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High numerical aperture metalens to generate an energy backflow
V.V. Kotlyar 1,2, S.S. Stafeev 1,2, L. O'Faolain 3,4, M.V. Kotlyar 3

1 IPSI RAS – Branch of the FSRC "Crystallography and Photonics" RAS,
443001, Samara, Russia, Molodogvardeyskaya 151,
2 Samara National Research University, 443086, Samara, Russia, Moskovskoye Shosse 34,
3 Centre for Advanced Photonics and Process Analysis, Cork Institute of Technology, Cork T12 P928, Ireland,
4 Tyndall National Institute, Cork T12R5CP, Ireland

 PDF, 2072 kB

DOI: 10.18287/2412-6179-CO-742

Pages: 691-698.

Full text of article: Russian language.

Abstract:
Using electronic beam lithography and reactive ion beam etching, a metalens is manufactured in a thin layer of amorphous silicon of a 130-nm depth, a 30-µm diameter, and a 633-nm focal length (equal to the illumination wavelength). The metalens is composed of 16 sectored subwavelength binary gratings with a 220-nm period. The uniqueness of this metalens is that when illuminated by left-handed circularly polarized light, it is capable of generating a left-handed circularly polarized vortex beam with a topological charge of 2, generating a second-order cylindrical vector beam when illuminated by linearly polarized light. Both for linear and circular incident polarization, an energy backflow is found to be generated in the vicinity of the tight focus. Transverse intensity distributions measured with a scanning near-field optical microscope near the focus of the metalens are in qualitative agreement with the intensity distributions calculated by the FDTD method. This confirms that a backward energy flow takes place at the focus of the metalens. A metalens generating an energy backflow near its focus is fabricated and characterized for the first time.

Keywords:
metalens, subwavelength grating, energy backflow.

Citation:
Kotlyar VV, Stafeev SS, O’Faolain L, Kotlyar MV. High numerical aperture metalens for the formation of energy backflow. Computer Optics 2020; 44(5): 691-698. DOI: 10.18287/2412-6179-CO-742.

Acknowledgements:
This work was financially supported by the RF Ministry of Science and Higher Education within a government project of FSRC "Crystallography and Photonics" RAS ("Introduction" and "Conclusions"), the Russian Science Foundation under project No. 18-19-00595 ("Experiment"), the Russian Foundation for Basic Research under project No. 18-29-2003 ("Numerical simulation"), and the Maria Skladovske-Curie TERRIFIC grant (#749143) ("Manufacturing of the metalens").

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