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Vectorial metasurface holography
Abstract
Tailoring light properties using metasurfaces made of optically thin and subwavelength structure arrays has led to a variety of innovative optical components with intriguing functionalities. Transmitted/reflected light field distribution with exquisite nanoscale resolution achievable with metasurfaces has been utilized to encode holographic complex amplitude, leading to arbitrary holographic intensity profile in the plane of interest. Vectorial metasurface holography, which not only controls the intensity profile, but also modifies the polarization distributions of the light field, has recently attracted enormous attention due to their promising applications in photonics and optics. Here, we review the recent progresses of the vectorial metasurface holography, from the basic concept to the practical implementation. Moreover, vectorial metasurfaces can also be multiplexed with other degrees of freedom, such as wavelength and nonlinearity, enriching and broadening its applications in both civil and military field.
... Unlike conventional bulk optical elements, metasurfaces provide benefits for optical system integration and size reduction of optical instruments. Presently, metasurfaces have found widespread applications in optical encryption [1][2][3], vortex beam generators [4][5][6][7][8], and holography [3,9,10]. In the applications of achromatic metalenses and multifunctional optical elements, controlling the phase of different wavelengths independently is of great significance and various solutions have been proposed. ...
... The first device is a dual-wavelength achromatic metalens, conforming to the hyperbolic phase formula [Eq. (9)], where f is the design focal length, r is the radial position of each meta-atom, and λ i (i = 1, 2) is the operating wavelength. We select NA = 0.45, ...
... Figures 6(b) and 6(d) display the far-field distribution of the pentagram and the ring by GSW. For comparison, we also calculate them through the Fraunhofer diffraction formula based on the near-field distribution of the LCP light from the holographic metasurface obtained by FDTD [9], as shown in Figs. 6(c) and 6(e). ...
Metasurfaces capable of controlling multiple wavelengths independently have attracted broad interests these years due to their significance in multi-channel information processing applications. Previous solving strategies include spatial multiplexing or extensive searching for appropriate structures, both of which have their own disadvantageous, such as low efficiency, large computer resource requirement, or time consumption. In this paper, by combining the Pancharatnam–Berry (PB) phase and propagation phase, we propose a strategy to simplify the design complexity in a dual-wavelength metasurface system, in which two simple rectangular-shaped dielectric pillars ( T 1 and T 2 ) with different aspect ratios are chosen as basic structures and crossed at the geometric center to achieve manipulation. The larger pillar T 2 controls the longer wavelength through the PB phase while the smaller T 1 acts as a perturbation to T 2 . The crossed T 1 & T 2 is studied as a whole to tune the short wavelength. The investigations by the multipole expansion method reveal that the polarization conversion ratio of the meta-atoms is dependent on the interference of the formed multipoles. To validate the proposed strategy, a dual-wavelength achromatic metalens and a wavelength-multiplexed holographic metasurface operating at the infrared thermal imaging band are designed. Our design strategy can find widespread applications in metasurfaces where multiple objectives are required to be realized.
... Beyond the ultra-thin attributes inherent to traditional refractive devices, metasurfaces offer a substantial advantage in polarization control [24]. Metasurface holography, with its high information density in a planar format, holds tremendous potential for cutting-edge displays [23][24][25][26][27][28], paving the way for the realization of high-fidelity holography. ...
The fast algorithms in Fourier optics have invigorated multifunctional device design and advanced imaging technologies. However, the necessity for fast computations has led to limitations in the widely used conventional Fourier methods, manifesting as fixed size image plane at a certain diffraction distance. These limitations pose challenges in intricate scaling transformations, 3D reconstructions and full-color displays. Currently, there is a lack of effective solutions, often resorting to pre-processing that compromise fidelity. In this paper, leveraging a higher-dimensional phase space method, we present a universal framework allowing for customized diffraction calculation methods. Within this framework, we establish a variable-scale diffraction computation model which allows the adjustment of the size of the image plane and can be operated by fast algorithms. We validate the model's robust variable-scale capabilities and its aberration automatic correction capability for full-color holography, achieving high fidelity. The large-magnification tomography experiment demonstrates that this model provides a superior solution for holographic 3D reconstruction. In addition, this model is applied to achieve full-color metasurface holography with near-zero crosstalk, showcasing its versatile applicability at nanoscale. Our model presents significant prospects for applications in the optics community, such as beam shaping, computer-generated holograms (CGHs), augmented reality (AR), metasurface optical elements (MOEs) and advanced holographic head-up display (HUD) systems.
... As optical skyrmions comprise a new direction [27] for the study of topological quantum states [28], their topological transformations have attracted much attention in the fields of vector holography [29], quantum communication [30], information processing and even in nonquantum systems. Our discovery allows for more precise tailoring of the skyrmion lattice. ...
The topological properties of optical skyrmions have enormous application value in fields such as optical communication and polarization sensing. At present, research on optical skyrmions focuses primarily on the topological principles of skyrmions and their applications. Nonetheless, extant research devoted to skyrmion-array manipulation remains meager. The sole manipulation scheme has a limited effect on the movement direction of the whole skyrmion array. Based on the interference principle of the surface plasmon polariton (SPP) wave, we propose an upgraded scheme for the tailoring of electric-field optical skyrmions. A distributed Gaussian-focused spots array is deployed. Unlike the existing manipulation, we customize the phase of the light source to be more flexible, and we have discovered optical-skyrmion tailoring channels and shaping channels. Specifically, we move the skyrmions within the channel in both directions and manipulate the shape of the topological domain walls to achieve customized transformation. This work will evolve towards a more flexible regulatory plan for tailoring optical-skyrmion arrays, and this is of great significance for research in fields such as optical storage and super-resolution microimaging.
... The birefringent meta-pillar is rotated with a rotation angle of δ that is able to perform circular polarization (CP) conversion jLi ! e i2δ |R〉 and jRi ! e Ài2δ jLi, i.e., the LCP and RCP beams are converted to the opposite spin with a geometric phase (or Pancharatnam-Berry (PB) phase) ϕ geometric of 2δ and À2δ, respectively. The combination of the propagation phase and geometric phase enables the decoupling of RCP and LCP light at the designed wavelength for multiplexing wavefront modulation applications 30 . Given the desired phase of two orthogonal CP light ϕ RCP and ϕ LCP , the required propagation phase and geometric phase at each meta-pillar can be calculated as 31 ...
Artificial intelligence has gained significant attention for exploiting optical scattering for optical encryption. Conventional scattering media are inevitably influenced by instability or perturbations, and hence unsuitable for long-term scenarios. Additionally, the plaintext can be easily compromised due to the single channel within the medium and one-to-one mapping between input and output. To mitigate these issues, a stable spin-multiplexing disordered metasurface (DM) with numerous polarized transmission channels serves as the scattering medium, and a double-secure procedure with superposition of plaintext and security key achieves two-to-one mapping between input and output. In attack analysis, when the ciphertext, security key, and incident polarization are all correct, the plaintext can be decrypted. This system demonstrates excellent decryption efficiency over extended periods in noisy environments. The DM, functioning as an ultra-stable and active speckle generator, coupled with the double-secure approach, creates a highly secure speckle-based cryptosystem with immense potentials for practical applications.
... Nowadays, polarization encoding in conventional platforms, such as image displays based on liquid crystals 14 or micro-wire grating polarizer arrays, are based on the projection relation between linear polarizations, as the conventional ML refers to the linear polarization basis. Recent advances in metasurfaces have enabled several breakthroughs in polarization control, enabling simultaneous amplitude and phase retardation modulation beyond linear polarization basis over an ultrathin and agile platform 15,16 , greatly expanding the scope of polarization manipulation and empowering intriguing applications such as metasurface vectorial holography [17][18][19][20][21] , quantum entanglement 22,23 , and polarization imaging [24][25][26][27] . Metasurfaces also provide a powerful platform for polarization information encoding in a pixelated level by treating each unit cell as a local waveplate or polarizer. ...
As a fundamental property of light, polarization serves as an excellent information encoding carrier, playing significant roles in many optical applications, including liquid crystal displays, polarization imaging, optical computation and encryption. However, conventional polarization information encoding schemes based on Malus’ law usually consider 1D polarization projections on a linear basis, implying that their encoding flexibility is largely limited. Here, we propose a Poincaré sphere (PS) trajectory encoding approach with metasurfaces that leverages a generalized form of Malus’ law governing universal 2D projections between arbitrary elliptical polarization pairs spanning the entire PS. Arbitrary polarization encodings are realized by engineering PS trajectories governed by either arbitrary analytic functions or aligned modulation grids of interest, leading to versatile polarization image transformation functionalities, including histogram stretching, thresholding and image encryption within non-orthogonal PS loci. Our work significantly expands the encoding dimensionality of polarization information, unveiling new opportunities for metasurfaces in polarization optics for both quantum and classical regimes.
... A metasurface can manipulate amplitude, phase, and polarization at a subwavelength scale [8]. With these merits of metasurfaces, many applications like focusing, holography, and polarization control [9][10][11][12] have been realized. The PVB and perfect vortex beams and HOPS beams can also be generated by metasurfaces [13][14][15][16]. ...
A high-order Poincaré sphere (HOPS) can be used to describe high-order modes of waveguides and vector beams, since it generalizes the feature of spin and the orbital angular momentum of light. HOPS beams are such beams with polarization states on the HOPS, which have potential applications in optical manipulation and optical communication. In general, the intensity distribution of this kind of beam changes with the topological charge, which limits their practical applications. Based on the concept of perfect vortex beams (PVBs), perfect HOPS beams have been proposed to solve this problem. Here, a flexible and compact scheme based on all-dielectric metasurfaces for realizing and manipulating perfect HOPS beams at near-infrared wavelength was demonstrated. Geometric-phase-only manipulation was employed for simultaneously controlling the phase and polarization of the incident light. By varying the incident polarization, several selected polarization states on the HOPS could be realized by the proposed metasurface. Further, the single ultra-thin metasurface can also realize high quality multiplexing perfect HOPS beams that carry different topological charges. Finally, a cascaded metasurface system has been proposed for generating and manipulating multiple HOPS beams. This compact flat-optics-based scheme for perfect HOPS beam generation and manipulation demonstrated here can be used for on-chip optical manipulation and integrated optical communication in the future.
