An efficient grating coupler for a semiconductor optical mode includes a tapered edge to couple light between waveguide modes constrained by differing waveguide thicknesses. An optical circuit or laser has a waveguide in a rib or strip waveguide section that is of different height (e.g., having different vertical constraints) than a waveguide section that has a grating coupler through which light passes off-circuit. The tapered edge can couple light between the two waveguide sections with very low loss and back-reflection. The low loss and minimal back-reflection enables testing of the photonics circuit on a wafer level, and improved performance through the grating coupler.