discoveries and explorations of mode splitting phenomenon in lossy dielectric waveguide

We discovered that a specific transmission mode in the fiber waveguide will split into two modes at near cut-off conditions when the fiber is coated with lossy dielectric nanofilms with higher refractive index. one of the two splitting modes is high lossy while the other is slightly lossy. we defined the “mode splitting coefficient” to describe the degree of mode splitting. we found that the biggest mode splitting coefficient was obtained at the mode cut-off wavelength using finite element method. finally, we put forward an explanation towards the mode splitting phenomenon and expounded the relationship between the mode splitting and mode coupling.