Bandwidth-unlimited polarization-maintaining metasurfaces

Dynamic Spatial-Selective Metasurface with Multiple-Beam Interference

The emergence of the metasurface has provided a versatile platform for the manipulation of light at the nanoscale. Recent research in metasurfaces has explored a plethora of dynamic control and switching of multifunctionalities, paving the way for innovative applications in fields such as imaging, sensing, and communication. However, current dynamic multifunctional metasurfaces face challenges in terms of functional scalability and selective activation. In this work, we introduce and experimentally demonstrate a strategy that utilizes multiple plane waves to create arbitrary periodic patterns on the metasurface, thus enabling the dynamic and arbitrary spatial-selective activation of its embedded multiplexed functionalities. Furthermore, our strategy facilitates dynamic light control through mechanical translation, as demonstrated by a high-speed, dynamically switchable beam deflection scenario. Our method effectively overcomes the limitations associated with traditional spatially multiplexing techniques, offering greater flexibility and selectivity for dynamic control in multifunctional metasurfaces.

Dual-mode vortex beam transmission metasurface antenna based on linear-to-circular polarization converter

The generation of multi-mode vortex beams at the same aperture is currently emerging as a research hotspot. In this paper, a method based on a linearly polarized-circularly polarized translational transmission metasurface (TM) is proposed to enable a dual-circularly polarized dual-mode vortex beam generation. Through the judicious implementation of an additional rotational phase and the combination of the initial transmission phase, the phases of the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) waves can be manipulated arbitrarily and independently. Meanwhile, the design of the array phase is utilized for the dual-mode dual-circularly polarized beam generation. Simulation and sample measurements provide validation data for the feasibility of this method, in which the measurement results are in excellent consistency with the simulation ones. This proposed method paves the way toward the enhancement of the channel capacity of mobile communication.

Hydrogel muscles powering reconfigurable micro-metastructures with wide-spectrum programmability

Stimuli-responsive geometric transformations endow metamaterials with dynamic properties and functionalities. However, using existing transformation mechanisms to program a single geometry to transform into diverse final configurations remains challenging, imposing crucial design restrictions on achieving versatile functionalities. Here, we present a programmable strategy for wide-spectrum reconfigurable micro-metastructures using linearly responsive transparent hydrogels as artificial muscles. Actuated by the hydrogel, the transformation of micro-metastructures arises from the collaborative buckling of their building blocks. Rationally designing the three-dimensional printing parameters and geometry features of the metastructures enables their locally isotropic or anisotropic deformation, allowing controllable wide-spectrum pattern transformation with programmable chirality and optical anisotropy. This reconfiguration mechanism can be applied to various materials with a wide range of mechanical properties. Our strategy enables a thermally reconfigurable printed metalattice with pixel-by-pixel mapping of different printing powers and angles for displaying or hiding complex information, providing opportunities for encryption, miniature robotics, photonics and phononics applications.

Ultra-broadband holography in visible and infrared regions with full-polarization nondispersive response

Holography is promising to fully record and reconstruct the fundamental properties of light, while the limitations of working bandwidth, allowed polarization states, and dispersive response impede further advances in the integration level and functionality. Here, we propose an ultra-broadband holography based on twisted nematic liquid crystals (TNLCs), which can efficiently work in both the visible and infrared regions with a working spectrum of over 1000 nm. The underlying physics is that the electric field vector of light through TNLCs can be parallelly manipulated in the broad spectral range, thus enabling to build the ultra-broadband TNLC hologram by dynamic photopatterning. Furthermore, by introducing a simple nematic liquid crystal (NLC) element, the cascaded device allows for an excellent nondispersive polarization-maintaining performance that can adapt to full-polarization incidence. We expect our proposed methodology of holography may inspire new avenues for usages in polarization imaging, augmented/virtual reality display, and optical encryption.

Inverse design of polarization conversion metasurfaces by deep neural networks

To address the problem of multiple solutions and improve the calculating speed, we construct a tandem architecture consisting of a forward modeling network and an inverse design network. Using this combined network, we inversely design the circular polarization converter and analyze the effect of different design parameters on the prediction accuracy of the polarization conversion rate. The average mean square error of the circular polarization converter is 0.00121 at an average prediction time of 1.56×10^-2 s. If only the forward modeling process is considered, it takes 6.15×10^-4 s, which is 2.1×10⁵ times faster than that using the traditional numerical full-wave simulation method. By slightly resizing the network input and output layers, the network is adaptable to the design of both the linear cross-polarization and linear-to-circular polarization converters.

