Recently, the increasing demand for high-integrated, high-speed, and energy-efficient optical computing and communication is stimulating the development of nanoscale optical devices. In miniaturization and promotion of optical devices, nanoplasmonics gives us great possibilities by its intrinsic subwavelength confinement and the slow wave nature of surface plasmon polariton (SPP). Therefore, nonplasmonic conventional optical waveguides have been replaced with plasmonic waveguides, such as the metal-dielectric waveguides, the dielectric loaded plasmonic waveguides, and the hybrid plasmonic waveguides. Such plasmonic waveguides can reduce the transverse size of the optical devices to the nanoscale. However, the longitudinal lengths of plasmonic devices have yet remained to the scale of micrometer. On the other hand, a simple building block using cavity coupled with optical waveguides is referred to as perfect candidates for compacting optical devices in longitudinal dimension as well as transversal one.
We suggested a plasmonic mode conversion between symmetric and antisymmetric modes in metal/dielectric/metal (MDM) waveguide coupled with the nano-disk resonator. The incident antisymmetric SPP mode propagating through one MDM waveguide can be converted to the symmetric SPP mode through the neighboring MDM waveguide under the mediation of the localized surface plasmon mode in the disk resonator. With the help of plasmonic structure and nanoresonator, one can reduce the size of plasmonic converter to subwavelength.
These devices are able to have a nanoscale footprint of about 500 nm×500 nm with a high conversion efficiency more than 80%.
The results have been published in "Applied Physics Letters" [127, 053501 (2025)], with the title of "Nanoscale plasmonic mode conversion mediated by localized surface plasmon in metal-dielectric-metal waveguide link"(https://doi.org/10.1063/5.0274860).
