Efficient coupling of a laser to a waveguide using a taper designed by conformal mapping

Maximising the optical power collected in a waveguide from the diffracting field of a semiconductor laser is desirable in optical fibre communication systems. However, the spot size and phase front curvature of the laser fiel d usually makes a poor overlap with the mode of the receiving waveguide. Va rious proposals have been made to improve this coupling. This paper present s the design of a tapered waveguide section, having the correct geometry an d refractive index profile, to efficiently capture and transform the rapidl y diffracting light from a semiconductor laser to a planar wavefront in a s traight waveguide. Experimentally, such an approach requires the refining o f available techniques (UV exposure, ion implantation or diffusion) to obta in the required grading of the refractive index profile within the tapered input section of the receiving waveguide.