We present a theoretical analysis of light scattering from a layered metal-dielectric microsphere. The system consists of two spherical resonators, coupled through concentric embedding. Solving for the modes of this system we find that near an avoided crossing the scattering cross section is dramatically suppressed, exhibiting a tunable optical transparency. Similar to electromagnetically induced transparency, this phenomenon is associated with a large group delay, which in our system is manifest as flat azimuthal dispersion.
We present a theoretical study of the dispersion relation of surface plasmon resonances of mesoscopic metal-dielectric-metal microspheres. By analyzing the solutions to Maxwell's equations, we obtain a simple geometric condition for which the system exhibits a band of surface plasmon modes whose resonant frequencies are weakly dependent on the multipole number. Using a modified Mie calculation, we find that a large number of modes belonging to this flat-dispersion band can be excited simultaneously by a plane wave, thus enhancing the absorption cross-section. We demonstrate that the enhanced a…
Hybrid mesoscale-structures that can combine dielectric optical resonances with plasmon-polaritons are of interest in chip-scale nano-optical communication and sensing. This experimental study shows how a fluorescent microsphere coupled to a silver nanowire can act as a remotely-excited optical antenna. To realize this architecture, self-assembly methodology is used to couple a fluorescent silica microsphere to a single silver nanowire. By exciting propagating surface plasmon polaritons at one end of the nanowire, remote excitation of the Stokes-shifted whispering gallery modes (WGMs) of the m…
We have theoretically investigated optical tweezing of gain-functionalized microspheres using a highly focused single beam in the nonparaxial regime. We employ the Mie-Debye theory of optical tweezers to calculate the optical force acting on homogeneous and core-shell Mie microspheres with gain. We demonstrate that the optical gain plays a crucial role in optical manipulation, especially to optimize the restoring force and thus allowing for trapping of large refractive index and plasmonic particles. Indeed we demonstrate that one can trap such particles, which is usually not possible in the ca…
The scattering and absorption suppression of the silica microspheres is experimentally achieved by semicontinuous gold shell synthesized on the silica microspheres. These fractal gold shells on the silica spheres are shown to have significant extinction in the visible and mid-infrared spectral range. It is found that the silica scattering peak in the visible and the relative contribution of the vibrational stretching band in the infrared gradually decreases with increasing of the gold coverage.
Extreme field localization and giant field enhancement are often achieved by using plasmonic nanostructures and metamaterials such as strongly coupled silver nanoparticles.Dielectric particles and structures can focus light beyond the diffraction limit (photonic nanojet effect), but with much weaker strengths. Recently, we showed that dielectric microspheres could support high-order Mie resonance modes ("super resonance mode") that can generate similar level of electric field intensity enhancement as plasmonic structures on the order of 10^4 - 10^7. In this work, we aim to further advance our …
Linear Arrays of Metal-Coated Microspheres: a Polarization-Sensitive Hybrid Colloidal Plasmonic-Photonic Crystal
National Institute for Research and Development of Isotopic and Molecular Technologies INCDTIM（同位素和分子技术研究与发展国家研究所）；Institute for Interdisciplinary Research in Bio-Nano-Sciences, Babes-Bolyai University（巴比什-博尧伊大学生物纳米科学跨学科研究所）
Metal-coated microsphere monolayers as surface plasmon resonance sensors operating in both transmission and reflection modes
National Institute for Research and Development of Isotopic and Molecular Technologies（同位素和分子技术研究发展中心）；Institute for Interdisciplinary Research in Bio-Nano-Sciences, Babes-Bolyai University（巴比什-博约伊大学生物纳米科学交叉研究所）
We analytically examine propagation of surface plasmon polaritons (SPPs) at a thin metallic film between glass substrate and electromagnetically-induced-transparency (EIT) medium. High-precision and high-resolution in frequency domain provided by EIT paves the way towards plasmonic group velocities reduction even by $4$ orders of magnitude and corresponding lifetime enhancement of SPPs up to microseconds.
