We report the design of highly efficient optical antennas employing a judicious synthesis of metallic and dielectric materials. In the proposed scheme, a pair of metallic coupled nanoparticles permits large enhancements in both excitation strength and radiative decay rates, while a high refractive index dielectric microsphere is employed to efficiently collect light without spoiling the emitter quantum efficiency. Our simulations indicate potential fluorescence rate enhancements of 3 orders of magnitude over the entire optical frequency range.
Under the sub-wavelength condition ($w<λ/2$), an analytical model of light transmission and reflection through $1$D metallo-dielectric gratings of real metals has been developed. It has been shown that the transmission intensity associated with the Fabry-Perot (FP) resonance of a $1$D metallo-dielectric grating of a real metal decreases with the increasing grating thickness and the dielectric constant of the ridge material. Further, it has also been demonstrated that the intensity of the FP resonance increases with the increasing slit width while it is independent of the grating period ($P$) a…
Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper we report a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals, like band gaps and defect modes, are exported to the metallic counterpart, with interesting applications to infrared science and technology, as for instance in quantum well infrared photodetectors, narrow-band spectral filters, and …
A metallo-dielectric multilayer structure is proposed as a novel approach to the analysis of lactose malabsorption. When lactose intolerance occurs, the bacterial overgrowth in the intestine causes an increased spontaneous emission of H2 in the human breath. By monitoring the changes in the optical properties of a multilayer palladium-polymeric structure, one is able to detect the patient's disease and the level of lactose malabsorption with high sensitivity and rapid response.
We show that a nonlinear metallo-dielectric layered slab of subwavelength thickness and very small average dielectric permittivity displays optical multistable behavior at arbitrary low optical intensities. This is due to the fact that, in the presence of the small linear permittivity, one of the multiple electromagnetic slab states exists no matter how small is the transmitted optical intensity. We prove that multiple states at ultra-low optical intensities can be reached only by simultaneously operating on the incident optical intensity and incidence angle. By performing full wave simulation…
The asymptotic closed-form solution to the fundamental diffraction problem of a linear horizontal Hertzian dipole radiating over the metallo-dielectric interface is provided. For observation points just above the interface, we confirm that the total surface near-field is the sum of two components: a long-range surface plasmon polariton and a short-range radiative cylindrical wave. The relative phases, amplitudes and damping functions of each component are quantitatively elucidated through simple analytic expressions for the entire range of propagation: near and asymptotic. Validation of the an…
We provide theoretical and numerical tools to quantitatively study the impact of nonlocality arising from free electrons in metals on the optical properties of metallo-dielectric multilayers. Though effects due to nonlocality are in general quite small, they nevertheless can be important for very thin (typically below 10 nm) metallic layers - as are used in structures characterized by relatively flat dispersion curves. Such structures include those with negative refractive index; hyperbolic metamaterials; and materials with index near zero. We find in all cases that the inclusion of nonlocal e…
We experimentally and theoretically investigate the second order nonlinear optical response of metallo-dielectric multilayer structures composed of Ag and Ta2O5 layers, deposited by magnetron sputtering. Second harmonic generation measurements were performed in reflection mode as a function of incidence angle, using femtosecond pulses originating from a Ti:Sapphire laser system tuned at 800 nm. The dependence of the generated signal was investigated as a function of pump intensity and polarization state. Our experimental results show that the conversion efficiency from a periodic metallo-diele…
We analyze the impact of nonlocality on the waveguide modes of metallo-dielectric multilayers and optical patch antennas, the latter formed from metal strips closely spaced above a metallic plane. We model both the nonlocal effects associated with the conduction electrons of the metal, as well as the previously overlooked response of bound electrons. We show that the fundamental mode of a metal-dielectric-metal waveguide, sometimes called the gap-plasmon, is very sensitive to nonlocality when the insulating, dielectric layers are thinner than 5 nm. We suggest that optical patch antennas, which…
One of the most appealing aspects of photonic crystal structures is the photonic bandgap created in structures with sufficiently high dielectric contrasts between constituent materials. Understanding how specific photonic crystal structures and their associated stopband positions can selectively interfere with incoming light is vital for implementing these structured dielectrics in a range of optical applications. Metallo-dielectric photonic crystals act to incorporate metal particles into the ordered arrangement of these structures. We examined copper, nickel and gold metal infiltration into …
