How can losses be measured in an optical tapered multimode to singlemode fiber simulation?
I have reviewed this article ( Optical losses in multimode simulation ) and the Wikipedia article that it references regarding S-matrices, and found that my system was lossless ( conj(S)^T * S = Identity ), according to the Wikipedia article.
It seemed that one could also take the total E field, summed over all modes, at each cell along the propagation direction ( from input source to output ) and after normalizing by the total input E field, calculate the loss as a function of propagation direction in this way. However, when I did this I found that the effective refractive indices increased as the taper narrowed, and similarly this method showed a marked decrease in power ( from normalized 100% at input to 20% at output ) for a taper starting at radius of 30 microns decreasing to a radius of 8 microns. What am I missing?