Geometric Metasurfaces Research Articles

Reconfigurable continuous-zoom metalens in visible band

The design of a conventional zoom lens is always challenging because it requires not only sophisticated optical design strategy, but also complex and precise mechanical structures for system adjustment. Here, we propose a continuous-zoom lens consisting of two chiral geometric metasurfaces with dielectric nanobrick arrays sitting on a transparent substrate. The metalens can continuously vary the focal length by rotating either of the two metasurfaces around its optical axis without changing any other conditions. Due to the polarization dependence of the geometric metasurface, the positive and negative polarities are interchangeable in one identical metalens only by changing the handedness of the incident circularly polarized light, which can generate varying focal lengths ranging from −∞ to +∞ in principle.

Order and Disorder Embedded in a Spectrally Interleaved Metasurface

Metasurfaces enable the manipulation of light’s disorder strength in a two-dimensional photonic system. Here we report on the spectral interleaving of an ordered and a disordered system within a geometric phase metasurface. The efficiency of prevalent interleaving techniques is limited by the number of functions incorporated within the metasurface. We present a shared-aperture extinction cross-section approach relying on interleaving of spectrally selective nanoantenna arrays, each having a large extinction cross-section, thus allowing to overcome this limitation. Using this approach, we realize a silicon-based spectral interleaving metasurface for spectrum-dependent disguise, holographic tagging, and imaging of a target object. The shared-aperture extinction cross-section concept opens the path for the generation of multiple, efficient, and spectrally resolved functions in a two-dimensional photonic system. The presented order–disorder interleaving approach offers new prospects for the manipulation of li...

Spectrally interleaved topologies using geometric phase metasurfaces.

Metasurfaces facilitate the interleaving of multiple topologies in an ultra-thin photonic system. Here, we report on the spectral interleaving of topological states of light using a geometric phase metasurface. We realize that a dielectric spectrally interleaved metasurface generates multiple interleaved vortex beams at different wavelengths. By harnessing the space-variant polarization manipulations that are enabled by the geometric phase mechanism, a vectorial vortex array is implemented. The presented interleaved topologies concept can greatly enhance the functionality of advanced microscopy and communication systems.

Chip-Integrated Geometric Metasurface As a Novel Platform for Directional Coupling and Polarization Sorting by Spin–Orbit Interaction

The focus of the research in metasurfaces has mainly been on the manipulation of the electromagnetic waves in free space during the past few years, which generally require thousands of subwavelength meta-atoms or even more. In this paper, we propose a conceptually new approach that chip-integrated metasurface can behave as a promising compact platform to control the propagation of guided waves when it is integrated with optical waveguide. As a proof of the concept, geometric metasurfaces consisting of only seven rotating anisotropic antennas, both metallic and dielectric, are integrated with silicon-on-insulator waveguide. Benefiting from the geometric phase shift stemming from spin–orbit interaction in metasurfaces, linearly gradient wavefront is generated along the waveguide, which is equivalent to introduce a unidirectional effective wavevector and thus leads to directional coupling. Inspired by the spin dependent gradient wavefront, opposite light flow is excited in the integrated waveguide by switching the handedness of incidence, which may provide a potential pathway to integrated polarization sorters and switchers.

Nonlinear Metasurfaces: Tripling the Capacity of Optical Vortices by Nonlinear Metasurface (Laser Photonics Rev. 12(11)/2018)

In article number 1800164, Shuqi Chen and co-workers introduce a second harmonic Pancharatnam–Berry phase and generate one linear and two second harmonic optical vortices with different topological charges focused into different focal lengths simultaneously from the proposed metasurface, which can store three-fold optical vortices compared with the conventional linear geometric metasurfaces. The proposed metasurface promises great applications in enhancing data capacity of optical communications and newer information security.

Spin-controlled wavefront shaping with plasmonic chiral geometric metasurfaces

Metasurfaces, as a two-dimensional (2D) version of metamaterials, have drawn considerable attention for their revolutionary capability in manipulating the amplitude, phase, and polarization of light. As one of the most important types of metasurfaces, geometric metasurfaces provide a versatile platform for controlling optical phase distributions due to the geometric nature of the generated phase profile. However, it remains a great challenge to design geometric metasurfaces for realizing spin-switchable functionalities because the generated phase profile with the converted spin is reversed once the handedness of the incident beam is switched. Here, we propose and experimentally demonstrate chiral geometric metasurfaces based on intrinsically chiral plasmonic stepped nanoapertures with a simultaneously high circular dichroism in transmission (CDT) and large cross-polarization ratio (CPR) in transmitted light to exhibit spin-controlled wavefront shaping capabilities. The chiral geometric metasurfaces are constructed by merging two independently designed subarrays of the two enantiomers for the stepped nanoaperture. Under a certain incident handedness, the transmission from one subarray is allowed, while the transmission from the other subarray is strongly prohibited. The merged metasurface then only exhibits the transmitted signal with the phase profile of one subarray, which can be switched by changing the incident handedness. Based on the chiral geometric metasurface, both chiral metasurface holograms and the spin-dependent generation of hybrid-order Poincaré sphere beams are experimentally realized. Our approach promises further applications in spin-controlled metasurface devices for complex beam conversion, image processing, optical trapping, and optical communications.

