Mode conversion caused by diameter changes of a round dielectric waveguide

This paper presents the theory of mode conversion and radiation losses of the lowest order circular electric mode in a dielectric rod (fiber) waveguide and its confirmation by a microwave experiment. The theoretical results were obtained from a theory whose detailed development has been presented in an earlier paper. The microwave experiment was carried out at approximately 50 GHz. The optical fiber with imperfect walls was simulated by a teflon rod of 1 cm diameter and 1 m length with a periodically corrugated wall. Mode conversion was observed in excellent agreement with theory. The observed radiation losses are somewhat less than the prediction of the perturbation theory, but the agreement is quite good. The direction and width of the far-field radiation pattern was observed in agreement with theory.