Integrated GaAs-Al<inf>x</inf>Ga<inf>1-x</inf>As double-heterostructure laser with independently controlled optical output divergence

Abstract

Liquid-phase-epitaxial growth procedures have been used to form a double-heterostructure (DH) laser in which the radiation is taper coupled from the active layer into a passive waveguide. The taper extends smoothly over distances <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim100 \mu</tex> m and efficiently couples the radiation from the electrically pumped section into a low-loss adjacent waveguide of comparable dimension (0.5 μm). The passive-waveguide dimension beyond the taper coupler is widened to any desired dimension by inserting a cooling fin (or spacer) into the growth melt, permitting control of the laser output divergence without mode conversion. These structures have been made with the following properties: threshold current density 2.6 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ; differential quantum efficiency 28 percent; taper coupling efficiency ∼90 percent; and half-power radiation field angles of 48 and 29° from the active (0.5 μm thick) and passive (1.5 μm thick) regions, respectively. Using similar growth procedures, devices have been constructed where the laser radiation is taper coupled into passive waveguides permitting both laser mirrors to be formed in passive regions.