Tripling the Capacity of Optical Vortices by Nonlinear Metasurface

AbstractOptical vortices have emerged as a potential approach to enhance data capacity for its extra degree of freedom of orbital angular momentum. Although linear metasurfaces have been used to generate optical vortices, their capacity can be further increased by involving nonlinear frequency conversions, providing new channels for data storage. Here, by introducing second harmonic Pancharatnam–Berry phase, one linear and two second harmonic optical vortices with different topological charges focused into different focal lengths can be generated simultaneously from the proposed metasurface, which can store threefold optical vortices compared with the conventional linear geometric metasurfaces have been demonstrated. Besides, the 2D multifocal metalens with same strength for each focus emerged from the parabolic phase factor has been experimentally observed. This nonlinear optical vortex generation process represents a new strategy for enhancing the capacity of optical communications and multi‐channels integrated optical communications.

High‐Efficiency and Wide‐Angle Beam Steering Based on Catenary Optical Fields in Ultrathin Metalens

AbstractRecent advances in artificial subwavelength structures promise the realization of ultrathin, lightweight, and flat metalens, providing a potential candidate for traditional bulky and curved lens. Nevertheless, most metalenses are generally suffering from serious off‐axis aberration, resulting in a limited field‐of‐view (FOV). Here, a methodology to extend the FOV of metalens is presented by exploring the local catenary optical fields and symmetry transformation from rotational symmetry to transversal symmetry. As a proof of the concept, a high efficiency (>80% even when the incidence angle is titled by 60°) and ultrathin (≈0.127 λ) metalens consisting of bilayer geometric metasurface is designed, fabricated, and characterized. The wide FOV of metalens benefiting from local catenary fields and symmetry transformation is numerically demonstrated by full‐wave simulation and ray tracing method. Moreover, the wide‐angle beam steering ability beyond ± 60° is experimentally demonstrated, which exhibits obvious advantages compared with previous beam steering transmitarrays. The novelty of the proposed methodology lies at the fact that both transversal and longitudinal local catenary fields are excited in a single component: the transversal catenary field is utilized for high efficiency spin–orbit interaction and phase modulation, while the longitudinal catenary field and symmetry transformation ensure wide‐angle operation.

Geometric Metasurfaces for Ultrathin Optical Devices

AbstractMetasurfaces, planar metamaterials consisting of a single layer or several layers of artificial structures, not only form the basis for fundamental physics research but also have considerable technological significance. Metasurfaces can locally modify the optical property within a subwavelength range, which can facilitate device miniaturization and system integration. Metasurfaces have shown extraordinary capabilities in the local manipulation of the light's amplitude, phase, and polarization, leading to a plethora of novel applications such as generalized Snell's law of refraction and photonic spin Hall effect. This progress report is focused on the recent advancements in the fundamental research of geometric metasurfaces and their applications in ultrathin optical devices, including planar metalenses, helicity multiplexed holograms, functionality switchable devices, polarization beam splitters, vector beam generation, arbitrary polarization control, and so on. The compactness, ease of fabrication, and unusual functionalities of these devices render geometric optical metasurface devices very attractive for new applications such as encryption, imaging, anti‐counterfeiting, optical communications, quantum science, and fundamental physics. This paper aims to bring readers some new insights, and to broaden the applications of geometric metasurfaces in more research fields of science and technology.

Geometric metasurface enabling polarization independent beam splitting

A polarization independent holographic beam splitter that generates equal-intensity beams based on geometric metasurface is demonstrated. Although conventional geometric metasurfaces have the advantages of working over a broad frequency range and having intuitive design principles, geometric metasurfaces have the limitation that they only work for circular polarization. In this work, Fourier holography is used to overcome this limitation. A perfect overlap resulting from the origin-symmetry of the encoded image enables polarization independent operation of geometric metasurfaces. The designed metasurface beam splitter is experimentally demonstrated by using hydrogenated amorphous silicon, and the device performs consistent beam splitting regardless of incident polarizations as well as wavelengths. Our device can be applied to generate equal-intensity beams for entangled photon light sources in quantum optics, and the design approach provides a way to develop ultra-thin broadband polarization independent components for modern optics.

