Subwavelength grating-based spiral metalens for tight focusing of laser light
| Autor: | Anton G. Nalimov, Sergey S. Stafeev, Liam O'Faolain, Victor V. Kotlyar |
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| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Diffraction
Materials science Physics and Astronomy (miscellaneous) 130 nm 02 engineering and technology Grating 01 natural sciences Metalens Optics 0103 physical sciences Thin film Diffraction grating 010302 applied physics Unity business.industry Numerical aperture Finite-difference time-domain method Amorphous silicon 021001 nanoscience & nanotechnology Ray 16-sector spiral metalens Wavelength Subwavelength binary diffractive gratings 0210 nano-technology business Optical vortex |
| Popis: | 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, λ = 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 = 0.32λ (±0.03λ) and FWHMy = 0.51λ (±0.03λ). The experimental results are close to those of a numerical simulation using the FDTD method, with FWHMx = 0.37λ and FWHMy = 0.49λ. The technological errors due to manufacturing were taken into account in the simulation. This is the smallest focal spot yet obtained with a metalens. |
| Databáze: | OpenAIRE |
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