DIGITAL ACCESS TOSCHOLARSHIP AT HARVARDHARVARD LIBRARYOffice for Scholarly CommunicationDASH.HARVARD.EDUAberration-Free Ultrathin Flat Lenses and Axiconsat Telecom Wavelengths Based on PlasmonicMetasurfacesCitationAieta,Francesco,Patrice Genevet,Mikhail A.Kats,Nanfang Yu,Romain Blanchard,ZenoGaburro,and Federico Capasso.2012."Aberration-Free Ultrathin Flat Lenses and Axicons atTelecom Wavelengths Based on Plasmonic Metasurfaces."Nano Letters 12(9]:4932-36.https://doi.org/10.1021/nl302516v.Permanent linkhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:41372497Terms of UseThis article was downloaded from Harvard University's DASH repository,and is made availableunder the terms and conditions applicable to Open Access Policy Articles,as set forth at http:/nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAPShare Your StoryThe Harvard community has made this article openly availablePlease share how this access benefits you.Submit a story.AccessibilityAberration-free ultra-thin flat lenses and axicons at telecomwavelengths based on plasmonic metasurfacesZeno Gaburro1.4 and Federico CapassoSchool of Engineering and Applied Sciences,Harvard University,Cambridge,Massachusetts 02138,USADipartimento di Scienzee Ingegneria della Materia,dell'Ambienteed Urbanistica,Universita Politecnicadelle Marche,via Brecce Bianche,60131 Ancona,ItalyPInstitute for Quantum Studies and Department of Physics,Texas A&M University,College Station,TexasDipartimento di Fisica,Universita degli Studi di Trento,via Sommarive 14,38100Trento,ItalyThe concept of optical phase discontinuities is applied to the design anddemonstration of aberration-free planar lenses and axicons,comprising a phasedarray of ultrathin subwavelength spaced optical antennas.The lenses and axiconsconsist of radial distributions of V-shaped nanoantennas that generate respectivelyspherical wavefronts and non-diffracting Bessel beams at telecom wavelengths.Simulations are also presented to show that our aberration-free designs areapplicable to high numerical aperture lenses such as flat microscope objectives.The fabrication of lenses with aberration correction is challenging in particular in themid-and near-infrared wavelength range where the choice of transparent materials is limited.Usually it requires complex optimization techniques such as aspheric shapes or multi-lensdesigns [1,2],which are expensive and bulky.Focusing diffracting plates offer the possibility of designing low weight and smallvolume lenses.For example the Fresnel Zone Plate focuses light by diffracting from a binarymask that blocks part of the radiation [1].A more advanced solution is represented by theFresnel lens,which introduces a gradual phase retardation in the radial direction to focus lightmore efficiently.By limiting the absorption losses and gathering oblique light more efficiently,Fresnel lenses are advantageous for optical systems with high numerical aperture(NA)[1].Toguarantee a smooth spherical phase profile responsible for light focusing,the Fresnel lensthickness has to be at least equal to the effective wavelength Ae=A/n where n is the refractiveindex of the medium.Moreover,the thickness of the lens needs to be continuously tapered,which becomes complicated in terms of fabrication [3].In the microwave and mm-wave regimes,local control of the phase ofelectromagnetic waves obtained with reflectarrays or frequency selective surfaces has enabledalternative designs for flat lenses.For example,in reflectarrays,scattering units comprisingmetallic patch antennas coupled with a ground plane can provide an arbitrary phase shiftbetween the scattered light and the incident light [4,5].At optical frequencies,planar focusing devices have been demonstrated using arraysof nanoholes [6],optical masks [7-9],or nanoslits [10].These techniques require complexdesign rules and do not provide the ability to tailor the phase of the transmitted light from 0 to2,which is necessary for a complete control of the optical wavefront.In addition flatmetamaterials based lenses such as hyperlenses and superlenses have been used to achievesubdiffraction focusing [11-14].The concept of optical phase discontinuities,which has been used in thedemonstration of new metasurfaces capable of beaming light in directions characterized bygeneralized laws of reflection and refraction [15],provides a different path for designing flatlenses.In this approach,the control of the wavefront no longer relies on the phaseaccumulated during the propagation of light,but is achieved via the phase shifts experiencedby radiation as it scatters off the optically thin array of subwavelength-spaced resonatorscomprising the metasurface.This strategy resembles reflectarrays and transmit-arrays used atmuch lower frequencies [16-18].Linear gradients of phase discontinuities lead to planarreflected and refracted wavefronts [15,19,20].On the other hand,nonlinear phase gradients2