Vector vortex beams (VVBs) possess ubiquitous applications from particle trapping to quantum information. Recently, the bulky optical devices for generating VVBs have been miniaturized by using ...metasurfaces. Nevertheless, it is quite challenging for the metasurface‐generated VVBs to possess arbitrary polarization and phase distributions. More critical is that the VVBs' annular intensity profiles demonstrated hitherto are dependent on topological charges and are hence not perfect, posing difficulties in spatially shared co‐propagation of multiple vortex beams. Here, a single‐layer metasurface to address all those aforementioned challenges in one go is proposed, which consists of two identical crystal‐silicon nanoblocks with varying positions and rotation angles (i.e., four geometric parameters throughout). Those four geometric parameters are found to be adequate for independent and arbitrary control of the amplitude, phase, and polarization of light. Perfect VVBs with arbitrary polarization and phase distributions are successfully generated, and the constant intensity profiles independent of their topological charges and polarization orders are demonstrated. The proposed strategy casts a distinct perception that a minimalist design of just one single‐layer metasurface can empower such robust and versatile control of VVBs. That provides promising opportunities for generating more complex vortex field for advanced applications in structural light, optical micromanipulation, and data communication.
A single‐layer dielectric metasurface, consisting of two crystal‐silicon nanoblocks within one unit, is proposed to control the amplitude, phase, and polarization of light independently and arbitrarily. A genetic algorithm is used to obtain the geometric parameters of the metasurface element. The proposed strategy enables perfect vector vortex beam generation with constant annular intensity profiles, arbitrary phase, and polarization distributions.
Thermal camouflage has been successful in the conductive regime, where thermal metamaterials embedded in a conductive system can manipulate heat conduction inside the bulk. Most reported approaches ...are background-dependent and not applicable to radiative heat emitted from the surface of the system. A coating with engineered emissivity is one option for radiative camouflage, but only when the background has uniform temperature. Here, we propose a strategy for radiative camouflage of external objects on a given background using a structured thermal surface. The device is non-invasive and restores arbitrary background temperature distributions on its top. For many practical candidates of the background material with similar emissivity as the device, the object can thereby be radiatively concealed without a priori knowledge of the host conductivity and temperature. We expect this strategy to meet the demands of anti-detection and thermal radiation manipulation in complex unknown environments and to inspire developments in phononic and photonic thermotronics.
Chirality is a universal geometric property in both micro‐ and macroworlds. Recently, optical chiral effects have drawn increased attention due to their great potential in fundamental studies and ...practical applications. Significantly, the optical chiral response of artificial structures can be enhanced by orders of magnitude compared to that of their naturally occurring counterparts. These man‐made structures generally exhibit two types of optical chirality: extrinsic chirality and intrinsic chirality. The former relies on external illumination conditions, while the latter arises from the geometric characteristics of 3D objects. Herein, this review mainly focuses on the intrinsic chirality of artificial structures and discusses the existing realizations based on their design principles. In particular, an overview is given of the recent demonstrations of nonlinear optical effects in chiral structures and active chiral structures. Lastly, some promising prospects for future studies in the field are outlined.
3D metaphotonic structures with intrinsic chirality support both optical rotation and circular dichroism, which are orders of magnitude higher than that of their naturally occurring counterparts. They have drawn increased attention due to their potential in fundamental studies in physics, chemistry and biology, and in practical applications, such as negative refractive index media, molecule sensors, and modulators.
Metasurfaces are used to enable acoustic orbital angular momentum (a‐OAM)‐based multiplexing in real‐time, postprocess‐free, and sensor‐scanning‐free fashions to improve the bandwidth of acoustic ...communication, with intrinsic compatibility and expandability to cooperate with other multiplexing schemes. The metasurface‐based communication relying on encoding information onto twisted beams is numerically and experimentally demonstrated by realizing real‐time picture transfer, which differs from existing static data transfer by encoding data onto OAM states. With the advantages of real‐time transmission, passive and instantaneous data decoding, vanishingly low loss, compact size, and high transmitting accuracy, the study of a‐OAM‐based information transfer with metasurfaces offers new route to boost the capacity of acoustic communication and great potential to profoundly advance relevant fields.
Acoustic communication is pivotal in applications such as ocean exploration, while its bandwidth is hitting the ceiling. Twisted acoustics for real‐time information transfer is theoretically proposed and experimentally demonstrated in a passive, postprocess‐free, and sensor scanning‐free fashion with metasurfaces and a single transducer. The study helps to boost the capacity of acoustic communication and advance relevant fields.
Artificially structured thermal metamaterials provide an unprecedented possibility of molding heat flow that is drastically distinct from the conventional heat diffusion in naturally conductive ...materials. The Laplacian nature of heat conduction makes the transformation thermotics, as a design principle for thermal metadevices, compatible with transformation optics. Various functional thermal devices, such as thermal cloaks, concentrators, and rotators, have been successfully demonstrated. How far can it possible go beyond just realizing a heat‐distribution function in a thermal metadevice? Herein, the concept of encrypted thermal printing is proposed and experimentally validated, which could conceal encrypted information under natural light and present static or dynamic messages in an infrared image. Regionalization transformation is developed for structuring thermal metamaterial‐strokes as infrared signatures, enabling letters of the alphabet to be written, paintings to be drawn, movies to be made, and information to be displayed. This strategy successfully demonstrates an extreme level of manipulation of heat flow for encryption, illusions, and messaging.
