Recently, optical bound states in continuum in various passive photonic crystals have been identified and similar structures incorporated with optical gain have been reported to exhibit lasing. However, no explicit control over the type of lasing BIC has been reported. In this work, we utilize all four fundamental BICs related to the lowest energy Gamma-point of a square photonic crystal lattice. We identify the associated topological charges from experimentally obtained dispersions, finite element method simulations, as well as from spherical decomposition method based on the microscopic polarization currents in the photonic crystal plane. By tailoring the periodicity and the hole diameter of the photonic crystal slab, we selectively bring each of the four BIC resonances to a wavelength regime, where fluorescent IR702 molecules overlaid with the photonic crystal provide sufficient gain for the onset of lasing. We experimentally analyze all four observed lasing BICs by imaging their far-field polarization vortices and their associated topological charges. The results correspond excellently with the transmission results as well as the simulation results in the absence of gain. Finally, we experimentally present a case where the lasing signal reveals the coexistence of two BICs with opposite topological charges, resulting in a unique polarization pattern. We believe our results enable tailoring the properties, such as polarization winding and topological charge of BICs, by a priori design and thus pave the way for a more general utilization of their appealing properties.
Radiative properties of lasing plasmonic bound state in continuum are analyzed. The topological charge of the lasing signal is analyzed in the far field as well as in the source plane of the finite sized plasmonic lattice. The physical mechanism enabling the coupling of the BIC to radiation continuum is identified. We show that while the BICs have their origin in multipolar resonances, their far-field radiation properties are governed by the position dependent dipole moment distribution induced by the symmetry breaking in a finite plasmonic lattice. Remarkably, this dipole-moment enabled coupl…
Non-Hermitian photonic systems with loss and gain attract much attention due to their exceptional abilities in molding the flow of light. Introducing asymmetry to the $\mathcal{PT}$-symmetric system with perfectly balanced loss and gain, we reveal the mechanism of transition from the quasibound state in the continuum (quasi-BIC) to the simultaneous coherent perfect absorption (CPA) and lasing in a layered structure comprising epsilon-near-zero (ENZ) media. Two types of asymmetry (geometric and non-Hermitian) are analyzed with the scattering matrix technique. The effect of the CPA-lasing associ…
Colloidal quantum dots (CQDs) are a promising gain material for solution-processed, wavelength-tunable lasers, with potential application in displays, communications, and biomedical devices. In this work, we combine a CQD film with an array of titanium dioxide (TiO2) nanoantennas to achieve lasing via bound states in the continuum (BICs), which are symmetry-protected cavity modes with giant quality factors. Here, the BICs arise from slab waveguide modes in the planar film, coupled to the periodic nanoantenna array. We engineer the thickness of the CQD film and size of the nanoantennas to achie…
In this Letter, we present a rigorous method to study the stability of periodic lasing systems. In a linear model, the presence of a continuum of modes (with arbitrarily close lasing thresholds) gives the impression that stable single-mode lasing cannot be maintained in the limit of an infinite system. However, we show that nonlinear effects of the Maxwell-Bloch equations can lead to stable systems near threshold given a simple stability condition on the sign of the laser detuning compared to the band curvature. We examine band-edge (1d) and bound-in-continuum (2d) lasing modes and validate ou…
Chiral lasing via broken parity-time symmetry in bound-state-in-the-continuum metasurfaces
ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Department of Electronic Materials Engineering, Research School of Physics, Australian National University（澳大利亚国立大学变革性超光学系统卓越中心）