Arbitrarily polarized bound states in the continuum with twisted photonic crystal slabs

Arbitrary polarized vortex beam induced by polarization singularity offers a new platform for both classical optics and quantum entanglement applications. Bound states in the continuum (BICs) have been demonstrated to be associated with topological charge and vortex polarization singularities in momentum space. For conventional symmetric photonic crystal slabs (PhCSs), BIC is enclosed by linearly polarized far fields with winding angle of 2π, which is unfavorable for high-capacity and multi-functionality integration-optics applications. Here, we show that by breaking σ_z-symmetry of the PhCS, asymmetry in upward and downward directions and arbitrarily polarized BIC can be realized with a bilayer-twisted PhCS. It exhibits elliptical polarization states with constant ellipticity angle at every point in momentum space within the vicinity of BIC. The topological nature of BIC reflects on the orientation angle of polarization state, with a topological charge of 1 for any value of ellipticity angle. Full coverage of Poincaré sphere (i.e., [Formula: see text] and [Formula: see text]) and higher-order Poincaré sphere can be realized by tailoring the twist angles. Our findings may open up new avenues for applications in structured light, quantum optics, and twistronics for photons.

Spin-decoupling of vertical cavity surface-emitting lasers with complete phase modulation using on-chip integrated Jones matrix metasurfaces

Polarization response of artificially structured nano-antennas can be exploited to design innovative optical components, also dubbed "vectorial metasurfaces", for the modulation of phase, amplitude, and polarization with subwavelength spatial resolution. Recent efforts in conceiving Jones matrix formalism led to the advancement of vectorial metasurfaces to independently manipulate any arbitrary phase function of orthogonal polarization states. Here, we are taking advantages of this formalism to design and experimentally validate the performance of CMOS compatible Jones matrix metasurfaces monolithically integrated with standard VCSELs for on-chip spin-decoupling and phase shaping. Our approach enables accessing the optical spin states of VCSELs in an ultra-compact way with previously unattainable phase controllability. By exploiting spin states as a new degree of freedom for laser wavefront engineering, our platform is capable of operating and reading-out the spin-momentum of lasers associated with injected spin carriers, which would potentially play a pivotal role for the development of emerging spin-optoelectronic devices.

An Ultra-Broadband High Efficiency Polarization Beam Splitter for High Spectral Resolution Polarimetric Imaging in the Near Infrared

A broadband, high efficiency polarized beam splitter (PBS) metagrating based on integrated resonant units (IRUs) to enable simultaneous polarization analysis, spectral dispersion, and spatial imaging in the near infrared (NIR) is developed. A PBS metagrating with a diameter of 60 mm is the key technology component of the high-resolution multiple-species atmospheric profiler in the NIR (HiMAP-NIR), which is a spaceborne instrument concept crafted to be a core payload of NASA's new generation Earth System Observatory. HiMAP-NIR will enable the aerosol profiling in Earth's planetary boundary layer (from surface to2 km altitude) by simultaneously measuring four spatial-spectral-polarimetric images from 680 to 780 nm. Through detailed optimization of hybridized resonant modes in IRUs, the PBS metagrating shows a diffraction efficiency of 70% (or better) for all four linear-polarized incident light, and polarization contrasts between orthogonal states are 0.996 (or better) from 680 to 780 nm. It meets the stringent performance required by the HiMAP-NIR exploiting a new paradigm for the broad applications of metasurfaces.

Active multiband varifocal metalenses based on orbital angular momentum division multiplexing

Metalenses as miniature flat lenses exhibit a substantial potential in replacing traditional optical component. Although the metalenses have been intensively explored, their functions are limited by poor active ability, narrow operating band and small depth of field (DOF). Here, we show a dielectric metalens consisting of TiO₂ nanofins array with ultrahigh aspect ratio to realize active multiband varifocal function. Regulating the orbital angular momentum (OAM) by the phase assignment covering the 2π range, its focal lengths can be switched from 5 mm to 35 mm. This active optical multiplexing uses the physical properties of OAM channels to selectively address and decode the vortex beams. The multiband capability and large DOFs with conversion efficiency of 49% for this metalens are validated for both 532 nm and 633 nm, and the incidence wavelength can further change the focal lengths. This non-mechanical tunable metalens demonstrates the possibility of active varifocal metalenses.

A dielectric metalens consisting of ultrahigh aspect ratio TiO₂ nanofins array is demonstrated to realize active multiband varifocal functionality. By regulating the orbital angular momentum, the focal length can be switched from 5 mm to 35 mm with large DOFs.

