Showing papers on "Photonic crystal published in 2018"
TL;DR: In this article, a topological invariant was proposed to topologically protect the mode frequency at mid-gap and minimize the volume of a photonic defect mode in a femtosecond-laser-written waveguide array.
Abstract: Defect modes in two-dimensional periodic photonic structures have found use in diverse optical devices. For example, photonic crystal cavities confine optical modes to subwavelength volumes and can be used for enhancement of nonlinearity, lasing and cavity quantum electrodynamics. Defect-core photonic crystal fibres allow for supercontinuum generation and endlessly single-mode fibres with large cores. However, these modes are notoriously fragile: small structural change leads to significant detuning of resonance frequency and mode volume. Here, we show that photonic topological crystalline insulator structures can be used to topologically protect the mode frequency at mid-gap and minimize the volume of a photonic defect mode. We experimentally demonstrate this in a femtosecond-laser-written waveguide array by observing the presence of a topological zero mode confined to the corner of the array. The robustness of this mode is guaranteed by a topological invariant that protects zero-dimensional states embedded in a two-dimensional environment—a novel form of topological protection that has not been previously demonstrated. Eigenmodes of photonic crystal defects have now been topologically protected in an experimental demonstration that also shows how to minimize the mode volume.
411 citations
TL;DR: In this paper, the authors demonstrate a strong interface between single quantum emitters and topological photonic states, and demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends.
Abstract: The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder. Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored. We demonstrate a strong interface between single quantum emitters and topological photonic states. Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals. We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends. This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing.
406 citations
TL;DR: In this article, the spin-orbit coupling in one of the VPC domains was used for topologically protected chiral edge (kink) transport in VPCs with opposite valley-Chern indices.
Abstract: A photonic crystal can realize an analogue of a valley Hall insulator, promising more flexibility than in condensed-matter systems to explore these exotic topological states. Recently discovered1,2 valley photonic crystals (VPCs) mimic many of the unusual properties of two-dimensional (2D) gapped valleytronic materials3,4,5,6,7,8,9. Of the utmost interest to optical communications is their ability to support topologically protected chiral edge (kink) states3,4,5,6,7,8,9 at the internal domain wall between two VPCs with opposite valley-Chern indices. Here we experimentally demonstrate valley-polarized kink states with polarization multiplexing in VPCs, designed from a spin-compatible four-band model. When the valley pseudospin is conserved, we show that the kink states exhibit nearly perfect out-coupling efficiency into directional beams, through the intersection between the internal domain wall and the external edge separating the VPCs from ambient space. The out-coupling behaviour remains topologically protected even when we break the spin-like polarization degree of freedom (DOF), by introducing an effective spin–orbit coupling in one of the VPC domains. This also constitutes the first realization of spin–valley locking for topological valley transport.
378 citations
TL;DR: In this paper, a photonic crystal made of Al O(2)O(3) cylinders exhibits topological time-reversal symmetric electromagnetic propagation, similar to the quantum spin Hall effect in electronic systems.
Abstract: We demonstrate experimentally that a photonic crystal made of Al_{2}O_{3} cylinders exhibits topological time-reversal symmetric electromagnetic propagation, similar to the quantum spin Hall effect in electronic systems A pseudospin degree of freedom in the electromagnetic system representing different states of orbital angular momentum arises due to a deformation of the photonic crystal from the ideal honeycomb lattice It serves as the photonic analogue to the electronic Kramers pair We visualized qualitatively and measured quantitatively that microwaves of a specific pseudospin propagate only in one direction along the interface between a topological photonic crystal and a trivial one As only a conventional dielectric material is used and only local real-space manipulations are required, our scheme can be extended to visible light to inspire many future applications in the field of photonics and beyond
326 citations
TL;DR: In this article, a two-dimensional second-order photonic crystal with zero-dimensional corner states and one-dimensional boundary states for optical frequencies is proposed. And the theory of topological polarization is used to tune the easily fabricated structure of the photonic crystals so that different topological phases can be realized straightforwardly.