Broadband full-color multichannel hologram with geometric metasurface.

Due to the abilities of manipulating the wavefront of light with well-controlled amplitude, and phase and polarization, optical metasurfaces are very suitable for optical holography, enabling applications with multiple functionalities and high data capacity. Here, we demonstrate encoding two- and three-dimensional full-color holographic images by an ultrathin metasurface hologram whose unit cells are subwavelength nanoslits with spatially varying orientations. We further show that it is possible to achieve full-color holographic multiplexing with such kind of geometric metasurfaces, realized by a synthetic spectrum holographic algorithm. Our results provide an efficient way to design multi-color optical display elements that are ready for fabrication.

Huygens' optical vector wave field synthesis via in-plane electric dipole metasurface.

We investigate Huygens' optical vector wave field synthesis scheme for electric dipole metasurfaces with the capability of modulating in-plane polarization and complex amplitude and discuss the practical issues involved in realizing multi-modulation metasurfaces. The proposed Huygens' vector wave field synthesis scheme identifies the vector Airy disk as a synthetic unit element and creates a designed vector optical field by integrating polarization-controlled and complex-modulated Airy disks. The metasurface structure for the proposed vector field synthesis is analyzed in terms of the signal-to-noise ratio of the synthesized field distribution. The design of practical metasurface structures with true vector modulation capability is possible through the analysis of the light field modulation characteristics of various complex modulated geometric phase metasurfaces. It is shown that the regularization of meta-atoms is a key factor that needs to be considered in field synthesis, given that it is essential for a wide range of optical field synthetic applications, including holographic displays, microscopy, and optical lithography.

All-dielectric planar chiral metasurface with gradient geometric phase.

Planar optical chirality of a metasurface measures its differential response between left and right circularly polarized (CP) lights and governs the asymmetric transmission of CP lights. In 2D ultra-thin plasmonic structures the circular dichroism is limited to 25% in theory and it requires high absorption loss. Here we propose and numerically demonstrate a planar chiral all-dielectric metasurface that exhibits giant circular dichroism and transmission asymmetry over 0.8 for circularly polarized lights with negligible loss, without bringing in bianisotropy or violating reciprocity. The metasurface consists of arrays of high refractive index germanium Z-shape resonators that break the in-plane mirror symmetry and induce cross-polarization conversion. Furthermore, at the transmission peak of one handedness, the transmitted light is efficiently converted into the opposite circular polarization state, with a designated geometric phase depending on the orientation angle of the optical element. In this way, the optical component sets before and after the metasurface to filter the light of certain circular polarization states are not needed and the metasurface can function under any linear polarization, in contrast to the conventional setup for geometry phase based metasurfaces. Anomalous transmission and two-dimensional holography based on the geometric phase chiral metasurface are numerically demonstrate as proofs of concept.

All-dielectric reflective half-wave plate metasurface based on the anisotropic excitation of electric and magnetic dipole resonances.

We present an all-dielectric metasurface that simultaneously supports electric and magnetic dipole resonances for orthogonal polarizations. At resonances, the metasurface reflects the incident light with nearly perfect efficiency and provides a phase difference of π in the two axes, making a low-loss half-wave plate in reflection mode. The polarization handedness of the incident circularly polarized light is preserved after reflection; this is different from either a pure electric mirror or magnetic mirror. With the features of high reflection and circular polarization conservation, the metamirror is an ideal platform for the geometric phase-based gradient metasurface functioning in reflection mode. Anomalous reflection with the planar meta-mirror is demonstrated as a proof of concept. The proposed meta-mirror can be a good alternative to plasmonic metasurfaces for future compact and high-efficiency metadevices for polarization and phase manipulation in reflection mode.

Back Cover: Ann. Phys. 2'2018

Annalen der PhysikVolume 530, Issue 2 1870015 BACK COVERFree Access Back Cover: Ann. Phys. 2'2018 First published: 16 February 2018 https://doi.org/10.1002/andp.201870015AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract An ultrathin microlens array based on the geometric metasurface is reported by Jinjin Jin and co-workers in article number 1700326. The mirolens array is composed of a serial of subwavelength gratings with different rotation angles, possessing ultrathin, flat and broadband properties. Simultaneously, the focus lights modulated by the ultrathin microlens have high intensity uniformity. This ultrathin microlens possesses significant potential application in three-dimensional information storage. Volume530, Issue2February 20181870015 RelatedInformation

Spin-controlled twisted laser beams: intra-cavity multi-tasking geometric phase metasurfaces.

