A Centimeter-Scale Dielectric Metasurface for the Generation of Cold Atoms.

The single-beam magneto-optical trap (MOT) based on the diffractive optical element offers a new route to develop compact cold atom sources. However, the optical efficiency in the previous single-beam MOT systems is usually low and unbalanced, which will affect the quality of the trapped atoms. To solve this issue, we developed a centimeter-scale dielectric metasurface optical chip with dynamic phase distributions, which was used to split a single incident laser beam into five separate ones with well-defined polarization states and uniform energy distributions. The measured diffraction efficiency of the metasurface is up to 47%. A single-beam MOT integrated with the metasurface optical chip was then used to trap the 87Rb atoms with numbers ∼1.4 × 108 and temperatures ∼7.0 µK. The proposed concept in this work may provide a promising solution for developing ultracompact cold atom sources.

3D Full-Color Image Projection Based on Reflective Metasurfaces under Incoherent Illumination.

Metasurfaces provide an efficient approach to control light wavefronts and have emerged at the forefront of digital holography. Nevertheless, full-color image projection remains challenging. Using a combination of specular and diffuse reflections from a metasurface, in analogy to the normal mapping technique, we designed a reflective metasurface performing in the whole visible spectral range to demonstrate 2D images with shading effects of 3D objects. The noninterleaved metasurface is based on aluminum nanostructures with high and relatively uniform efficiency across the visible spectrum. It operates under incoherent illumination and does not require polarizing optics to observe images. The integration of the metasurface behind pre-existing transparent color images is also demonstrated for introduction of 3D effects. Emulating color 3D images with flat metasurfaces can be useful for security applications and decorative purposes. The design of broadband metasurface diffusers is also interesting for flat optical diffusing elements with engineered properties and display technology.

Nonlinear Diatomic Metasurface for Real and Fourier Space Image Encoding.

In linear optics, the metasurface represents an ideal platform for encoding optical information because of its unprecedented abilities of manipulating the intensity, polarization, and phase of light wave with subwavelength meta-atoms. However, controlling various degrees of freedom of light in nonlinear optics remains elusive. Here, we propose a nonlinear plasmonic metasurface working in the near-infrared regime that can simultaneously encode optical images in the real and Fourier spaces. This is achieved by designing a diatomic meta-molecule, which enables the independent control of the nonlinear geometric phase, polarization, and intensity of second harmonic waves. The proposed nonlinear diatomic metasurface provides an ultracompact platform for implementing multidimensional optical information encoding and may hold great potential in optical information security and optical anticounterfeiting.

Quasicrystal Photonic Metasurfaces for Radiation Controlling of Second Harmonic Generation.

Photonic metasurfaces, a kind of 2D structured medium, represent a novel platform to manipulate the propagation of light at subwavelength scale. In linear optical regime, many interesting topics such as planar meta-lenses, metasurface optical holography, and so on have been widely investigated. Recently, metasurfaces have gone into the nonlinear optical regime. While it is recognized that the local symmetry of the meta-atoms plays a vital role in determining the polarization, phase, and intensity of the nonlinear waves, much less attention has been paid to the global symmetry of the nonlinear metasurfaces. According to the Penrose tiling and the newly proposed hexagonal quasicrystalline tiling, nonlinear optical quasicrystal metasurfaces are designed and fabricated based on the geometric-phase-controlled plasmonic meta-atoms with local rotational symmetry. It is found that the far-field radiation behavior of second harmonic generation waves are determined by both the tiling schemes of quasicrystal metasurfaces and the local symmetry of meta-atoms they consist of. The proposed concept may open new avenues for designing nonlinear optical sources with metasurface crystals.