Plasmonic meta-slit: Shaping and controlling near-field focus

In the field of nanophotonics, tuning the focus of near-field signals has been a great issue due to the demands on near-field imaging for, e.g., biomedical sensors and plasmonic tweezers. Using subwavelength structures for active control of plasmonic systems would be highly desirable. Here, we propose a plasmonic meta-slit, a simple but powerful structure that can switch the direction and length of its focus by changing optical polarization. It is composed of single or double arrays of nanoslit segments with a specific tilted angle distribution for a strong and flexible polarization dependency. Three representative examples of metaslits for polarization-sensitive focusing, directional switching, and asymmetric focusing are theoretically and experimentally demonstrated. We expect that the proposed scheme can be applied not only to plasmonic switches and tunable lenses, but also as a design method for shaping near-field signals.