Abstract: Higher-order topological insulators (HOTIs) which go beyond the description of conventional bulk-boundary correspondence, broaden the understanding of topological insulating phases. Being mainly focused on electronic materials, HOTIs have not yet been found in photonic crystals. Here, we propose a type of two-dimensional second-order photonic crystals with zero-dimensional corner states and one-dimensional boundary states for optical frequencies. All of these states are topologically nontrivial and can be understood based on the theory of topological polarization. Moreover, by tuning the easily fabricated structure of the photonic crystals, different topological phases can be realized straightforwardly. Our study can be generalized to higher dimensions and provides a platform for higher-order photonic topological insulators and semimetals.
308 citations
TL;DR: This work realizes topologically protected, robust and unidirectional coupling as well as optical transport on a silicon-on-insulator platform by exploiting the valley degree of freedom, and shows the prototype of robustly integrated devices.
Abstract: Silicon-on-insulator (SOI) enables for capability improvement of modern information processing systems by replacing some of their electrical counterparts. With the miniaturization of SOI platform, backscattering suppression is one of the central issues to avoid energy loss and signal distortion in telecommunications. Valley, a new degree of freedom, provides an intriguing way for topologically robust information transfer and unidirectional flow of light, in particular for subwavelength strategy that still remains challenge in topological nanophotonics. Here, we realize topological transport in a SOI valley photonic crystal (VPC) slab. In such inversion asymmetry slab, singular Berry curvature near Brillouin zone corners guarantees valley-dependent topological edge states below light cone, maintaining a balance between in-plane robustness and out-of-plane radiation. Topologically robust transport at telecommunication wavelength is observed along two sharp-bend VPC interfaces with a compact size (< 10 um), showing flat-top high transmission of around 10% bandwidth. Furthermore, topological photonic routing is achieved in a bearded-stack VPC interface, originating from broadband unidirectional excitation of the valley-chirality-locked edge state by using a microdisk as a phase vortex generator. Control of valley in SOI platform not only shows a prototype of integrated photonic devices with promising applications for delay line, routing, optical isolation and dense wavelength division multiplexing for information processing based on topological nanophotonics, but also opens a new door towards the observation of non-trivial states even in non-Hermitain systems.
285 citations
TL;DR: In this article, the propagation of plasmon polaritons in twisted bilayer graphene (TBG) was studied by infrared nano-imaging, and it was shown that the atomic reconstruction occurring at small twist angles transforms the TBG into a natural plasmor photonic crystal for propagating nano-light.
Abstract: Graphene is an atomically thin plasmonic medium that supports highly confined plasmon polaritons, or nano-light, with very low loss. Electronic properties of graphene can be drastically altered when it is laid upon another graphene layer, resulting in a moire superlattice. The relative twist angle between the two layers is a key tuning parameter of the interlayer coupling in thus-obtained twisted bilayer graphene (TBG). We studied the propagation of plasmon polaritons in TBG by infrared nano-imaging. We discovered that the atomic reconstruction occurring at small twist angles transforms the TBG into a natural plasmon photonic crystal for propagating nano-light. This discovery points to a pathway for controlling nano-light by exploiting quantum properties of graphene and other atomically layered van der Waals materials, eliminating the need for arduous top-down nanofabrication.
270 citations
TL;DR: In this article, the authors theoretically proposed and experimentally demonstrate a class of guided resonances in photonic crystal slabs, where out-of-plane scattering losses are strongly suppressed due to their topological nature.
Abstract: Due to their ability to confine light, optical resonators are of great importance to science and technology, yet their performances are often limited by out-of-plane scattering losses from inevitable fabrication imperfections. Here, we theoretically propose and experimentally demonstrate a class of guided resonances in photonic crystal slabs, where out-of-plane scattering losses are strongly suppressed due to their topological nature. Specifically, these resonances arise when multiple bound states in the continuum - each carrying a topological charge - merge in the momentum space and enhance the quality factors of all resonances nearby. We experimentally achieve quality factors as high as $4.9\times 10^5$ based on these resonances in the telecommunication regime, which is 12-times higher than ordinary designs. We further show this enhancement is robust across the samples we fabricated.Our work paves the way for future explorations of topological photonics in systems with open boundary condition and their applications in improving optoelectronic devices in photonic integrated circuits.
