Traditional infrared lenses cannot meet the requirements of planarization and lightweight of infrared optical systems due to their large volume and mass. An infrared metasurface with almost zero thickness can control the incident beam’s amplitude, phase and polarization arbitrarily, which make it possible to circumvent these limitations. However, no metasurface has been designed to realize sub-diffraction focusing in the long-wave infrared band. In this article, a longwave infrared meta spiral zone plate (LWIR-MSZP) is designed, which converts the incident linearly polarized beam to an azimuthally polarized beam and focuses the latter into a sub-diffraction solid spot. The designed LWIR-MSZP works at a wavelength of 10.6 μm and has a diameter of 480 μm and numerical aperture (NA) of 0.8. The simulated full width at half maximum (FWHM) and depth of focus (DOF) of the focal spot are 0.6λ and 2.24λ, respectively. The simulated efficiency is 24.04%. The proposed design procedure greatly simplifies the long-wave infrared sub-diffractive focusing optical system and complements the technical gap to achieve sub-diffractive focusing in long-wave infrared using a metasurface. To make it further, the all-silicon meta-atom employed in this work has the advantage of low cost once semiconductor fabrication techniques are introduced. We believe that this result can be applied to the related fields of super-resolution imaging and laser processing in long-wave infrared band.
Orbital angular momentum (OAM) of an optical vortex has attracted great interest from the scientific community due to its significant values in high-capacity optical communications such as mode or wavelength division multiplexer/demultiplexer. Although several configurations have been developed to demultiplex an optical vortex, the multiwavelength high-order optical vortex (HOOV) demultiplexer remains elusive due to lack of effective control technologies. In this study, we present the design, fabrication, and test of metasurface optical elements for multiwavelength HOOV demultiplexing based on optical gyrator transformation transformations in the visible light range. Its realization in a metasurface form enables the combined measurement of OAM, the radial index p, and wavelength using a single optical component. Each wavelength channel HOOV can be independently converted to a high-order Hermitian–Gaussian beam mode, and each of the OAM beams is demultiplexed at the converter output. Furthermore, we extend the scheme to realize encoding of the three-digit gray code by controlling the wavelength or polarization state. Experimental results obtained at three wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and HOOV recognition ability, our approach may provide great potential applications in photonic integrated devices and systems for high-capacity and demultiplex-channel OAM communication.
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