Designing reconfigurable metasurfaces that can dynamically control scattered electromagnetic waves and work in the near-infrared (NIR) and optical regimes remains a challenging task, which is hindered by the static material property and fixed structures. Phase change materials (PCMs) can provide high contrast optical refractive indexes at high frequencies between amorphous and crystal states, therefore are promising as feasible materials for reconfigurable metasurfaces. Here, we propose a hybrid metasurface that can arbitrarily modulate the complex amplitude of incident light with uniform amplitude and full $2π$ phase coverage by utilizing composite concentric rings (CCRs) with different ratios of gold and PCMs. Our designed metasurface possesses a bi-functionality that is capable of splitting beams or generating vortex beams by thermal switching between metal and semiconductor states of vanadium oxide (VO2), respectively. It can be easily integrated into low loss photonic circuits with an ultra-small footprint. Our metadevice serves as a novel paradigm for active control of beams, which may open new opportunities for signal processing, memory storage, holography, and anti-counterfeiting.
Establishing and approaching the fundamental limit of orbital angular momentum (OAM) multiplexing are necessary and increasingly urgent for current multiple-input multiple-output research. In this work, we elaborate the fundamental limit in terms of independent scattering channels (or degrees of freedom of scattered fields) through angular-spectral analysis, in conjunction with a rigorous Green function method. The scattering channel limit is universal for arbitrary spatial mode multiplexing, which is launched by a planar electromagnetic device, such as antenna, metasurface, etc, with a predef…
Expanding the use of physical degrees of freedom to employ spatial multiplexing of data in optical communication is considered the most disruptive and effective solution to meet the capacity demand of the growing information traffic. Development of space-division-multiplexing methods stimulated research on spatial modulation, detection and processing of data, attracting interest from various fields of science. A passive all-dielectric metasurface with near-unity transmission is used to engineer spatial mode profiles, potentially of arbitrary complexity. The broadband response of the metasurfac…
Metasurfaces are promising two-dimensional metamaterials that are engineered to provide unique properties or functionalities absent in naturally occurring homogeneous surfaces. Here, we report a type of metasurface for tailored reconstruction of surface plasmon waves from light. The design is generic in a way that one can selectively generate different surface plasmon waves through simple variation of the wavelength or the polarization state of incident light. The ultra-thin metasurface demonstrated in this paper provides a versatile interface between the conventional free-space optics and a t…
This work theoretically and experimentally studies metasurfaces with spatially-discrete, traveling-wave modulation (SD-TWM). A representative metasurface is considered consisting of columns of time-modulated subwavelength unit cells, referred to as stixels. SD-TWM is achieved by enforcing a time delay between temporal waveforms applied to adjacent columns. In contrast to the continuous traveling-wave modulation commonly assumed in studies of space-time metasurfaces, here the modulation is spatially discretized. In order to account for the discretized spatial modulation, a modified Floquet anal…
In display technologies or data processing, planar and subwavelength free-space components suited for flat photonic devices are needed. Metasurfaces, which shape the optical wavefront within hundreds of nanometers, can provide a solution for thin and portable photonic devices, e.g. as CMOS-compatible modules. While conventional electro-optic modulators are inconvenient to operate in free space configurations, its principle can largely be applied to the development of active metasurfaces with the prospect of modulation speeds up to the GHz region. Here, we use this concept to realize fast and c…
Dynamic optical metasurfaces with ultrafast temporal response, i.e., spatiotemporal optical metasurfaces, provide attractive solutions and open fascinating perspectives for modern highly integrated optics and photonics. In this work, electro-optically controlled optical metasurfaces operating in reflection and utilizing resonant waveguide mode excitation are demonstrated from the viewpoint of free-space propagating light modulation. The modulation of reflected light power with superior characteristics in comparison with prior research is achieved by identifying a suitable low-loss waveguide mo…
