Mu Wang

• Nanjing University

Orthogonal polarization multiplexing is typically required to avoid crosstalk between channels. However, for practical applications in optical information encryption, orthogonal polarization channels are vulnerable to decoding. Using non-orthogonal polarization channels can enhance information security. Here, we extend the conventional Jones matrix...

Metasurface polarization optics, manipulating polarization using metasurfaces composed of subwavelength anisotropic nanostructure array, has enabled a lot of innovative integrated strategies for versatile and on-demand polarization generation, modulation, and detection. Compared with conventional bulky optical elements for polarization control, met...

Smith-Purcell radiation (SPR) is a versatile platform for finely tuning nanoscale light across a broad spectral range. This study introduces a theoretical approach for shaping SPR wavefronts using aperiodic metagratings (AMGs). The AMGs consist of arrays of identical metal nano-rods (MNRs), with each MNR's spatial position precisely adjustable. Thi...

Conventional dielectric solid materials, both natural and artificial, lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space. Here, we present a class of dielectric metamaterials that are effectively self-dual and vacuum-like, thereby exhibiting full-polarization omnidirectional impedanc...

Dewdrops, the droplets of water naturally occurring on leaves and carapaces of insects, are a fascinating phenomenon in nature. Here, a man‐made array of dewdrops with arbitrary shapes and arrangements, which can function as an electromagnetic metasurface, is demonstrated. The realization of the dewdrop array is enabled by a surface covered by a ta...

The long-standing paradox between matte appearance and transparency has deprived traditional matte materials of optical transparency. Here, we present a solution to this centuries-old optical conundrum by harnessing the potential of disordered optical metasurfaces. Through the construction of a random array of meta-atoms tailored in asymmetric back...

We report a giant enhancement of the third harmonic generation (THG) at 343 nm by periodically notched silicon waveguide arrays supporting guided mode resonances (GMRs) at 1030 nm. Maximum efficiency of the third harmonic generation η = 7.71 × 10⁻⁵ is achieved with a peak pump power density of 5.31 GW/cm². The enhancement factor of the THG from the...

Conventional dielectric solid materials, both natural and artificial, lack electromagnetic self-duality and fail to achieve impedance matching with free space. Here, we present a class of dielectric metamaterials that exhibit effective self-duality and also enable full-polarization omnidirectional impedance matching, thereby extending the Brewster...

The bound states in the continuum (BICs) have attracted much attention in designing metasurface due to their high Q-factor and effectiveness in suppressing radiational loss. Here we report on the realization of the third harmonic generation (THG) at a near-ultraviolet wavelength (343 nm) via accidental BICs in a metasurface. The absolute conversion...

We introduce a programmable flip-metasurface that can dynamically control the reflection while leaving the transmitted wavefront undistorted in an ultra-broad spectrum, i.e., the same as that of the incidence. This metasurface is constructed by unique meta-atoms that can be dynamically switched between two flip states, which correspond to the spati...

Traditional optical elements, such as waveplates and polarization beam splitters, are essential for classical and quantum information techniques. Yet their bulky size and heavy weight are prejudicial for miniaturizing information systems. Here, we present our recent studies on polarization manipulation and multiplexing with optical metasurfaces, wh...

Higher-order topological insulators (HOTIs) have emerged as unique topological materials hosting topological corner or hinge states. This work investigates terahertz (THz) higher-order topological states in C3 symmetric valley photonic crystals (VPCs) in theory and experiment. Based on numerical simulations of photonic band structure, phase profile...

Organic molecular vibrations, typically occurring in the terahertz (THz) regime, can resonate with a metastructure. A hallmark Rabi splitting occurs when the coupling strength is sufficiently strong. In this work, we observe the strong coupling of localized surface plasmons (LSPs) and intermolecular vibration mode at THz on a metasurface spin-coate...

To prevent the crosstalk between adjacent waveguides in photonic integrated circuits, the minimum thickness of the cladding layers is around half a wavelength, which imposes a fundamental limitation to further integration and miniaturization of photonic circuits. Here, we reveal that epsilon-near-zero claddings, either isotropic or anisotropic, can...

Smith–Purcell radiation (SPR) refers to the far-field, strong, spike radiation generated by the interaction of the evanescent Coulomb field of the moving charged particles and the surrounding medium. In applying SPR for particle detection and nanoscale on-chip light sources, wavelength tunability is desired. Here we report on tunable SPR achieved b...

