Perovskite Metasurfaces Research Articles

Chiral polaritons in semiconductor perovskite metasurface enhanced by bound states in the continuum

Abstract The exploration of novel chiral optical platforms holds both fundamental and practical importance, which have shown great promise towards applications in valleytronics, chiral sensing and nanoscopic chiroptics. In this work, we combine two key concepts — chiral bound states in the continuum and exciton polaritons — to showcase a strong chiral response from polaritons. Using the Finite Element Method, we numerically design a CsPbBr3 based metasurface that supports intrinsically chiral bound states in the continuum and verify the chirality by calculating the reflection spectrum and eigen-polarization mapping. We further demonstrate chirality-dependent exciton polariton angular dispersion arising from the strong coupling between the chiral BIC and excitons in CsPbBr3 through simulating the polariton angle-resolved absorption spectrum. Reciprocity analysis reveals that the polariton photoluminescence in different momentum space locations is selectively enhanced by chiral pumping light. Our results suggest a promising first step towards chiral polaritonics.

Long-Range Ballistic Propagation of 80% Excitonic Fraction Polaritons in a Perovskite Metasurface at Room Temperature.

Exciton-polaritons, hybrid light-matter excitations arising from the strong coupling between excitons in semiconductors and photons in photonic nanostructures, are crucial for exploring the physics of quantum fluids of light and developing all-optical devices. Achieving room temperature propagation of polaritons with a large excitonic fraction is challenging but vital, e.g., for nonlinear light transport. We report on room temperature propagation of exciton-polaritons in a metasurface made from a subwavelength lattice of perovskite pillars. The large Rabi splitting, much greater than the optical phonon energy, decouples the lower polariton band from the phonon bath of the perovskite. These cooled polaritons, in combination with the high group velocity achieved through the metasurface design, enable long-range propagation, exceeding hundreds of micrometers even with an 80% excitonic component. Furthermore, the design of the metasurface introduces an original mechanism for unidirectional propagation through polarization control, suggesting a new avenue for the development of advanced polaritonic devices.

Prediction of strong coupling in resonant perovskite metasurfaces by deep learning.

Resonant metasurfaces are often used to achieve strong coupling, and numerical simulations are the common method for designing and optimizing structural parameters of metasurfaces, while their calculation process takes a lot of time and occupies more computing resources. In this work, the deep learning strategy is proposed to simulate the strong coupling phenomenon in resonant perovskite metasurfaces. The designed fully connected neural network is constructed based on the deep learning algorithm that is used to predict transmission spectra, multipole decomposition spectral lines, and anti-cross phenomena of a perovskite metasurface. Through comparison of numerical simulation results, it can be seen that the neural network can efficiently and accurately predict the strong coupling phenomenon. Compared with the traditional design process, the proposed deep learning model can guide the design of the resonant metasurface more quickly, which significantly improves the feasibility of the design in complex metasurface structures.

Chiral Emission from Optical Metasurfaces and Metacavities

Chiral emission exhibiting a large degree of circular polarization (DCP) is important in diverse applications ranging from displays and optical storage to optical communication, bioimaging, and medical diagnostics. Although chiral luminescent materials can generate chiral emissions directly, they frequently suffer from either low DCP or low quantum efficiencies. Achieving high DCP and quantum efficiencies simultaneously remains extremely challenging. This review introduces an alternative approach to chiral emission. Chiral emission with large DCP can be readily achieved by combining conventional achiral emitters with chiral metasurfaces. Particularly, this article focuses on recent experimental and theoretical studies on perovskite metasurfaces and metacavities that employ achiral perovskite materials. First, chiral photoluminescence from extrinsic and intrinsic perovskite metasurfaces is explained together with theoretical discussions on metasurface design based on reciprocity and critical coupling. Chiral photoluminescence from other achiral materials is also explained. Subsequently, chiral electroluminescence from perovskite metacavities and other achiral materials is discussed. Finally, it is concluded with future perspectives. This review provides physical insights into how ideal chiral emission can be realized by optimizing the design of metasurfaces and metacavities. Compact chiral light sources with both near‐unity DCP and strong emission intensities can have far‐reaching consequences in a wide range of future applications.

Cryogenic Electron-Beam Writing for Perovskite Metasurface.

Halide perovskites (HPs) metasurfaces have recently attracted significant interest due to their potential to not only further enhance device performance but also reveal the unprecedented functionalities and novel photophysical properties of HPs. However, nanopatterning on HPs is critically challenging as they are readily destructed by the organic solvents in the standard lithographic processes. Here, we present a novel, subtle, and fully nondestructive HPs metasurface fabrication strategy based on cryogenic electron-beam writing. This technique allows for high-precision patterning and in situ imaging of HPs with excellent compatibility. As a proof-of-concept, broadband absorption enhanced metasurfaces were realized by patterning nanopillar arrays on CH3NH3PbI3 film, which results in photodetectors with approximately 14-times improvement on responsivity and excellent stability. Our findings highlight the great feasibility of cryogenic electron-beam writing for producing perovskite metasurface and unlocking the unprecedented photoelectronic properties of HPs.

