Integrated external cavity quantum well laser array using single epitaxial growth on a patterned substrate

We report the monolithic integration of a quantum well laser array and a transparent waveguide with higher band-gap material using a single step of molecular beam epitaxy on a patterned, nonplanar substrate. The substrate has a periodically corrugated patterned section longitudinally adjacent to an unpatterned, planar section. The laser heterostructure on the corrugated section of the substrate has a thicker quantum well and, thus, lower effective band gap than that of the one grown on the planar section. Hence, a waveguide transparent at the laser array emission wavelength is formed on the planar section. We demonstrate phase locking of the otherwise uncoupled laser array using diffraction coupling through the transparent waveguide section. Emission wavelength tuning of ∼80 Å is also obtained using carrier injection into the waveguide section.