Balancing the conflicting demands of transparency and matte appearance has long been a challenge in optics. Smooth surfaces are necessary for transparency but can result in unwanted specular reflection and glare, while rough structures possess a matte appearance and cause random light scattering and translucency. In this work, we propose a novel so...

Noise is usually undesired yet inevitable in science and engineering. However, by introducing the engineered noise to the precise solution of Jones matrix elements, we break the fundamental limit of polarization multiplexing capacity of metasurfaces that roots from the dimension constraints of the Jones matrix. We experimentally demonstrate up to 1...

Manipulating directional chiral optical emissions on a nanometer scale is significant for material science research. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna (LENA) with two identical orthogonal arms. B...

Manipulating directional chiral optical emissions on a nanometer scale is significant for material science studies. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna (LENA) with two identical orthogonal arms. By...

In this work, we study the broadband manipulation of polarization states of terahertz (THz) waves with flexible metamaterial both theoretically and experimentally. Firstly, we construct a chiral THz metamaterial with asymmetric L-shaped metal-dielectric-metal structure, generating a series of electric dipoles via its interacting with terahertz wave...

Traditional optical elements, such as waveplates and polarization beam splitters, are essential for quantum state tomography (QST). Yet, their bulky size and heavy weight are prejudicial for miniaturizing quantum information systems. Here, we introduce nondiffractive silicon metasurfaces with high transmission efficiency to replace the traditional...

A metalens made of compact planar metastructure exhibits an excellent capability of focusing. The high-quality transmissive and reflective focusing simultaneously provides Fourier transform (FT) operation for optical information processing. Here we show a transflective on-chip metalens (TOM) made of orthogonal nano-grooves (ONGs). The TOM simultane...

Photonic quantum information processing relies on operating the quantum state of photons, which usually involves bulky optical components unfavorable for system miniaturization and integration. Here, we report on the transformation and distribution of polarization-entangled photon pairs with multichannel dielectric metasurfaces. The entangled photo...

Getting wireless signals around obstacles or passing them through walls is proven to be challenging for electromagnetic waves with a short wavelength and some energy-efficient buildings due to thick insulating materials. Here, we propose a scheme of through-wall wireless communication by applying purposely designed passive metalenses for an asymmet...

Cladding layers of waveguides prevent interchannel interference yet are unfavorable for the integration of photonic circuits. Here, we report the realization of ultracompact waveguide arrays, bends, and circuits with essentially zero interchannel separation. This supercompactness is achieved via arrays of waveguides with shifted spatial dispersions...

Allowing microwaves to transmit through without changing the wavefront is one of the essential requirements of the dome structures of antenna arrays like radars. Here, we demonstrate a microwave metasurface as an array of two types of meta-atoms, which are the flip counterparts to each other. Due to the reciprocity and space-inversion symmetry, the...

In this work, we propose and demonstrate a scheme to realize broadband coherent perfect absorption of spoof surface plasmon polaritons (SPPs) using an ultrathin conductive film vertically placed on a plasmonic metasurface that supports spoof SPPs. When the conductive film possesses an appropriate sheet resistance, two incident coherent beams of spo...

Topological photonics offers the possibility of robust transport and efficiency enhancement of information processing. Terahertz (THz) devices, such as waveguides and beam splitters, are prone to reflection loss owing to their sensitivity to defects and lack of robustness against sharp corners. Thus, it is a challenge to reduce backscattering loss...

As 2D metamaterials, metasurfaces provide an unprecedented means to manipulate light with the ability to multiplex different functionalities in a single planar device. Currently, most pursuits of multifunctional metasurfaces resort to empirically accommodating more functionalities at the cost of increasing structural complexity, with little effort...

Nanowires typically grow along their longitudinal axis, and the long-range order among wires sustains only when a template exists. Here, we report an unprecedented electrochemical growth of ordered metallic nanowire arrays from an ultrathin electrolyte layer, which is achieved by solidifying the electrolyte solution below the freezing temperature....

Most polarization-sensitive photodetectors detect either linearly polarized (LP) or circularly polarized (CP) light. Here, we experimentally demonstrate a multiple-polarization photodetector based on a hybrid organic–inorganic perovskite (HOIP) metasurface, which is sensitive to both LP and CP light simultaneously. The perovskite metasurface is com...