... Our results should inspire new directions in engineering topological quantum states, for instance, for a quantum version of vectorial holography 49 , and could benefit from resonant metasurfaces for compact sources of such states 50 . The fact that the Skyrme number can take any quantized integer value should also inspire the use of non-local topology as a high-dimensional encoding alphabet, which can be useful for quantum communication and information processing. ...
In the early 1960s, inspired by developing notions of topological structure, Tony Skyrme suggested that sub-atomic particles can be described as natural excitations of a single quantum field. Although never adopted for its intended purpose, the notion of a skyrmion as a topologically stable field configuration has proven to be highly versatile, finding application in condensed-matter physics, acoustics and more recently, optics, but it has been realized as localized fields and particles in all instances. Here we report the first non-local quantum entangled state with a non-trivial topology that is skyrmionic in nature, even though each individual photon has no salient topological structure. We demonstrate how the topology makes such quantum states robust to smooth deformations of the wavefunction, remaining intact until the entanglement itself vanishes. Our work points to a nascent connection between entanglement classes and topology, opens exciting questions into the nature of map-preserving quantum channels and offers a promising avenue for the preservation of quantum information by topologically engineered quantum states that persist even when entanglement is fragile.
... Metasurfaces or flat optics refer to subwavelength-spaced arrays of scatterers with spatially varying geometries (shape, size, and orientation) and have been widely utilized as a compact wavefront shaping tool [1][2][3][4][5][6][7][8][9]. Metasurfaces made of shape-birefringent nanofins have unlocked many possibilities in polarization optics ranging from vectorial structured light and holography to imaging and polarimetry [10][11][12][13][14][15][16][17]. While many wavefront shaping capabilities have been demonstrated using plasmonic metasurfaces [18][19][20][21][22][23][24], dielectric metasurfaces have gained much attention recently, especially for phase and polarization control, due to their relatively low loss. ...
Flat optics or metasurfaces have opened new frontiers in wavefront shaping and its applications. Polarization optics is one prominent area which has greatly benefited from the shape-birefringence of metasurfaces. However, flat optics comprising a single layer of meta-atoms can only perform a subset of polarization transformations, constrained by a symmetric Jones matrix. This limitation can be tackled using metasurfaces composed of bilayer meta-atoms but exhausting all possible combinations of geometries to build a bilayer metasurface library is a very daunting task. Consequently, bilayer metasurfaces have been widely treated as a cascade (product) of two decoupled single-layer metasurfaces. Here, we test the validity of this assumption for dielectric metasurfaces by considering a metasurface made of titanium dioxide on fused silica substrate at a design wavelength of 532 nm. We explore regions in the design space where the coupling between the top and bottom layers can be neglected, i.e., producing a far-field response which approximates that of two decoupled single-layer metasurfaces. We complement this picture with the near-field analysis to explore the underlying physics in regions where both layers are strongly coupled. We also show the generality of our analysis by applying it to silicon metasurfaces at telecom wavelengths. Our unified approach allows the designer to efficiently build a multi-layer dielectric metasurface, either in transmission or reflection, by only running one full-wave simulation for a single-layer metasurface.
... Metasurfaces [1] are gaining momentum in scientific research for the advantages in controlling properties of light such as phase [2] , intensity [3] , and polarization [4] . These properties have recently extended the scope of metasurfaces for use in holography. ...
... In particular, metasurface conventionally fabricated on an ultra-thin interface via nanofabrications, modulates the wavefront of light through spatially varying geometric structures [6,7]. Since the optical response of a metasurface is engineered locally addressing large degrees of freedom, it has become a mainstay platform for harnessing the intrinsic high-dimension of light, such as amplitude, phase, polarization and wavelength, etc [8][9][10]. In contrast to the fast development of light field manipulation, the integrated optical detection systems for multi-dimensional light fields are only emerging recently [11][12][13], although they have important applications in optical communications, biomedical imaging and autonomous vehicles [12]. ...
The complete description of a continuous-wave light field includes its four fundamental properties: wavelength, polarization, phase and amplitude. However, the simultaneous measurement of a multi-dimensional light field of such four degrees of freedom is challenging in conventional optical systems requiring a cascade of dispersive and polarization elements. In this work, we demonstrate a disordered-photonics-assisted intelligent four-dimensional light field sensor. This is achieved by discovering that the speckle patterns, generated from light scattering in a disordered medium, are intrinsically sensitive to a high-dimension light field given their high structural degrees of freedom. Further, the multi-task-learning deep neural network is leveraged to process the single-shot light-field-encoded speckle images free from any prior knowledge of the complex disordered structures and realizes the high-accuracy recognition of full-Stokes vector, multiple orbital angular momentum (OAM), wavelength and power. The proof-of-concept study shows that the states space of four-dimensional light field spanning as high as 1680=4 (multiple-OAM) $$\times$$ × 2 (OAM power spectra) $$\times$$ × 15 (multiple-wavelength) $$\times$$ × 14 (polarizations) can be well recognized with high accuracy in the chip-integrated sensor. Our work provides a novel paradigm for the design of optical sensors for high-dimension light fields, which can be widely applied in optical communication, holography, and imaging.
... Conventional refractive optical components, allowing precise control of the optical wavefront by relying on gradual phase accumulations as light propagates through bulky media, are generally bulky, costly, and time-consuming to manufacture with high precision, which significantly hinders their application, especially in miniaturized and highly integrated devices. In recent years, metasurfaces, consisting of subwavelength-spaced phase shifters at an interface, have emerged as a flexible platform for shaping the wavefront by tailoring the phase, amplitude, and polarization at will, enabling the realization of various ultracompact optical components, ranging from lenses, 1-6 holograms, [7][8][9][10] and carpet cloaks 11,12 to beam deflectors. [13][14][15] Among these devices, metalenses, metasurfaces encoded with hyperbolical phase profiles, have attracted intense attention due to their great potential for future efficient portable or wearable optical devices with small footprints and light weights. ...
... Metasurfaces, as two-dimensional metamaterials, have drawn considerable attention due to their unprecedented capabilities of tailoring the electromagnetic (EM) wave front [13][14][15][16][17][18][19]. By directly introducing abrupt changes of phase, numerous intriguing functionalities have been realized with metasurfaces made of arrays of scatters, such as holography [20][21][22], flat lensing [23,24], optical vortices generation [25,26], and also RCS reduction [27][28][29][30][31][32][33][34][35][36][37]. ...
This paper presents a novel metasurface design strategy to realize broadband radar cross section (RCS) reduction. The phase distribution across the metasurface aperture can be regard as applying an additional parabolic phase upon periodic arranged parabolic subarrays. Such design fully utilizes the diffusive scattering nature of the parabolic phase distribution. Since the proposed metasurface is governed by only two focal lengths, the optimization procedure is quite easy compared to metasurface with random coding sequence. Experimental results show that the proposed metasurface can achieve more than 10 dB RCS reduction from 7.52 GHz to 19.66 GHz with a fractional bandwidth of 89.3% under both linearly and circularly polarized normal incidences, and keeping a performance of more than 7 dB RCS reduction until the incident angle increases to 40° for both x-polarized and y-polarized incidences in the frequency range of 8-19.35 GHz. When the incident angle increases to 60°, 7 dB RCS reduction can still be obtained for x-polarized incidence from 7.9 GHz to 19.35 GHz with a fractional bandwidth of 84%.
... Recent years have seen a surge of interest in the advancement of transmitters with diverse functionalities, aiming to enhance information capacity in various fields such as sensing and imaging systems. Over the past decade, the fields of antenna array design and pattern synthesis have witnessed a remarkable transformation through the advent of metasurfaces [1][2][3][4][5][6] . These artificial structures have introduced a new paradigm for manipulating electromagnetic waves, enabling precise control over properties such as amplitude, phase, polarization, and frequency [7][8][9][10][11][12][13][14] . ...
Multi-diverse metasurfaces play a crucial role in enhancing the capacity of sensing, radar, imaging, and communication systems through electromagnetic wave manipulation across different diversity controls. Currently, the primary approach for achieving multidimensional manipulation is through the use of dynamic metasurfaces. However, this method has drawbacks when it comes to fast sensing and imaging because of limitations in pattern switching speed. To address this issue, we propose a novel microwave-to-millimeter-wave meta-atom that provides polarization and frequency diversities. The meta-atoms formed in an array with a disordered permutation enable a wide-angle near-field fast sensing for tracking the moving trajectory of an object. Moreover, employing a dispersion-engineered strategy to arrange the meta-atoms in an array allows for high-gain through-wall imaging, enabling the detection of a sparse object with varying shapes and positions. The achieved result confirms that the proposed technology paves the way for developing multi-diverse metasurfaces that possess fast detecting and through-wall imaging capabilities. This breakthrough creates opportunities for identifying previously unseen modalities, and opens up new possibilities in various applications such as autonomous vehicles, all-weather sensing in surveillance, and radar integrated communication systems in 6G and beyond.
... Metamaterials, with their exotic electromagnetic characteristics not found in natural materials, have paved the way for numerous applications and devices previously considered unreachable [1]. In recent years, a flat meta-material with sub-wavelength thickness called metasurface has been a central area of research due to its broad spectrum of applications such as negative refraction, electromagnetic cloaking [2][3][4], perfect lensing [5][6][7][8], holography [9,10] and polarization control [11][12][13][14], low-profile broadband antennas [15][16][17], polarizers [18], and super-resolution imaging [19]. The sub-wavelength unit cells or meta-atoms can be engineered to obtain a desirable, effective electromagnetic response with which the amplitude, phase and polarization of illuminated EM waves can be controlled [20][21][22][23][24][25][26]. ...
In this article, a single-layer reflective anisotropic metasurface (MS) is proposed, which presents both half- and quarter-wave plate operation in different microwave frequency regimes. The unit cell of the proposed metasurface consists of a tilted rectangular plane with triangular ends accompanied by an equidistant-filled triangle on both sides. The unit cell is printed on a dielectric substrate backed by a metallic plane. The proposed meta-plate transforms horizontal polarization into vertical and vice versa in two wide frequency bands, 7.1-15.3 GHz and 19.8-21.7 GHz. Similarly, a linearly polarized (LP) wave is transformed into a circularly polarized (CP) wave and vice versa at 7.9 GHz and 21.8 GHz. The wide bandwidth is acquired through three plasmonic resonances occurring at 8.2 GHz, 12.7 GHz and 20.8 GHz, where the cross-polarization conversion ratio reaches almost 100%. Moreover, quarter and half-wave plate operations occurring at 7.9 GHz and 7.1-15.3 GHz, respectively, are robust to changes in oblique incidence angle (up to 45°) both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The physical mechanism behind polarization conversion is also explained through surface current distribution. The proposed meta-plate structure is fabricated and validated through experimental measurements. The wide bandwidth, high efficiency, angular stability, and simple structure make the proposed metastructure incredible for numerous microwave applications such as antennas, radars, and satellite communication.