Semiconductor lasers with ultra-low thresholds and minimal footprints are a topic of active research. Such devices require a combination of high quality factor laser cavities with small active region volumes, which drives the quest for novel cavity geometries exploiting nano-optic concepts. For high-reflectivity coated ridge lasers, where light is tightly confined in the waveguide, a low threshold can only be achieved by strongly reducing the diffraction losses arising at the laser facet. We show here that, somewhat counter-intuitively, opening a carefully designed aperture in a metallic facet…
It was widely accepted that embedding of metallic layers into optoelectronic structures is detrimental to lasing due absorption in metal. However, recently macroscopic optical coherence and lasing was observed in microcavities with intra-cavity single metallic layer. Here we propose the design of the of microcavity-type structure with two intra-cavity metallic layers which could serve as contacts for electrical pumping. The design of optical modes based on utilizing peculiarities of Tamm plasmon provides vanishing absorption due to fixing of the node of electric field of optical mode to metall…
Recently emerged dielectric resonators and metasurfaces offer a low-loss platform for efficient manipulation of electromagnetic waves from microwave to visible. Such flat meta-optics can focus electromagnetic waves, generate structured beams and vortices, enhance local fields for sensing as well as provide additional functionalities for advanced MRI machinery. Recent advances are associated with exotic optical modes called bound states in the continuum, which can give rise to extremely large quality factors and supercavity lasing. Here, we experimentally demonstrate subwavelength active superc…
Photoluminescence is a phenomenon of significant interest due to its wide range of technological applications in plasmonics, nanolasers, spasers, lasing spasers, loss compensation and gain in metamaterials, and luminescent media. Nanostructured materials are known to have very different luminescence characteristics to bulk samples or planar films. Here we show that by engineering a nanostructured meta-surface, we can choose the position of photoluminescence absorption and emission lines of thin gold films. The nanostructuring also aids to strong enhancement of the emission from gold, by a fact…
Metal halide perovskites have emerged as promising gain materials for on-chip lasers in photonic integrated circuits (PICs). However, stable continuous wave (CW) lasing behavior under optical pumping at room temperature - a prerequisite for electrically pumped lasing - has not yet been demonstrated. To achieve stable CW operation, we introduce a multiplex of strategies that include morphological, structural and interfacial engineering of CH3NH3PbBr3 (MAPbBr3) thin films to improve perovskite's intrinsic stability, as well as high quality cavity design to reduce the operational power. We demons…
We report polariton lasing in localised gap states in a honeycomb lattice of coupled micropillars. Localisation of the modes is induced by the optical potential created by the excitation beam, requiring no additional engineering of the otherwise homogeneous polariton lattice. The spatial shape of the gap states arises from the interplay of the orbital angular momentum eigenmodes of the cylindrical potential created by the excitation beam and the hexagonal symmetry of the underlying lattice. Our results provide insights into the engineering of defect states in two-dimensional lattices.
Line lasing in a two-dimensional lattice of orbital photonic resonators
Univ. Lille, CNRS, UMR 8523 – PhLAM – Physique des Lasers Atomes et Molécules（里尔大学，法国国家科学研究中心，UMR 8523 – 激光物理原子与分子物理实验室）；Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies（巴黎萨克雷大学，法国国家科学研究中心，纳米科学与工程中心）
We experimentally observe lasing in a hexamer plasmonic lattice and find that when tuning the scale of the unit cell, the polarization winding of the emission changes. By a theoretical analysis we identify the lasing modes as quasi bound states in continuum (quasi-BICs) of topological charges of zero, one or two. A T-matrix simulation of the structure reveals that the mode quality(Q)-factors depend on the scale of the unit cell, with highest-Q modes favored by lasing. The system thus shows a loss-driven transition between lasing in modes of trivial and high-order topological charge.