Manipulating the polarization state of light is essential for on-chip photonics and quantum information processing. We demonstrate the generation of different polarization states via a single metasurface based on geometrical-scaling-induced phase modulations.

It is known that most of metastructures cannot dynamically tune the optoelectric properties once their structures are fabricated. Naturally, developing active materials and dynamically tunable devices becomes especially desired and necessary. In this work, we have made several active metasurfaces and dynamically-tunable metadevices based on phase c...

Ultraviolet (UV) photodetection has attracted much attention for applications like monitoring ozone holes and light communication. Although UV photodetectors based on conventional inorganic semiconductors have been widely investigated, fast response devices with high sensitivity remain needed for UV communication systems. This Letter reports on fle...

Rough surfaces lead to diffused light in both reflection and transmission, thereby blurring the reflected and transmitted images. Here, we merge the traditionally incompatible diffuse reflection and undistorted transmission by introducing the concept of random-flip metasurfaces made of randomly flipped components. These metasurfaces have a globally...

Manipulation of polarization states with metasurfaces is a compelling approach for on-chip photonics and portable information processing. Yet it remains challenging to generate different types of polarization states with a single piece of a metasurface. This paper demonstrates a metasurface to resolve this issue, which is made of L-shaped resonator...

In this Letter, we theoretically propose and experimentally demonstrate a three-dimensional soundproof acoustic cage structure, hereby denoted as an acoustic metacage. The metacage is composed of six acoustic metamaterial slabs with open holes and hidden bypass space coiling tunnels connected to the holes. Band structure analysis reveals a novel ph...

Broadband tuning of polarization states is pivotal yet challenging in modern photonics technologies, especially for miniaturized or integrated systems. Metasurfaces potentially provide an effective approach to resolve this challenge. However, once a metadevice is fabricated, its functionalities are determined, and it is hard to actively tune the po...

Reflection inherently occurs on the interfaces between different media. In order to perfectly manipulate waves on the interfaces, integration of antireflection function in metasurfaces is highly desired. In this work, we demonstrate an approach to realize exceptional metasurfaces that combine the two vital functionalities of antireflection and arbi...

Optical nanoantennas have attracted significant attention over the past decades, owing to their exceptional capabilities in terms of light manipulation and versatile optical applications. Recently, active nanoantennas have been developed by introducing phase change materials, to achieve specific tunable electromagnetic responses. However, most of t...

Phase change materials (PCMs), such as GeSbTe (GST) alloys and vanadium dioxide (VO2), play an important role in dynamically tunable optical metadevices. However, the PCMs usually require high thermal annealing temperatures above 700 K, but most flexible metadevices can only work below 500 K owing to the thermal instability of polymer substrates. T...

Ultrathin hybrid organic-inorganic perovskite (HOIP) films have significant potential for use in integrated high-performance photoelectric devices. However, the relatively low optical absorption capabilities of thinner films, particularly in the long-wavelength region, pose a significant challenge to the further improvement of photoelectrical conve...

Symmetry usually plays a key role in the formation of the Dirac cone in the band structure of triangular or hexagonal systems. In this work, we demonstrate a systematic method to create Dirac cones of accidental degeneracy in general photonic crystals without symmetry. With this method, a band gap can be closed gradually through a series of modific...

In this work, we propose a non-Hermitian effective medium theory to interpret the spawning rings of exceptional points out of the Dirac cones in the band structures of photonic crystals with loss/gain. Based on this theory, we predict and demonstrate two unique types of band dispersions of fully passive photonic crystals. In one type, the exception...

Mimicry is a biological camouflage phenomenon whereby an organism can change its shape and color to resemble another object. Herein, the idea of biological mimicry and rich degrees of freedom in metasurface designs are combined to realize holographic mimicry devices. A general mathematical method, called phase matrix transformation, to accomplish t...

The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle. However, when loss is introduced into the permittivity of the dielectric, the Brewster condition breaks down and reflection unavoidably appears. In this work, we found an exception to this long-standing dilemma by creating a class of nonmagn...

