Far-Field Subwavelength Resolution Imaging by Spatial Spectrum Sampling

Abstract

Imaging below the diffraction limit is always of public interest because of the restricted resolution of conventional imaging systems. To beat the limit, evanescent harmonics decaying in space must participate in the imaging process. We introduce the method of spatial spectrum sampling, a far-field superresolution imaging method for microwave and terahertz regimes. Strong dispersion and momentum conservation allow the spoof surface plasmon polaritons (SSP) structure to become a sensitive probe for spatial harmonics. This allows the spatial information of the targets, including both propagating and evanescent components, to be extracted by tuning and recording SSP in the far field. Then, the image with subwavelength resolution is constructed by the inversed Fourier transform of the sampled spatial spectrum. Using the modified subwavelength metallic grating as the probe, a far-field resolution of 0.17λ is numerically and experimentally verified, and two-dimensional imaging ability is also fully discussed. The imaging ability and flexibility can be further improved by optimizing the SSP structures. We are confident that our working mechanism will have great potentials in superresolution imaging applications in the microwave and terahertz frequency ranges.