Design and characterization of a micron-focusing plasmonic device

We design and experimentally demonstrate a focusing plasmonic device consisting of a central slit surrounded by the grooves with the fixed width and depth in Au/Cr metal layers. By modulating the phases of the radiation lights decoupled by the grooves from surface plasmon polaritons waves, the focal length can be controlled in the range of several wavelengths. A micron-focusing device is fabricated by the focused ion beam and the focusing performance is characterized using the scanning near-field optical microscope. The experimental results show a significant focusing effect and have agreement with the theoretical analysis and simulation results. Such a focusing plasmonic device with the predicted focal length has potential practical applications in integrated photonics due to the simplicity of the design and fabrication.