Metalenses possess the extraordinary capability to tailor the wavefront of light with compact metastructures. However, it remains challenging to eliminate chromatic aberration and realize multifunctionality. Here we report an achromatic bifocal metalens (ABM) made of three-dimensional standing nano blocks (SNBs). By introducing a height gradient to...

We experimentally demonstrate the Anderson localization of surface plasmon polaritons (SPPs) at optical frequencies in two-dimensional (2D) nanostructures. By increasing the positional disorder of the silver nanohole arrays on a glass substrate, strong 2D localization of SPPs appears with an exponentially decreased electric field, the reduced propa...

Manipulating the polarization state of light is essential for integrated photonics and quantum information technology. By introducing geometrical-scaling-induced phase modulations, we report here the simultaneous generation of different types of polarization states with a single metasurface.

Energetic photoinduced hot electrons have been attracting increased scientific attention owing to their potential applicability in numerous photoelectrical and photochemical processes. Normally, the energy of electrons quickly converts into heat by ultrafast cooling, which is considered as the bottleneck for high-efficiency utilization of hot elect...

Traditional microlens focuses the beam with spherical convex surface, which achieves high transmission by restraining the scattering loss yet brings spherical aberration and chromatic aberration. While recently‐developed metalens, which relies on phase modulation by elaborately designing local resonators, has realized diffraction‐limited focusing....

Flexible optoelectronic devices attract considerable attention due to their prominent role in creating novel wearable apparatus for bionics, robotics, health care, and so forth. Although bulk single-crystalline perovskite-based materials are well-recognized for the high photoelectric conversion efficiency than the polycrystalline ones, their stiff...

The Brewster's law predicts the maximum polarization of light for incidence on a dielectric surface at a particular angle. However, when loss is introduced into the permittivity of the dielectric, the impedance matching condition breaks down, unavoidably invalidating the Brewster effect. In this work, we have found an exception to this centuries-ol...

Manipulating the polarization of light on the microscale or nanoscale is essential for integrated photonics and quantum optical devices. Nowadays, the metasurface allows one to build on-chip devices that efficiently manipulate the polarization states. However, it remains challenging to generate different types of polarization states simultaneously,...

Dielectric metamaterials with high refractive indices may have an incredible capability to manipulate the phase, amplitude, and polarization of the incident light. Combining the high refractive index and the excellent electrical characteristics of the hybrid organic-inorganic perovskites (HOIPs), for the first time we experimentally demonstrate tha...

Edge-mode graphene plasmons (EGPs) supported by graphene nanoribbons are highly confined, and they can show versatile tunability under electrostatic bias. In order to efficiently enhance and actively control the near-field intensity in integrated plasmonic devices, we theoretically study Anderson localization of EGPs in a graphene nanoribbon with a...

Surface plasmon polaritons (SPPs) propagating on a metal–dielectric interface suffer from inevitable energy losses originating from metals, especially in a visible regime, which degrades the quality of SPP-based devices. However, if the size of the devices is sufficiently miniaturized, we can thereby limit the propagation length of the signals and...

We experimentally demonstrate a bendable cloaking structure composed of obliquely stacked planar metallic shells that individually enclose the objects to be hidden. The ensemble of shells acts as a disordered oblique grating capable of bending along a curved structure and exhibits broadband invisibility from 0.2 to 1.0 THz. Hiding cloaked objects s...

In this work, we present our recent work on passive or active manipulation of the polarization state of light with both 2D and 3D metastructures. We start from how to tune the polarization states of light via time retardation with a microstructured surface, and then to control them based on a dispersion-free metastructure. Further, we show a freely...

We investigate circularly polarized photoluminescence (PL) in the MoS2/MoO3 heterostructure, which was fabricated by transferring MoS2 monolayer to cover the MoO3 few layers on the SiO2/Si substrate. It is shown that the PL with the same helicity as the excitation light is dominant due to the inherent chiral optical selectivity, which allows exciti...

Electromagnetic metastructures stand for the artificial structures with a characteristic size smaller than the wavelength, which may efficiently manipulate the states of light. However, their applications are often restricted by the bandwidth of the electromagnetic response of the metastructures. It is therefore essential to reassert the principles...

Unlike periodic and random structures, many aperiodic structures exhibit unique hierarchical natures. Aperiodic photonic micro/nanostructures usually support optical multimodes due to either the rich variety of unit cells or their hierarchical structure. Mainly based on our recent studies on this topic, here we review some developments of aperiodic...

