Plasmonic analogue of geometric diodes realizing asymmetric optical transmission

Geometric diodes represent a relatively new class of diodes used in rectennas that rely on the asymmetry of a conducting thin film. Here, we numerically investigate a plasmonic analogue of geometric diodes to realize nanoscale optical asymmetric transmission. The device operates based on spatial symmetry breaking that relies on a unique property of surface plasmon polaritons (SPPs), namely, adiabatic nanofocusing. We show that the structure can realize onchip asymmetric electromagnetic transmission with a total dimension of ∼2 7mu;m×6 μm. We demonstrate a signal contrast of 0.7 and an asymmetric optical transmission ratio of 4.77 dB.We investigate the origin of the asymmetric transmission and show that it is due mainly to asymmetric out-coupling of SPPs to far-field photons.We highlight the role of evanescent field coupling of SPPs in undermining the asymmetric transmission efficiency and show that by adjusting the plasmonic waveguide dimensions, a signal contrast of 0.94 and an asymmetric optical transmission ratio of 5.18 dB can be obtained. Our work presents a new paradigm for on-chip nanoscale asymmetric optical transmission utilizing the unique properties of SPPs.