Anisotropic waveguides weakly guiding

When the anisotropic waveguide is weakly guiding, all six values of the refractive index in Eq. (12-38) are approximately equal, and thus = 1... 

Now we modify the early sections of this chapter to include weakly guiding waveguides constructed from the anisotropic material discussed above, i.e. = = = n. To do this, we first recall from Section 11-23 that the two... 

If the principal axes of the anisotropic material are parallel to the optical axes of a fiber of noncircular cross-section, it is intuitive that the two fundamental modes must also be polarized along these axes. We then have a situation identical to the circular cross-section, discussed above, except that (r) in Eq. (13-20) is replaced by P,(x,y) and P,(r) by P,(x,y). Thus, all results for weakly guiding isotropic waveguides apply to weakly guiding anisotropic waveguides by following the simple substitution discussed above. 

Next, we consider the absorbance due to a dichroic adlayer adsorbed onto the waveguide surface with the optical constants as indicated in Fig. 4. The optical properties of the dichroic layer are described by the different extinction coefficients k, ky, and k in each Cartesian direction. The reflectance of the waveguide-adlayer-cover system follows the analysis found in Macleod [9] with the anisotropic coefficients taken from Horowitz and Mendes [10]. By assuming a thin and weakly absorbing adlayer, the following expressions are obtained for the absorbance as measured through a guided mode at each polarization [8] ... 

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