We devise new optical antennas that reduce the excited-state radiative lifetimes of emitters to the order of 100 femtoseconds while maintaining quantum efficiencies of about 80% at a broadband operation. Here, we combine metallic nanoparticles with planar dielectric structures and exploit design strategies from plasmonic nanoantennas and concepts from Cavity Quantum Electrodynamics to maximize the local density of states and minimize the nonradiative losses incurred by the metallic constituents. The proposed metallo-dielectric hybrid antennas promise important impact on various fundamental and…
Metasurfaces consisting of hybrid metal/dielectric nanostructures carry advantages of both material platforms. The hybrid structures can not only tightly confine subwavelength electromagnetic fields but also lower the absorption losses. Such optical characteristics are difficult to realize in metamaterials with only metal or dielectric structures. Hybrid designs also expand the scope of material choices and the types of optical modes that can be excited in a metasurface, thereby allowing novel light matter interactions. Here we present a metallo-dielectric hybrid metasurface design consisting …
We investigate theoretically and numerically the photonic band structure in the optical domain of an array of core-shell metal-semiconductor nanowires. Corresponding negative-index photonic bands are calculated, showing isotropic equifrequency surfaces. The effective (negative) electric permittivity and magnetic permeability, retrieved from S parameters, are used to compare the performance of such nanowire arrays with homogeneous media in canonical examples, such as refraction through a prism and flat-lens focusing. Very good agreement is found, indeed confirming the effective medium behavior …
Materials showing electromagnetic properties that are not attainable in naturally occurring media, the so called metamaterials, have been lately, and still are, among the most active fields in optical and materials physics and engineering. Among those properties, one of the most attractive is the sub-diffraction resolving capability predicted for media having index of refraction of -1. Here we propose a fully 3D, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems fro…
We propose a novel antenna structure which funnels single photons from a single emitter with unprecedented efficiency into a low-divergence fundamental Gaussian mode. Our device relies on the concept of creating an omnidirectional photonic bandgap to inhibit unwanted large-angle emission and to enhance small-angle defect-guided-mode emission. The new photon collection strategy is intuitively illustrated, rigorously verified and optimized by implementing an efficient body-of-revolution finite-difference time-domain method for in-plane dipole emitters. We investigate a few antenna designs to cov…
It is shown that small inclusions of a low absorbing metal can have a dramatic effect on the photonic band structure. In the case of diamond and zinc-blende photonic crystals, several complete photonic band gaps (CPBG's) can open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike in the purely dielectric case, in the presence of small inclusions of a low absorbing metal the largest CPBG for a moderate dielectric constant (epsilon<=10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most important CPBG, because it is the most stable against disorder. For a diamon…
We demonstrate, for the first time, an all-dielectric metamaterial resonator in the mid-wave infrared based on high-index tellurium cubic inclusions. Dielectric resonators are desirable compared to conventional metallo-dielectric metamaterials at optical frequencies as they are largely angular invariant, free of ohmic loss, and easily integrated into three-dimensional volumes. With these low-loss, isotropic elements, disruptive optical metamaterial designs, such as wide-angle lenses and cloaks, can be more easily realized.
We study the optical interaction in a coupled dielectric microdisks by investigating the splitting of resonance positions of interacting whispering gallery modes (WGMs) and their pattern change, depending on the distance between the microdisks. It is shown that the interaction between the WGMs with odd parity about y-axis becomes appreciable at a distance less than a wavelength and causes directional emissions of the resulting interacting WGMs. The directionality of the interacting WGMs can be understood in terms of an effective boundary deformation in ray dynamical analysis. We also discuss a…
In the Terahertz (THz) domain, we investigate both numerically and experimentally the directional emission of whispering gallery mode resonators that are perturbed by a small scatterer in the vicinity of the resonators rim. We determine quality factor degradation, the modal structure and the emission direction for various geometries. We find that scatterers do allow for directional emission without destroying the resonator's quality factor. This finding allows for new geometries and outcoupling scenarios for active whispering gallery mode structures such as quantum cascade lasers and passive r…
An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry. A promising way to circumvent the…
The phenomenon of trapping broad spectrum of light is known as `rainbow trapping' and achieved using all-dielectric, hybrid metallo-dielectric or all-metallic configurations. In the latter cases, unavoidable ohmic losses result in sub-picosecond trapped-mode lifetimes. For all practical purposes, novel strategies are required to be devised for trapping and subsequently, releasing broadband electromagnetic (em) field with lifetime > 1 ps. We present a rainbow trapping configuration using the excitation of multiple optical Tamm (OT) modes in an one-dimensional chirped photonic crystal (PC) desig…