Plasmon-induced-transparency (PIT) in nanostructures has been intensively investigated, however, no existing metasurface nanostructure exhibits all-optically tunable properties, where the number of transparency windows can be tuned successively, and switched to off-state. Here, we theoretically investigate and demonstrate dynamically tunable, multichannel PIT at optical frequencies. The inplane destructive interference between bright and dark dipolar resonances in coupled plasmonic nanobar topologies is exploited to produce tunable PIT with unique characteristics. In particular, we demonstrate…
A gain-assisted plasmonic waveguide with two detuned resonators is investigated in the plasmon-induced transparency window. Phase map is employed to study power transmittance and group delay for varying gain coefficients and frequency detunings of the two resonators. The gain coefficient for lasing oscillation condition is analytically shown to vary quadratically with the frequency detuning. In the amplification regime below the lasing threshold, the spectrum implies not only large group delay, but also high transmittance and narrow linewidth. This is in contrast to those in the loss-compensat…
We consider a simple configuration for realizing one-dimensional slow-light metamaterials with large bandwidth-delay products using stub-shaped Fabry-Perot resonators as building blocks. Each metaatom gives rise to large group indices due to a classical analog of the dressed-state picture of electromagnetically-induced transparency. By connecting up to eight metaatoms, we find bandwidth-delay products over unity and group indices approaching 100. Our approach is quite general and can be applied to any type of Fabry-Perot resonators and tuned to different operating wavelengths.
We present theoretical and numerical analysis of a plasmonic-dielectric hybrid system for symmetric and asymmetric coupling between silver cut-wire pairs and silicon grating waveguide with periodic grooves. The results show that both couplings can induce electromagnetically-induced transparency (EIT) analogous to the quantum optical phenomenon. The transmission spectrum shows a single transparency window for the symmetric coupling. The strong normal phase dispersion in the vicinity of this transparent window results in the slow light effect. However, the transmission spectrum appears an additi…
Absorption induced transparency is an optical phenomenon that occurs in metallic arrays of nanoholes when materials featuring narrow lines in their absorption spectra are deposited on top of it. First reported in the visible range, using dye lasers as cover materials, it has been described as transmission peaks unexpectedly close to the absorption energies of the dye laser. In this work, amplification of light is demonstrated in the active regime of absorption induced transparency. Amplification of stimulated emission can be achieved when the dye laser behaves as a gain material. Intense illum…
A hybrid metal-graphene metamaterial (MM) is reported to achieve the active control of the broadband plasmon-induced transparency (PIT) in THz region. The unit cell consists of one cut wire (CW), four U-shape resonators (USRs) and monolayer graphene sheets under the USRs. Via near-field coupling, broadband PIT can be produced through the interference between different modes. Based on different arrangements of graphene positions, not only can we achieve electrically switching the amplitude of broadband PIT, but also can realize modulating the bandwidth of the transparent window. Simultaneously,…
Plasmon induced transparency (PIT) effect in a terahertz graphene metamaterial is numerically and theoretically analyzed. The proposed metamaterial comprises of a pair of graphene split ring resonators placed alternately on both sides of a graphene strip of nanometer scale. The PIT effect in the graphene metamaterial is studied for different vertical and horizontal configurations. Our results reveal that there is no PIT effect in the graphene metamaterial when the centers of both the split ring resonators and the graphene strip are collinear to each other. This is a noteworthy feature, as the …
In this study, we investigate plasmon-induced transparency (PIT) in a resonator structure consisting of two orthogonally-arranged metal-insulator-metal (MIM) nanocavities with the aim of spectral modulation of a specific resonant order of the resonator. Our FDTD simulations demonstrate that when both cavities in this structure resonate at the same frequency, the PIT effect can be used to induce spectral modulation. This spectral modulation depends on the resonance order of the cavity coupled directly to the external field, occurring when first-order resonance is exhibited, but not with second-…