263 citations
TL;DR: It is shown that truncated rhombic dodecahedral particles of the metal-organic framework (MOF) ZIF-8 can self-assemble into millimetre-sized superstructures with an underlying three-dimensional rhombohedral lattice that behave as photonic crystals.
Abstract: Self-assembly of particles into long-range, three-dimensional, ordered superstructures is crucial for the design of a variety of materials, including plasmonic sensing materials, energy or gas storage systems, catalysts and photonic crystals. Here, we have combined experimental and simulation data to show that truncated rhombic dodecahedral particles of the metal-organic framework (MOF) ZIF-8 can self-assemble into millimetre-sized superstructures with an underlying three-dimensional rhombohedral lattice that behave as photonic crystals. Those superstructures feature a photonic bandgap that can be tuned by controlling the size of the ZIF-8 particles and is also responsive to the adsorption of guest substances in the micropores of the ZIF-8 particles. In addition, superstructures with different lattices can also be assembled by tuning the truncation of ZIF-8 particles, or by using octahedral UiO-66 MOF particles instead. These well-ordered, sub-micrometre-sized superstructures might ultimately facilitate the design of three-dimensional photonic materials for applications in sensing.
244 citations
TL;DR: An overview of the state-of-the-art in evanescent field biosensing technologies including interferometer, microcavity, photonic crystal, and Bragg grating waveguide-based sensors, as well as real biomarkers for label-free detection are exhibited and compared.
Abstract: Thanks to advanced semiconductor microfabrication technology, chip-scale integration and miniaturization of lab-on-a-chip components, silicon-based optical biosensors have made significant progress for the purpose of point-of-care diagnosis In this review, we provide an overview of the state-of-the-art in evanescent field biosensing technologies including interferometer, microcavity, photonic crystal, and Bragg grating waveguide-based sensors Their sensing mechanisms and sensor performances, as well as real biomarkers for label-free detection, are exhibited and compared We also review the development of chip-level integration for lab-on-a-chip photonic sensing platforms, which consist of the optical sensing device, flow delivery system, optical input and readout equipment At last, some advanced system-level complementary metal-oxide semiconductor (CMOS) chip packaging examples are presented, indicating the commercialization potential for the low cost, high yield, portable biosensing platform leveraging CMOS processes
239 citations
TL;DR: In this paper, an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported, which exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances.
Abstract: The realization of an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported. Liquids with different refractive indices, ranging from 1.4000 to 1.4480, are infiltrated in a microfluidic chamber bonded to the sensing dielectric metasurface. A bulk liquid sensitivity of 178 nm/RIU is achieved, while a Q-factor of about 2000 gives a sensor figure of merit up to 445 in air at both visible and infrared excitations. Furthermore, the detection of ultralow-molecular-weight (186 Da) molecules is demonstrated with a record resonance shift of 6 nm per less than a 1 nm thick single molecular layer. The system exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances, overcoming the limits of standard photonic crystals and plasmonic resonant configurations.
20 Mar 2018
TL;DR: It is shown that the Laplacian can be implemented in the transmission mode by a photonic crystal slab device, and points to new opportunities in optical analog computing as provided by nanophotonic structures.
Abstract: Spatial differentiation is important in image-processing applications such as image sharpening and edge-based segmentation. In these applications, of particular importance is the Laplacian, the simplest isotropic derivative operator in two dimensions. Spatial differentiation can be implemented electronically. However, in applications requiring real-time and high-throughput image differentiation, conventional digital computations become challenging. Optical analog computing may overcome this challenge by offering high-throughput low-energy-consumption operations using compact devices. However, previous works on spatial differentiation with nanophotonic structures are restricted to either one-dimensional differentiation or reflection mode, whereas operating in the transmission mode is important because it is directly compatible with standard image processing/recognition systems. Here, we show that the Laplacian can be implemented in the transmission mode by a photonic crystal slab device. We theoretically derive the criteria for realizing the Laplacian using the guided resonances in a photonic crystal slab. Guided by these criteria, we show that the Laplacian can be implemented using a carefully designed photonic crystal slab with a non-trivial isotropic band structure near the Γ point. Our work points to new opportunities in optical analog computing as provided by nanophotonic structures.
