A gain-coupled DFB laser diode includes a multiple quantum well active layer
and
a pair of cladding layers sandwiching the multiple quantum well active layer vertically,
wherein the multiple quantum well active layer includes a plurality of gain regions
aligned in a direction of propagation of a laser beam and repeated periodically,
each of the gain regions having a multiple quantum well structure, and a buried
layer fills a gap between a pair of adjacent gain regions, wherein the buried layer
includes a plurality of high-refractive index layers and a plurality of low-refractive
index layers, each of the high-refractive index layers is formed of a first semiconductor
material having a first bandgap, while each of the low-refractive index layers
is formed of a second semiconductor material having a second, larger bandgap.