As an analogue of electromagnetically induced transparency (EIT), plasmon-induced transparency (PIT) has been realized both in plasmonic metamaterial and waveguide structures. Via near-field coupling within unit cells, PIT with broadband could be produced by plasmonic metamaterials, which, however, has not been realized in on-chip plasmonic waveguide structures. Here, we introduce broadband PIT based on a plasmonic metal-insulator-metal (MIM) waveguide system. Utilizing the direct coupling structure, PIT emerges based on an easy-fabricated structure without gap. By tuning coupling distance, th…
In this article, we examine plasmon induced transparency (PIT) effect in a parallel plate waveguide (PPWG) comprising of two similar pyramidal shaped grooves. One of the grooves is filled with air, while the other is filled with a dielectric material whose refractive index can be varied. The resonant frequencies corresponding to the air and dielectric grooves in the proposed configuration results in the transparency window which can be modulated with the refractive index of the dielectric material. The approach provides flexibility to actively control transparency effect in a waveguide configu…
We present a microscopic model for exciton-induced transparency (ExIT) in a hybrid system comprised of an emitter resonantly coupled to a surface plasmon in a metal-dielectric structure. We obtain an effective optical polarizability of such a system with coupling between the system components expressed in terms of energy transfer rates. We demonstrate that, in the weak coupling regime, the underlying mechanism of ExIT is the energy exchange imbalance between the plasmon and the emitter in a narrow frequency region. We derive in analytic form a frequency-dependent function that accurately descr…
We present a microscopic model describing the transition to strong coupling regime for an emitter resonantly coupled to a surface plasmon in a metal-dielectric structure. We demonstrate that the shape of scattering spectra is determined by an interplay of two distinct mechanisms. First is the near-field coupling between the emitter and the plasmon mode which underpins energy exchange between the system components and gives rise to exciton-induced transparency minimum in scattering spectra prior the transition to strong coupling regime. The second mechanism is Fano interference between the plas…
We study the interband self-induced transmission of surface plasmon polaritons in a gold film surrounded by an external Kerr medium. We model the optical propagation by using a version of the generalized nonlinear Schrodinger equation for the field envelope coupled to Bloch equations for valence electrons of gold, predicting self-induced transparency of ultrashort plasmon solitons with a pulse duration below 10 fs. We demonstrate that the Kerr nonlinearity from the surrounding dielectric can be used to compensate for the group velocity dispersion, and that the impact of dephasing and decay pro…
Hybrid systems of excitons strongly coupled to localized surface plasmons supported by metallic nanoparticles define a new approach to control light-matter interactions. Here, we report exciton-plasmon coupling in two-dimensional (2D) semiconductors, such as MoS2 and WS2, hybridized with silver nanoparticles. Prominent photoluminescence enhancement in monolayer MoS2 was observed with localized surface plasmon resonance (LSPR) tuned to the exciton resonance. By tuning the excitation energy, the contributions from near field enhancement and radiative emission rate enhancement via Purcell effect …
A scheme for a surface plasmon resonance system under conditions of electromagnetically induced transparency (EIT) is proposed. The system is composed of three layers: a prism, a thin metal film, and a hybrid dielectric consisting of EIT atoms and a background substance. A probe and a coupling laser beam are input. Corresponding analytical formulas are derived for the cases when one or both of the laser beams excite surface plasmon polaritons at the metal/dielectric interface. Under resonance conditions, an extremely sharp dip appears in the reflectivity-frequency spectrum of the probe field, …
We propose a scheme for the coupler-free excitation of surface polaritonic solitons and breathers in a planar plasmonic waveguide structure comprising of a transparent layer, a metal layer and a layer of three-level lambda-type atomic medium. In the proposed system, an enhanced Kerr nonlinearity is achieved via electromagnetically induced transparency (EIT) in the bottom atomic medium, which can be controlled through proper modulation of the frequency detunings and Rabi frequencies of the driving laser fields. This nonlinearity balances the dispersion in the system, thus providing the necessar…
We report hybridization induced transparency (HIT) in a composite medium consisting of a metamaterial and a dielectric. We develop an analytic model that explains HIT by coherent coupling between the hybridized local fields of the metamaterial and the dielectric or an atomic system in general. In a proof-of-principle experiment, we evidence HIT in a split ring resonator metamaterial that is coupled to α-lactose monohydrate. Both, the analytic model and numerical calculations confirm and explain the experimental observations. HIT can be considered as a hybrid analogue to electromagnetically ind…