Rapid progress in nonlinear plasmonic metasurfaces enabled many novel optical characteristics for metasurfaces, with potential applications in frequency metrology, timing characterization and quantum information. However, the spectrum of nonlinear optical response was typically based upon the linear optical resonance. In this work, a wavelength-multiplexed nonlinear plasmon-MoS2 hybrid metasurface with suppression phenomenon was proposed, where multiple nonlinear signals could to be simultaneously processed and optionally tuned. A clear physical picture to depict the nonlinear plasmonic bound …
Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time modulated metasurfaces can be successfully used to manipulate the frequency content and time variations of the impinging field. In this paper, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler…
All-dielectric optical metasurfaces can locally control the amplitude and phase of light at the nanoscale, enabling arbitrary wavefront shaping. However, lack of post-fabrication tunability has limited the true potential of metasurfaces for many applications. Here, we utilize a thin liquid crystal (LC) layer as a tunable medium surrounding the metasurface to achieve a phase-only spatial light modulator (SLM) with high reflection in the visible frequency, exhibiting an active and continuous resonance tuning with associated 2pi phase control and uncoupled amplitude. Dynamic wavefront shaping is …
We report a THz reflectarray metasurface which uses graphene as active element to achieve beam steering, shaping and broadband phase modulation. This is based on the creation of a voltage controlled reconfigurable phase hologram, which can impart different reflection angles and phases to an incident beam, replacing bulky and fragile rotating mirrors used for terahertz imaging. This can also find applications in other regions of the electromagnetic spectrum, paving the way to versatile optical devices including light radars, adaptive optics, electro-optical modulators and screens.
Metasurfaces provide the disruptive technology enabling miniaturization of complex cascades of optical elements on a plane. We leverage the benefits of such a surface to develop a planar integrated photonic beam collimator for on-chip optofluidic sensing applications. While most of the current work focuses on miniaturizing the optical "detection" hardware, little attention is given to develop on-chip hardware for optical "excitation". In this manuscript, we propose a flat metasurface for beam collimation in optofluidic applications. We implement an inverse design approach to optimize the metas…
Metasurfaces have attracted extensive interests due to their ability to locally manipulate optical parameters of light and easy integration to complex optical systems. Particularly, metasurfaces can provide a novel platform for splitting and diffracting light into several beams with desired profile, which is in contrast to traditional gratings. Here, we propose and experimentally demonstrate a novel method for generating independently selective diffraction orders. Our method is based on complex amplitude modulation with ultrathin dielectric metasurfaces. By tailoring the geometric parameters o…
Space-time modulation induced non-reciprocity in EM metasurfaces is proposed and numerically demonstrated using rigorous Generalized Sheet Transitions Conditions (GSTCs) under oblique plane-wave incidence. It is phenomenologically shown that the space-time modulation of surface susceptibilities create an inherent asymmetry with respect to the directional perturbation on the metasurface and the transverse wave momentum of the input wave, between forward and backward propagations, resulting in non-reciprocal wave transmission. Exploiting the periodicity of the surface susceptibilities in both ti…
Known coherent metasurfaces control interference of waves of a given frequency with other coherent waves at the same frequency, either illuminating from a different direction or created as intermodulation products. In this paper, we introduce a class of metasurfaces that are modulated in time coherently with the illuminating radiation. Importantly, such modulation opens a possibility to control reflection, absorption, and transmission at multiple frequencies, including illuminations by two or more incoherent waves. In particular, we study dynamic resistive layers and show how to use them to de…
Metasurfaces are believed as one of the best candidates in nano-optical devices, attributed to the key feasible modulation features of phase, polarization, and local field enhancement by structural designing. However, current methods of propagation- and geometric-phase modulation are interrelated between two eigen spin-states. This means that when the left-handed component phase of a beam is modulated by metasurfaces, its right-handed component phase will change accordingly, which limits the versatility of spin-decoupled applications. In this paper, we experimentally and numerically demonstrat…
