Recently, metasurfaces have received increasing attention due to their ability to locally manipulate the amplitude, phase and polarization of light with high spatial resolution. Transmissive metasurfaces based on high-index dielectric materials are particularly interesting due to the low intrinsic losses and compatibility with standard industrial processes. Here, it is demonstrated numerically and experimentally that a uniform array of silicon nanodisks can exhibit close-to-unity transmission at resonance in the visible spectrum. A single-layer gradient metasurface utilizing this concept is shown to achieve around 45% transmission into the desired order. These values represent an improvement over existing state-of-the-art, and are the result of simultaneous excitation and mutual interference of magnetic and electric-dipole resonances in the nanodisks, which enables directional forward scattering with a broad bandwidth. Due to CMOS compatibility and the relative ease of fabrication, this approach is promising for creation of novel flat optical devices.
High-index dielectric and semiconductor nanoparticles supporting strong electric and magnetic resonances have drawn significant attention in recent years. However, until now, there have been no experimental reports of lasing action from such nanostructures. Here, we demonstrate directional lasing, with a low threshold and high quality factor, in active dielectric nanoantenna arrays achieved through a leaky resonance excited in coupled gallium arsenide (GaAs) nanopillars. The leaky resonance is formed by partially breaking a bound state in the continuum generated by the collective, vertical electric dipole resonances excited in the nanopillars for subdiffractive arrays. We control the directionality of the emitted light while maintaining a high quality factor (Q = 2,750). The lasing directivity and wavelength can be tuned via the nanoantenna array geometry and by modifying the gain spectrum of GaAs with temperature. The obtained results provide guidelines for achieving surface-emitting laser devices based on active dielectric nanoantennas that are compact and highly transparent.
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