TL;DR: The proposed plasmonic sensing scheme with the miniaturized photonic crystal fiber attributes is able to detect the analyte refractive indices in the range of 1.33-1.42 and will find the possible applications in the medical diagnostics, biomolecules, organic chemical, and chemical analyte detection.
Abstract: Highly sensitive and miniaturized sensors are highly desirable for real-time analyte/sample detection In this Letter, we propose a highly sensitive plasmonic sensing scheme with the miniaturized photonic crystal fiber (PCF) attributes A large cavity is introduced in the first ring of the PCFs for the efficient field excitation of the surface plasmon polariton mode and proficient infiltration of the sensing elements Due to the irregular air-hole diameter in the first ring, the cavity exhibits the birefringence behavior which enhances the sensing performance The novel plasmonic material gold has been used considering the chemical stability in an aqueous environment The guiding properties and the effects of the sensing performance with different parameters have been investigated by the finite element method, and the proposed PCFs have been fabricated using the stack-and-draw fiber drawing method The proposed sensor performance was investigated based on the wavelength and amplitude sensing techniques and shows the maximum sensitivities of 11,000 nm/RIU and 1,420 RIU−1, respectively It also shows the maximum sensor resolutions of 91×10−6 and 7×10−6 RIU for the wavelength and amplitude sensing schemes, respectively, and the maximum figure of merits of 407 Furthermore, the proposed sensor is able to detect the analyte refractive indices in the range of 133–142; as a result, it will find the possible applications in the medical diagnostics, biomolecules, organic chemical, and chemical analyte detection
TL;DR: Sub-wavelength-thick, one-dimensional photonic crystals are demonstrated as a designable, compact, and practical platform for strong coupling with atomically thin van der Waals crystals.
Abstract: Semiconductor microcavity polaritons, formed via strong exciton-photon coupling, provide a quantum many-body system on a chip, featuring rich physics phenomena for better photonic technology. However, conventional polariton cavities are bulky, difficult to integrate, and inflexible for mode control, especially for room-temperature materials. Here we demonstrate sub-wavelength-thick, one-dimensional photonic crystals as a designable, compact, and practical platform for strong coupling with atomically thin van der Waals crystals. Polariton dispersions and mode anti-crossings are measured up to room temperature. Non-radiative decay to dark excitons is suppressed due to polariton enhancement of the radiative decay. Unusual features, including highly anisotropic dispersions and adjustable Fano resonances in reflectance, may facilitate high temperature polariton condensation in variable dimensions. Combining slab photonic crystals and van der Waals crystals in the strong coupling regime allows unprecedented engineering flexibility for exploring novel polariton phenomena and device concepts.
TL;DR: In this paper, the latest advances in the development of photonic crystal photocatalysts are highlighted, targeting primarily on the design, fabrication, structure-activity and performance evaluation of visible light activated (VLA) TiO2 inverse opals in the degradation of water and air pollutants as well as water splitting.
Abstract: Photonic crystals have been established as unique periodic structures to promote photon capture and control over light-matter interactions. Their application in semiconductor, mainly TiO2, photocatalysis has emerged as a promising structural modification to boost light harvesting of photocatalytic materials by means of slow photons i.e. light propagation at reduced group velocity near the edges of the photonic band gap (PBG). In this review, the latest advances in the development of TiO2 photonic crystal photocatalysts are highlighted, targeting primarily on the design, fabrication, structure-activity and performance evaluation of visible light activated (VLA) TiO2 inverse opals in the degradation of water and air pollutants as well as water splitting. Up to date work demonstrating the amplification effect of PBG engineered photonic crystals on the photocatalytic and photoelectrochemical performance under UV excitation is accordingly presented. Recent developments on the combination of enhanced light trapping, mainly via slow photons, mass transport and adsorption of macro/mesoporous inverse opals with targeted compositional and electronic modifications currently pursued to promote charge separation and visible light activation, i.e. dye sensitization, non-metal and self-doping, coupling with metallic nanoparticles and plasmonic effects, heterostructuring with narrow band gap semiconductors, quantum dots and graphene as well as the use of alternative metal oxide photocatalysts beyond TiO2 are thoroughly reviewed with respect to their potential for key improvements of the photocatalytic efficiency under visible light. Pertinent challenges and future prospects in photonic crystal-assisted VLA photocatalysts are addressed aimed at advanced photon management routes that could step up photocatalytic applications.
