<title>Deep surface grating DFB and DBR quantum well diode lasers in AlGaAs/GaAs for photonic integration</title>

Abstract

Deep surface grating structures make possible the fabrication of DFB and DBR structures where the usual epitaxial regrowth processes which compromise device yield and reliability are avoided. A key requirement is that the gratings are etched to a well-controlled depth position close to the waveguide core. This paper describes the fabrication processes for the grating/stripe waveguide structures in both DFB lasers with gratings exterior to a central stripe (effectively providing refractive index confinement) and DBR lasers with gratings etched into the central ridge region. Issues of etch depth precision, grating pattern definition using either electron beam lithography or holography and measurement of the grating coupling coefficient, K, are addressed. Both pulsed and CW measurements of DFB laser performance have been carried out including lasers with a novel (lambda) /4 shift. In the DBR lasers, quantum well intermixing via impurity free vacancy disordering has been used to reduce the optical absorption in the unpumped region below the reflector grating. A direction extension of this intermixing approach will allow the development of a more general waveguide-based integration technology in which DFB and DBR lasers are combined with passive waveguide sections and other discrete devices to form a complete photonic chip. The prospects for successful implementation of this integration discussed and an example given using a surface grating DFB laser.