Minimization of plasmonic mode converter using ultra-high mode asymmetry in a metal slab asymmetric waveguide and its robustness

The miniaturization of plasmonic devices is one of the key terms for developing highly integrated photonic chips. In this letter, we propose a potential candidate for plasmonic mode conversion with a nanoscale length as well as a transversal size based on a metal slab asymmetric waveguide possessing a plasmonic mode with an ultra-high asymmetry in its field distribution. The ultra-high mode asymmetry can be obtained by adjusting the width of the waveguide with a sufficiently large dielectric asymmetry of more than 1. The plasmonic mode conversion can be implemented by using the inter-mode coupling between two propagating modes with the ultra-high mode asymmetry. Our plasmonic converter has a minimized length up to one wavelength or less and also high conversion efficiency up to 90%. To our knowledge, the suggested structure is the most optimized structure among all previously presented mode converters. Furthermore, the conversion performance of the converter is very stable with respect to the deterioration or fabrication imperfection of the width of the metal layer. The suggested device will pave the way to achieve highly integrated and robust photonic computing networks.