Longitudinal Multifoci Metalens for Circularly Polarized Light

Abstract

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 ...

Visible light focusing flat lenses based on hybrid dielectric-metal metasurface reflector-arrays

“…By employing the superimposed phase design idea, various functionalities can be achieved such as multifocal focusing with the same or opposite chirality252627 and achromatic focusing28293031. For multifocal focusing with the same chirality, such as RCP light, according to the Eq.…”

Phase Manipulation of Electromagnetic Waves with Metasurfaces and Its Applications in Nanophotonics

“…[225] Moreover, by adding the phase arrays of optical vortices into this multifoci design, a nanostructured focusing optical vortex generator with multiple focal planes is enabled, as shown in Figure 9b. As a result of this division, a reduction of the angular resolution is inevitable.…”

Tunable microwave metasurfaces for high-performance operations: dispersion compensation and dynamical switch

“…Many fascinating effects were discovered based on metasurfaces in different frequency domains, such as anomalous light refraction/reflection91011121314151617, surface wave (SW) couplers218, vortex beam generation19, flat lens202122232425262728, polarization control2930, holograms31323334, and photonic spin-Hall effect3536. To design a metasurface with certain functionality, one typically combines a set of resonant meta-atoms with distinct electromagnetic (EM) responses to form a planar structure, such that the whole device exhibits the desired profiles of transmission/reflection amplitude/phase.…”

“…To design a metasurface with certain functionality, one typically combines a set of resonant meta-atoms with distinct electromagnetic (EM) responses to form a planar structure, such that the whole device exhibits the desired profiles of transmission/reflection amplitude/phase. Such a strategy has been successfully implemented in the past years to design various metasurfaces working for different purposes123456789101112131415161718192021222324252627282930313233343536.…”

“…1c). Such an issue seems inherent to all metasurfaces based on passive resonant meta-atoms, working in both reflection2111213272829333435 and transmission1489101415161718192021222324252630313236 geometries and relying on either phase or amplitude modulations67. Although the phase profiles in geometric-phase-based metasurfaces can immune from the frequency change, the real performances of such devices are dictated by the EM responses of their basic meta-atoms, which are still strongly frequency dependent20343536.…”