Before revision: End-fire coupling Planar or ridge waveguides are employed to confine the optical mode in the active region of the QCD, provided that the semiconductor heterostructure is grown on a substrate exhibiting a lower refractive index.
After revision: Waveguide end-fire coupling Planar or ridge waveguides are employed to confine the optical mode in the active region of the QCD, provided that the semiconductor heterostructure is grown on a substrate exhibiting a lower refractive index.