RESUMO
The development of two-dimensional metasurfaces has shown great potential in quantum-optical technologies because of the excellent flexibility in light-field manipulation. By integrating a metalens array with a nonlinear crystal, we demonstrate a 100-path spontaneous parametric down-conversion photon-pair source in a 10 × 10 array, which shows promise for high-dimensional entanglement and multiphoton-state generation. We demonstrate two-, three- and four-dimensional two-photon path entanglement with different phases encoded by metalenses with fidelities of 98.4, 96.6, and 95.0%, respectively. Furthermore, four-photon and six-photon generation is observed with high indistinguishability of photons generated from different metalenses. Our metalens-array-based quantum photon source is compact, stable, and controllable, indicating a new platform for integrated quantum devices.
RESUMO
Metasurfaces are 2D metamaterials composed of subwavelength nanoantennas according to specific design. They have been utilized to precisely manipulate various parameters of light fields, such as phase, polarization, amplitude, etc., showing promising functionalities. Among all meta-devices, the metalens can be considered as the most basic and important application, given its significant advantage in integration and miniaturization compared with traditional lenses. However, the resonant dispersion of each nanoantenna in a metalens and the intrinsic chromatic dispersion of planar devices and optical materials result in a large chromatic aberration in metalenses that severely reduces the quality of their focusing and imaging. Consequently, how to effectively suppress or manipulate the chromatic aberration of metalenses has attracted worldwide attention in the last few years, leading to variety of excellent achievements promoting the development of this field. Herein, recent progress in chromatic dispersion control based on metalenses is reviewed.
RESUMO
We theoretically investigate the dipolar whispering-gallery modes (WGMs) with different mode orders supported by spherical hyperbolic metamaterial (HMM) cavities consisting of alternating metal and dielectric layers. Associated with the excitations of the WGMs with the highest and the second highest mode orders, the HMM cavities are capable of creating highly enhanced and uniformly distributed local fields in the entire dielectric core region. Variation on the metal filling ratio allows for easily tuning the resonant wavelengths of WGMs over a wide spectral range. By integrating a nonlinear nanocrystal into the HMM cavities, we show enhancements of intensity of second harmonic generation up to a factor of 3.9 × 1010, which is two orders of magnitude higher than the largest enhancement achieved in the single-layer plasmonic core-shell cavities.
