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Subwavelength grating-based spiral metalens for tight focusing of laser light
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Date
2019-04-12
Authors
Kotlyar, Victor V.
Stafeev, Sergey S.
Nalimov, Anton G.
O'Faolain, Liam
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Publisher
AIP Publishing
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Abstract
In this paper, we investigate a 16-sector spiral metalens fabricated on a thin film (130 nm) of amorphous silicon, consisting of a set of subwavelength binary diffractive gratings and with a numerical aperture that is close to unity. The metalens converts linearly polarized incident light into an azimuthally polarized optical vortex and focuses it at a distance approximately equal to the wavelength of the incident light, k ¼ 633 nm. Using a scanning near-field optical microscope, it is shown experimentally that the metalens forms an elliptical focal spot with diameters smaller than the diffraction limit: FWHMx ¼ 0.32k (60.03k) and FWHMy ¼ 0.51k (60.03k). The experimental results are close to those of a numerical simulation using the FDTD method, with FWHMx ¼ 0.37k and FWHMy ¼ 0.49k. The technological errors due to manufacturing were taken into account in the simulation. This is the smallest focal spot yet obtained with a metalens.
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Keywords
Metalens , 16-sector spiral metalens , Thin film , 130 nm , Amorphous silicon , Subwavelength binary diffractive gratings , Numerical aperture , Unity
Citation
Kotlyar, V. V., Stafeev, S. S., Nalimov, A. G. and O'Faolain, L. (2019) ‘Subwavelength grating-based spiral metalens for tight focusing of laser light’, Applied Physics Letters, 114(14), 141107 (5pp). doi: 10.1063/1.5092760
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© 2019, the Authors. Published by AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared as Kotlyar, V. V., Stafeev, S. S., Nalimov, A. G. and O'Faolain, L. (2019) ‘Subwavelength grating-based spiral metalens for tight focusing of laser light’, Applied Physics Letters, 114(14), 141107 (5pp). doi: 10.1063/1.5092760 and may be found at https://doi.org/10.1063/1.5092760