... On the other hand, it has been shown that a new class of subwavelength optical elements, metasurface [15][16][17][18][19][20][21][22][23][24][25], may serve as an ultracompact and versatile platform to manipulate the amplitude [26][27][28][29][30], phase [31][32][33][34][35], and polarization [35][36][37][38][39][40][41][42][43] of light over a short light propagation distance. Specifically, for polarization manipulation, waveplate-type metasurface based on birefringence has been proposed for arbitrary SOP conversion [35,42,43]. ...
The combination of conventional polarization optical elements, such as linear polarizers and waveplates, is widely adopted to tailor light’s state of polarization (SOP). Meanwhile, less attention has been given to the manipulation of light’s degree of polarization (DOP). Here, we propose metasurface-based polarizers that can filter unpolarized incident light to light with any prescribed SOP and DOP, corresponding to arbitrary points located both at the surface and within the solid Poincaré sphere. The Jones matrix elements of the metasurface are inverse-designed via the adjoint method. As prototypes, we experimentally demonstrated metasurface-based polarizers in near-infrared frequencies that can convert unpolarized light into linear, elliptical, or circular polarizations with varying DOPs of 1, 0.7, and 0.4, respectively. Our Letter unlocks a new degree of freedom for metasurface polarization optics and may break new ground for a variety of DOP-related applications, such as polarization calibration and quantum state tomography.
... Metasurfaces composed of subwavelength structure arrays have been actively studied to replace conventional bulky optics, and with the exceptional ability to modulate light at the nanoscale have been applied to numerous applications such as metalenses 9,10 , biosensors 11,12 , metaholograms [13][14][15][16][17][18][19][20][21] , and color printing [22][23][24][25][26] . However, UV metasurfaces have long faced challenges such as a lack of UV transparent materials and high-resolution patterning techniques with low cost and high throughput. ...
A single-step printable platform for ultraviolet (UV) metasurfaces is introduced to overcome both the scarcity of low-loss UV materials and manufacturing limitations of high cost and low throughput. By dispersing zirconium dioxide (ZrO2) nanoparticles in a UV-curable resin, ZrO2 nanoparticle-embedded-resin (nano-PER) is developed as a printable material which has a high refractive index and low extinction coefficient from near-UV to deep-UV. In ZrO2 nano-PER, the UV-curable resin enables direct pattern transfer and ZrO2 nanoparticles increase the refractive index of the composite while maintaining a large bandgap. With this concept, UV metasurfaces can be fabricated in a single step by nanoimprint lithography. As a proof of concept, UV metaholograms operating in near-UV and deep-UV are experimentally demonstrated with vivid and clear holographic images. The proposed method enables repeat and rapid manufacturing of UV metasurfaces, and thus will bring UV metasurfaces more close to real life. Facile nanostamping of the high-refractive index nanoparticle-embedded-resin for the direct fabrication of highly efficient metaholographic devices down to the deep-ultraviolet region.
... In this way, the intensity distribution of the target image I(x, y) becomes I(−x, −y) and these two images are centrosymmetric. To fully eliminate the twin image, additional degrees of freedom must be included in the phase modulation method, such as using a point source with varied locations [34] or utilizing the spatial freedom of the pixeled meta-atom [35,36]. A change of incident spin can therefore be seen as a mirror operation and both holographic images are always visible. ...
Metasurface-generated holograms have emerged as a unique platform for arbitrarily shaping the reflected/transmitted wavefronts with the advantages of subwavelength large pixel sizes and multiple information channels. However, achieving multiple holographic images with large operation bandwidths is a rather complicated and arduous issue due to the dissimilar dispersion of all meta-atoms involved. In this work, we design and experimentally demonstrate single-celled metasurfaces to realize broadband and spin-multiplexed holograms, whose phase modulation is based only on the geometric phase supplied by a judiciously designed high-performance nanoscale half-wave plate operating in reflection. Four different multiplexing strategies are implemented, and the resulting holograms are systemically assessed and compared with respect to background levels, image fidelities, holograms efficiencies, and polarization conversion ratios. Our work complements the methodologies available for designing multiplexed meta-holograms with versatile functionalities.
Light-emitting diodes (LEDs) have been known as the most widely used light source in lighting and displays for more than 60 years. There is still room for progress in the performance of LEDs, especially since the current devices with various types of different light-emitting layer materials have converged to unity in terms of internal quantum efficiency, and there is an urgent need to improve the light extraction efficiency. Metasurfaces (MSs) have received attention from researchers as structures that can be integrated with LEDs to efficiently modulate the phase and amplitude of light through resonance and scattering, which can reduce light loss. This paper reviews the development of metasurfaces in LEDs so far. The different working mechanisms of metasurfaces composed of different materials are first analyzed in depth. Subsequently, three aspects of light extraction, angle change, and polarization modulation are described in detail according to different applications of metasurfaces in LEDs. Finally, the current status of metasurface applications in LEDs is summarized, and the future development prospects are envisioned.
Recently, metasurfaces have received widespread attention due to their superior performance in regulating the physical properties of light. In the field of optical encryption, the most common methods utilizing metasurfaces mainly include metasurface coloration, malus metasurfaces and metasurface holography. However, such methods are complex to achieve and prone to noise interference. Here, a spin and intensity multiplexed compact metasurface optical element is proposed and its feasibility for stable optical encryption is verified through simulations. Based on the photon spin Hall effect, a series of optical ciphertexts are generated with continuous changes in the spin state and intensity. As a concept demonstration, this spin and intensity multiplexed encryption metasurface will promote advanced applications of metasurfaces in many fields, such as optical communication and holography.
The diffraction-free beams with curved trajectories and shaped wavefronts have wide application prospects in many fields. This paper proposes the generation of diffraction-free beam with winding trajectory and spiral wavefront based on holographic metasurface. The holographic metasurface consists of rotated rectangular nanoholes and the winding trajectory for the generated diffraction-free beam may be in two or three dimensional space under the control of the rotated nanoholes. The multiple diffraction-free beams are exemplified and the performance of holographic metasurfaces are testified by the simulation and experiment results. The utilization of compact metasurface enables the flexible generation of the diffraction-free beams with complex trajectories and tailored wavefronts. It may bring more new applications of diffraction-free beams with on-demand trajectories and customized wavefronts.
Replacing the conventional imaging optics in machine vision systems with diffractive optical neural networks (DONNs) that leverage spatial light modulation and optical diffraction have been promising to enable new machine learning intelligence and functionality in optical domain and reduce computing energy and resource requirements in electrical domain. In this chapter, the fundamental models to describe and design DONNs are first reviewed. Passive DONNs systems operating in the terahertz and short wavelength ranges are then introduced. Moreover, the advanced architectures that are resilient to hardware imperfections, that demonstrate improved performance, and that are implemented in photonic integrated circuits, are discussed. Furthermore, the implementations of system reconfigurability through hybrid optoelectronic approaches are described. In addition, the effects from the physical model inaccuracy and how physics-aware training is used to correct deployment errors from both models and hardware are discussed. Finally, an all-optical reconfigurable DONNs system based on cascaded liquid-crystal spatial light modulators is demonstrated.
Vectorial holography through a strongly scattering medium can facilitate various applications in optics and photonics. However, the realization of vectorial holography with arbitrary distribution of optical intensity is still limited because of experimental noise during the calibration of vectorial transmission matrix (TM) and reconstruction noise during the retrieval of input wavefront for a given holographic target. Herein, we propose and experimentally demonstrate the vectorial holography with arbitrary distribution of optical intensity over a multimode fiber (MMF) using the Tikhonov regularization. By optimizing the noise factor, the performance of vectorial holography over an MMF is improved compared with the conjugate transpose and inverse TM methods. Our results might shed new light on the optical communication and detection mediated by MMFs.
Metasurfaces have great advantages in the field of laser detection because of their ability to generate large amounts of point sources or various diffraction patterns. Here,cascaded metasurfaces (CM) for generating switchable spatial light distributions is utilized, which can be used for optical scanning and identifications. The light distribution is composed of several distinct diffraction patterns, and the scanning of the diffraction space is realized by multiple pixel‐scale alignment strategies between two pieces of CM. Through combining Dammann optimization and the gradient descent method, various diffraction patterns under different matching situations can be guaranteed by phase superposition. Various diffraction conditions with highly identifiable intensity distribution are guaranteed by using the optimization method. Such optical scanning devices based on CM have small footprints, high integration, flexible composition, and stable diffractive combination features. By manipulating CM to generate changeable spatial diffraction phenomenon may provide flexible modulation properties to optical scanning, measurement, and other applications.
Exceptional points (EPs) can achieve intriguing asymmetric control in non-Hermitian systems due to the degeneracy of eigenstates. Here, we present a general method that extends this specific asymmetric response of EP photonic systems to address any arbitrary fully-polarized light. By rotating the meta-structures at EP, Pancharatnam-Berry (PB) phase can be exclusively encoded on one of the circular polarization-conversion channels. To address any arbitrary wavefront, we superpose the optical signals originating from two orthogonally polarized -yet degenerate- EP eigenmodes. The construction of such orthogonal EP eigenstates pairs is achieved by applying mirror-symmetry to the nanostructure geometry flipping thereby the EP eigenmode handedness from left to right circular polarization. Non-Hermitian reflective PB metasurfaces designed using such EP superposition enable arbitrary, yet unidirectional, vectorial wavefront shaping devices. Our results open new avenues for topological wave control and illustrate the capabilities of topological photonics to distinctively operate on arbitrary polarization-state with enhanced performances.
