Switchable polarization-multiplexed super-oscillatory metasurfaces for achromatic sub-diffraction focusing

Computational hyperspectral devices based on quasi-random metasurface supercells

Computational hyperspectral devices that use artificial filters have shown promise as compact spectral devices. However, the current designs are restricted by limited types and geometric parameters of unit cells, resulting in a high cross-correlation between the transmission spectra. This limitation prevents the fulfillment of the requirement for compressed-sensing-based spectral reconstruction. To address this challenge, we proposed and simulated a novel design for computational hyperspectral devices based on quasi-random metasurface supercells. The size of the quasi-random metasurface supercell was extended above the wavelength, which enables the exploration of a larger variety of symmetrical supercell structures. Consequently, more quasi-random supercells with lower polarization sensitivity and their spectra with low cross-correlation were obtained. Devices for narrowband spectral reconstruction and broadband hyperspectral single-shot imaging were designed and fabricated. Combined with the genetic algorithm with compressed sensing, the narrowband spectral reconstruction device reconstructs the complex narrowband hyperspectral signal with 6 nm spectral resolution and ultralow errors. The broadband hyperspectral device reconstructs a broadband hyperspectral image (λ/λ ∼ 0.001) with a high average signal fidelity of 92%. This device has the potential to be integrated into a complementary metal-oxide-semiconductor (CMOS) chip for single-shot imaging.

Superoscillation focusing with suppressed sidebands by destructive interference

Optical superoscillation, a phenomenon that the local optical field can oscillate much faster than that allowed by its highest harmonic, can significantly overcome the Abbe diffraction limit. However, as the spot size is compressed below the superoscillation criteria of 0.38λ/NA, huge sidebands will inevitably appear around the central lobe with intensity hundreds of times higher than that of the central lobe. Here, we propose an approach to realize superoscillation by using destructive interference. The central lobe size can be compressed beyond the superoscillation criteria without formation of strong sidebands by destructive interference between focused fields. Such a super-resolution metalens can find its application in label-free far-field super-resolution microscopy.

Environmentally robust immersion supercritical lens with an invariable sub-diffraction-limited focal spot

Planar metalenses provide an effective way to break the diffraction barrier in the far field. Their physical mechanism and applications have been intensively studied in the past decade. These investigations on sub-diffraction-limited light modulations have only been applied to specified single immersion environments; however, changing immersion environments can severely degrade their focusing performance, limiting their application potential. In this work, we propose and experimentally demonstrate an environmentally robust immersion supercritical lens (SCL) that can work in various immersion environments. The design of such a lens is based on the vectorial Rayleigh-Sommerfeld diffraction theory combined with a multi-objective optimization algorithm. The sub-diffraction-limited focusing effect has been experimentally demonstrated in commonly used media, including air, water, and oil, with refractive indices of 1.0, 1.33, and 1.51, respectively. Moreover, such a lens can maintain its effective numerical aperture at a fixed value, bringing a unique advantage in that the lateral size of the focal spots exhibits a similar value of ${{317}}\;{{\pm}}\;{{7}}\;{\rm{nm}}$ in all three media. Our demonstration provides the feasibility of SCLs in various application scenarios with multi-immersion environments, such as bioimaging, light trapping, and optical storage.

Broadband achromatic metasurfaces for sub-diffraction focusing in the visible

Conventional achromatic optical systems are matured to achieve effective chromatic aberration correction and diffraction-limited resolution by the multiple bulky lenses. The emergence of the super-oscillation phenomenon provides an effective method for non-invasive far-field super-resolution imaging. Nevertheless, most super-oscillatory lenses are significantly restricted by the chromatic aberration due to the reliance on delicate interference; on the other hand, most achromatic lenses cannot break the diffraction limit. In this article, a single-layer broadband achromatic metasurface comprising sub-wavelength anisotropic nanostructures has been proposed to achieve sub-diffraction focusing with a focal length of f=60 µm and a diameter of 20 µm in the visible ranging from 400 nm to 700 nm, which are capable of generating sub-diffraction focal spots under the left-handed circularly polarized incident light with arbitrary wavelength in the working bandwidth at the same focal plane. This method may find promising potentials in various applications such as super-resolution color imaging, light field cameras, and machine vision.