Heat conduction has long been considered in an omnidirectional diffusive way. Such a stereotype is successfully broken in this work and extreme heat flow manipulation is achieved, based on which encrypted thermal printing and regionalization transformation for structuring thermal metamaterial‐strokes as infrared signatures are proposed, enabling the writing of letters, the drawing of paintings, and the display of information.
Metasurfaces have enabled a plethora of emerging functions within an ultrathin dimension, paving way towards flat and highly integrated photonic devices. Despite the rapid progress in this area, ...simultaneous realization of reconfigurability, high efficiency, and full control over the phase and amplitude of scattered light is posing a great challenge. Here, we try to tackle this challenge by introducing the concept of a reprogrammable hologram based on 1-bit coding metasurfaces. The state of each unit cell of the coding metasurface can be switched between '1' and '0' by electrically controlling the loaded diodes. Our proof-of-concept experiments show that multiple desired holographic images can be realized in real time with only a single coding metasurface. The proposed reprogrammable hologram may be a key in enabling future intelligent devices with reconfigurable and programmable functionalities that may lead to advances in a variety of applications such as microscopy, display, security, data storage, and information processing.Realizing metasurfaces with reconfigurability, high efficiency, and control over phase and amplitude is a challenge. Here, Li et al. introduce a reprogrammable hologram based on a 1-bit coding metasurface, where the state of each unit cell of the coding metasurface can be switched electrically.
Janus monolayers, a class of two‐faced 2D materials, have received significant attention in electronics, due to their unusual conduction properties stemming from their inherent out‐of‐plane ...asymmetry. Their photonic counterparts recently allowed for the control of hydrogenation/dehydrogenation processes, yielding drastically different responses for opposite light excitation spins. A passive Janus metasurface composed of cascaded subwavelength anisotropic impedance sheets is demonstrated. By introducing a rotational twist in their geometry, asymmetric transmission with the desired phase function is realized. Their broken out‐of‐plane symmetry realizes different functions for opposite propagation directions, enabling direction‐dependent versatile functionalities. A series of passive Janus metasurfaces that enable functionalities including one‐way anomalous refraction, one‐way focusing, asymmetric focusing, and direction‐controlled holograms are experimentally demonstrated.
Direction‐encoded wave manipulations are experimentally achieved through the use of Janus metasurfaces composed of cascaded metasheets. By introducing a rotational twist in metasurface geometry, asymmetric electromagnetic wavefront manipulation can be realized. This is demonstrated both theoretically and experimentally by a series of passive metadevices, which enable functionalities including one‐way anomalous refraction, one‐way focusing, asymmetric focusing, and direction‐controlled holograms.
Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin ...and opposite helicity OAM states (±ℓ) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching ℓ = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δℓ = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light.A metasurface laser generates orbital angular momentum states with quantum numbers reaching ℓ = 100. Simultaneous output vortex beams, with Δℓ as great as 90, are demonstrated in the visible regime.
Bulk photovoltaic effect (BPVE), featuring polarization-dependent uniform photoresponse at zero external bias, holds potential for exceeding the Shockley-Queisser limit in the efficiency of existing ...opto-electronic devices. However, the implementation of BPVE has been limited to the naturally existing materials with broken inversion symmetry, such as ferroelectrics, which suffer low efficiencies. Here, we propose metasurface-mediated graphene photodetectors with cascaded polarization-sensitive photoresponse under uniform illumination, mimicking an artificial BPVE. With the assistance of non-centrosymmetric metallic nanoantennas, the hot photocarriers in graphene gain a momentum upon their excitation and form a shift current which is nonlocal and directional. Thereafter, we demonstrate zero-bias uncooled mid-infrared photodetectors with three orders higher responsivity than conventional BPVE and a noise equivalent power of 0.12 nW Hz
. Besides, we observe a vectorial photoresponse which allows us to detect the polarization angle of incident light with a single device. Our strategy opens up alternative possibilities for scalable, low-cost, multifunctional infrared photodetectors.
“Fata Morgana” or “Mirage” phenomena have long been captivated as optical illusions, which actually relies on gradient‐density air or vapor. Man‐made optical illusions have witnessed significant ...progress by resorting to artificially structured metamaterials. Nevertheless, two long‐standing challenges remain formidable: first, exotic parameters (negative or less than unity) become inevitable; second, the signature of original object is altered to that of a virtual counterpart. It is thus not able to address the holy grail of illusion per se, since a single virtual object still exposes the location. In this study, those problems are successfully addressed in a particular setup—illusion thermotics, which identically mimics the exterior thermal behavior of an equivalent reference and splits the interior original heat source into many virtual signatures. A general paradigm to design thermal illusion metadevices is proposed to manipulate thermal conduction, and empower robust simultaneous functions of moving, shaping, rotating, and splitting heat sources of arbitrary cross sections. The temperature profile inside the thermal metadevice can mislead the awareness of the real location, shape, size, and number of the actual heat sources. The present concept may trigger unprecedented development in other physical fields to realize multiple functionalized illusions in optics, electromagnetics, etc.
Existing optical/thermal illusions fail to address the holy grail of illusion per se, since a single virtual object still exposes the location. A solution to this problem is found in illusion thermotics, which identically mimics the exterior thermal behavior of an equivalent reference and splits the interior original heat source into many virtual signatures to enhance the deceptiveness unprecedentedly.
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