A Metalens with a Near-Unity Numerical Aperture.

The numerical aperture (NA) of a lens determines its ability to focus light and its resolving capability. Having a large NA is a very desirable quality for applications requiring small light-matter interaction volumes or large angular collections. Traditionally, a large NA lens based on light refraction requires precision bulk optics that ends up being expensive and is thus also a specialty item. In contrast, metasurfaces allow the lens designer to circumvent those issues producing high-NA lenses in an ultraflat fashion. However, so far, these have been limited to numerical apertures on the same order of magnitude as traditional optical components, with experimentally reported NA values of <0.9. Here we demonstrate, both numerically and experimentally, a new approach that results in a diffraction-limited flat lens with a near-unity numerical aperture (NA > 0.99) and subwavelength thickness (∼λ/3), operating with unpolarized light at 715 nm. To demonstrate its imaging capability, the designed lens is applied in a confocal configuration to map color centers in subdiffractive diamond nanocrystals. This work, based on diffractive elements that can efficiently bend light at angles as large as 82°, represents a step beyond traditional optical elements and existing flat optics, circumventing the efficiency drop associated with the standard, phase mapping approach.

[1]  Yuri S. Kivshar,et al.  High‐Efficiency Dielectric Huygens’ Surfaces , 2015 .

[2]  B. Chichkov,et al.  All-dielectric nanophotonics: the quest for better materials and fabrication techniques , 2017, 1702.00677.

[3]  M W Farn,et al.  Binary gratings with increased efficiency. , 1992, Applied optics.

[4]  W. T. Chen,et al.  Metalenses at visible wavelengths: Diffraction-limited focusing and subwavelength resolution imaging , 2016, Science.

[5]  A. Kildishev,et al.  Planar Photonics with Metasurfaces , 2013, Science.

[6]  R. Blanchard,et al.  Aberration-free ultrathin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces. , 2012, Nano letters.

[7]  A. Arbabi,et al.  Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission. , 2014, Nature nanotechnology.

[8]  Yuan Hsing Fu,et al.  Asymmetric Nanoantennas for Ultrahigh Angle Broadband Visible Light Bending. , 2017, Nano letters.

[9]  Vladimir M. Shalaev,et al.  Metasurface holograms for visible light , 2013, Nature Communications.

[10]  Philippe Lalanne,et al.  Design and fabrication of blazed binary diffractive elements with sampling periods smaller than the structural cutoff , 1999 .

[11]  Q. Gong,et al.  Visible-Frequency Dielectric Metasurfaces for Multiwavelength Achromatic and Highly Dispersive Holograms. , 2016, Nano letters.

[12]  C. Rockstuhl,et al.  Insights into directional scattering: from coupled dipoles to asymmetric dimer nanoantennas. , 2016, Optics express.

[13]  N. Engheta,et al.  Traditional and emerging materials for optical metasurfaces , 2017 .

[14]  Philippe Lalanne,et al.  Metalenses at visible wavelengths: past, present, perspectives , 2016 .

[15]  W Stork,et al.  Artificial distributed-index media fabricated by zero-order gratings. , 1991, Optics letters.

[16]  N. Yu,et al.  Flat optics with designer metasurfaces. , 2014, Nature materials.

[17]  S. Tcvetkova,et al.  Perfect control of reflection and refraction using spatially dispersive metasurfaces , 2016, 1605.02044.

[18]  G. Swanson.  Binary Optics Technology: The Theory and Design of Multi-Level Diffractive Optical Elements , 1989 .

[19]  B. Chichkov,et al.  Demonstration of magnetic dipole resonances of dielectric nanospheres in the visible region. , 2012, Nano letters.

[20]  N. Yu,et al.  Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction , 2011, Science.

[21]  J. Aizpurua,et al.  Strong magnetic response of submicron silicon particles in the infrared. , 2010, Optics express.

[22]  Igal Brener,et al.  Polarization-Independent Silicon Metadevices for Efficient Optical Wavefront Control. , 2015, Nano letters.

[23]  David Sell,et al.  Periodic Dielectric Metasurfaces with High‐Efficiency, Multiwavelength Functionalities , 2017 .

[24]  D. Lynch,et al.  Handbook of Optical Constants of Solids , 1985 .

[25]  Ye Feng Yu,et al.  High‐transmission dielectric metasurface with 2π phase control at visible wavelengths , 2015 .

[26]  Jingbo Sun,et al.  High-Efficiency All-Dielectric Metasurfaces for Ultracompact Beam Manipulation in Transmission Mode. , 2015, Nano letters.

[27]  Jianji Yang,et al.  Topology-optimized metasurfaces: impact of initial geometric layout. , 2017, Optics letters.

[28]  A. Arbabi,et al.  Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays , 2014, Nature Communications.

[29]  Andrea Alù,et al.  Visible Light, Wide-Angle Graded Metasurface for Back Reflection , 2017 .

[30]  Boris N. Chichkov,et al.  Optical response features of Si-nanoparticle arrays , 2010 .

[31]  E. Wolf,et al.  Principles of Optics (7th Ed) , 1999 .

[32]  B. Luk’yanchuk,et al.  Optically resonant dielectric nanostructures , 2016, Science.

[33]  Erez Hasman,et al.  Dielectric gradient metasurface optical elements , 2014, Science.

[34]  Federico Capasso,et al.  Immersion Meta-Lenses at Visible Wavelengths for Nanoscale Imaging. , 2017, Nano letters.

[35]  Mikael Käll,et al.  Directional scattering and hydrogen sensing by bimetallic Pd-Au nanoantennas. , 2012, Nano letters.

[36]  Martin Wegener,et al.  Eliminating Scattering Loss in Anomalously Reflecting Optical Metasurfaces , 2017 .

[37]  S. Maier,et al.  Experimental Demonstration of Tunable Directional Scattering of Visible Light from All-Dielectric Asymmetric Dimers , 2017 .

[38]  I. Staude,et al.  Metamaterial-inspired silicon nanophotonics , 2017, Nature Photonics.

[39]  A. Alú,et al.  Wave-front Transformation with Gradient Metasurfaces , 2016 .

[40]  S. Maier,et al.  Switchable directional scattering of electromagnetic radiation with subwavelength asymmetric silicon dimers , 2015, Scientific Reports.

[41]  Andrea Alù,et al.  Metagratings: Beyond the Limits of Graded Metasurfaces for Wave Front Control. , 2017, Physical review letters.

[42]  P. R. West,et al.  All-dielectric subwavelength metasurface focusing lens. , 2014, Optics express.

[43]  Andrey E. Miroshnichenko,et al.  Generalized Brewster effect in dielectric metasurfaces , 2015, Nature Communications.