In sufficiently strong scattering media, light transport is suppressed and modes are exponentially localized. Anderson-like localized states have long been recognized as potential candidate for high-Q optical modes for low-threshold, cost effective random lasers. Operating in this regime remains however a challenge since Anderson localization is difficult to achieve in optics and nonlinear mode interaction compromise its observation. Here, we exhibit individually each lasing mode of a low-dimension solid-state random laser by applying a non-uniform optical gain. By undoing gain competition and…
We explore absorbing open-boundary modes in non-Hermitian photonic systems. The modes have a continuum spectrum in the infinite system-size limit and can exhibit the non-Hermitian skin effect. In contrast to the conventional non-Hermitian skin modes under the fixed-end open-boundary condition, the modes concerned exhibit a strongly size-dependent spectrum that gradually converges to the non-Bloch-band dispersion. The modes correspond to the poles of the $S$ matrix, and are closely related to the lasing. We demonstrate these properties in a two-dimensional non-Hermitian photonic crystal with ga…
On-chip light sources are critical for the realization of fully integrated photonic circuitry. So far, semiconductor miniaturized lasers have been mainly limited to sizes on the order of a few microns. Further reduction of sizes is challenging fundamentally due to the associated radiative losses. While using plasmonic metals helps to reduce radiative losses and sizes, they also introduce Ohmic losses hindering real improvements. In this work, we show that, making use of quasi-bound states in the continuum, or supercavity modes, we circumvent these fundamental issues and realize the smallest pu…
The pursuit of compact lasers with low-thresholds has imposed strict requirements on tight light confinements with minimized radiation losses. Bound states in the continuum (BICs) have been recently demonstrated as an effective mechanism to trap light along the out-of-plane direction, paving the way to low-threshold lasers. To date, most reported BIC lasers are still bulky due to the absence of in-plane light confinement. In this work, we combine BICs and photonic band gaps to realize three-dimensional (3D) light confinements, as referred to miniaturized (mini-) BICs. Together with 3D carrier …
Bianisotropy is a powerful concept enabling asymmetric optical response, including asymmetric reflection, absorption, optical forces, light trapping, and lasing. The physical origin of these asymmetric effects can be understood from magnetoelectric coupling and asymmetrical field enhancement. Here, we theoretically propose highly asymmetric second-harmonic generation (SHG) in bianisotropic AlGaAs metasurfaces. We show that around four orders of magnitude second-harmonic power difference for the forward and backward illuminations can be obtained by altering geometrical parameters that coincide …
Metasurfaces have attracted a lot of attention in recent years due to novel ways they provide for the efficient wavefront control and engineering of the resonant transmission. We discuss an approach allowing effectively control appearance of the sharp Fano resonances in metasurfaces associated with the {\it bound states in the continuum}. We demonstrate that by breaking the symmetry transversely, in the direction perpendicular to a metasurface with a complex unit cell, we can control the number, frequency, and type of high-$Q$ resonances originating from bound states in the continuum. As examp…
Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Recent experiments have demonstrated the existence of exotic modes which occur in off-$Γ$\ points not accessible by symmetry-protected BICs, Freidrich-Wintgen (FW) BICs. In previous works, FW BICs were formed by either varying the incident angle or through geometric manipulation. On the contrary, in this work we demonstrate the formation of FW BICs induced by different linear polari…
The recent advancement in lithium niobate on insulator (LNOI) technology is revolutionizing the optoelectronic industry as devices of higher performance, lower power consumption, and smaller footprint can be realized due to the high optical confinement in the structures. The LNOI platform offers both large \c{hi}(2) and \c{hi}(3) nonlinearities along with the power of dispersion engineering, enabling brand new nonlinear photonic devices and applications towards the next generation of integrated photonic circuits. However, the Raman scattering, one of the most important nonlinear phenomena, hav…
