Graphene surface plasmon off-axis superlens based on tilted one-dimensional Si/SiO₂ gratings

Graphene surface plasmon (GSP) superlenses, induced from the negative refraction, have recently been demonstrated in various two-dimensional photonic crystal systems. However, inplane GSP superlenses have never been reported in a one-dimensional (1D) photonic crystal system. Here, we propose a graphene-Si/SiO₂ system, by transferring a graphene sheet on the tilted 1D subwavelength silicon/silica gratings. By discussing the dispersion relations of the inplane GSP in this system, the GSP negative refraction is found in the mid-infrared region. When the tilted angle, working wavelength, and Fermi level are set to be 60°, 11.22 μm, and 0.2 eV, respectively, the off-axis subwavelength focusing has the best resolution, and the full width at half-maximum (FWHM) of the image is 0.0091λ (102.1 nm). Further, we investigate the effects of the Fermi level on the superlens frequency range, and the image's FWHM, the broadband, and the deep subwavelength superlens are achieved. The full-wave numerical simulations are conducted by the finite element method. Our findings can be applied to the manipulation of inplane GSP propagation and biological imaging.