direct coupling strategy in plasmonic nanocircuits for low loss and easy fabrication

Plasmonic nanocircuits can deliver light in subwavelength scale, however, require state-of-the-art fabrication process due to the ultra-small footprints. here, we introduce direct coupling strategy based on metal-insulator-metal (mim) waveguide systems to reduce the system loss as well as the fabrication difficulty and increase the structural stability. following this strategy, the coupling between the input waveguide and square ring resonator (srr) can be realized via an aperture, and for the coupling between srrs, the metal gap can be removed. the numerical results show that such direct coupling can produce similar effects with conventional indirect coupling in mim waveguide systems, and the physics mechanism behind as well as influences of geometric parameters on transmission spectrum is also investigated. this work provides a simpler approach to realize on-chip plasmonic nanodevices, such as filters, sensors, and optical delay lines, in practice.