TL;DR: In this article, the authors design and engineer suspended photonic crystal cavities from hexagonal boron nitride (hBN) and demonstrate quality (Q) factors in excess of 2000.
Abstract: Development of scalable quantum photonic technologies requires on-chip integration of photonic components. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of high-quality optical resonators. In this letter, we design and engineer suspended photonic crystal cavities from hBN and demonstrate quality (Q) factors in excess of 2000. Subsequently, we show deterministic, iterative tuning of individual cavities by direct-write EBIE without significant degradation of the Q-factor. The demonstration of tunable cavities made from hBN is an unprecedented advance in nanophotonics based on van der Waals materials. Our results and hBN processing methods open up promising avenues for solid-state systems with applications in integrated quantum photonics, polaritonics and cavity QED experiments.
Journal Article•
TL;DR: In this article, the authors demonstrate a strong interface between single quantum emitters and topological photonic states and demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends.
Abstract: The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored We demonstrate a strong interface between single quantum emitters and topological photonic states Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing
TL;DR: Optical probing of spectrally resolved single Nd^{3+} rare-earth ions in yttrium orthovanadate allows for the observation of coherent optical Rabi oscillations, which could enable optically controlled spin qubits, quantum logic gates, and spin-photon interfaces for future quantum networks.
Abstract: We demonstrate optical probing of spectrally resolved single Nd^{3+} rare-earth ions in yttrium orthovanadate. The ions are coupled to a photonic crystal resonator and show strong enhancement of the optical emission rate via the Purcell effect, resulting in near radiatively limited single photon emission. The measured high coupling cooperativity between a single photon and the ion allows for the observation of coherent optical Rabi oscillations. This could enable optically controlled spin qubits, quantum logic gates, and spin-photon interfaces for future quantum networks.
TL;DR: In this paper, a topological PhC nanocavity with a near-diffraction-limited mode volume and its application to single-mode lasing was reported, and the observed lasing accompanied a high spontaneous emission coupling factor stemming from the nanoscale confinement.
Abstract: Topological edge states exist at the interfaces between two topologically distinct materials. The presence and number of such modes are deterministically predicted from the bulk band topologies, known as the bulk-edge correspondence. This principle is highly useful for predictably controlling optical modes in resonators made of photonic crystals (PhCs), leading to the recent demonstrations of microscale topological lasers. Meanwhile, zero-dimensional topological trapped states in the nanoscale remained unexplored, despite its importance for enhancing light–matter interactions and for wide applications including single-mode nanolasers. Here, we report a topological PhC nanocavity with a near-diffraction-limited mode volume and its application to single-mode lasing. The topological origin of the nanocavity, formed at the interface between two topologically distinct PhCs, guarantees the existence of only one mode within its photonic bandgap. The observed lasing accompanies a high spontaneous emission coupling factor stemming from the nanoscale confinement. These results encompass a way to greatly downscale topological photonics. For most lasing and photonic applications, it is essential to control the number of lasing modes that are present. In this work, an interface between two topologically distinct photonic crystals is used to ensure single-mode lasing with enhanced light-matter interactions due to a near-diffraction-limited mode volume.
TL;DR: A convenient way to imprint robust invisible patterns in colloidal crystals of hollow silica spheres is presented, evaluated by thermodynamic predictions and subsequently verified by exposure to various vapors with different surface tension.
Abstract: The colors of photonic crystals are based on their periodic crystalline structure. They show clear advantages over conventional chromophores for many applications, mainly due to their anti-photobleaching and responsiveness to stimuli. More specifically, combining colloidal photonic crystals and invisible patterns is important in steganography and watermarking for anticounterfeiting applications. Here a convenient way to imprint robust invisible patterns in colloidal crystals of hollow silica spheres is presented. While these patterns remain invisible under static environmental humidity, even up to near 100% relative humidity, they are unveiled immediately (≈100 ms) and fully reversibly by dynamic humid flow, e.g., human breath. They reveal themselves due to the extreme wettability of the patterned (etched) regions, as confirmed by contact angle measurements. The liquid surface tension threshold to induce wetting (revealing the imprinted invisible images) is evaluated by thermodynamic predictions and subsequently verified by exposure to various vapors with different surface tension. The color of the patterned regions is furthermore independently tuned by vapors with different refractive indices. Such a system can play a key role in applications such as anticounterfeiting, identification, and vapor sensing.
