Surface Plasmon-Based Pulse Splitter and Polarization Multiplexer

Surface plasmon polaritons (SPPs) launched from a protruded silver spherical cap structure using <i>s</i>-polarized femtosecond laser excitation are investigated using photoemission electron microscopy. The resulting SPP is comparable in intensity to SPPs launched with <i>p</i>-polarized excitation but propagates with a distinct spatial profile. The spatial and temporal properties of the nascent SPP are determined by splitting the femtosecond pulse into a spatially separated pump–probe pair of orthogonal polarizations. The <i>s</i>-polarized pump pulse initiates the SPP, which is then visualized by the photoelectron emission induced by a spatially and temporally separated <i>p</i>-polarized probe pulse. The <i>s</i>-polarization launched SPP displays a bifurcated spatial structure with an antisymmetric mirror plane and may be regarded as two spatially distinct, temporally phase-locked wave packets. Significantly, the wave packets are one-half period out of phase with each other governed by the phase of the driving laser field. Finite difference time domain calculations corroborate the experimental results. The resulting SPP can be utilized for either polarization multiplexing or as a pulse splitter in nanophotonic circuits.