Double-Layer Metallic Holes Lens Based on Continuous Modulation of Phase and Amplitude

We have demonstrated numerically a lens design based on continuous modulation of both phase and amplitude utilizing array of double-layer metallic aluminum holes filled with silicon dioxide. The tuning range is 0-pi and 0-0.3 for phase and amplitude, respectively, at wavelength 365 nm, allowing flexible lens design. Two lenses are designed and compared. At wavelength 365 nm, the lens based on pure phase modulation generates a 600-nm hot spot at a distance of 6.5 mu m, while the phase-amplitude-modulation-based lens leads to an improved focusing spot size of 450 nm, which is beyond the diffraction limit 608 nm and the superoscillation criterion 462 nm. An example of subwavelength superoscillation focusing (0.32 lambda) is also demonstrated with a continuous amplitude modulated lens, which shows small sidelobe and broad view field. Our approach shows great potential in superoscillation lens design and can be applied to other optical spectrum ranges as well.