Chiral Photonics Research Articles

Biomimetic Self-Assembled Chiral Inorganic Nanomaterials: A New Strategy for Solving Medical Problems.

The rapid expansion of the study of chiral inorganic structures has led to the extension of the functional boundaries of inorganic materials. Nature-inspired self-assembled chiral inorganic structures exhibit diverse morphologies due to their high assembly efficiency and controlled assembly process, and they exhibit superior inherent properties such as mechanical properties, chiral optical activity, and chiral fluorescence. Although chiral self-assembled inorganic structures are becoming more mature in chiral catalysis and chiral optical regulation, biomedical research is still in its infancy. In this paper, various forms of chiral self-assembled inorganic structures are summarized, which provides a structural starting point for various applications of chiral self-assembly inorganic structures in biomedical fields. Based on the few existing research statuses and mechanism discussions on the chiral self-assembled materials-mediated regulation of cell behavior, molecular probes, and tumor therapy, this paper provides guidance for future chiral self-assembled structures to solve the same or similar medical problems. In the field of chiral photonics, chiral self-assembled structures exhibit a chirality-induced selection effect, while selectivity is exhibited by chiral isomers in the medical field. It is worth considering whether there is some correspondence or juxtaposition between these phenomena. Future chiral self-assembled structures in medicine will focus on the precise treatment of tumors, induction of soft and hard tissue regeneration, explanation of the biochemical mechanisms and processes of its medical effects, and improvement of related theories.

Chirality-dependent unidirectional routing of WS2 valley photons in a nanocircuit.

Valleytronics is a promising candidate to address low-energy signal transport on chip, leveraging the valley pseudospin of electrons as a new degree of freedom to encode, process and store information1-7. However, valley-carrier nanocircuitry is still elusive, because it essentially requires valley transport that overcomes three simultaneous challenges: high fidelity, high directionality and room-temperature operation. Here we experimentally demonstrate a nanophotonic circuit that can route valley indices of a WS2 monolayer unidirectionally via the chirality of photons. Two propagating modes are supported in the gap area of the circuit and interfere with each other to generate beating patterns, which exhibit complementary profiles for circular dipoles of different handedness. Based on the spin-dependent beating patterns, we showcase valley fidelity of chiral photons up to 98%, and the circulation directionality is measured to be 0.44 ± 0.04 at room temperature. The proposed nanocircuit can not only enable the construction of large-scale valleytronic networks but also serve as an interactive interface to integrate valleytronics3-5, spintronics8-10 and integrated photonics11-13, opening new possibilities for hybrid spin-valley-photon ecosystems at the nanoscale.

Modulating the Chiroptical Response of Chiral Polymers with Extended Conjugation within the Structural Building Blocks.

Advancing the emerging area of chiral photonics requires modeling-guided concepts of chiral material design to enhance optical activity and associated optical rotatory dispersion. Herein, we introduce conformational engineering achieved by tuning polymer backbone conjugation through introduction of thiophene structural units in a chiral fluorene polymer backbone. Our theoretical calculations reveal a relationship between the structural conformation and the resultant rotational strength. We further synthesize a series of chiral fluorene-based polymers copolymerized with thiophene whose optical chirality trend is in qualitative agreement with predictions of our quantum chemical calculations. Varying the number of thiophene units in the monomer building block allows us to modulate the rotational strength by tuning the intrafibril helicity of single-stranded polymer chains, whereby the monomer conjugation is retained throughout the whole length of the polymer backbone. Our design concept delineates an underexamined approach: the concept of tuning backbone conjugation and helicity within the main chain to enhance the optical activity of chiral polymer systems.