Diffractive optical elements (DOEs) are intricately designed devices with the purpose of manipulating light fields by precisely modifying their wavefronts. The concept of DOEs has its origins dating back to 1948 when D. Gabor first introduced holography. Subsequently, researchers introduced binary optical elements (BOEs), including computer-generated holograms (CGHs), as a distinct category within the realm of DOEs. This was the first revolution in optical devices. The next major breakthrough in light field manipulation occurred during the early 21st century, marked by the advent of metamaterials and metasurfaces. Metasurfaces are particularly appealing due to their ultra-thin, ultra-compact properties and their capacity to exert precise control over virtually every aspect of light fields, including amplitude, phase, polarization, wavelength/frequency, angular momentum, etc. The advancement of light field manipulation with micro/nano-structures has also enabled various applications in fields such as information acquisition, transmission, storage, processing, and display. In this review, we cover the fundamental science, cutting-edge technologies, and wide-ranging applications associated with micro/nano-scale optical devices for regulating light fields. We also delve into the prevailing challenges in the pursuit of developing viable technology for real-world applications. Furthermore, we offer insights into potential future research trends and directions within the realm of light field manipulation.
Metasurface‐based vectorial holography manifests itself as an advanced platform for large‐capacity information storage, holographic display, and cryptography. However, a convenient and effective reconfigurable vectorial hologram generation mechanism still remains a challenge. Here, a rotation‐driven reconfigurable vectorial holography scheme is developed via a dual‐layer hybrid metasurface device, in which radiation‐type and birefringent metasurfaces are cascaded hybridly. Thus, reconfigurable and highly customizable intensity and polarization response of holograms in the 3D space is achieved. Rotatable radiation‐type metasurface (RTM) serves as an incidence‐wavefront modulator to excite the non‐rotatable birefringent metasurface (BM). The gradient descent optimization inverse design method is introduced to achieve the high‐efficiency reconstruction of the Jones vector and Jones matrix distribution on both RTM and BM. On this basis, numerical analysis and experimental verification of 3‐D reconfigurable vectorial holography are demonstrated in the microwave region. This scheme implies a new paradigm for 3‐D reconfigurable vectorial holography and can lead to advances in high‐capacity optical display, switchable meta‐devices, and cryptography.
Optical metasurfaces (OMs) offer unprecedented control over electromagnetic waves, enabling advanced optical multiplexing. The emergence of deep learning has opened new avenues for designing OMs. However, existing deep learning methods for OMs primarily focus on forward design, which limits their design capabilities, lacks global optimization, and relies on prior knowledge. Additionally, most OMs are static, with fixed functionalities once processed. To overcome these limitations, we propose an inverse design deep learning method for dynamic OMs. Our approach comprises a forward prediction network and an inverse retrieval network. The forward prediction network establishes a mapping between meta-unit structure parameters and reflectance spectra. The inverse retrieval network generates a library of meta-unit structure parameters based on target requirements, enabling end-to-end design of OMs. By incorporating the dynamic tunability of the phase change material Sb 2 Te 3 with inverse design deep learning, we achieve the design and verification of dynamic multifunctional OMs. Our results demonstrate OMs with multiple information channels and encryption capabilities that can realize multiple physical field optical modulation functions. When Sb 2 Te 3 is in the amorphous state, near-field nano-printing based on meta-unit amplitude modulation is achieved for X -polarized incident light, while holographic imaging based on meta-unit phase modulation is realized for circularly polarized light. In the crystalline state, the encrypted information remains secure even with the correct polarization input, achieving double encryption. This research points towards ultra-compact, high-capacity, and highly secure information storage approaches.
A beam shaping method based on the vectorial diffraction is proposed in this paper. We modify the Rayleigh–Sommerfeld vectorial diffraction integrals based on the time reversal symmetry of Maxwell’s equations. Thus, the forward and backward vectorial diffraction transformations can maintain the self-consistency of the iterative beam propagations in the vectorial diffraction beam shaping system. The proposed method can be used to design a phase plate that can be used to reconstruct an optical field with the desired intensity distribution. The proposed method is more rigorous than the scalar diffraction-based method and has constraints on the design of each component of the optical field.
Taking advantage of multimaterial additive manufacturing, this work demonstrates a kind of polarization‐maintaining metasurface (MS) for spin‐decoupled beam shaping. The wavefronts of the two spin states, i.e., the left‐hand circular polarization (LHCP) and the right‐hand circular polarization (RHCP), can be independently manipulated while the output spin state remains the same as the input. The meta‐atom is implemented with dual‐polarized antennas at the top and the bottom with phase delay lines connecting them. The dual‐polarized antenna on the receiving side is fixed to receive the LHCP/RHCP incident waves, while the dual‐polarized transmitting antenna is rotated, providing the opposite phase shifts for the LHCP and RHCP. The absolute value of the phase shift is the same as the transmitting antenna's rotation angle. Meanwhile, varying the length of phase delay lines introduces 2π phase shifts for both LHCP and RHCP inputs. Thus, combining the two phase‐shifting degrees of freedom, the LHCP and RHCP wavefronts can be independently controlled while the polarization is not flipped after transmitting through the MS. One MS produces vortex beams with different topological charges for LHCP and RHCP. The other achieves spin‐decoupled focusing. The multilayered MSs are conveniently printed using multimaterial additive manufacturing without postprocessing.
Scattered optical field modulations can enable the function of traditional optical technologies, such as the dynamic holographic display, in a scattering environment. Nonetheless, only part of the degrees of freedom in the optical field can be effectively modulated so far. Here, this work proposes spatial full degree‐of‐freedom scattered optical field modulation (SF‐SOM) to impose a control on the amplitude, phase, and polarization of the optical field. To do so, this method independently modulates the complex amplitude of two orthogonally polarized components. It also contains a full degree‐of‐freedom vector transmission matrix model to describe the transformation from the incident field to the scattered field. Compared with the single degree‐of‐freedom modulation methods against the same scattering environment, SF‐SOM increases the contrast of focus by a factor of five. Furthermore, the experiments demonstrate a holographic display and orbital angular momentum control with SF‐SOM to show its ubiquitous utility in optics.
The design of wavefront-shaping devices is conventionally approached using real-frequency modeling. However, since these devices interact with light through radiative channels, they are by default non-Hermitian objects having complex eigenvalues (poles and zeros) that are marked by phase singularities in a complex frequency plane. Here, by using temporal coupled mode theory, we derive analytical expressions allowing to predict the location of these phase singularities in a complex plane and as a result, allowing to control the induced phase modulation of light. In particular, we show that spatial inversion symmetry breaking—implemented herein by controlling the coupling efficiency between input and output radiative channels of two-port components called metasurfaces—lifts the degeneracy of reflection zeros in forward and backward directions, and introduces a complex singularity with a positive imaginary part necessary for a full $2\pi$ 2 π -phase gradient. Our work establishes a general framework to predict and study the response of resonant systems in photonics and metaoptics.
The ever‐growing demand for ultracompact micro‐ and nano‐optics is guided by efficient applications in augmented/virtual reality, displays, and Fourier optics. The current technologies, mainly based on meta‐solutions, suffer in terms of efficiency and tunability, as well as complex and multi‐step fabrication methods that may limit their full‐scale potential. Herein, a broadband laser composed of close and highly correlated lines allows, via interference patterning, for simultaneous encoding of multiplexed, independent, and cross‐talk free holograms with nanometric separation. The reported findings show that such light, unusual for holographic recording, unlocks new features of organized collective phenomena, overcoming the usual spatial resolution limitations of the optical techniques. This approach gives promising perspectives for in situ design of reconfigurable structured optics, besides the obvious advantages of full‐scalability, easiness, cost effectiveness, and time and energy consumption.
Polarization and wavelength are two important properties of light for understanding optics. Engineered polarization and wavelength profiles have received considerable interest due to their unusual optical features and more degrees of freedom. However, to simultaneously control polarization and wavelengths, conventional methods suffer from big pixel size, complicated fabrication process, and limited levels in phase control. The unprecedented capability of metasurfaces in the light control has shown much promise to tackle these challenges. Polarization digital numbers with ten different wavelengths are proposed and experimentally realized. A geometric metasurface is used to simultaneously realize wavelength multiplexing, phase multiplexing, and polarization rotation, creating wavelength‐selective polarization digital numbers. A deep learning approach is used to increase the identification accuracy of the digital numbers. The approach can simultaneously control wavelength and polarization, providing more design flexibility. This work may find applications in many fields such as virtual reality, image steganography, and anti‐counterfeiting.
The capability to dynamically modulate electromagnetic wavefronts can revolutionize and be crucial for future wireless technology. Electromagnetic waves can be fundamentally described in terms of amplitude, phase, polarization, and angular frequency. However, reported reconfigurable metasurfaces can only control one or two fundamental parameters and require different tuning/switching elements or materials that remain challenging to control those continuously. In this work, an approach is presented for designing electrically tunable reflective metasurfaces that enable independent and simultaneous control of amplitude and phase, while also providing frequency tuning capability. This is achieved by arranging two varactor diodes on the top layer and a lumped resistor on the bottom layer. The proposed metasurface is fabricated and several electromagnetic functionalities experimentally demonstrated as proof‐of‐concept applications, including reflector, radar absorbing, dual and single‐beam steering, and amplitude control. The proposed metasurface will open avenues for realizing advanced multifunctional devices to fully control electromagnetic parameters, offering numerous applications in future communication technologies, radar systems, and information processing.
Recent rapid progress in metasurfaces is underpinned by the physics of local and nonlocal resonances and the modes coupling among them, leading to tremendous applications such as optical switching, information transmission, and sensing. In this review paper, we provide an overview of the recent advances in a broad range of dimensional optical field manipulation based on metasurfaces categorized into different classes based on design strategies. We start from the near-field optical resonances of artificial nanostructures and discuss the far-field optical wave manipulation based on fundamental mechanisms such as mode generation and mode coupling. We summarize the recent advances in optical field manipulation based on metasurfaces in different optical dimensions such as phase and polarization and discuss newly-developed dimensions, such as the orbital angular momentum and the coherence dimensions resulting from phase modulation. Then, we review the recent achievements of multiplexing and multifunctional metasurfaces empowered by multidimensional optical field manipulation for optical information transmission and integrated applications. Finally, we conclude with a few perspectives on emerging trends, possible directions, and existing challenges in this fast-developing field. This article is protected by copyright. All rights reserved.