Electrically reconfigurable extended lasing state in an organic liquid-crystal microcavity
University of Southampton（南安普顿大学）；University of Iceland（冰岛大学）；Institute of Experimental Physics, Faculty of Physics, University of Warsaw（华沙大学物理学院实验物理研究所）；Durham University（杜伦大学）；Institut Pascal, Université Clermont Auvergne, CNRS, ClermontINP（帕斯卡尔研究所，克莱蒙奥弗涅大学，法国国家科学研究中心，克莱蒙理工学院）；Institute of Applied Physics, Military University of Technology（军事科技大学应用物理研究所）；Institute of Optoelectronics, Military University of Technology（军事科技大学光电子研究所）；Institute of Chemistry, Military University of Technology（军事科技大学化学研究所）
The concept of optical bound states in the continuum (BICs) underpins the existence of strongly localized waves embedded into the radiation spectrum that can enhance the electromagnetic fields in subwavelength photonic structures. Early studies of optical BICs in waveguides and photonic crystals uncovered their topological properties, and the concept of quasi-BIC metasurfaces facilitated applications of strong light-matter interactions to biosensing, lasing, and low-order nonlinear processes. Here we employ BIC-empowered dielectric metasurfaces to generate efficiently high optical harmonics up…
Identifying phases and analyzing the stability of dynamic states are ubiquitous and important problems which appear in various physical systems. Nonetheless, drawing a phase diagram in high-dimensional and large parameter spaces has remained challenging. Here, we propose a data-driven method to derive the phase diagram of lasing modes in topological insulator lasers. The classification is based on the temporal behaviour of the topological modes obtained via numerical integration of the rate equation. A semi-supervised learning method is used and an adaptive library is constructed in order to d…
Exceptional Points, Lasing, and Coherent Perfect Absorption in Floquet Scattering Systems
Vienna University of Technology (TU Wien)（维也纳工业大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；University of Graz（格拉茨大学）；NAWI Graz（NAWI格拉茨）；Riga Technical University（里加技术大学）
We theoretically propose and numerically demonstrate that perfect feeding of a polaritonic system with full electromagnetic energy under one-port beam incidence, referred to as polaritonic critical coupling, can be achieved in a hybrid dielectric metasurface-WS$_2$ monolayer structure. Polaritonic critical coupling, where the critical coupling and strong coupling are simultaneously attained, is determined by the relative damping rates of the cavity resonance, $\rm γ_Q$, provided by a symmetry-protected quasi-bound states in the continuum, and excitonic resonance of WS$_2$ monolayer, $\rm γ_X$.…
Fano resonances and bound states in the continuum (BICs) exhibit a rich phenomenology stemming from, respectively, their asymmetric line shapes and infinite quality factors. Here, we show experimentally and theoretically that rod dimer metasurfaces exhibit narrow (high-Q) Fano resonances at THz frequencies. These resonances evolve continuously into a BIC as the rods in each dimer become identical. We demonstrate analytically that this is a universal behavior occurring in arrays of dimers consisting of detuned resonant dipoles. Fano resonances arise as a result of the interference between broad…
Novel physical concepts that originate from quantum mechanics, such as non-Hermitian systems (dealing mostly with PT and anti-PT symmetry) and bound states in the continuum (BICs), have attracted great interest in the optics and photonics community. To date, BICs and anti-PT symmetry seem to be two independent topics. Here, we for the first time propose a parallel cascaded-resonator system to achieve BICs and anti-PT symmetry simultaneously. We found that the requirements for the Fabry-Pérot BIC and anti-PT symmetry can both be satisfied when the phase shift between any two adjacent resonators…
Bound state in the continuum (BIC) is a mathematical concept with an infinite radiative quality factor (Q) that exists only in an ideal infinite array. It was first proposed in quantum mechanics, and extended to general wave phenomena such as acoustic, water, elastic, and electromagnetic waves. In photonics, it is essential to achieve high Q resonances for enhanced light-mater interactions that could enable low-threshold lasers, ultrasensitive sensors, and optical tweezers. Here, we demonstrate dual bound states in the continuum in a subwavelength planar metamaterial cavity that reveal symmetr…