Acoustic analogs of electronic or photonic topological insulators provide unique approaches to manipulate sound wave propagation. Inspired by twist-induced topological photonic insulators, here we propose a type of two-dimensional acoustic topological insulator (TI) via projecting a section of a three-dimensional twisting structure to a plane, asse...

The plasmonic nanoantenna has attracted intensive attention over the last decades owing to its unique optical response. Although various nanoantennas have been designed, so far very few efforts have been devoted to their dynamic tunability. Here we present a study on dynamically tunable bowtie nanoantennas integrated on a vanadium dioxide thin film...

Manipulating the polarization of light on the micro/nano scale is essential for integrated photonics and quantum optical devices. Nowadays, metasurface allows building on-chip devices that may efficiently manipulate polarization states. However, it remains challenging to generate different types of polarization states simultaneously, which is requi...

Driven by the development of nanophotonics and integrated optics, manipulating polarization of light with metastructures has been extensively studied in recent decades. So far there is still a high demand for more efficient ways to control the polarization state of light with extraordinary performance. In this Letter, we report on constructing mult...

We have experimentally demonstrated several dynamically-tunable plasmonic devices based on phase transition of vanadium dioxide, which include dynamic plasmonic color generators and dynamically switchable polarizers. The investigations can be applied in dynamic digital displays, optical data storage, and imaging sensors.

As is well known, plasmonics bridges the gap between nanoscale electronics and dielectric photonics, and is expected to be applied to light generation, photonic integration and chips, optical sensing and nanofabrication technology. So far, most of plasmonic microstructures and nanostructures cannot dynamically tune the properties once their structu...

The hybrid perovskite CH3NH3PbX3 (X= Cl, Br, I) is a promising material for developing novel optoelectronic devices. Owing to the intrinsic non-layer structure, it remains challenging to synthesize molecularly thin CH3NH3PbX3 with large size. Here, we report a low-cost and highly efficient fabrication route to obtain large-scale single-crystalline...

The hybrid organic-inorganic perovskites (HOIPs) have attracted much attention recently due to their preeminent efficiency in solar cells. According to the difference on the crystalline structure, the HOIPs could be classified into layered and non-layered perovskites. Very recently, it has been realized that the non-layered HOIPs with common-vertex...

The efficiency of photoluminescence (PL) of transition-metal dichalcogenides (TMDCs) significantly influences their practical applications in optoelectronic devices. In this work, we study multiple coupling among excitons, surface plasmons, and optical modes, and their effects on PL of monolayer MoS 2 atop plasmonic nanohole arrays. Under the illum...

Pauli blockade occurs when the excited electrons fill up the states near the conduction bands and block subsequent absorption in semiconductors, and has been widely applied in mode-locking for passively-pulsed-laser systems. In this letter, we report the first direct observation that the Pauli blockade is broken by ultrafast cooling of hot electron...

There have been great endeavors devoted to manipulating the polarization state of light by plasmonic nanostructures in recent decades. However, the topic of active polarizers has attracted much less attention. We present a composite plasmonic nanostructure consisting of vanadium dioxide that can dynamically modulate the polarization state of the re...

In this work, we experimentally demonstrate for the first time strong localization of surface plasmon polaritons (SPPs) at visible regime in metallic nanogratings with short-range correlated disorder. By increasing the degree of disorder, the confinement of SPPs is significantly enhanced, and the effective SPP propagation length dramatically shrink...

In this work, we demonstrate broadband integrated polarization rotator (IPR) with a series of three-layer rotating metallic grating structures. This transmissive optical IPR can conveniently rotate the polarization of linearly polarized light to any desired directions at different spatial locations with high conversion efficiency, which is nearly c...

Surface plasmons (SPs), the resonance of free electrons on the metal-air interface, may strongly interact with light and generate some extraordinary optical effects. Instead of using conventional planar light excitation, here we excite SPs with a focused electron beam on metallic nanostructures with different geometrical symmetries. With the help o...

We investigate the transport properties of Dirac fermions on the surface of a three-dimensional topological insulator (TI) with magnetic modulation potentials. By using the transfer-matrix method, the transmission coefficients are obtained as a function of incident energy and incident angle. It is shown that the forward and backward propagating car...