A study is reported of the effect of the refractive index of the medium adjacent to the waveguide on the waveguide refractive index. Also studied is the possibility of using the observed change in n//b to determine the characteristics of film and graded-index optical waveguides. It is shown that the method described above can be used to determine the refractive index, the thickness, the extent of ... [Show full abstract] the anisotropy, and the dispersion of the refractive index for single-mode flat-index and graded-index optical waveguides. The method can also be used to construct the profile of the refractive index by the WKB method for few-mode waveguides. 8 refs.