Determination of field profiles in buffer superconducting multilayer optical planar waveguides

The effect on the propagation characteristics due to a low-index buffer layer added over a lossy superconductive leaky waveguide in a high-index substrate is related to a transition from the guided modes to the leaky one. For a guided waveguide structure, neglecting the high-index substrate, the TM mode field amplitude is more confined within the core layer and in superconducting thin film and more evanescent in the air claddings than the corresponding TE mode profile. Moreover, both the TE and TM mode profiles of the buffered waveguide leaks out more into the high-index substrate in comparison with those of the waveguide with a larger buffer thickness. This behaviour is confirmed by the fraction of the power carried by the modes along of the propagation direction.