Coupling Coefficients for Imperfect Asymmetric Slab Waveguides

Mode coupling phenomena and radiation losses caused by corecladding interface irregularities have been studied extensively for symmetric slab waveguides and for round optical fibers. 1-7 These results are not immediately applicable to the asymmetric slab waveguides used in integrated optics circuits. It is the purpose of this paper to collect the formulas for the normal modes of the asymmetric slab waveguides, and for the coupling coefficients between guided modes and guided and radiation modes caused by core boundary irregularities of these waveguides. The coupling coefficients between guided modes are useful for the design of distributed feedback sections for lasers and for an evaluation of unintentional mode coupling caused by core boundary roughness. The results collected in this paper are further necessary for the evaluation of radiation losses caused by core boundary roughness. Because of the many parameters that enter into the theory, it is impossible to evaluate the formulas in graphical form for all cases of practical interest. This paper is thus a collection of the required formulas which the reader can use to evaluate his particular problems. 63