High-performance switchable perfect composite vortex beam generator based on halogen perovskite metasurfaces

We propose and realize a novel high-performance switchable perfect composite vortex beam (PCVB). We introduce the concept of composite vortex beam and then present a design for a PCVB generator based on halogen perovskite metasurfaces, which can convert circularly polarized light into a parametrically tunable PCVB using a single halogen perovskite fully dielectric metasurface. The PCVB exhibits a constant toroidal intensity distribution and the ability to superimpose different topological charges. We demonstrate the high feasibility of this design to generate PCVBs with different operating wavelengths, topological charges, and numerical apertures. Additionally, we explore the practical application potential of our design by demonstrating reversible exchange between three halogen perovskite metasurfaces using chemical vapor deposition. This exchange leads to corresponding imaging effects at specific wavelengths. The proposed generator has significant application prospects in optical communication encryption, optical data storage, and optical tweezers.

Giant Ultrafast All-Optical Modulation Based on Exceptional Points in Exciton-Polariton Perovskite Metasurfaces.

Ultrafast all-optical modulation with optically resonant nanostructures is an essential technology for high-speed signal processing on a compact optical chip. Key challenges that exist in this field are relatively low and slow modulations in the visible range as well as the use of expensive materials. Here we develop an ultrafast all-optical modulator based on MAPbBr3 perovskite metasurface supporting exciton-polariton states with exceptional points. The additional angular and spectral filtering of the modulated light transmitted through the designed metasurface allows us to achieve 2500% optical signal modulation with the shortest modulation time of 440 fs at the pump fluence of ∼40 μJ/cm2. Such a value of the modulation depth is record-high among the existing modulators in the visible range, while the main physical effect behind it is polariton condensation. Scalable and cheap metasurface fabrication via nanoimprint lithography along with the simplicity of perovskite synthesis and deposition make the developed approach promising for real-life applications.

Anapole assisted self-hybridized exciton-polaritons in perovskite metasurfaces.

The exciton-polaritons in a lead halide perovskite not only have great significance for macroscopic quantum effects but also possess vital potential for applications in ultralow-threshold polariton lasers, integrated photonics, slow-light devices, and quantum light sources. In this study, we have successfully demonstrated strong coupling with huge Rabi splitting of 553 meV between perovskite excitons and anapole modes in the perovskite metasurface at room temperature. This outcome is achieved by introducing anapole modes to suppress radiative losses, thereby confining light to the perovskite metasurface and subsequently hybridizing it with excitons in the same material. Our results indicate the formation of self-hybridized exciton-polaritons within the perovskite metasurface, which may pave the way towards achieving high coupling strengths that could potentially bring exciting phenomena to fruition, such as Bose-Einstein condensation as well as enabling applications such as efficient light-emitting diodes and lasers.

Highly and tunable full-Stokes chiral metasurface polarization response based on CH3NH3PbI3 perovskites

Owning to the unique optical chiral response, chiral metasurfaces are demand in a wide range of applications. Circular dichroism (CD) as an important index of optical chirality response has been widely concerned by researchers. However, the reported high CD values require complex metasurface structures. Here, we propose a simple structure, high chiral response, terahertz (THz) chiral metasurface based on CH3NH3PbI3(MAPbI3) perovskite regulated by light field. The full Stokes parameters of 0.1THz are obtained, including intensity, direction, and ovality. The results show that CD values of chiral metasurface are improved by integrating of MAPbI3. Moreover, the CD values (0.2–0.49) can be regulated by changing MAPbI3 thickness, metasurface geometric phase and conductivity. This work demonstrates that perovskite metasurface is a promising candidate for the biosensing, polarization control, polarization sensitive imaging and so on.

Strong coupling of excitons and electric/magnetic toroidal dipole modes in perovskite metasurfaces.

