|
Metamaterials---artificial electromagnetic media that are structured on the subwavelength scale---were initially suggested for the realization of negative index media, and later they became a paradigm for engineering electromagnetic space and controlling propagation of waves. However, applications of metamaterials in optics are limited due to inherent losses in metals employed for the realisation of artificial optical magnetism. Recently, we observe the emergence of a new field of all-dielectric resonant metaoptics aiming at the manipulation of strong optically-induced electric and magnetic Mie-type resonances in dielectric and semiconductor nanostructures with relatively high refractive index [1]. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low dissipative losses and the enhancement of both electric and magnetic fields that provide competitive alternatives for plasmonic structures including optical nanoantennas, efficient biosensors, passive and active metasurfaces, and functional metadevices [2, 3]. Here, we aim to summarize the most recent advances in all-dielectric Mie-resonant meta-optics including active nanophotonics as well as the recently emerged fields of topological photonics and nonlinear metasurfaces.
In addition, we also aim to review the physics of bound states in the continuum and their applications in meta-optics and metasurfaces [4]. First, we discuss strong coupling between the modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator’s aspect ratio varies [5]. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are nearly suppressed due to the Friedrich–Wintgen scenario of destructive interference. Our theoretical findings are confirmed by microwave and optical experiments for the scattering of high-index subwavelength resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-Q factor helps to extend substantially many functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices. Next, we discuss how bound states in the continuum can appear in the physics of metasurfaces. We reveal that metasurfaces created by seemingly different lattices of (dielectric or metallic) meta-atoms with broken in-plane symmetry can support sharp high-Q resonances that originate from the physics of bound states in the continuum [6]. We demonstrate a direct link between the bound states in the continuum and Fano resonances, and discuss a general theory of such metasurfaces, suggesting the way for smart engineering of resonances for many applications in nanophotonics and meta-optics.
[1] A. I. Kuznetsov, A. E. Miroshnichenko, M. L. Brongersma, Y.S. Kivshar, and B. Lukayanchuk, Optically resonant dielectric nanostructures, Science 354, aag2472 (2016).
[2] S. Kruk and Y. Kivshar, Functional meta-optics and nanophotonics governed by Mie resonances, ACS Photonics 4, 2638 (2017).
[3] Y.S. Kivshar, All-dielectric meta-optics and nonlinear nanophotonics,
National Science Review 5, 144 (2018).
[4] K. Koshelev, A. Bogdanov, and Y. Kivshar, Meta-optics and bound states in the continuum, submitted to Science Bulletin; arXiv: 1810.08698v1 (2018).
[5] M.V. Rybin, K.L. Koshelev, Z.F. Sadrieva, K.B. Samusev, A.A. Bogdanov, M.F. Limonov, and Y.S. Kivshar, High-Q supercavity modes in subwavelength dielectric resonators, Phys. Rev. Lett. 119, 243901 (2017).
[6] K. Koshelev, S. Lepeshov, M. Liu, A. Bogdanov, and Y.S. Kivshar, Asymmetric metasurfaces and high-Q resonances governed by bound states in the continuum, Phys. Rev. Lett. 121 (2018); arXiv: 1809.00330 (2018).
|