Metasurfaces can perform high-performance multi-functional integration by manipulating the abundant physical dimensions of light, demonstrating great potential in high-capacity information technologies. The orbital angular momentum (OAM) and spin angular momentum (SAM) dimensions have been respectively explored as the independent carrier for information multiplexing. However, fully managing these two intrinsic properties in information multiplexing remains elusive. Here, we propose the concept of angular momentum (AM) holography which can fully synergize these two fundamental dimensions to act as the information carrier, via a single-layer, non-interleaved metasurface. The underlying mechanism relies on independently controlling the two spin eigenstates and arbitrary overlaying them in each operation channel, thereby spatially modulating the resulting waveform at will. As a proof of concept, we demonstrate an AM meta-hologram allowing the reconstruction of two sets of holographic images, i.e., the spin-orbital locked and the spin-superimposed ones. Remarkably, leveraging the designed dual-functional AM meta-hologram, we demonstrate a novel optical nested encryption scheme, which is able to achieve parallel information transmission with ultra-high capacity and security. Our work opens a new avenue for optionally manipulating the AM, holding promising applications in the fields of optical communication, information security and quantum science.
Metasurfaces have exhibited powerful abilities for manipulating multiple fundamental properties of light including amplitude, phase, polarization, and so on. However, these strategies are commonly concentrated on the modulations at a single transverse plane of output light. The spatial evolutions of these properties, especially the polarizations along longitudinal direction, are rarely investigated. Here, a stereo Jones matrix holography method is presented for understanding the spatial evolution including polarization, amplitude, and phase variations along the longitudinal direction. Stereo holographic algorithms in matrix framework are developed to generate multiplane and even continuously varied vectorial holographic images that exhibit distinct polarization states at each transverse plane. This method provides a benchmark of longitudinal polarization transformations as well as beam modulations by simply using a single planar metasurface without extra burdens on optical path. In addition, the obtained propagation‐dependent features can favor the realizing of on‐demand transverse and longitudinal spatial evolution from the perspective of the holographic method. Furthermore, it may also promote the development of related areas including polarization‐switchable devices, optical trapping, microscopy, laser processing, etc. A matrix framework is established for generating stereo vectorial holography by imposing amplitude, phase, and polarization restrictions to specific planes at three‐dimensional space. The reconstructed holographic image can exhibit propagation‐dependent vectorial features under arbitrary polarization incidence. The proposed method may promote the advancement of applications including polarization‐switchable devices, optical trapping, and microscopy, as well as laser processing.
Metasurfaces have provided an unprecedented degree of freedom (DOF) in the manipulation of electromagnetic waves. A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface. Nevertheless, such geometric phases are usually spin-coupled, with the same magnitude but opposite signs for left- and right-handed circularly polarized (LCP and RCP) waves. To achieve independent control of LCP and RCP waves, it is crucial to obtain spin-decoupled geometric phases. In this paper, we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms. Based on the rotational Doppler effect, the rotation manner is first analyzed, and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms. Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other, it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated. To obtain spin-decoupled geometric phases, the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles. In this way, LCP and RCP waves can acquire different geometric phase changes. Proof-of-principle prototypes were designed, fabricated, and measured. Both the simulation and experiment results verify spin-decoupled geometric phases. This work provides a robust means to obtain a spin-dependent geometric phase and can be readily extended to higher frequency bands such as the terahertz, IR, and optical regimes.
Tunability is essential for unlocking a range of practical applications of high‐efficiency metasurface‐based nanophotonic devices and systems. Increased research efforts in this area during recent years led to significant progress regarding tuning mechanisms, speed, and diverse active functionalities. However, so far almost all the demonstrated works are based on a single type of physical stimulus, thereby excluding important opportunities to enhance the modulation range of the metadevices, the available design options, as well as interaction channels between the metadevices and their environment. In this article, it is experimentally demonstrated that multi‐responsive metasurfaces can be realized by combining asymmetric, highly resonant metasurfaces with multi‐responsive polymeric materials. The respective copolymers combine light‐ and temperature‐responsive comonomers in an optimized ratio. This work demonstrates clearly reversible light‐responsive, temperature‐responsive, and co‐responsive tuning of the metasurface optical resonance positions at near‐infrared wavelengths, featuring maximum spectral resonance shifts of nearly twice the full‐width‐at‐half‐maximum and accompanied by more than 60% absolute modulation in transmittance. This work provides new design freedom for multifunctional metadevices and can potentially be expanded to other types of copolymers as well. Furthermore, the studied hybrid multiresponsive systems are promising candidates for multi‐dimensional sensing applications.
The past few years have witnessed exciting developments in non-Hermitian physics, showing unconventional phenomena and unique features associated with exceptional points (EPs). EPs exist in many open systems, leading to a spectral singularity. The research team from CNRS-CRHEA in France collaborating with the University of California, Berkeley in US utilizes the topological feature around an EP to introduce a novel design in metasurface to achieve a new wavefront phase encoding technique. They show that the intriguing polarization response of singular plasmonic meta-atoms encircling an EP leads to 2π-phase modulation on a chosen outgoing channel, which is topologically protected by the EP. In auxiliary, combining the exceptional topological phase with Pancharatnam-Berry phase, they achieve arbitrary wavefront engineering on cross polarization channels independently. Their breakthrough explorations not only provide a new degree of freedom to address optical phase in a full 2π range, but also open the way to a new class of optical and photonic applications.
High-throughput computational imaging requires efficient processing algorithms to retrieve multi-dimensional and multi-scale information. In computational phase imaging, phase retrieval (PR) is required to reconstruct both amplitude and phase in complex space from intensity-only measurements. The existing PR algorithms suffer from the tradeoff among low computational complexity, robustness to measurement noise and strong generalization on different modalities. In this work, we report an efficient large-scale phase retrieval technique termed as LPR . It extends the plug-and-play generalized-alternating-projection framework from real space to nonlinear complex space. The alternating projection solver and enhancing neural network are respectively derived to tackle the measurement formation and statistical prior regularization. This framework compensates the shortcomings of each operator, so as to realize high-fidelity phase retrieval with low computational complexity and strong generalization. We applied the technique for a series of computational phase imaging modalities including coherent diffraction imaging, coded diffraction pattern imaging, and Fourier ptychographic microscopy. Extensive simulations and experiments validate that the technique outperforms the existing PR algorithms with as much as 17dB enhancement on signal-to-noise ratio, and more than one order-of-magnitude increased running efficiency. Besides, we for the first time demonstrate ultra-large-scale phase retrieval at the 8K level ( $$7680\times 4320$$ 7680 × 4320 pixels) in minute-level time.
The performance of metasurfaces measured experimentally often discords with expected values from numerical optimization. These discrepancies are attributed to the poor tolerance of metasurface building blocks with respect to fabrication uncertainties and nanoscale imperfections. Quantifying their efficiency drop according to geometry variation are crucial to improve the range of application of this technology. Here, we present a novel optimization methodology to account for the manufacturing errors related to metasurface designs. In this approach, accurate results using probabilistic surrogate models are used to reduce the number of costly numerical simulations. We employ our procedure to optimize the classical beam steering metasurface made of cylindrical nanopillars. Our numerical results yield a design that is twice more robust compared to the deterministic case.
Metasurfaces provide a compact and powerful platform for manipulating the fundamental properties of light, and have shown unprecedented capabilities in both optical holographic display and information encryption. For increasing information display/storage capacity, metasurfaces with more polarization manipulation channel and full‐color holographic functionality are now an urgent requirement. Here, a minimalist dielectric metasurface with the capability of full‐color holography encoded with arbitrary polarization is proposed and experimentally demonstrated. Without the daunting exploratory and computational problem in nanostructure searching, full‐color holographic images can be multiplexed into arbitrary polarization channels through vectorial ptychography and k‐space ptychography based on tetratomic macropixel geometric phase metasurfaces. Thanks to the full degree of freedom tuning in polarization and color spaces, the application scenarios such as holographic 3D imaging and information encryption are realized. The strategy exhibits promising potential in applications of 3Dl display, augmented/virtual reality, high‐density data storage, and encryption. A minimalist metasurface assembling geometric phase meta‐atoms in a tetratomic macro pixel is proposed, which enables the full degree of freedom tuning in polarization (orientation, ellipticity, and chirality) and color (real hue, saturation, and brightness) spaces simultaneously. The proposed strategy has great potential in multiplex‐oriented applications, such as holographic data storage and information transfer.
Metasurfaces achieving arbitrary phase profiles within ultrathin thickness, emerge as miniaturized, ultracompact, and kaleidoscopic nanophotonic platforms. However, it is often required to segment or interleave independent subarray metasurfaces to multiplex holograms in a single nanodevice, which in turn affects the device's compactness and channel capacity. Here, a flexible strategy is proposed for multiplexing vectorial holographic images by controlling the phase distributions of holographic images in far field. Benefitting from precisely controlling the phase difference of reconstructed images through the modified Gerchberg–Saxton algorithm, two different holographic images are independently designed for the circular light by two interleaved metasurfaces and an extra vectorial hologram is flexibly encrypted in far field without additional set of structures on the metasurface plane. An unlimited number of polarization can be achieved in the holographic image and additional information can be decrypted when different polarization‐dependent holographic images overlap. By continually varying phase difference between the incident right and left circular polarized light, the image within the overlap area can be modulated. The silicon dielectric metahologram with record absolute multiplexed efficiency (>25%) is achieved in the experiment. This technique, as far as it is known, promises an enormous data capacity as well as a high level of information security.
The Jones matrix is a useful tool to deal with polarization problems, and its number of degrees of freedom (DOFs) that can be manipulated represents its polarization-controlled capabilities. A metasurface is a planar structure that can control light in a desired manner, which, however, has a limited number of controlled DOFs (≤4) in the Jones matrix. Here, we propose a metasurface design strategy to construct a Jones matrix with six DOFs, approaching the upper-limit number of a 2D planar structure. We experimentally demonstrate several polarization functionalities that can only be achieved with high (five or six) DOFs of the Jones matrix, such as polarization elements with independent amplitude and phase tuning along its fast and slow axes, triple-channel complex-amplitude holography, and triple sets of printing-hologram integrations. Our work provides a platform to design arbitrary complex polarization elements, which paves the way to a broader exploitation of polarization optics.
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.
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.
Planar and ultrathin liquid crystal (LC) polarization optical elements have found promising applications in augmented reality (AR), virtual reality (VR), and photonic devices. In this paper, we give a comprehensive review on the operation principles, device fabrication, and performance of these optical elements. Optical simulations methods for optimizing the device performance are discussed in detail. Finally, some potential applications of these devices in AR and VR systems are illustrated and analyzed.