Soliton formation in a bound state in the continuum GaN waveguide polariton laser
Laboratoire Charles Coulomb, Université de Montpellier, CNRS（蒙彼利埃大学查尔斯·库隆实验室）；Institut Pascal, PHOTON-N2, Université Clermont Auvergne, CNRS, Clermont INP（克莱蒙奥弗涅大学帕斯卡尔研究所）；B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine（乌克兰国家科学院B.维尔金低温物理与工程研究所）；Naturwissenschaftlich-Technische Fakultät, Universität Siegen（锡根大学自然科学技术学院）；CRHEA, Université Cote d’Azur, CNRS（蔚蓝海岸大学CRHEA研究中心）；Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Saclay（巴黎萨克雷大学纳米科学和纳米技术研究中心）
The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound states in the continuum (BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q facto…
All-optical programming of polarization singularities in a photonic-crystal laser
Ecole Centrale de Lyon, CNRS, INSA Lyon, Université Claude Bernard Lyon 1, CPE Lyon, Institut des Nanotechnologies de Lyon (INL)（里昂中央理工学院，法国国家科学研究中心，里昂国立应用科学学院，里昂第一大学，里昂高等化工学院，里昂纳米技术研究所）；Department of Physics, NISM Institute, University of Namur（纳慕尔大学物理系，NISM研究所）；Centre for OptoElectronics and Biophotonics (COEB), School of Electrical and Electronic Engineering, Nanyang Technological University（南洋理工大学电气与电子工程学院光电与生物光子学中心）；CNRS-International-NTU-Thales Research Alliance (CINTRA)（法国国家科学研究中心-国际南洋理工大学-泰雷兹研究联盟）
Enhancement of light-matter interactions is of great importance for many nanophotonic devices, and one way to achieve it is to feed energy perfectly to the strongly coupled system. Here, we propose gap-perturbed dimerized gratings based on bulk WS2 for flexible control of the strong coupling between quasi-bound state in the continuum (quasi-BIC) and exciton. The simulation results show that when a gap perturbation is introduced into the system resulting in the Brillouin zone folding, BIC transforms into quasi-BIC whose quality factor (Q-factor) is related to the value of gap perturbation. The …
Photonic-crystal surface-emitting lasers (PCSELs), which utilize a two-dimensional (2D) optical resonance inside a photonic crystal for lasing, feature various outstanding functionalities such as single-mode high-power operation and arbitrary control of beam polarizations. Although most of the previous designs of PCSELs employ spatially uniform photonic crystals, it is expected that lasing performance can be further improved if it becomes possible to optimize the spatial distribution of photonic crystals. In this paper, we investigate the structural optimization of PCSELs via quantum annealing…
Engineering thermal emission with enhanced emissivity and quality factor using bound states in the continuum and electromagnetically-induced absorption
Recent progress in nanophotonics is driven by the desire to engineer light-matter interaction in two-dimensional (2D) materials using high-quality resonances in plasmonic and dielectric structures. Here, we demonstrate a link between the radiation control at critical coupling and the metasurface-based bound states in the continuum (BIC) physics, and develop a generalized theory to engineer light absorption of 2D materials in coupling resonance metasurfaces. In a typical example of hybrid graphene-dielectric metasurfaces, we present the manipulation of absorption bandwidth by more than one orde…
Bound-states-in-the-continuum (BIC)is a wave-mechanical concept that generates resonances with vanishing spectral linewidths. It has many practical applications in Optics, such as narrow-band filters, mirror-less lasing, and nonlinear harmonic generation. As true BIC optical modes non-radiative and confined to the near field of nanostructures, they cannot be excited using propagating light. As a result, their direct experimental observation has been elusive. Rather than using light, we demonstrate probing BIC modes on arrays of silicon nanoantennas using a focused beam of electrons in a tranmi…
In this article, we developed a generalized coupled-mode theory for mixing an isolated state with the gapped continuum to unify the engineering mechanism of gap-protected zero modes, Fano resonance and Tamm surface states, even though those phenomena are diverse in numerous branches of physics and optics. By tuning the on-site potential and coupling strength of/with the isolated state, we found the operating characteristics from zero modes, Fano resonance and to Tamm modes, with explicitly demonstrating their localization, transmission spectra and distinct evolution dynamics of the 'bound stat…