TL;DR: It is demonstrated that inter-valley scattering is inhibited at a Y-junction between three sections with different valley topology, opening up the possibility of using the valley degree of freedom to control the flow of optical signals in 2D structures.
Abstract: Pseudo-spin and valley degrees of freedom engineered in photonic analogues of topological insulators provide potential approaches to optical encoding and robust signal transport. Here we observe a ballistic edge state whose spin-valley indices are locked to the direction of propagation along the interface between a valley photonic crystal and a metacrystal emulating the quantum spin-Hall effect. We demonstrate the inhibition of inter-valley scattering at a Y-junction formed at the interfaces between photonic topological insulators carrying different spin-valley Chern numbers. These results open up the possibility of using the valley degree of freedom to control the flow of optical signals in 2D structures.
TL;DR: The generation of metallosupramolecular polymer-based photonic elastomers with tunable mechanical strength, angle-independent structural color, and self-healing capability is reported, which enables their chameleon-skin-like mechanochromic capability.
Abstract: Photonic elastomers that can change colors like a chameleon have shown great promise in various applications. However, it still remains a challenge to produce artificial photonic elastomers with desired optical and mechanical properties. Here, the generation of metallosupramolecular polymer-based photonic elastomers with tunable mechanical strength, angle-independent structural color, and self-healing capability is reported. The photonic elastomers are prepared by incorporating isotropically arranged monodispersed SiO2 nanoparticles within a supramolecular elastomeric matrix based on metal coordination interaction between amino-terminated poly(dimethylsiloxane) and cerium trichloride. The photonic elastomers exhibit angle-independent structural colors, while Young's modulus and elongation at break of the as-formed photonic elastomers reach 0.24 MPa and 150%, respectively. The superior elasticity of photonic elastomers enables their chameleon-skin-like mechanochromic capability. Moreover, the photonic elastomers are capable of healing scratches or cuts to ensure sustainable optical and mechanical properties, which is crucial to their applications in wearable devices, optical coating, and visualized force sensing.
TL;DR: The different modulating effects of photonic crystal dimensions, light-emitter positions, Photonic crystal structure type, and the refractive index of photonics crystal building blocks are highlighted with the aim of evaluating the fundamental principles that determine light propagation.
Abstract: The modulation of luminescence is essential because unwanted spontaneous-emission modes have a negative effect on the performance of luminescence-based photonic devices. Photonic crystals are promising materials for the control of light emission because of the variation in the local density of optical modes within them. They have been widely investigated for the manipulation of the emission intensity and lifetime of light emitters. Several groups have achieved greatly enhanced emission by depositing emitters on the surface of photonic crystals. Herein, the different modulating effects of photonic crystal dimensions, light-emitter positions, photonic crystal structure type, and the refractive index of photonic crystal building blocks are highlighted, with the aim of evaluating the fundamental principles that determine light propagation. The applications of using photonic crystals to manipulate spontaneous emission in light-emitting diodes and sensors are also reviewed. In addition, potential future challenges and improvements in this field are presented.
TL;DR: Lova et al. as discussed by the authors reviewed solution-processed polymer and inorganic mesoporous planar 1D photonic crystals and discussed properties, growth techniques, and applications of such structures in the field of emission control, lasing, sensing and photovoltaics.
Abstract: solution-processed polymer and inorganic mesoporous planar 1D photonic crystals are reviewed. Solution processing of these structures offers really low-cost and easy to scale-up fabrication, which attracted a wide technological interest. Properties, growth techniques, and applications of such structures are discussed in the field of emission control, lasing, sensing, and photovoltaics. P. Lova,* G. Manfredi, D. Comoretto* .......................... 1800730
06 Jun 2018
TL;DR: Flatband photonic lattices consist of arrays of coupled waveguides or resonators where the peculiar lattice geometry results in at least one completely flat or dispersionless band in its photonic band structure.