Effective manipulation of the interactions between light and matter is crucial for the advancement of various high-performance optoelectronic devices. It is noted that the toroidal dipole resonance refers to an electromagnetic excitation that exists beyond the conventional understanding of electric and magnetic multipoles, which shows great potential for enhancing light-matter interactions. In this work, we investigate the strong coupling properties of electric toroidal dipole (ETD) and magnetic toroidal dipole (MTD) with excitons in (PEA)2PbI4 perovskite metasurfaces. The nanostructure consists of two identical nanobars on a SiO2 substrate, which support ETD and MTD responses. The strong coupling between ETD/MTD modes and perovskite excitons is achieved when adjusting oscillator strength f0, which can be charactered by the clearly anti-crossing behavior appeared in the transmission spectra. The Rabi splitting can be readily tuned by controlling f0. When f0 increases to 1.0, their Rabi splitting values reach as high as 371 meV and 300 meV, respectively. The proposed strong coupling between excitons and ETD/MTDs paves the way for large-scale, low-cost integrated polaritonic devices operating at room temperature.

Nonlinear two-photon pumped vortex lasing based on quasi-bound states in the continuum from perovskite metasurface.

The experimental observation of nonlinear two-photon pumped vortex lasing from perovskite metasurfaces is demonstrated. The vortex lasing beam is based on symmetry-protected quasi-bound states in the continuum (QBICs). The topological charge is estimated to be +1 according to the simulation result. The quality factor and lasing threshold are around 1100 and 4.28 mJ/cm2, respectively. Theoretical analysis reveals that the QBIC mode originates from the magnetic dipole mode. The lasing wavelength can be experimentally designed within a broad spectral range by changing the diameter and periodicity of the metasurface. The finite array size effect of QBIC can affect the quality factor of the lasing and be used to modulate the lasing. Results shown in this study can lead to more complex vortex beam lasing from a single chip and previously unidentified ways to obtain ultrafast modulation of the QBIC lasing via the finite array size effect.

Directional Emission from Electrically Injected Exciton–Polaritons in Perovskite Metasurfaces

We present a new approach to achieving strong coupling between electrically injected excitons and photonic bound states in the continuum of a dielectric metasurface. Here a high-finesse metasurface cavity is monolithically patterned in the channel of a perovskite light-emitting transistor to induce a large Rabi splitting of ∼200 meV and more than 50-fold enhancement of the polaritonic emission compared to the intrinsic excitonic emission of the perovskite film. Moreover, the directionality of polaritonic electroluminescence can be dynamically tuned by varying the source-drain bias, which induces an asymmetric distribution of exciton population within the transistor channel. We argue that this approach provides a new platform to study strong light-matter interactions in dispersion engineered photonic cavities under electrical injection and paves the way to solution-processed electrically pumped polariton lasers.

Room‐Temperature Exceptional‐Point‐Driven Polariton Lasing from Perovskite Metasurface

AbstractExcitons in lead bromide perovskites exhibit high binding energy and high oscillator strength, allowing for a strong light‐matter coupling regime in the perovskite‐based cavities localizing photons at the nanoscale. This opens up the way for the realization of exciton‐polariton Bose–Einstein condensation and polariton lasing at room temperature – the inversion‐free low‐threshold stimulated emission. However, polariton lasing in perovskite planar photon cavities without Bragg mirrors has not yet been observed and proved experimentally. In this study, perovskite metasurface is employed, fabricated with nanoimprint lithography, supporting so‐called exceptional points to demonstrate the room‐temperature polariton lasing. The exceptional points in exciton‐polariton dispersion of the metasurface appear upon optically pumping in the nonlinear regime in the spectral vicinity of a symmetry‐protected bound state in the continuum providing high mode confinement with the enhanced local density of states beneficial for polariton condensation. The observed lasing emission possesses high directivity with a divergence angle of 1° over one axis. The employed nanoimprinting approach for solution‐processable large‐scale polariton lasers is compatible with various planar photonic platforms suitable for on‐chip integration.

Maximally Chiral Emission via Chiral Quasibound States in the Continuum

AbstractAlthough numerous natural materials exhibit chiral optical phenomena, they are typically very weak. Chiral nanophotonic structures can significantly enhance the chiroptical responses and provide unprecedented design flexibility. However, achieving extreme chirality that approaches the ultimate theoretical limit remains challenging. Here, chiral quasibound states in the continuum are realized in the visible range, and maximally chiral emission from a perovskite metasurface is demonstrated. A perovskite film is spin‐coated on a patterned glass substrate. Grayscale lithography is employed to control the etching depths in the substrate and induce out‐of‐plane symmetry breaking. An extremely high level of chiral emission is experimentally achieved in the normal direction at room temperature. Chiral emission is maximally enhanced for one helicity via critical coupling, while strongly suppressed for the other helicity. The physical mechanism is explained using the reciprocity principle. Approaching the ultimate limit of chiral responses may lead to far‐reaching consequences in various important applications as well as fundamental studies.

