Off-axis focusing by using nanoimprinted dielectric metasurface with free-form phase distribution

This study presents the design and fabrication of a dielectric metasurface with free-form phase distribution and with a large period unit cell. The dielectric metasurface is fabricated using i-line stepper, dry etching, and nanoimprint technology. The phase distribution of the meta-device is the combination of a blazed grating for deflection and an aspherical lens for eliminating the off-axis aberration. The optical measurement result shows the off-axis focusing spot is with loss aberration and the corresponding Strehl ratio is 0.34. The diffraction efficiency is around 2%. The low efficiency is mainly attributed to the rounding of the rectangular nanostructures during the pattern transfer and relatively thin thickness. Moreover, the polarization-dependency of this large period metasurface is also discussed. (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This study presents the design and fabrication of a dielectric metasurface with free-form phase distribution and with a large period unit cell using i-line stepper, dry etching, and nanoimprint technology. The optical measurement result shows the off-axis focusing spot is with loss aberration and the corresponding Strehl ratio is 0.34, with a diffraction efficiency of around 2%. The low efficiency is mainly attributed to the rounding of the rectangular nanostructures during the pattern transfer and relatively thin thickness, and the polarization-dependency of this large period metasurface is also discussed.