Ultrafast spatiotemporal control of directional launching of surface plasmon polaritons in a plasmonic nano coupler

Ultrafast spatiotemporal control of a surface plasmon polariton (SPP) launch direction is a prerequisite for ultrafast information processing in plasmonic nanocircuit components such as ultrafast on–off of plasmonic switching and information recording. Here we realize for the first time, to the best of our knowledge, ultrafast spatiotemporal control of the preferential launch direction of an SPP at the nano-femtosecond scale via a plasmonic nano directional coupler. The spatiotemporal switching of the SPP field was revealed using time-resolved photoemission electron microscopy (TR-PEEM). Experimental results show that the extinction ratio of the SPP directional coupler can be substantially optimized by properly selecting the amplitude and time delay of the two incident light pulses in the experiment. More importantly, we demonstrate a solution for the launch direction of the SPP field, switched in a plasmonic nano directional coupler on the femtosecond timescale, by adjusting the instantaneous polarization state of the excitation light. The TR-PEEM images are supported by finite-difference time-domain (FDTD) simulations. We believe the results of this study can be used to develop high-speed, miniaturized signal processing systems.