Reflective plasmonic super-oscillatory metasurfaces with simultaneous phase and amplitude controls for sub-diffraction focusing

Optical super-oscillatory phenomena, coming from the delicate interference of the propagating light through an elaborate-designed structure, have been successfully applied to realize far-field focusing and imaging with a resolution beyond the diffraction limit. However, most reported super-oscillatory lenses only modulate either the amplitude or phase of the incident light. Here, a reflective plasmonic super-oscillatory metasurface (RSOM), made of aluminum-nanorods/glass-spacer-layer/aluminum-mirror, is proposed to simultaneously engineer a desired amplitude and phase profile of the incoming light and realize far-field sub-diffraction focusing. The used reflective configuration with a high polarization conversion can be helpful to concentrate more energy into the super-oscillatory spot. Sub-diffraction hotspots are further numerically verified and precisely formed at the preset plane. The compressed spot sizes for one RSOM are 0.666 and 0.714 times the diffraction limit along the x and y directions, respectively. The numerical results agree well with theoretical predictions. The novel complex amplitude control of the light field gives more degrees of freedom in manipulating the propagation of light and provides a better tradeoff among conflicting factors of a super-oscillatory field.