Parity-dependent unidirectional and chiral photon transfer in reversed-dissipation cavity optomechanics

Nonreciprocal elements, such as isolators and circulators, play an important role in classical and quantum information processing. Recently, strong nonreciprocal effects have been experimentally demonstrated in cavity optomechanical systems. In these approaches, the bandwidth of the nonreciprocal photon transmission is limited by the mechanical resonator linewidth, which is arguably much smaller than the linewidths of the cavity modes in most electromechanical or optomechanical devices. In this work, we demonstrate broadband nonreciprocal photon transmission in the reversed-dissipation regime, where the mechanical mode with a large decay rate can be adiabatically eliminated while mediating anti-PT-symmetric dissipative coupling with two kinds of phase factors. Adjusting the relative phases allows the observation of periodic Riemann-sheet structures with distributed exceptional points (Eps). At the Eps, destructive quantum interference breaks both the T- and P-inversion symmetry, resulting in unidirectional and chiral photon transmissions. In the reversed-dissipation regime, the nonreciprocal bandwidth is no longer limited by the mechanical mode linewidth but is improved to the linewidth of the cavity resonance. Furthermore, we find that the direction of the unidirectional and chiral energy transfer could be reversed by changing the parity of the Eps. Extending non-Hermitian couplings to a three-cavity model, the broken anti-PT-symmetry allows us to observe high-order Eps, at which a parity-dependent chiral circulator is demonstrated. The driving-phase controlled periodical Riemann sheets allow observation of the parity-dependent unidirectional and chiral energy transfer and thus provide a useful cell for building up nonreciprocal array and realizing topological, e.g., isolators, circulators, or amplifiers.

Optimizing the chiral Purcell factor for unidirectional single-photon emitters in topological photonic crystal waveguides using inverse design

We present an inverse design approach to significantly improve the figures-of-merit for chiral photon elements and quantum emitters in topological photonic crystal slab waveguides. Beginning with a topological waveguide mode with a group index of approximately 10 and a maximum forwards or backwards Purcell factor at a chiral point of less than 0.5, we perform optimizations of the directional Purcell factor. We use a fully three dimensional guided-mode expansion method to efficiently calculate waveguide band dispersion properties and modes, while automatic differentiation is employed to calculate the gradient of objective functions. We present two example improved designs: (i) a topological mode with an accessible group index of approximately 30 and a maximum unidirectional Purcell factor at a chiral point greater then 4.5 representing a nearly 10-fold improvement to the Purcell factor, and (ii) a slow light mode, well away from the Brillouin zone edge with a group index greater then 350 and a maximum unidirectional Purcell factor at a chiral point greater than 45.

Reciprocal and Non‐reciprocal Chiroptical Features in Thin Films of Organic Dyes

AbstractThe study of chiroptical properties in thin films of chiral organic π‐conjugated dyes is more complex than isotropic solutions, due to the interference of macroscopic anisotropies often present in the solid state. The experimental circularly polarized (CP) absorption (electronic circular dichroism, ECD) and CP emission (circularly polarized luminescence, CPL) of a thin film can be expressed as the sum of several terms, some of which are non‐reciprocal upon film flipping. In this review, we shall discuss the fundamental theoretical concepts about reciprocal and non‐reciprocal chiroptical features in thin films of organic dyes, describing their correlation with the solid‐state structural organization and suggesting a practical toolbox to quantify their relative weight on an experimental ECD or CPL spectrum. Moreover, we shall also take into account the literature on thin films of organic π‐conjugated dyes showing strong non‐reciprocal CP absorption and/or CP emission, due to their potential high interest in the flourishing field of chiral photonics and electronics.

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.

Polarization-sensitive optoionic membranes from chiral plasmonic nanoparticles.

Optoelectronic effects differentiating absorption of right and left circularly polarized photons in thin films of chiral materials are typically prohibitively small for their direct photocurrent observation. Chiral metasurfaces increase the electronic sensitivity to circular polarization, but their out-of-plane architecture entails manufacturing and performance trade-offs. Here, we show that nanoporous thin films of chiral nanoparticles enable high sensitivity to circular polarization due to light-induced polarization-dependent ion accumulation at nanoparticle interfaces. Self-assembled multilayers of gold nanoparticles modified with L-phenylalanine generate a photocurrent under right-handed circularly polarized light as high as 2.41 times higher than under left-handed circularly polarized light. The strong plasmonic coupling between the multiple nanoparticles producing planar chiroplasmonic modes facilitates the ejection of electrons, whose entrapment at the membrane-electrolyte interface is promoted by a thick layer of enantiopure phenylalanine. Demonstrated detection of light ellipticity with equal sensitivity at all incident angles mimics phenomenological aspects of polarization vision in marine animals. The simplicity of self-assembly and sensitivity of polarization detection found in optoionic membranes opens the door to a family of miniaturized fluidic devices for chiral photonics.

