Gain-coupled DFB laser with index coupling compensation

DETAILED DESCRIPTION It is an object of the present invention to provide a high performance DFB lasing device.
It is a further object of the present invention to provide a purely gain coupled DFB laser demonstrating efficient, single-mode operation.
Therefore in accordance with a first aspect of the present invention there is provided a gain-coupled, distributed feedback (DFB), semi-conducting lasing device comprising a substrate, an active region on the substrate including material having a first bandgap E.
sub.
g1 and capable of generating light and gain in response to a current flowing therethrough.
A gain coupling grating having periodic grooves etched through the active region is provided.
The grooves are regrown with a first layer having a second bandgap E.
sub.
g2 wherein E.
sub.
g2 >E.
sub.
g1.
A second regrown layer on top of the first layer has a third bandgap, E.
sub.
g3 wherein: E.
sub.
g2 >E.
sub.
g3 >E.
sub.
g1.
A current confining ridge is on the active region and contacts are provided on the ridge and substrate.
In accordance with a second aspect of the invention there is provided a method of fabricating a gain-coupled DFB semi-conducting lasing device.
The method includes the steps of: (a) growing material capable of generating light and gain for optical amplification on a substrate, the material including a cladding layer, a first separate confinement layer, a plurality of quantum wells separated by quantum barriers, and a second separate confinement layer, the quantum wells having a first bandgap E.
sub.
g1 ; (b) etching periodic grooves through the quantum wells; (c) regrowing a first layer of a first material in the grooves, the first material having a second bandgap E.
sub.
g2 wherein E.
sub.
g2 >E.
sub.
g1 ; (d) regrowing a second layer of a second material on the first layer, the second layer having a third bandgap E.
sub.
g3 wherein E.
sub.
g2 >E.
sub.
g3 >E.
sub.
g1 ; (e) regrowing on the second layer a buffer layer, an etch stop layer, a second cladding layer and a capping layer; (f) forming a current confinement ridge in the capping and cladding layers; and (g) forming contacts on the ridge and substrate