Plasmonic wavelength-dependent optical switch.

We design and experimentally demonstrate an optical switch based on the interference of plasmonic modes in whispering gallery mode (WGM) antennas. Simultaneous excitation of even and odd WGM modes, enabled by a small symmetry breaking via non-normal illumination, allows switching the plasmonic near field between opposite sides of the antenna, depending on the excitation wavelength used in a wavelength range of 60 nm centered around 790 nm. This proposed switching mechanism is experimentally demonstrated by combining photoemission electron microscopy (PEEM) with a tunable wavelength femtosecond laser source in the visible and infrared.