Abstract: A distributed feedback semiconductor laser may have (1) a controlled complex-coupling coefficient which is not affected by grating etching depth variation, and (2) facet power asymmetry with no facet reflection which eliminates a random effect of facet grating phase. The device comprises a multiple-quantum-well active region, and a complex-coupled grating formed by periodically etching grooves through a part of the active region. The semiconductor materials for a barrier layer where the groove etching is to be stopped, a regrown layer in the etched groove, and a laser cladding layer, are chosen all the same, so as to form an active grating entirely buried in the same material, providing a complex-coupling coefficient which is defined independently of the etching depth. Facet power symmetry may also be provided by composing the laser cavity of two sections (“front” and “back” sections) having different (“front” and “back”) Bragg wavelengths.

Abstract: A directly modulated distributed feedback (DFB) laser with improved optical field uniformity and mode stability may include a laser cavity and a distributed reflector and/or external reflectors. The distributed reflector may be a Bragg grating and may extend asymmetrically over a only portion of the laser cavity. The external reflectors may themselves be distributed Bragg reflectors and may have unequal reflectances. Optical field uniformity may be improved by adjusting the length and/or position of the distributed reflector in the laser cavity. Optical field uniformity may be improved by adjusting a coupling strength parameter, which is a function of a coupling coefficient, ?, and the length of the distributed reflector.