While nanoscale color generations have been studied for years, the high performance transmission structural color, simultaneously equipped with large gamut, high resolution, and optical multiplexing abilities, still remains as a hanging issue. Here, a silicon metasurface embedded Fabry-Pérot cavity is demonstrated to address this problem. By changing the planar geometries of metasurface units, the cavities provide transmission colors with 194% sRGB gamut coverage and 141111 DPI resolution, along with more than 300% enhanced angular tolerance. Such high density allows two-dimensional color mixi…
Vortex beams carrying orbital angular momentum (OAM) have been widely applied in various electromagnetic, optical, and quantum systems. A tailored OAM spectrum composed of several specific modes as expected holds a promise for expanding the degrees of freedom of the systems. However, such a broadband high-purity tailored spectrum is difficult to be achieved by the present devices, where the broadband amplitude manipulation has not been explored yet. In this work, inspired by the envelope-modulation theory, an elegant and universal way to manipulate the OAM spectrum in wide bandwidth is propose…
Amplified up-conversion of electromagnetic waves using time-varying metasurfaces
ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Research School of Physics, The Australian National University（澳大利亚国立大学变革性超光学系统卓越研究中心物理研究学院）；Instituto de Telecomunicações and Department of Electronics, Telecommunications and Informatics, University of Aveiro（阿威罗大学电信研究所电子、电信与信息系）
Creating materials with time-variant properties is critical for breaking reciprocity that imposes fundamental limitations to wave propagation. However, it is challenging to realize efficient and ultrafast temporal modulation in a photonic system. Here, leveraging both spatial and temporal phase manipulation offered by an ultrathin nonlinear metasurface, we experimentally demonstrated nonreciprocal light reflection at wavelengths around 860 nm. The metasurface, with traveling-wave modulation upon nonlinear Kerr building blocks, creates spatial phase gradient and multi-terahertz temporal phase w…
The recently proposed extreme-ultraviolet (EUV) beams with time-varying orbital angular momentum (OAM) realized by high-harmonic generation (HHG) provides extraordinary tools for quantum excitation control and particle manipulation. However, such an approach is not easily scalable to other frequency regimes. Here, we design a space-time-coding digital metasurface operating in microwave frequencies to experimentally generate different modes of time-varying OAM. We also introduce a concept of superhelicity of time-varying OAM with a higher-order twist of the wavefront structure, which can be fur…
We present the concept, theoretical model and experimental implementation of a full-duplex nonreciprocal-beam-steering transmissive phase-gradient metasurface. Such a metasurface is realized by exploiting the unique properties of the frequency-phase transition in coupled time-modulated twin meta-atoms. The metasurface may be placed on top of a source antenna to transform the radiation pattern of the source antenna, and introduce different radiation patterns for the transmit and receive states. In contrast to the recently proposed applications of time modulation, here the incident and transmitt…
On-chip mode-division multiplexing (MDM) has been emerging as a promising technology to further enhance the link capacity and bandwidth of data communications with multiple mode channels. Both mode converters and mode exchangers are indispensable fundamental components for flexible mode operations. While several configurations have been developed previously, it is still very challenging to efficiently manipulate arbitrary high-order modes in a versatile way to reduce the R&D and prototyping costs. Here we initiate a breakthrough with a simple yet universal generic mode operator building block …
Metasurfaces possess the outstanding ability to tailor phase, amplitude and even spectral responses of light with an unprecedented ultrahigh resolution, thus have attracted significant interests. Here, we propose and experimentally demonstrate a novel meta-device that integrates color printing and computer-generated holograms within a single-layer dielectric metasurface by modulating spectral and spatial responses at subwavelength scale, simultaneously. In our design, such metasurface appears as a microscopic color image under white light illumination, while encrypting two different holographi…
Plasmonic metasurfaces represent a promising platform for enhancing light-matter interaction. Active control of the optical response of metasurfaces is desirable for applications such as beam-steering, modulators and switches, biochemical sensors, and compact optoelectronic devices. Here we use a plasmonic metasurface with two Fano resonances to enhance the interaction of infrared light with electrically controllable single layer graphene. It is experimentally shown that the narrow spectral width of these resonances, combined with strong light/graphene coupling, enables reflectivity modulation…
