Abstract

I.O. (integrated optical) circuits will probably find their greatest use in single mode data transfer systems which utilize monomode fibers as the transmission lines. Single mode fibers will be connected to IO circuits which in turn will act to process and/or generate optical data signals. In the construction of any system one encounters many problems which are associated with the fact that conventional optical fiber geometries are circular, whereas I.O. circuit geometries tend to be rectangular. Coupling from a circular to rectangular waveguide of small dimensions represents one of the outstanding problems in the technology today. A second problem and the subject of this paper is IO device performance degradation caused by propagating TE and TM modes simultaneously in the waveguide. By virtue of their rectangular construction, I.O. circuits possess a fixed axis with regard to which TE and TM modes are defined. There is no corresponding polarization axis in fibers of circular cross sections. As a result, the polarization of a light wave propagating through a fiber is usually not conserved. As has been previously shown,¹ linearly polarized light transmitted down circular fibers emerges as elliptically polarized light which when coupled to an IO device would excite both the TE and TM components. If the IO device possesses TE and TM components with different efficiencies, device degradation will result.

© 1976 Optical Society of America