Fraunhofer interference of a dielectric interface with travelling wave radiation and the consequent reduction in dielectric waveguide bending loss

The radiation pattern is evaluated of a travelling wave antenna situated on the interface between two dielectrics. When the dielectric constant is the same on either side, the beam emitted by the travelling wave has a narrow Gaussian profile, and is paraxial with its plane. As the dielectric becomes different on the two sides the paraxial beam property remains, but the discontinuity inhibits considerably the radiated power. Bearing in mind the beam-restricted nature of the bending loss from smooth curved optoelectronic waveguides, this suggests interference as a physical mechanism for reducing their bending loss. This confirms and justifies previous calculations using simpler boundary conditions. The range of dielectric constants for which the effect would operate is predicted.