We report here and experimentally demonstrate an actively controlled gatetunable plasmonic metasurface operating in the visible region of the electromagnetic spectrum, where strikingly the operating voltages for reflectance modulation are much less than 1V. The electrically tunable metasurface consists of inverse dolmen structures (iDolmen) patterned on silver and chromium on a quartz substrate and subsequently covered with a 5 nm thin layer of Al2O3 followed by a 110 nm indium tin oxide (ITO) layer, which acts as a transparent electrode. Our designed structures show up to 78 percent change in…
In typical single-pixel detection multiplexing, an unknown object is sequentially illuminated with intensity patterns: the total signal is summed into a single-pixel detector and is then demultiplexed to retrieve the object. Because of measurement noise, the retrieved object differs from the ground truth by some error quantified by the signal-to-noise ratio (SNR). In situations where the noise only arises from the photon counting process, it has not been made clear if single-pixel detection multiplexing leads to a better SNR than simply scanning the object with a focused intensity spot - a mod…
Plasmonic metasurfaces are able to modify the wavefront by altering the light intensity, phase and polarization state. Active plasmonic metasurfaces would allow dynamic modulation of the wavefront which give rise to interesting application such as beam-steering, holograms and tunable waveplates. Graphene is an interesting material with dynamic property which can be controlled by electrical gating at an ultra-fast speed. We use a graphene-integrated metasurface to induce a tunable phase change to the wavefront. The metasurface supports a Fano resonance which produces high-quality resonances aro…
Elusive features in photonic and electronic devices can be detected by means of advanced, time-domain spectroscopic techniques. In this letter we introduce a novel kind of modulation spectroscopy, based on the optomechanical interaction of photonic and mechanical modes. Applying the technique to a Si metasurface and its drum-like mechanical modes, we detect narrow-band quasi-Bound-State-in-the-Continuum (q-BIC) modes close to normal incidence, where their measurement can be hindered by a high symmetry protection and undesired background modes. Showing a visibility enhancement of more than one …
Unconstrained by Lorentz reciprocity, nonreciprocal metasurfaces are uniquely capable of encoding distinctive optical functions on forward- and backward-propagating waves. The nonreciprocal metasurfaces reported to date require external electric or magnetic field biasing or rely on nonlinear effects, both of which are challenging to practically implement. Here, we propose and experimentally realize a magnet-free, linear, and passive nonreciprocal metasurface based on self-biased magnetic meta-atoms. Record transmittance up to 77% and operation angle reaching 64 degree are experimentally demons…
Optical metasurfaces enable to engineer the electromagnetic space and control light propagation at an unprecedented level, offering a powerful tool to achieve modulation of light over multiple physical dimensions. Here, we demonstrate a Sb$_{2}$S$_{3}$ phase-change metasurface platform that allows active manipulation of both amplitude and phase. In particular, we implement dynamic nanoprinting and holographic image display through tuning crystallization levels of this phase-change material. The Sb$_{2}$S$_{3}$ nanobricks tailored to function the amplitude, geometric and propagation phase modul…
Resonant lattice Kerker effect in periodic resonators is one of the most interesting generalizations of the Kerker effect that relates to various fascinating functionalities such as scattering management and Huygens metasurfaces. However, so far this effect has been shown to be sensitive to the incident polarization, restricting its applications. Here, we report, for the first time, polarization-independent resonant lattice Kerker effect in metasurfaces composed of periodic Ge$_2$Se$_2$Te$_5$ (GST) disks. For such a metasurface of square lattice, the spectrally overlap of the electric dipole a…
Hologram is an ideal method for naked eye three-dimensional (3D) display, and computer-generated holography (CGH) makes it possible to reconstruct virtual objects. However, the large pixel size of common CGH devices results in shortages in the applications of hologram, such as narrow field of view, twin images, multi-diffraction orders, et al. Meanwhile, metasurfaces consisted of subwavelength structures show great potential in controlling of light which is suitable for hologram design. There are many inspired works to achieve dynamic meta-hologram as we summary in this paper. And it can be co…