Novel multi-tasking geometric phase metasurfaces were incorporated into a modified degenerate cavity laser as an output coupler to efficiently generate spin-dependent twisted light beams of different topologies. Multiple harmonic scalar vortex laser beams were formed by replacing the laser output coupler with a shared-aperture metasurface. A variety of distinct wave functions were obtained with an interleaving approach - random interspersing of geometric phase profiles within shared-aperture metasurfaces. Utilizing the interleaved metasurfaces, we generated vectorial vortices by coherently superposing of scalar vortices with opposite topological charges and spin states. We also generated multiple partially coherent vortices by incorporating harmonic response metasurfaces. The incorporation of the metasurface platforms into a laser cavity opens a pathway to novel types of nanophotonic functionalities and enhanced light-matter interactions, offering exciting new opportunities for light manipulation.

Ultrathin Planar Microlens Arrays Based on Geometric Metasurface

AbstractAscribing to the properties of two dimensional parallel focusing and imaging, low propagation loss, integration and miniaturization, microlens array has been widely used in imaging, optical communication, organic light emitting devices, adaptive optics, photolithography, biomedical and other applications. However, the existing traditional microlens array suffers from difficulty in fabrication, large‐thickness, curved surface, non‐uniformity of light spots, or requirement of additional discrete components to control the microlens. Herein, a planar microlens array is experimentally demonstrated based on the geometric metasurface. The single microlens is composed of space‐variant subwavelength metallic gratings with high polarization conversion efficiency and thus exhibits gradient phase distribution. The focused spot diameter of 22.5 μm with radius of 350 μm, focal length of 1 cm and the light spots intensity uniformity of 0.9885 (standard deviation 0.0115) at the focal plane are obtained. Moreover, the broadband property of microlens array is also confirmed. The novel design strategy for microlens array would facilitate the miniaturization of optical devices and be easily integrated in the optical interconnected devices.

Geometric Phase Generated Optical Illusion

An optical illusion, such as “Rubin’s vase”, is caused by the information gathered by the eye, which is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source. Metasurfaces are metamaterials of reduced dimensionality which have opened up new avenues for flat optics. The recent advancement in spin-controlled metasurface holograms has attracted considerate attention, providing a new method to realize optical illusions. We propose and experimentally demonstrate a metasurface device to generate an optical illusion. The metasurface device is designed to display two asymmetrically distributed off-axis images of “Rubin faces” with high fidelity, high efficiency and broadband operation that are interchangeable by controlling the helicity of the incident light. Upon the illumination of a linearly polarized light beam, the optical illusion of a ‘vase’ is perceived. Our result provides an intuitive demonstration of the figure-ground distinction that our brains make during the visual perception. The alliance between geometric metasurface and the optical illusion opens a pathway for new applications related to encryption, optical patterning, and information processing.

Manipulation of vector beam polarization with geometric metasurfaces.

Describing a class of beams with space-variant polarization, vector beams find many applications in both classical and quantum optics. However, simultaneous manipulation of its space-dependent polarization states is still a challenge with a single optical element. Here we demonstrate polarization modulation of a vector field by employing a plasmonic metasurface exhibiting strong and controllable optical activity. By changing the lateral phase shift between two reflective metasurface supercells, the rotation angle of a linear polarized light can be continuously tuned from zero to π with a high efficiency. As the optical activity of our metasurface devices only depends on geometrical phase, the metasurfaces can simultaneously modulate the rotation angle of a vector beam regardless of its space-variant polarization distribution. Our work provides a high efficient method in manipulating the polarization state of vector beams, especially with metasurface in a compact space, which presents great potential in research fields involving vector beams.

Super-resolution imaging with a Bessel lens realized by a geometric metasurface.

In the super resolution imaging system, a lens and an axicon that can generate spherical wavefronts and non-diffracting Bessel beams respectively are both essential yet difficult to integrate using the traditional approach. We propose a new concept of a "Bessel-lens" to indicate unique optical elements that merge the functionalities of lenses and axicons simultaneously. The Bessel-lens is a mission that is extremely difficult if not impossible for state-of-the-art technology because of the exotic phase profile. Via the geometric phases in space-variant nanoslits, planar Bessel-lenses are designed and experimentally characterized for the first time to generate subdiffraction beams. Compared with a planar lens and axicon with the same dimensions and numerical aperture, the proposed Bessel-lens possesses a higher imaging resolution, which may find applications in microscopy, nanofabrication and dense data storage.