Constant polarization generation metasurface for arbitrarily polarized light

State of polarization (SoP) of light is one of the fundamental characteristics of light and has great significance to optical communication, imaging, quantum optics and medical facilities. The generation and maintenance of polarized light have always been research concerns in polarization optics. Polarization-maintaining fibers are frequently used to transmit polarized light without changing its polarization in optical systems, but the high cost and coupling efficiency problems hinder their usage in large-scale light paths. Polarization controllers, which operate arbitrary polarization generation and conversion at the expense of utilizing at least two optical elements such as a half-wave plate and quarter-wave plate, are too bulky for some special applications. Meanwhile, they can only generate desired output polarization of light by transcendentally determining the input polarization, which means that the existing polarization controllers cannot respond in real time. Metasurfaces composed of subwavelength nanoscatterers offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Here, we propose and experimentally demonstrate a real-time polarization controller realized by combining a depolarizer and polarizer into one monolithic metasurface. Arbitrary polarization states can be transferred to the required polarization with no requirement to determine the incident polarization in advance. Through combining with ordinary optical fibers, the proposed metasurface may also replace polarization-maintaining fibers and optical fiber polarizers in some polarization-dependent applications. This versatile concept may settle the problems of arbitrary polarization conversion once and for all.

Photonic slide rule with metasurfaces

As an elementary particle, a photon that carries information in frequency, polarization, phase, and amplitude, plays a crucial role in modern science and technology. However, how to retrieve the full information of unknown photons in an ultracompact manner over broad bandwidth remains a challenging task with growing importance. Here, we demonstrate a versatile photonic slide rule based on an all-silicon metasurface that enables us to reconstruct incident photons' frequency and polarization state. The underlying mechanism relies on the coherent interactions of frequency-driven phase diagrams which rotate at various angular velocities within broad bandwidth. The rotation direction and speed are determined by the topological charge and phase dispersion. Specifically, our metasurface leverages both achromatically focusing and azimuthally evolving phases with topological charges +1 and -1 to ensure the confocal annular intensity distributions. The combination of geometric phase and interference holography allows the joint manipulations of two distinct group delay coverages to realize angle-resolved in-pair spots in a transverse manner- a behavior that would disperse along longitudinal direction in conventional implementations. The spin-orbital coupling between the incident photons and vortex phases provides routing for the simultaneous identification of the photons' frequency and circular polarization state through recognizing the spots' locations. Our work provides an analog of the conventional slide rule to flexibly characterize the photons in an ultracompact and multifunctional way and may find applications in integrated optical circuits or pocketable devices.

Dynamic circular birefringence response with fractured geometric phase metasurface systems

Optical activity is a fundamental property of symmetry-broken three-dimensional systems and enables control of the polarization state of electromagnetic waves. This work introduces a type of reconfigurable geometric phase response in which shearing displacements between two Pancharatnam–Berry-phase metasurfaces transduce chiral symmetry breaking within nanoscale waveguide structures. These metasurface systems, termed fractured metasurface waveplates, can be tailored to support dynamically tunable, broadband circular birefringence responses. Polarization modulation is based on microscopic motions and uniquely enables high-speed modulation over large area apertures. Our system paves the way for new classes of nanophotonic devices that feature systems-level symmetry breaking for controlling electromagnetic waves, which is relevant for sensing, imaging, and quantum-control applications.

Control over symmetry breaking in three-dimensional electromagnetic systems offers a pathway to tailoring their optical activity. We introduce fractured Pancharatnam–Berry-phase metasurface systems, in which a full-waveplate geometric phase metasurface is fractured into two half-waveplate-based metasurfaces and actively configured using shear displacement. Local relative rotations between stacked half-nanowaveplates within the metasurface system are transduced by shear displacement, leading to dynamic modulation of their collective geometric phase properties. We apply this concept to pairs of periodic Pancharatnam–Berry-phase metasurfaces and experimentally show that these systems support arbitrary and reconfigurable broadband circular birefringence response. High-speed circular birefringence modulation is demonstrated with modest shearing speeds, indicating the potential for these concepts to dynamically control polarization states with fast temporal responses. We anticipate that fractured geometric phase metasurface systems will serve as a nanophotonic platform that leverages systems-level symmetry breaking to enable active electromagnetic wave control.

Photonic Encryption Platform via Dual-Band Vectorial Metaholograms in the Ultraviolet and Visible

Metasurface-driven optical encryption devices have attracted much attention. Here, we propose a dual-band vectorial metahologram in the visible and ultraviolet (UV) regimes for optical encryption. Nine polarization-encoded vectorial holograms are observed under UV laser illumination, while another independent hologram appears under visible laser illumination. The proposed engineered silicon nitride, which is transparent in UV, is employed to demonstrate the UV hologram. Nine holographic images for different polarization states are encoded using a pixelated metasurface. The dual-band metahologram is experimentally implemented by stacking the individual metasurfaces that operate in the UV and visible. The visible hologram can be decrypted to provide the first key, a polarization state, which is used to decode the password hidden in the UV vectorial hologram through the use of an analyzer. Considering the property of UV to be invisible to the naked eye, the multiple polarization channels of the vectorial hologram, and the dual-band decoupling, the demonstrated dual-band vectorial hologram device could be applied in various high-security and anticounterfeiting applications.