Abstract: Flatbands are receiving increasing theoretical and experimental attention in the field of photonics, in particular in the field of photonic lattices. Flatband photonic lattices consist of arrays of coupled waveguides or resonators where the peculiar lattice geometry results in at least one completely flat or dispersionless band in its photonic band structure. Although bearing a strong resemblance to structural slow light, this independent research direction is instead inspired by analogies with “frustrated” condensed matter systems. In this Perspective, we critically analyze the research carried out to date, discuss how this exotic physics may lead to novel photonic device applications, and chart promising future directions in theory and experiment.
20 Nov 2018
TL;DR: In this article, the topological band structures in photonic time crystals were studied and the topology invariant associated with the momentum bands, which is expressed in the phase between the forward-and backward-propagating waves, was calculated.
Abstract: We find topological band structures in photonic time crystals—materials in which the refractive index varies periodically and abruptly in time. When the refractive index changes abruptly, the light experiences time refraction and time reflection, analogous to refraction and reflection in photonic crystals. The interference between time-refracted and time-reflected waves gives rise to dispersion bands, which are gapped in the momentum. We show theoretically that photonic time crystals can be in a topologically nontrivial phase, and calculate the topological invariant associated with the momentum bands, which is expressed in the phase between the forward- and backward-propagating waves. When an interface is generated between two time crystals of different topologies, the Zak phase yields a localized interface state, manifested as a localized temporal peak.
TL;DR: Biodegradable cellulose-based photonic and plasmonic architectures are fabricated via soft nanoimprinting lithography, and are used for structural colour generation, photoluminescence enhancement and as disposable surface-enhanced Raman scattering substrates.
Abstract: As contamination and environmental degradation increase nowadays, there is a huge demand for new eco-friendly materials. Despite its use for thousands of years, cellulose and its derivatives have gained renewed interest as favourable alternatives to conventional plastics, due to their abundance and lower environmental impact. We report the fabrication of photonic and plasmonic structures by moulding hydroxypropyl cellulose into sub-micrometric periodic lattices, using soft lithography. This is an alternative way to achieve structural colour in this material which is usually obtained exploiting its chiral nematic phase. Cellulose based photonic crystals are biocompatible and can be dissolved in water or not depending on the derivative employed. Patterned cellulose membranes exhibit tuneable colours and may be used to boost the photoluminescence of a host organic dye. Furthermore, we show how metal coating these cellulose photonic architectures leads to plasmonic crystals with excellent optical properties acting as disposable surface enhanced Raman spectroscopy substrates.
TL;DR: In this article, a 3D nonlinear photonic crystal, fabricated in ferroelectric barium calcium titanate, is presented, which enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures.
Abstract: The performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of materials. This modulation ensures efficient energy exchange between optical waves at different frequencies via quasi-phase matching1. In general, quasi-phase-matching structures, also known as nonlinear photonic crystals2–4, offer a variety of properties and functionalities that cannot be obtained in uniform nonlinear crystals5–9. So far, nonlinear photonic crystals have been restricted to one- or two-dimensional geometries owing to a lack of fabrication technologies capable of three-dimensional (3D) nonlinearity engineering. Here, we provide an experimental example of a 3D nonlinear photonic crystal, fabricated in ferroelectric barium calcium titanate, by applying an ultrafast light domain inversion approach. The resulting full flexibility of 3D nonlinearity modulation enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures. A three-dimensional nonlinear photonic crystal in ferroelectric barium calcium titanate that enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures, is experimentally realized.
TL;DR: In this paper, anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves.
Abstract: Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic co-integration. However, the large spatial extent of evanescent waves arising from nanoscale confinement, ubiquitous in silicon photonic devices, causes significant cross-talk and scattering loss. Here, we demonstrate that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves. We experimentally show the reduction of cross-talk by greater than 30 times and the bending loss by greater than 3 times in densely integrated, ultra-compact photonic circuit blocks. Our prototype all-dielectric metamaterial-waveguide achieves a low propagation loss of approximately 3.7±1.0 dB/cm, comparable to those of silicon strip waveguides. Our approach marks a departure from interference-based confinement as in photonic crystals or slot waveguides, which utilize nanoscale field enhancement. Its ability to suppress evanescent waves without substantially increasing the propagation loss shall pave the way for all-dielectric metamaterial-based dense integration.