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COMMUNICATION metalenses, [ 27,28 ] aberration-free quarter-wave plates (QWPs), [ 29 ] spin-hall effect of light and spin-controlled photonics, [ 30,31 ] unidirectional surface plasmon polariton excitation [31][32][33][34] and 3D optical holography. [35][36][37][38] As a fundamental optical device, a lens lies in the heart of many important applications in various scientifi c communities such as physics, optics, biology, medicine, and security. People have been fascinated by using different technologies to develop lenses with unusual features, such as ultrathin metalenses based on metasurface [ 27,28,39,40 ] and multifoci diffractive lenses [ 41,42 ] based on diffraction optics. A multifoci diffractive lens allows a single incident beam to focus at different positions along the longitudinal axis or along the transverse direction, which has been widely used in imaging systems, detectors, optical data storage, laser printing and optical freespace communications. [41][42][43][44] However, all the polarization states of the focal points are the same as that of the incident light. Moreover, the traditional method to design and fabricate such a lens is based on diffractive optics, thus the thickness is much larger than the wavelength of light. While there has been great progress in the miniaturization of optical lenses by using metasurfaces, much attention has been paid to constructing a lens with a single focal point by using different geometry structures such as V-shape, [ 22,23,45,46 ] nanorods, [ 27,32,36 ] and nanoslits. [ 47 ] Although the work on metasurface lenses is in its infancy, it offers in the long run major opportunities if multifunction nanostructured lenses can be experimentally realized in ultrathin and fl at confi gurations. Here, we apply the concept of controllable interfacial phase discontinuity to realize an ultrathin fl at metasurface lens with multiple focal points along the longitudinal direction. Unlike the traditional multifoci diffractive lenses, the position and the polarization of the focal points can be controlled by changing the helicity of the incident light. Furthermore, the developed devices are ultrathin (40 nm) and planar, which can facilitate the system integration. Figure 1 shows the schematic of the plasmonic metasurface lens. It consists of nanorods with spatially varying orientation in three different regions marked by I, II, and III, as shown in Figure 1 a. The radius of region I (R-I) is r 1 , and the inner radius and outer radius of region II (R-II) are r 1 and r 2 . r 2 and r 3 are the inner radius and outer radius of region III (R-III). The relationship among r 1 , r 2 , and r 3 is governed by r r r : : 1: 2 : 3where r 1 = 40.0 µm, r 2 = 56.6 µm, and r 3 = 69.3 µm, which can ensure that the three regions R-I, R-II, and R-III have the same area. Therefore, the three parts of the metasurface will receive the same light energy fl ux when illuminated by a wellcollimated incident light beam.Metamaterials with artifi cially engineered subwavelength structures have been used to ...

Optical metasurfaces have shown unprecedented capabilities in the local manipulation of the light's phase, intensity, and polarization profiles, and represent a new viable technology for applications such as high-density optical storage, holography and display. Here, a novel metasurface platform is demonstrated for simultaneously encoding color and intensity information into the wavelength-dependent polarization profile of a light beam. Unlike typical metasurface devices in which images are encoded by phase or amplitude modulation, the color image here is multiplexed into several sets of polarization profiles, each corresponding to a distinct color, which further allows polarization modulation-induced additive color mixing. This unique approach features the combination of wavelength selectivity and arbitrary polarization control down to a single subwavelength pixel level. The encoding approach for polarization and color may open a new avenue for novel, effective color display elements with fine control over both brightness and contrast, and may have significant impact for high-density data storage, information security, and anticounterfeiting.

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