Subwavelength optical resonators and scatterers are dramatically expanding the toolset of the optical sciences and photonics engineering. By offering the opportunity to control and shape light waves in nanoscale volumes, recent developments using high-refractive-index dielectric scatterers gave rise to efficient flat-optical components such as lenses, polarizers, phase plates, color routers, and nonlinear elements with a subwavelength thickness. Here, we take a deeper look into the unique interaction of light with amorphous silicon scatterers by tapping into their resonant modes with a localized subwavelength light source—an aperture scanning near-field probe [1,2]. Scanning near-field optical microscopy (SNOM) is a powerful tool to image the near-field distribution of resonant optical modes supported by nanophotonic structures with sub-diffraction resolution. Our experimental configuration essentially constitutes a dielectric antenna that is locally driven by the aperture probe .
In stark contrast to the mostly uneventful far-field extinction response, a rich variety of distinct patterns of bright spots—corresponding to enhanced transmittance of the probe excitation—is observed in the near-field scans. Various transverse magnetic (TM) and transverse electric (TE) Fabry-Perot-like modes of different mode parities in a variety of nanostructure geometries can be revealed using full field 3D finite difference time domain simulations and group theory.
 A. Frolov et al. Nano Letters 2017, 17 (12), 7629–7637
 A. Frolov et al. in preparation 2018
 D. Denkova et al., ACS Nano 2013, 7, 3168–3176
Niels Verellen, Alexandr Yu. Frolov, Xuezhi Zheng, Guy A. E. Vandenbosch, Pol Van Dorpe, Andrey A. Fedyanin, and Victor V. Moshchalkov, "Sub-wavelength visualisation of optical modes in all-dielectric nanostructures (Conference Presentation)," Proc. SPIE 10928, High Contrast Metastructures VIII, 1092804 (Presented at SPIE OPTO: February 04, 2019; Published: 8 March 2019); https://doi.org/10.1117/12.2509959.6011672337001.
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