The design of a low-loss coupler for coupling a planar waveguide to a strip waveguide. II - Investigation of end-face coupling

Approaches of parallel end-butt coupling used by Hunsperger et al. (1977) for optical integrated circuits are considered along with optical-waveguide lens technologies, resonators with internal lenses, a coupling circuit using a combination of a cylindrical lens and a Selfoc lens, and the coupling of optical waveguides by tapers. Attention is also given to coupling between a strip waveguide and an adjacent glass fiber. On the basis of an evaluation of the characteristics of the various coupling methods, it is concluded that a combination of two cemented lenses with a parabolalike wide taper produced in the first part of the strip waveguide represents the best solution for coupling a planar waveguide to a strip waveguide.