Metasurfaces consisting of subwavelength structures, so‐called meta‐atoms, have steadily attracted considerable attention for advanced holography due to their advantages in terms of high‐resolution holographic images, large field of view, and compact device volume. In contrast to conventional holographic displays using bulky conventional diffractive optical elements, metasurface holography enables arbitrary complex wavefront shaping with a much smaller footprint. In this review, we classify metasurface holography according to the meta‐atom design methodologies, which can further expand hologram functionalities. We describe light‐matter interactions, particularly in metasurface systems, using the relevant the Jones matrix to rigorously explain modulations of the amplitude, phase, and polarization of light. Six different types of meta‐atoms are presented, and the corresponding achievable wavefronts that form the holographic images in the far‐field are also provided. Such a simple classification will give a straightforward approach to design and further realize advanced metasurface holographic devices.
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Vectorial optical fields (VOFs) exhibiting arbitrarily designed wavefronts and polarization distributions are highly desired in photonics. However, current methods to generate them either require complicated setups or exhibit limited functionalities, which is unfavorable for integration-optics applications. Here, we propose a generic approach to efficiently generate arbitrary VOFs based on metasurfaces exhibiting full-matrix yet inhomogeneous Jones-matrix distributions. We illustrate our strategy with analytical calculations on a model system and an experimental demonstration of a meta-device that can simultaneously deflect light and manipulate its polarization. Based on these benchmark results, we next experimentally demonstrate the generation of a far-field VOF exhibiting both a vortex wavefront and an inhomogeneous polarization distribution. Finally, we design/fabricate a meta-device and experimentally demonstrate that it can generate a complex near-field VOF—a cylindrically polarized surface plasmon wave possessing orbital angular momentum—with an efficiency of ~34%. Our results establish an efficient and ultracompact platform for generating arbitrary predesigned VOFs in both the near- and far-fields, which may find many applications in optical manipulation and communications.
With inherent orthogonality, both the spin angular momentum (SAM) and orbital angular momentum (OAM) of photons have been utilized to expand the dimensions of quantum information, optical communications, and information processing, wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated. Here, a single azimuthal-quadratic phase metasurface-based photonic momentum transformation (PMT) is illustrated and utilized for vortex recognition. Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT, OAMs within a large mode space can be determined through a single-shot measurement. Moreover, spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting, which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase. Interestingly, our proposed method can detect vectorial vortices with both phase and polarization singularities, as well as superimposed vortices with a certain interval step. Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and prominent vortex recognition ability, our approach may underpin the development of integrated and high-dimensional optical and quantum systems.
Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications.
Any arbitrary state of polarization of light beam can be decomposed into a linear superposition of two orthogonal oscillations, each of which has a specific amplitude of the electric field. The dispersive nature of diffractive and refractive optical components generally affects these amplitude responses over a small wavelength range, tumbling the light polarization properties. Although recent works suggest the realization of broadband nanophotonic interfaces that can mitigate frequency dispersion, their usage for arbitrary polarization control remains elusively chromatic. Here, we present a general method to address broadband full-polarization properties of diffracted fields using an original superposition of circular polarization beams transmitted through metasurfaces. The polarization-maintaining metasurfaces are applied for complex broadband wavefront shaping, including beam deflectors and white-light holograms. Eliminating chromatic dispersion and dispersive polarization response of conventional diffractive elements lead to broadband polarization-maintaining devices of interest for applications in polarization imaging, broadband-polarimetry, augmented/virtual reality imaging, full color display, etc.
Polarization plays a key role in science; hence its versatile manipulation is crucial. Existing polarization optics, however, can only manipulate polarization in a single transverse plane. Here we demonstrate a new class of polarizers and wave plates—based on metasurfaces—that can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization. The underlying mechanism relies on transforming an incident waveform into an ensemble of pencil-like beams with different polarization states that beat along the optical axis thereby changing the resulting polarization at will, locally, as light propagates. Remarkably, using form-birefringent metasurfaces in combination with matrix-based holography enables the desired propagation-dependent polarization response to be enacted without a priori knowledge of the incident polarization—a behaviour that would require three polarization-sensitive holograms if implemented otherwise. Our work expands the use of polarization in the design of multifunctional metasurfaces and may find application in tunable structured light, optically switchable devices and versatile light–matter interactions. Using a metasurface that allows shaping of the polarization state of a light beam independently at each point of space along its propagation direction, longitudinally variable polarization optical components are demonstrated, inspiring new directions in structured light, polarization-switchable devices and light–matter interaction.
Vectorial optical fields (VOFs) exhibiting tailored wave fronts and spatially inhomogeneous polarization distributions are particularly useful in photonic applications. However, devices to generate them, made by natural materials or recently proposed metasurfaces, are either bulky in size or less efficient, or exhibit restricted performances. Here, we propose a general approach to design metadevices that can efficiently generate two distinct VOFs under illuminations of circularly polarized lights with different helicity. After illustrating our scheme via both Jones matrix analyses and analytical model calculations, we experimentally demonstrate two metadevices in the near-infrared regime, which can generate vortex beams carrying different orbital angular momenta yet with distinct inhomogeneous polarization distributions. Our results provide an ultracompact platform for bifunctional generations of VOFs, which may stimulate future works on VOF-related applications in integration photonics.
A very large dynamic optical reflection modulation from a simple unpatterned layered stack of phase‐change material ultra‐thin films is experimentally demonstrated. Specifically, this work demonstrates that properly designed systems comprising deeply subwavelength GeSbTe (GST) films, a dielectric spacer, and a metallic mirror produce a dynamic modulation of light in the near‐infrared from very strong reflection (up to R≈80%) to perfect absorption (A>99.995%) by simply controlling the crystalline state of the phase‐change material. While the amplitude of modulation experimentally reaches an optical contrast higher than 10⁴, intermediate levels of reflection in between extreme values can also be actively encoded, corresponding to partial crystallization of the GST layer. Several layered system designs are further explored and guidelines are provided to tailor the efficient wavelength range, the angle of operation, and the degree of crystallization leading to perfect absorption.
Digital optical holograms can achieve nanometre-scale resolution as a result of recent advances in metasurface technologies. This has raised hopes for applications in data encryption, data storage, information processing and displays. However, the hologram bandwidth has remained too low for any practical use. To overcome this limitation, information can be stored in the orbital angular momentum of light, as this degree of freedom has an unbounded set of orthogonal helical modes that could function as information channels. Thus far, orbital angular momentum holography has been achieved using phase-only metasurfaces, which, however, are marred by channel crosstalk. As a result, multiplex information from only four channels has been demonstrated. Here, we demonstrate an orbital angular momentum holography technology that is capable of multiplexing up to 200 independent orbital angular momentum channels. This has been achieved by designing a complex-amplitude metasurface in momentum space capable of complete and independent amplitude and phase manipulation. Information was then extracted by Fourier transform using different orbital angular momentum modes of light, allowing lensless reconstruction and holographic videos to be displayed. Our metasurface can be three-dimensionally printed in a polymer matrix on SiO2 for large-area fabrication.
Geometric-phase metasurfaces, recently utilized for controlling wavefronts of circular polarized (CP) electromagnetic waves, are drastically limited to the cross-polarization modality. Combining geometric with propagation phase allows to further control the co-polarized output channel, nevertheless addressing only similar functionality on both co-polarized outputs for the two different CP incident beams. Here we introduce the concept of chirality-assisted phase as a degree of freedom, which could decouple the two co-polarized outputs, and thus be an alternative solution for designing arbitrary modulated-phase metasurfaces with distinct wavefront manipulation in all four CP output channels. Two metasurfaces are demonstrated with four arbitrary refraction wavefronts, and orbital angular momentum modes with four independent topological charge, showcasing complete and independent manipulation of all possible CP channels in transmission. This additional phase addressing mechanism will lead to new components, ranging from broadband achromatic devices to the multiplexing of wavefronts for application in reconfigurable-beam antenna and wireless communication systems. Here the authors propose an approach to construct metasurfaces, which activate all circularly polarized channels and make full utilization of transmitted energy simultaneously. By introducing chirality-assisted phase all the components in the Jones matrix can be decoupled and independently tuned.
Securing optical information to avoid counterfeiting and manipulation by unauthorized persons and agencies requires innovation and enhancement of security beyond basic intensity encryption. In this paper, we present a new method for polarization-dependent optical encryption that relies on extremely high-resolution near-field phase encoding at metasurfaces, down to the diffraction limit. Unlike previous intensity or color printing methods, which are detectable by the human eye, analog phase decoding requires specific decryption setup to achieve a higher security level. In this work, quadriwave lateral shearing interferometry is used as a phase decryption method, decrypting binary quick response (QR) phase codes and thus forming phase-contrast images, with phase values as low as 15°. Combining near-field phase imaging and far-field holographic imaging under orthogonal polarization illumination, we enhanced the security level for potential applications in the area of biometric recognition, secure ID cards, secure optical data storage, steganography, and communications.
A metasurface is a thin array of subwavelength elements with designable scattering responses, and metasurface holography is a powerful tool for imaging and field control. The existing metasurface holograms are classified into two types: one is based on phase‐only metasurfaces (including the recently presented vectorial metasurface holography), which has high power efficiency but cannot control the phases of generated fields; while the other is based on phase‐amplitude‐modulated metasurfaces, which can control both field amplitudes and phases in the region of interest (ROI) but has very low efficiency. Here, for the first time, it is proposed to synthesize the field amplitudes and phases in ROI simultaneously and independently by using high‐efficiency phase‐only metasurfaces. All points in ROI may have independent values of field amplitudes and phases, and the requirements for X and Y components may be different in achieving spatially varied polarization states. To this end, an efficient design method based on equivalent electromagnetic model and gradient‐based nonlinear optimization is proposed. Full‐wave simulations and experimental results demonstrate that the phase‐only metasurface designed by the method has 10 times higher efficiency than the phase‐amplitude‐modulated metasurface. This work opens a way to realize more complicated and high‐efficiency metasurface holography.
The hologram is an ideal method for displaying three-dimensional images visible to the naked eye. Metasurfaces consisting of subwavelength structures show great potential in light field manipulation, which is useful for overcoming the drawbacks of common computer-generated holography. However, there are long-existing challenges to achieving dynamic meta-holography in the visible range, such as low frame rate and low frame number. In this work, we demonstrate a design of meta-holography that can achieve 2 ²⁸ different holographic frames and an extremely high frame rate (9523 frames per second) in the visible range. The design is based on a space channel metasurface and a high-speed dynamic structured laser beam modulation module. The space channel consists of silicon nitride nanopillars with a high modulation efficiency. This method can satisfy the needs of a holographic display and be useful in other applications, such as laser fabrication, optical storage, optics communications, and information processing.
