Focusing of laser light by sectoral spiral metalens

Sergey S. Stafeev; Victor V. Kotlyar; Anton G. Nalimov; Liam O'Faolain

doi:10.1117/12.2520461

30 April 2019 Focusing of laser light by sectoral spiral metalens

Sergey S. Stafeev, Victor V. Kotlyar, Anton G. Nalimov, Liam O'Faolain

Author Affiliations +

Proceedings Volume 11025, Metamaterials XII; 110250Z (2019) https://doi.org/10.1117/12.2520461
Event: SPIE Optics + Optoelectronics, 2019, Prague, Czech Republic

Abstract

A large number of scientific papers are currently devoted to the investigation of metasurfaces, based on the subwavelength gratings. Such subwavelength gratings are anisotropic – TE- and TM-polarized waves propagated through them have a different phase. Based on this effect it is possible to create analogues of the classical half-wave plates, which rotate the direction of polarization. In this work we proposed a spiral metalens, which simultaneously converts linearly polarized light into an azimuthally polarized vortex beam and focuses it. This metalens is a combination of a spiral zone plate with a topological charge m = 1 (focal length f = 633 nm) and a sector subwavelength grating (period of 220 nm, relief depth of 120 nm, illumination wavelength of λ = 633 nm). The metalens was fabricated using electron beam lithography and ion etching in 130-nm thick amorphous silicon film. Using FDTD-method it was numerically shown that the metalens illuminated by a plane wave with linear polarization forms a circular focal spot with dimensions smaller than the scalar diffraction limit: FWHMx = 0.435λ and FWHMy = 0.457λ. The focusing by the fabricated metalens was investigated experimentally using scanning near-field optical microscope (Ntegra Spectra, NTMDT).

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Sergey S. Stafeev, Victor V. Kotlyar, Anton G. Nalimov, and Liam O'Faolain "Focusing of laser light by sectoral spiral metalens", Proc. SPIE 11025, Metamaterials XII, 110250Z (30 April 2019); https://doi.org/10.1117/12.2520461

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