Machine learning and optimization algorithms have been widely applied in the design and optimization for photonic devices. In this article, we briefly review recent progress of this field of research and show some data-driven applications (e.g. spectrum prediction, inverse design and performance optimization) for novel graphene metamaterials (GMs). The structure of the GMs is well-designed to achieve the wideband plasmon induced transparency effect, which is regarded as optimization object and can be theoretically demonstrated by using transfer matrix method. Some classical machine learning al…
We investigate the dynamics of a plasmonic oscillation over a metal nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum dot, molecule). We simulate the density matrix evolution for a simple model; coupled classical--quantum oscillators system. We show that lifetime of the plasmonic oscillations can be increased several orders of magnitude, upto the decay time of the quantum emitter. This effect shows itself as the narrowing of the plasmon emission band in the spaser (surface plasmon amplification by stimulated emission of radiation) experiment [{\it Nature}, {\bf 2009},…
Recently, the coupling of two different modes of a homogeneous plasmonic particle and their sharply varying spectra were elucidated as Fano resonances; an 'interference' of two spatially orthogonal modes driving each other. On the other hand, the scattering (and extinction) cross-section of a non-absorbing dielectric particle is always the sum of the cross-sections of all mode numbers; and this rules out any such Fano type interference between two different mode numbers. So delectric particles exhibit an interference structure in their extinction spectra only if it manifests in the individual …
In this work, we compare the performance of plasmonic waveguide integrated stub resonators based on 2D metal-dielectric-metal and 3D slot waveguide (SWG) geometries. We show that scattering matrix theory can be extended to 3D devices, and by employing scattering matrix theory, we provide the guidelines for designing plasmonic 2D and 3D single-stub and double-stub resonators with a desired spectral response at the design wavelength. We provide transmission maps of 2D and 3D double-stub resonators versus stub lengths, and we specify the different regions on these maps that result in a minimum, a…
We investigate the scattering properties of spherical nanoparticles by employing a Cartesian multipole expansion method which has incorporated radiating toroidal multipoles. It is shown that toroidal dipoles, which are negligible under long-wavelength approximations, can be excited within high-permittivity dielectric nanoparticles and significantly influence the scattering profile in the optical regime. We further reveal that the scattering transparencies of core-shell plasmonic nanoparticles can be classified into two categories: i) the trivial transparency with no effective multipole excitat…
We study transverse spin in a sub-wavelength metal-dielectric-metal (MDM) sphere when the MDM sphere exhibits avoided crossing due to hybridization of the surface plasmon with the Mie localized plasmon. We show that the change in the absorptive and dipersive character near the crossing can have significant effect on the transverse spin. An enhancement in the transverse spin is shown to be possible associated with the transparency (suppression of extinction) of the MDM sphere. The effect is attributed to the highly structured field emerging as a consequence of competition of the electric and ma…
We demonstrate on-demand control of localized surface plasmons in metamaterials by means of incident light polarization. An asymmetric mode, selectively excited by s-polarized light, interfere destructively with a bright element, thereby allowing the incident light to propagate at a fairly low loss, corresponding to electromagnetically induced transparency (EIT) in an atomic system. In contrast, a symmetric mode, excited by p-polarized light, directly couples with the incident light, which is analogous to the switch-off of EIT. The light polarization-dependent excitation of asymmetric and symm…
In the phenomenon of electromagnetically induced transparency1 (EIT) of a three-level atomic system, the linear susceptibility at the dipole-allowed transition is canceled through destructive interference of the direct transition and an indirect transition pathway involving a meta-stable level, enabled by optical pumping. EIT not only leads to light transmission at otherwise opaque atomic transition frequencies, but also results in the slowing of light group velocity and enhanced optical nonlinearity. In this letter, we report an analogous behavior, denoted as phonon-induced transparency (PIT)…
