A simple computational formalism has been derived for the analysis of splicing and return losses between different optical waveguides. It has been found that the splicing loss can be approximated by the overlap integral method as long as total reflectance is negligible. The reciprocity of splicing loss between two single-mode waveguide is theoretically confirmed while return loss is found nonreciprocal. The return loss can be tolerably approximated by simple Fresnel formula except near the resonance. When close to the resonance, the deviation from Fresnel approximation is found to be strongly dependent on the structure of the waveguide and the refractive index difference between the core and clad.
Gyeong-il Kweon and In-shik Park, "Splicing Losses Between Dissimilar Optical Waveguides," J. Lightwave Technol. 17, 690- (1999)