Animation for a metasurface hologram was achieved using a cinematographic approach. Time-lapsed images were reconstructed using sequentially arranged metasurface hologram frames. An Au rectangular nanoaperture was adopted as a meta-atom pixel and arrayed to reproduce the phase distribution based on the help of a Pancharatnam–Berry phase. We arrayed 48 hologram frames on a 2-cm² substrate and measured and assessed the retardation of fabricated meta-atoms to reconstruct the holographic image, successfully demonstrating the movie with a frame rate of 30 frames per second.
Metasurfaces, composed of specifically designed subwavelength units in a two-dimensional plane, offer a new paradigm to design ultracompact optical elements that show great potentials for miniaturizing optical systems. In the past few decades, metasurfaces have drawn broad interests in multidisciplinary communities owing to their capability of manipulating various parameters of the light wave with plentiful functionalities. Among them, pixelated polarization manipulation in the subwavelength scale is a distinguished ability of metasurfaces compared to traditional optical components. However, the inherent ohmic loss of plasmonic-type metasurfaces severely hinders their broad applications due to the low efficiency. Therefore, metasurfaces composed of high-refractive-index all-dielectric antennas have been proposed to achieve high-efficiency devices. Moreover, anisotropic dielectric nanostructures have been shown to support large refractive index contrast between orthogonal polarizations of light and thus provide an ideal platform for polarization manipulation. Herein, we present a review of recent progress on all-dielectric metasurfaces for polarization manipulation, including principles and emerging applications. We believe that high efficient all-dielectric metasurfaces with the unprecedented capability of the polarization control can be widely applied in areas of polarization detection and imaging, data encryption, display, optical communication and quantum optics to realize ultracompact and miniaturized optical systems.
Controlling light properties with diffractive planar elements requires full-polarization channels and accurate reconstruction of optical signal for real applications. Here, we present a general method that enables wavefront shaping with arbitrary output polarization by encoding both phase and polarization information into pixelated metasurfaces. We apply this concept to convert an input plane wave with linear polarization to a holographic image with arbitrary spatial output polarization. A vectorial ptychography technique is introduced for mapping the Jones matrix to monitor the reconstructed metasurface output field and to compute the full polarization properties of the vectorial far field patterns, confirming that pixelated interfaces can deflect vectorial images to desired directions for accurate targeting and wavefront shaping. Multiplexing pixelated deflectors that address different polarizations have been integrated into a shared aperture to display several arbitrary polarized images, leading to promising new applications in vector beam generation, full color display and augmented/virtual reality imaging.
Metasurface holography has the advantage of realizing complex wavefront modulation by thin layers together with the progressive technique of computer-generated holographic imaging. Despite the well-known light parameters, like amplitude, phase, polarization and frequency, the orbital angular momentum (OAM) of a beam can be regarded as another degree of freedom. Here, we propose and demonstrate orbital angular momentum multiplexing at different polarization channels using a birefringent metasurface for holographic encryption. The OAM selective holographic information can only be reconstructed with the exact topological charge and a specific polarization state. By using an incident beam with different topological charges as erasers, we mimic a super-resolution case for the reconstructed image, in analogy to the well-known STED technique in microscopy. The combination of multiple polarization channels together with the orbital angular momentum selectivity provides a higher security level for holographic encryption. Such a technique can be applied for beam shaping, optical camouflage, data storage, and dynamic displays.
The achievement of structural color has shown advantages in large-gamut, high-saturation, high-brightness, and high-resolution. While a large number of plasmonic/dielectric nanostructures have been developed for structural color, the previous approaches fail to match all the above criterion simultaneously. Herein we utilize the Si metasurface to demonstrate an all-in-one solution for structural color. Due to the intrinsic material loss, the conventional Si metasurfaces only have a broadband reflection and a small gamut of 78% of sRGB. Once they are combined with a refractive index matching layer, the reflection bandwidth and the background reflection are both reduced, improving the brightness and the color purity significantly. Consequently, the experimentally demonstrated gamut has been increased to around 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020. Meanwhile, high refractive index of silicon preserves the distinct color in a pixel with 2 × 2 array of nanodisks, giving a diffraction-limit resolution. Here, the authors fabricate a metasurface with high brightness and large gamut structured colors by combining a silicon metasurface with a refractive index matching layer. The experimentally demonstrated gamut is 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020.
The three-dimensional (3D) vectorial nature of electromagnetic waves of light has not only played a fundamental role in science but also driven disruptive applications in optical display, microscopy, and manipulation. However, conventional optical holography can address only the amplitude and phase information of an optical beam, leaving the 3D vectorial feature of light completely inaccessible. We demonstrate 3D vectorial holography where an arbitrary 3D vectorial field distribution on a wavefront can be precisely reconstructed using the machine learning inverse design based on multilayer perceptron artificial neural networks. This 3D vectorial holography allows the lensless reconstruction of a 3D vectorial holographic image with an ultrawide viewing angle of 94° and a high diffraction efficiency of 78%, necessary for floating displays. The results provide an artificial intelligence-enabled holographic paradigm for harnessing the vectorial nature of light, enabling new machine learning strategies for holographic 3D vectorial fields multiplexing in display and encryption.
Lateral optical forces induced by linearly polarized laser beams have been predicted to deflect dipolar particles with opposite chiralities toward opposite transversal directions. These “chirality-dependent” forces can offer new possibilities for passive all-optical enantioselective sorting of chiral particles, which is essential to the nanoscience and drug industries. However, previous chiral sorting experiments focused on large particles with diameters in the geometrical-optics regime. Here, we demonstrate, for the first time, the robust sorting of Mie (size ~ wavelength) chiral particles with different handedness at an air–water interface using optical lateral forces induced by a single linearly polarized laser beam. The nontrivial physical interactions underlying these chirality-dependent forces distinctly differ from those predicted for dipolar or geometrical-optics particles. The lateral forces emerge from a complex interplay between the light polarization, lateral momentum enhancement, and out-of-plane light refraction at the particle-water interface. The sign of the lateral force could be reversed by changing the particle size, incident angle, and polarization of the obliquely incident light.
Phase, polarization, amplitude, and frequency represent the basic dimensions of light, playing crucial roles for both fundamental light–material interactions and all major optical applications. Metasurfaces have emerged as a compact platform to manipulate these knobs, but previous metasurfaces have limited flexibility to simultaneous control them. A multi‐freedom metasurface that can simultaneously and independently modulate phase, polarization, and amplitude in an analytical form is introduced, and frequency multiplexing is further realized by a k‐space engineering technique. The multi‐freedom metasurface seamlessly combines geometric Pancharatnam–Berry phase and detour phase, both of which are frequency independent. As a result, it allows complex‐amplitude vectorial hologram at various frequencies based on the same design strategy, without sophisticated nanostructure searching of massive geometric parameters. Based on this principle, full‐color complex‐amplitude vectorial meta‐holograms in the visible are experimentally demonstrated with a metal–insulator–metal architecture, unlocking the long‐sought full potential of advanced light field manipulation through ultrathin metasurfaces. A multi‐freedom metasurface is proposed to manipulate multiple dimensions of light simultaneously. A general metasurface design strategy seamlessly combining geometric phase and detour phase in the 1st diffraction order is developed, which can modulate phase, amplitude, and polarization in an analytical and wavelength/angle‐independent formation. Frequency multiplexing is further applied by k‐space engineering, ultimately achieving the full‐color complex‐amplitude vectorial holography.
Nonlinear Pancharatnam–Berry phase metasurfaces facilitate the nontrivial phase modulation for frequency conversion processes by leveraging photon‐spin dependent nonlinear geometric‐phases. However, plasmonic metasurfaces show some severe limitation for nonlinear frequency conversion due to the intrinsic high ohmic loss and low damage threshold of plasmonic nanostructures. Here, the nonlinear geometric‐phases associated with the third‐harmonic generation process occurring in all‐dielectric metasurfaces is studied systematically, which are composed of silicon nanofins with different in‐plane rotational symmetries. It is found that the wave coupling among different field components of the resonant fundamental field gives rise to the appearance of different nonlinear geometric‐phases of the generated third‐harmonic signals. The experimental observations of the nonlinear beam steering and nonlinear holography realized in this work by all‐dielectric geometric‐phase metasurfaces are well explained with the developed theory. This work offers a new physical picture to understand the nonlinear optical process occurring at nanoscale dielectric resonators and will help in the design of nonlinear metasurfaces with tailored phase properties.
Understanding fragile topology
Exploiting topological features in materials is being pursued as a route to build in robustness of particular properties. Stemming from crystalline symmetries, such topological protection renders the properties robust against defects and provides a platform of rich physics to be studied. Recent developments have revealed the existence of so-called fragile topological phases, where the means of classification due to symmetry is unclear. Z.-D. Song et al. and Peri et al. present a combined theoretical and experimental approach to identify, classify, and measure the properties of fragile topological phases. By invoking twisted boundary conditions, they are able to describe the properties of fragile topological states and verify the expected experimental signature in an acoustic crystal. Understanding how fragile topology arises could be used to develop new materials with exotic properties.
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Exceptional points (EPs), also known as non-Hermitian degeneracies, have been observed in parity-time symmetric metasurfaces as parity-time symmetry breaking points. However, the parity-time symmetry condition puts constraints on the metasurface parameter space, excluding the full examination of unique properties that stem from an EP. Here, we thus design a general non-Hermitian metasurface with a unit cell containing two orthogonally oriented split-ring resonators (SRRs) with overlapping resonance but different scattering rates and radiation efficiencies. Such a design grants us full access to the parameter space around the EP. The parameter space around the EP is first examined by varying the incident radiation frequency and coupling between SRRs. We further demonstrate that the EP is also observable by varying the incident radiation frequency along with the incident angle. Through both methods, we validate the existence of an EP by observing unique level crossing behavior, eigenstate swapping under encirclement, and asymmetric transmission of circularly polarized light.