Circular Polarized Light Emission in Chiral Inorganic Nanomaterials.

Chiral inorganic nanostructures strongly interact with photons changing their polarization state. The resulting circularly polarized light emission (CPLE) has cross-disciplinary importance for a variety of chemical/biological processes and is essential for development of chiral photonics. However, the polarization effects are often complex and their interpretation is dependent on the several structural parameters of the chiral nanostructure. CPLE in nanostructured media has multiple origins and several optical effects are typically convoluted into a single output. Analyzing CPLE data obtained for nanoclusters, nanoparticles, nanoassemblies, and nanocomposites from metals, chalcogenides, perovskite, and other nanostructures, it is shown here that there are several distinct groups of nanomaterials for which CPLE is dominated either by circularly polarized luminescence (CPL) or circularly polarized scattering (CPS); there are also many nanomaterials for which they are comparable. The following points are also demonstrated: 1) CPL and CPS contributions involve light-matter interactions at different structural levels; 2) contribution from CPS is especially strong for nanostructured microparticles, nanoassemblies, and composites; and 3) engineering of materials with strongly polarized light emission requires synergistic implementation of CPL and CPS effects. These findings are expected to guide development of CPLE materials in a variety of technological fields, including 3D displays, information storage, biosensors, optical spintronics, and biological probes.

Quantum Squeezing Induced Optical Nonreciprocity.

We propose an all-optical approach to achieve optical nonreciprocity on a chip by quantum squeezing one of two coupled resonator modes. By parametric pumping a χ^{(2)}-nonlinear resonator unidirectionally with a classical coherent field, we squeeze the resonator mode in a selective direction due to the phase-matching condition, and induce a chiral photon interaction between two resonators. Based on this chiral interresonator coupling, we achieve an all-optical diode and a three-port quasicirculator. By applying a second squeezed-vacuum field to the squeezed resonator mode, our nonreciprocal device also works for single-photon pulses. We obtain an isolation ratio of >40 dB for the diode and fidelity of >98% for the quasicirculator, and insertion loss of <1 dB for both. We also show that nonreciprocal transmission of strong light can be switched on and off by a relative weak pump light. This achievement implies a nonreciprocal optical transistor. Our protocol opens up a new route to achieve integrable all-optical nonreciprocal devices permitting chip-compatible optical isolation and nonreciporcal quantum information processing.

Recent Progress in Chiral Topological Quantum Interface

Chiral quantum optics and Topological photonics are both emerging field of research, which have attracted great attention in recent years. Chiral quantum optics provides a new approach to achieve full quantum control of light-matter interaction in a novel manner, which has potential possibility for the implementation of complex quantum information networks. Meanwhile, topological photonics provides a novel route for designing and realizing optical device with unprecedented functionality, such as robust light propagation, the immunity to various structural imperfection, back-scattering suppression as well as unidirectional transmission. The application of topological photonics in chiral quantum optics will promote the whole performance of integrated quantum device with topological protection. In this review, we summarize the progress of chiral quantum optics and topological photonics firstly. Then, we mainly focus on the research of topological chiral edge states based on photonic quantum spin-Hall effect and photonic quantum valley-Hall effect. Furthermore, we introduce the recent work of chiral topological quantum interface formed by embedding quantum dot into the interface between two topologically distinct photonic crystal structures. At last, we give short outlook on the future development direction and prospect for application of topological chiral quantum interface.