Free-Space Optical Merging via Meta-Grating Inverse-Design

Despite various advances in achieving arbitrary optics steering, one of the longstanding challenges is to achieve optical merging for combining multidirectional beams through single-time reflection/transmission in free space. Typically, dual-directional beam merging is conducted by combining half-transmission and half-reflection using beam splitters; however, it leads to a bulky system with stray light and low merging efficiency. The difficulty of free-space beam merging lies in imparting respective distinct wavevectors to different directional beams. Herein, we originally proposed and successfully demonstrated the free-space optical merging (FOM) functionality based on the inverse-designed meta-grating architecture in the visible regime. By utilizing the inverse problem solver, two proposed meta-grating schemes experimentally enable merging of dual-directional beams into the same outgoing angle for the first time merely through single-time reflection. We envision that the creation of free-space merging performance can be widely applicable to the future optical system and facilitate the miniature optical devices and integration.

Vectorial Compound Metapixels for Arbitrary Nonorthogonal Polarization Steganography

Malus' law regulating the intensity of light when passed through a polarizer, forms the solid basis for image steganography based on orthogonal polarizations of light to convey hidden information without adverse perceptions, which underpins important practices in information encryptions, anti-counterfeitings, and security labels. Unfortunately, the restriction to orthogonal states being taken for granted in the common perceptions fails to advance cryptoinformation to upgraded levels of security. By introducing a vectorial compound metapixel design, arbitrary nonorthogonal polarization multiplexing of independent grayscale images with high fidelity and strong concealment is demonstrated. The Jones matrix treatment of compound metapixels consisting of double atoms with tailored in-plane orientation sum and difference allows point-by-point configuring of both the amplitude and polarization rotations of the output beam in an analytical and linear form. With this, both multiplexing two continuous grayscale images in arbitrary nonorthogonal polarization angles and concealing grayscale image on another in an arbitrary disclosure angle window are experimentally demonstrated in the visible TiO₂ metasurface platform. The methods shed new light on multifarious metaoptics by harnessing the new degree of freedom and unlock the full potential of metasurface polarization optics.

Plasmonic topological metasurface by encircling an exceptional point

[Figure: see text].

Broadband decoupling of intensity and polarization with vectorial Fourier metasurfaces

Intensity and polarization are two fundamental components of light. Independent control of them is of tremendous interest in many applications. In this paper, we propose a general vectorial encryption method, which enables arbitrary far-field light distribution with the local polarization, including orientations and ellipticities, decoupling intensity from polarization across a broad bandwidth using geometric phase metasurfaces. By revamping the well-known iterative Fourier transform algorithm, we propose "à la carte" design of far-field intensity and polarization distribution with vectorial Fourier metasurfaces. A series of non-conventional vectorial field distribution, mimicking cylindrical vector beams in the sense that they share the same intensity profile but with different polarization distribution and a speckled phase distribution, is demonstrated. Vectorial Fourier optical metasurfaces may enable important applications in the area of complex light beam generation, secure optical data storage, steganography and optical communications.

Pixelated bifunctional metasurface-driven dynamic vectorial holographic color prints for photonic security platform

Vectorial holography has gained a lot of attention due to the promise of versatile polarization control of structured light for enhanced optical security and multi-channel optical communication. Here, we propose a bifunctional metasurface which combines both structural color printing and vectorial holography with eight polarization channels towards advanced encryption applications. The structural colour prints are observed under white light while the polarization encoded holograms are reconstructed under laser illumination. To encode multiple holographic images for different polarization states, a pixelated metasurface is adopted. As a proof-of-concept, we devise an electrically tunable optical security platform incorporated with liquid crystals. The optical security platform is doubly encrypted: an image under white light is decrypted to provide the first key and the corresponding information is used to fully unlock the encrypted information via projected vectorial holographic images. Such an electrically tunable optical security platform may enable smart labels for security and anticounterfeiting applications.

The authors present a bi-functional metasurface, combining structural color printing observed under white light and polarization encoded It is appropriate. vectorial holography. A pixelated design is used encode multiple holographic images, and they demonstrate an electrically tunable optical security platform.