This paper introduces a procedure aimed to quantitatively measure the optical properties of nanoparticles, namely the complex polarizability and the extinction, scattering, and absorption cross sections, simultaneously. The method is based on the processing of intensity and wavefront images of a light beam illuminating the nanoparticle of interest. Intensity and wavefront measurements are carried out using quadriwave lateral shearing interferometry, a quantitative phase imaging technique with high spatial resolution and sensitivity. The method does not require any preknowledge on the particle and involves a single interferogram image acquisition. The full determination of the actual optical properties of nanoparticles is of particular interest in plasmonics and nanophotonics for the active search and characterization of new materials, e.g., aimed to replace noble metals in future applications of nanoplasmonics with less-lossy or refractory materials.
Vertical cavity surface-emitting lasers (VCSELs) have made indispensable contributions to the development of modern optoelectronic technologies. However, arbitrary beam shaping of VCSELs within a compact system has remained inaccessible until now. The emerging ultra-thin flat optical structures, namely metasurfaces, offer a powerful technique to manipulate electromagnetic fields with subwavelength spatial resolution. Here, we show that the monolithic integration of dielectric metasurfaces with VCSELs enables remarkable arbitrary control of the laser beam profiles, including self-collimation, Bessel and Vortex lasers, with high efficiency. Such wafer-level integration of metasurface through VCSEL-compatible technology simplifies the assembling process and preserves the high performance of the VCSELs. We envision that our approach can be implemented in various wide-field applications, such as optical fibre communications, laser printing, smartphones, optical sensing, face recognition, directional displays and ultra-compact light detection and ranging (LiDAR). Non-intrusive integration of metasurfaces with vertical cavity surface-emitting lasers enables fully arbitrary wavefront control for directional laser emission.
Metasurfaces hold great potentials for advanced holographic display with extraordinary information capacity and pixel sizes in an ultrathin flat profile. Dual-polarization channel to encode two independent phase profiles or spatially multiplexed meta-holography by interleaved metasurfaces are captivated popular solutions to projecting multiplexed and vectorial images. However, the intrinsic limit of orthogonal polarization-channels, their crosstalk due to coupling between meta-atoms, and interleaving-induced degradation of efficiency and reconstructed image quality set great barriers for sophisticated meta-holography from being widely adopted. Here we report a non-interleaved TiO2 metasurface holography, and three distinct phase profiles are encoded into three orthogonal polarization bases with almost zero crosstalk. The corresponding three independently constructed intensity profiles are therefore assigned to trichromatic (RGB) beams, resulting in high-quality and high-efficiency vectorial meta-holography in the whole visible regime. Our strategy presents an unconventionally advanced holographic scheme by synergizing trichromatic colors and tri-polarization channels, simply realized with a minimalist non-interleaved metasurface. Our work unlocks the metasurface’s potentials on massive information storage, polarization optics, polarimetric imaging, holographic data encryption, etc.
Cylindrical vector vortex beams, a particular class of higher‐order Poincaré sphere beams, are generalized forms of waves carrying orbital angular momentum with inhomogeneous states‐of‐polarization on their wavefronts. Conventional methods as well as the more recently proposed segmented/interleaved shared‐aperture metasurfaces for vortex beam generation are either severely limited by bulky optical setups or by restricted channel capacity with low efficiency and mode number. Here, a noninterleaved vortex multiplexing approach is proposed, which utilizes superimposed scattered waves with opposite spin states emanating from all meta‐atoms in a coherent manner, counter‐intuitively enabling ultrahigh‐capacity, high‐efficiency, and flexible generation of massive vortex beams with structured state‐of‐polarization. A series of exemplary prototypes, implemented by sub‐wavelength‐thick metasurfaces, are demonstrated experimentally, achieving kaleidoscopic vector vortex beams. This methodology holds great promise for structured wavefront shaping, vortex generation, and high information‐capacity planar photonics, which may have a profound impact on transformative technological advances in fields including spin‐Hall photonics, optical holography, compressive imaging, electromagnetic communication, and so on. A noninterleaved vortex multiplexing approach is proposed, which utilizes superimposed scattered waves with opposite spin states emanating from all meta‐atoms on a shared‐aperture metasurface in a coherent manner. This counter‐intuitively enables ultrahigh‐capacity, high‐efficiency, and flexible generation of massive higher‐order Poincaré sphere beams. This methodology may have a profound impact on advances for wavefront sculpturing, electromagnetic communication, planar photonics, etc.
Upon reflection, modulate phase
Metasurfaces provide a platform to fabricate optical devices in a compact form much thinner than their corresponding bulk optical components. Recognizing that metasurfaces are also open systems interacting with their environment, Song et al . designed a metasurface that exploits those non-Hermitian properties such that they can encircle an exceptional point. Subsequent scattering from such an exceptional point was shown to be polarization dependent, thus providing an additional control knob in designing metasurfaces for wave front engineering. —ISO
Infrared metasurface, especially that having a working range covering wavelengths from 0.75 to 25 μm, has been exploited as a revolutionary tool to manipulate the properties of electromagnetic waves owing to its potential applications in military and civilian fields. It owns the capacity to steer electromagnetic waves within subwavelength scale, with full degrees of freedom such as phase, amplitude and polarization, allowing the development of a number of planar meta-devices including the metalens, hologram, wave-plate and polarimeter. In particular, polarization, which determines the interaction of electromagnetic waves with matter, is important in almost every area of science. However, conventional materials for infrared polarization control inevitably introduce extra optical components and bulky configurations, hindering future miniaturization and integration. Moreover, compared with their short wavelength counterparts, polarization nanodevices in the infrared band and especially those in the long-wavelength infrared region have been far less explored due to the loss of material and immature fabrication techniques. Here, we review recent progress in the development of infrared metasurfaces in terms of generating, manipulating and detecting the polarization on standard and higher-order Poincaré spheres. The principles, typical strategies and emerging applications of these processes are introduced. We also discuss the challenges and outlook of future developments in this emerging field.
Quasi-bound states in the continuum (QBICs) are Fano resonant states with long optical lifetimes controlled by symmetry-breaking perturbations. While conventional Fano responses are limited to linear polarizations and do not support tailored phase control, here we introduce QBICs born of chiral perturbations that encode arbitrary elliptical polarization states and enable geometric phase engineering. We thereby design metasurfaces with ultrasharp spectral features that shape the impinging wave front with near-unity efficiency. Our findings extend Fano resonances beyond their conventional limits, opening opportunities for nanophotonics, classical and quantum optics, and acoustics.
Metasurface-based holography presents opportunities for applications that include optical displays, data storage, and optical encryption. Holograms that control polarization are sometimes referred to as vectorial holograms. Most studies on this topic have concerned devices that display different images when illuminated with different polarization states. Fewer studies have demonstrated holographic images whose polarization varies spatially, i.e., as a function of the position within the image. Here, we experimentally demonstrate a vectorial hologram that produces an image with a spatially continuous distribution of polarization states, for the first time to our knowledge. An unlimited number of polarization states can be achieved within the image. Furthermore, the holographic image and its polarization map (polarization vs position in image) are independent. The same image can be thus encoded with different polarization maps. As far as we know, our approach is conceptually new. We anticipate that it could broaden the application scope of metasurface holography.
We demonstrate phase-matched second-harmonic generation (SHG) from three-dimensional metamaterials consisting of stacked metasurfaces. To achieve phase matching, we utilize a novel mechanism based on phase engineering of the metasurfaces at the interacting wavelengths, facilitating phase-matched SHG in the unconventional backward direction. Stacking up to five metasurfaces,we obtain a phase-matched SHG signal, which scales superlinearly with the number of layers. Our results motivate further investigations to achieve higher conversion efficiencies also with more complex wave fronts.
Geometric metasurfaces have shown great potential in holography due to their straightforward geometric nature of phase control. The incident angles, spins, and wavelengths of the light provide various degrees of freedom to multiplex metasurface holographic images, which, however, are usually interrelated and hence challenging to be fully decoupled. Here, we report a synergetic recipe to break such seemingly inevitable interrelation by incorporating an effective point source (a pinhole), with which the spin, wavelength, and coordinate of the point source can be fully decoupled in meta-holograms. We experimentally demonstrate spin-decoupled, full-colored metasurface holography and dynamic holography controlled with the position of the point source. The significance of this work is not merely to offer an alternative approach to break the interrelation limitations of the geometric metasurface, but more importantly, it provides a promising route for point sources in reality to realize advanced functionalities with meta-optics, such as single-photon holography, fluorescence holography, etc.
Advances in polarization optics and integrated photonics require fundamentally new polarization‐managing strategies allowing for efficient generation and complete control over vectorial fields with well‐defined polarization states using surface‐confined configurations with ultracompact footprints and extended bandwidths. Recently, metasurfaces have been extensively explored to demonstrate compact planar devices enabling diverse polarization control. However, the main drawback of the state‐of‐the‐art metasurface‐based polarization converters is related to their limitations resulting in individual simple functionalities and low‐efficiencies. Here, the strategy for producing dielectric metasurfaces that efficiently generate diversified polarization states with controllable wavefronts and high efficiencies over a broadband spectrum range from a linearly‐polarized light source by generalizing an existing theory of simultaneous phase and polarization control with birefringent meta‐atoms, is demonstrated. Advanced polarization and wavefront manipulation functionalized to realize an efficient polarization‐resolved multifocal metalens and vectorial holographic display is accomplished using judiciously designed dielectric metasurfaces composed of segmented sub‐arrays capable of manipulating, simultaneously and independently, both polarization and phase of the transmitted beams. The versatility of this concept provides opportunities to develop a complete set of flat polarization optics for integrated photonics and quantum optics.
We demonstrate that rotationally symmetric chiral metasurfaces can support sharp resonances with the maximum optical chirality determined by precise shaping of bound states in the continuum (BICs). Being uncoupled from one circular polarization of light and resonantly coupled to its counterpart, a metasurface hosting the chiral BIC resonance exhibits a narrow peak in the circular dichroism spectrum with the quality factor limited by weak dissipation losses. We propose a realization of such chiral BIC metasurfaces based on pairs of dielectric bars and validate the concept of maximum chirality by numerical simulations.
Metalens-array–based quantum source
Spontaneous down-conversion is an exotic optical process in a nonlinear crystal in which a high-energy photon splits into two lower-energy photons that are quantum mechanically entangled. These entangled pairs are valuable commodities for quantum information processing and quantum communications. Because the experimental setup is usually performed with bulk optical components, there is a need to decrease the size scale for application. Li et al. combined an array of specialized metalenses with a nonlinear crystal and show that the scale of the process can be shrunk substantially. The approach should prove useful for developing miniaturized integrated quantum optical technologies.
Science , this issue p. 1487