Highly tunable directional optical antennas with large local angular chiroptical effects

The highly localized field of the plasmonic nanostructures can amplify the chiroptical effects. While most efforts have been focused on spectral responses in real space for chiroptical effects of the plasmonic nanostructures, we present alternative extrinsic chiroptical effects with respect to angular emission patterns in momentum space based on the designed directional nanoantennas. First, the chiroptical effects with respect to spectral responses for the antenna are investigated and decomposed based on the multipolar expansion method. Through the traditional spectral responses, there seems to be no chirality. However, when we turn to the angular emission patterns in the momentum space for the nanoantenna, large local angular chiroptical effects are observed. The chiroptical effects assessed by the difference of azimuth angle emission lobes under left- and right-circularly polarized light illumination can reach 180°. The multipolar analysis combined with Green's function method in a stratified medium is constructed to explain the unidirectional emission and chiral phenomenon, which agrees well with the simulation results. Moreover, the local angular chiroptical effects are also highly tunable by changing the refractive index of the surrounding medium. Our study on local angular chiroptical effects provides a new perspective to understand the chirality, and the large extrinsic chirality for the nanoantenna sheds a new light for biosensing and chiral photon detection.

Machine Learning‐Based Optimization of Chiral Photonic Nanostructures: Evolution‐ and Neural Network‐Based Designs

Chiral photonics opens new pathways to manipulate light–matter interactions and tailor the optical response of metasurfaces and ‐materials by nanostructuring nontrivial patterns. Chirality of matter, such as that of molecules, and light, which in the simplest case is given by the handedness of circular polarization, have attracted much attention for applications in chemistry, nanophotonics and optical information processing. The design of chiral photonic structures using two machine learning methods, the evolutionary algorithm, and neural network approach, for rapid and efficient optimization of optical properties for dielectric metasurfaces, is reported. The design recipes obtained for visible light in the range of transition‐metal dichalcogenide exciton resonances show a frequency‐dependent modification in the reflected light's degree of circular polarization, that is represented by the difference between left‐ and right‐circularly polarized intensity. Our results suggest the facile fabrication and characterization of optical nanopatterned reflectors for chirality‐sensitive light–matter coupling scenarios employing tungsten disulfide as possible active material with features such as valley Hall effect and optical valley coherence.

Cellulose Nanocrystal Chiral Photonic Micro-Flakes for Multilevel Anti-Counterfeiting and Identification

Cellulose Nanocrystal Chiral Photonic Micro-Flakes for Multilevel Anti-Counterfeiting and Identification

Circularly Polarized Light Detection by Chiral Photonic Cellulose Nanocrystal with ZnO Photoconductive Layer in Ultraviolet Region.

Circularly polarized light (CPL) detection and polarization state recognition are required for a wide range of applications. Conventional polarization detection with optical components causes difficulties for miniaturization and integration. An effective design strategy is proposed for direct CPL detection with chiral material. Here, we realized direct CPL detection based on the combination of chiral photonic cellulose nanocrystal (CNC) and ultraviolet-sensitive ZnO photoconductive material. The CNC layer deposited by evaporation-induced self-assembly established the left-handed chiral nematic structure with a photonic bandgap (PBG) to recognize left-handed CPL (LCPL) and right-handed CPL (RCPL) at specific wavelengths. The PBG of CNC layer has been modulated by the adjustment of chiral nematic pitch to match the semiconductor bandgap of ZnO film in ultraviolet region. The photocurrents under RCPL and LCPL are 2.23 × 10−6 A and 1.77 × 10−6 A respectively and the anisotropy factor Δgpc of 0.23 is acquired for the CPL detection based on the chiral photonic CNC. This design provides a new approach to the detection of CPL polarization state with competitive performance.

Long-Range Directional Routing and Spatial Selection of High-Spin-Purity Valley Trion Emission in Monolayer WS2.

Valley-dependent excitation and emission in transition metal dichalcogenides (TMDCs) have recently emerged as a new avenue for optical data manipulation, quantum optical technologies, and chiral photonics. The valley-polarized electronic states can be optically addressed through photonic spin-orbit interaction of excitonic emission, typically with plasmonic nanostructures, but their performance is limited by the low quantum yield of neutral excitons in TMDC multilayers and the large Ohmic loss of plasmonic systems. Here, we demonstrate a valleytronic system based on the trion emission in high-quantum-yield WS2 monolayers chirally coupled to a low-loss microfiber. The integrated system uses the spin properties of the waveguided modes to achieve long-range directional routing of valley excitations and also provides an approach to selectively address valley-dependent emission from different spatial locations around the microfiber. This valleytronic interface can be integrated with fiber communication devices, allowing for merging valley polarization and chiral photonics as an alternative mechanism for optical information transport and manipulation in classical and quantum regimes.

