Analytical and numerical study of semi-infinite reciprocal and non-reciprocal plasmonic sub-diffraction chains

In reciprocal guiding structures, modes are arranged in reciprocal pairs. Therefore, at the termination of a waveguide, well confined forward propagating mode poorly couples to free space waves since the mode profile overlap with its backward propagating counterpart is perfect. Non-reciprocity breaks this picture, yielding a potential for strong coupling between guided modes and free space waves. In this paper we explore these concepts analytically and numerically using plasmonic sub-diffraction chains as a waveguiding platform.