phase shift induced by the variation in the coupling amplitude.