Anisotropic Iridescence and Polarization Patterns in a Direct Ink Written Chiral Photonic Polymer (Adv. Mater. 39/2021)

Chiral Photonic Polymers In article number 2103309, Albertus P. H. J. Schenning, Michael G. Debije, and co-workers show that using direct ink writing, unconventional chiral nematic objects can be generated, which show a bright iridescent color from normal incidence, or only from sharp angles of observation depending on the writing speed. The cover is a polarized optical microscopy image showing a detail from the free-standing Morpho-inspired print.

Nanocellulose‐Based Functional Materials: From Chiral Photonics to Soft Actuator and Energy Storage

AbstractNanocellulose is currently in the limelight of extensive research from fundamental science to technological applications owing to its renewable and carbon‐neutral nature, superior biocompatibility, tailorable surface chemistry, and unprecedented optical and mechanical properties. Herein, an up‐to‐date account of the recent advancements in nanocellulose‐derived functional materials and their emerging applications in areas of chiral photonics, soft actuators, energy storage, and biomedical science is provided. The fundamental design and synthesis strategies for nanocellulose‐based functional materials are discussed. Their unique properties, underlying mechanisms, and potential applications are highlighted. Finally, this review provides a brief conclusion and elucidates both the challenges and opportunities of the intriguing nanocellulose‐based technologies rooted in materials and chemistry science. This review is expected to provide new insights for nanocellulose‐based chiral photonics, soft robotics, advanced energy, and novel biomedical technologies, and promote the rapid development of these highly interdisciplinary fields, including nanotechnology, nanoscience, biology, physics, synthetic chemistry, materials science, and device engineering.

Symmetry‐Protected Photonic Chiral Spin Textures by Spin–Orbit Coupling

AbstractChiral spin textures are widely researched in condensed matter systems and have shown potential for use in spintronics and storage applications. Photonic counterparts of these textures are observed in various optical systems with broken inversion symmetry. Unfortunately, the resemblances are only phenomenological. This work proposes a theoretical framework based on the variational theorem to show that the photonic chiral spin textures in an optical interface originate from the system's symmetry and relativity. Analysis of the rotational symmetry in optical systems indicates that the conservation of the total angular momentum is preserved from the local variations of spin vectors. Specifically, although the integral spin momentum does not carry net energy, the local spin momentum distribution, which determines the local subluminal energy transport and minimization variation of the square of the total angular momentum, results in the chiral twisting of the local spin vectors. The findings of this study deepen the understanding of the symmetries, conservative laws, and energy transport in optical systems, reveal the similarities in the formation mechanisms and the geometries of photonic and condensed‐matter chiral spin textures, and have potential applications in chiral and spin photonics.

Switchable Chiroptical Flexible Films Based on Chiral Helical Superstructure: Handedness Inversion and Dissymmetric Adjustability by Stretching

AbstractIntelligent and controllable circularly polarized absorption and emission switching with high dissymmetric factors have attracted great attention due to the significant potential applications in chiral chemistry, chiral photonics, and electronics. However, the lack of examples to achieve freely switchable and adjustable chiroptical properties within a single material, especially in the deformable solid materials, limits the further continuous progress. Herein, an unprecedented, simple, and scalable way to achieve the above goal is presented. A stretchable spin‐coated thin film is fabricated from chiral helical substituted polyacetylene and thermoplastic polyurethane. Macromolecular chains self‐organize into hierarchically chiral superstructures under stretching, facilitating the film to absorb/emit circularly polarized light with opposite handedness from the two faces of the film. The dissymmetry intensity can be adjusted flexibly by controlling the elongation and recovery of the film. The nonreciprocity and chirality adjustability behaviors in stretchable solid materials represent a fundamental advancement and provide new opportunities for the design, preparation, and applications of chiroptical materials.