Mie Exciton-Polariton in a Perovskite Metasurface

Exciton-polariton arising from strong light-matter interaction between exciton and optical cavity has attracted considerable attention due to its potential applications in Bose-Einstein condensation, low-threshold lasing, and slow light. In recent years, two-dimensional lead halide perovskite has emerged as an ideal candidate for realizing exciton polariton at room temperature because it has large exciton binding energy and quantum yield. Here, we demonstrate that strong coupling could be enabled with a perovskite metasurface that supports multipolar Mie resonance, including magnetic quadrupole dominant, anapole, and toroidal resonances. For an array of perovskite nanodisks, the strong coupling behavior between these resonances and exciton is confirmed by the anticrossing features in absorption spectra mapping, while the Rabi splitting is increased from 230.7 meV in magnetic quadrupole-exciton strong coupling to 253 meV in both anapole-exciton and toroidal-exciton strong coupling. The enhanced Rabi splitting is attributed to the stronger field localization within the perovskite instead of within the air gap. In addition, we find that the Rabi splitting depends on the oscillatory strength of the exciton mode and can then be boosted to 362 meV in anapole-exciton strong coupling. Our results provide promising ways to improve the performance of optoelectronic devices such as low-threshold lasers and slow-light devices.

Phase-change perovskite metasurfaces for dynamic color tuning

Abstract Halide perovskite metasurfaces are attracting increasing interest for applications in light-emitting and display technologies. To access the wide range of colors required for these applications, the main mechanism exploited thus far has been chemical engineering of the perovskite compounds – this constitutes a significant limitation for the dynamic switching of optical response desirable in actual devices. Here we demonstrate polarization-dependent, dynamic control of structural color and emission wavelength in an all-dielectric phase-change halide perovskite nanograting metasurface, by temperature tuning. This is underpinned by the significant change in the perovskite optical constants which accompanies its phase-transition around room temperature. The functionalities demonstrated in our work bearing potential for applications in light-emitting devices, displays and spatial-light-modulators.

Perovskite metasurfaces with large superstructural chirality

Recent attempts to synthesize hybrid perovskites with large chirality have been hampered by large size mismatch and weak interaction between their structure and the wavelength of light. Here we adopt a planar nanostructure design to overcome these limitations and realize all-dielectric perovskite metasurfaces with giant superstructural chirality. We identify a direct spectral correspondence between the near- and the far- field chirality, and tune the electric and magnetic multipole moments of the resonant chiral metamolecules to obtain large anisotropy factor of 0.49 and circular dichroism of 6350 mdeg. Simulations show that larger area metasurfaces could yield even higher optical activity, approaching the theoretical limits. Our results clearly demonstrate the advantages of nanostructrure engineering for the implementation of perovskite chiral photonic, optoelectronic, and spintronic devices.

Realization of Polaritonic Topological Charge at Room Temperature Using Polariton Bound States in the Continuum from Perovskite Metasurface (Advanced Optical Materials 6/2022)

In article number 2102386, Hai Son Nguyen and co-workers demonstrate experimentally polariton bound states in the continuum (“pol-BICs”) in an excitonic metasurface based on 2D halide perovskite. These hybrid light–matter states, operating at room temperature, exhibit all peculiar features of BICs: a total uncoupling from the radiative continuum associated to an infinite radiative quality factor, and a topological charge associated to a polarization singularity in the farfield emission.

Optical Rashba Effect in a Light-Emitting Perovskite Metasurface.

The Rashba effect, i.e., the splitting of electronic spin-polarized bands in the momentum space of a crystal with broken inversion symmetry, has enabled the realization of spin-orbitronic devices, in which spins are manipulated by spin-orbit coupling. In optics, where the helicity of light polarization represents the spin degree of freedom for spin-momentum coupling, the optical Rashba effect is manifested by the splitting of optical states with opposite chirality in the momentum space. Previous realizations of the optical Rashba effect relied on passive devices determining the surface plasmon or light propagation inside nanostructures, or the directional emission of chiral luminescence when hybridized with light-emitting media. An active device underpinned by the optical Rashba effect is demonstrated here, in which a monolithic halide perovskite metasurface emits highly directional chiral photoluminescence. An all-dielectric metasurface design with broken in-plane inversion symmetry is directly embossed into the high-refractive-index, light-emitting perovskite film, yielding a degree of circular polarization of photoluminescence of 60% at room temperature.

Multiple-polarization-sensitive photodetector based on a perovskite metasurface.

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 composed of a HOIP antenna array on a single-crystal HOIP film. Owing to the antenna anisotropy, the absorption of linearly polarized light at the metasurface depends on the polarization angle; also, due to the mirror asymmetry of the antenna elements, the metasurface is also sensitive to different circular polarizations. Polarization-dependent photocurrent responses to both LP and CP light are detected. Our results highlight the potential of perovskite metasurfaces for integrated photoelectric applications.