Selectively launching propagating surface plasmon from designed symmetric plasmonic structures*

The next generation signal processing technology demands high speed and energy efficient information carriers. Surface plasmon polaritons (SPPs) can be one of the most promising candidates since they propagate at almost the speed of light, and can be confined to sub-wavelength dimensions using designed nanostructures. In our studies, we show the intensity of propagating SPPs launched from opposing edges of a symmetric trench structure can be controlled by the linear polarization of the optical field. Through the FDTD simulations, we reveal that the coupling efficiency of the propagating SPPs is inversely proportional to that of the localized surface plasmon excited at the trench edges. We also explored the generation of propagating SPPs from a protruded silver cap structure with s-polarized femtosecond laser excitation. Surprisingly, our results show the SPPs propagate with a bifurcated spatial structure with an antisymmetric mirror plane and may be regarded as two spatially distinct, temporally phase-locked wave packets. Our findings can facilitate the design of plasmonic devices/components in nanophotonic circuits.