The strong electric and magnetic resonances in dielectric subwavelength structures have enabled unique opportunities for efficient manipulation of light-matter interactions. Besides, the dramatic enhancement of nonlinear light-matter interactions near so-called bound states in the continuum (BICs) has recently attracted enormous attention due to potential advancements in all-optical and quantum computing. However, the experimental realizations and the applications of high- Q factor resonances in dielectric resonances in the visible regime have thus far been considerably limited. In this work, …
In this research, we report the experimental evidence of the directional Fano resonances at the scattering of a plane, linearly polarized electromagnetic wave by a homogeneous dielectric sphere with high refractive index and low losses. We observe a typical asymmetric Fano profile for the intensity scattered in, practically, any given direction, while the overall extinction cross section remains Lorentzian. The phenomenon is originated in the interference of the selectively excited electric dipolar and quadrupolar modes. The selectivity of the excitation is achieved by the proper choice of the…
We investigate propagation of a transverse magnetic field through a nonlinear metamaterial slab of sub-wavelength thickness and with a very small and negative linear dielectric permittivity. We prove that, for a given input intensity, the output intensity is a multi-valued function of the field incidence angle so that the transmissivity exhibits angular multi-stability and a pronounced directional hysteresis behavior. The predicted directional hysteresis is a consequence of the fact that the linear and nonlinear contributions to the overall dielectric response can be comparable so that the ele…
We present a new design of dielectric microcavities supporting modes with large quality factors and highly directional light emission. The key idea is to place a point scatterer inside a dielectric circular microdisk. We show that, depending on the position and strength of the scatterer, this leads to strongly directional modes in various frequency regions while preserving the high Q-factors reminiscent of the whispering gallery modes of the microdisk without scatterer. The design is very appealing due to its simplicity, promising a cleaner experimental realisation than previously studied micr…
Creation of correlated photon pairs is one of the key topics in contemporary quantum optics. Here, we theoretically describe the generation of photon pairs in the process of spontaneous parametric down-conversion in a resonant spherical nanoparticle made of a dielectric material with bulk $χ^{(2)}$ nonlinearity. We pick the nanoparticle size that satisfies the condition of resonant eigenmodes described by Mie theory. We reveal that highly directional photon-pair generation can be observed utilising the nonlinear Kerker-type effect, and that this regime provides useful polarisation correlations…
Substrate-engineered tunable bound states in the continuum and directional radiation in dielectric metasurfaces
Neijiang Normal University（内江师范学院）；Neijiang Optoelectronic Devices Engineering Research Center（内江光电器件工程研究中心）；Shenzhen University（深圳大学）；Great Bay University（大湾区大学）；Chongqing University（重庆大学）
We show that any metallo-dielectric multilayer with a hyperbolic dispersion relation can actually be characterized by a complex effective index. This refractive index, extracted from the complex Bloch band diagram, can be directly linked to the super-resolution of a flat lens made of this so- called indefinite metamaterials. This allows for a systematic optimization of the lens design, leading to structures that are outperforming state-of-art flat lenses. We show that, even when fully taking absorption into account, our design provides super-resolved images for visible light up to a distance o…
Directional lasing, with a low threshold and high quality factor, in active dielectric nanoantenna arrays is demonstrated. This is achieved through a leaky resonance excited in coupled gallium arsenide (GaAs) nanopillars. The leaky resonance is formed by partially breaking a bound state in the continuum (BIC) generated by the collective, vertical electric dipole resonances excited in the nanopillars for sub-diffractive arrays. By opening an unprotected, diffractive channel along one of the periods of the array one can control the directionality of the emitted light without sacrificing the high…
Slow light and rainbow trapping attract many attentions in last twenty years, and in most of the previous works, the researchers achieve the slow light and rainbow trapping with complicate configurations or techniques, for example, metamaterial techniques. In this paper, we propose a simple waveguide consisted with semiconductor and dielectric layers, and we find that the slow-light peaks appear in the dispersion curves. Besides, the cutoff frequency with $v_g = 0$ ($v_g$ is the group velocity) in the slow-light peaks is depending on the thicknesses of the semiconductor and dielectric. Then, w…
In this manuscript, we demonstrate the design and experimental proof of an optical cloaking structure which multi-directionally conceals a perfectly electric conductor (PEC) object from an incident plane wave. The dielectric modulation around the highly reflective scattering PEC object is determined by an optimization process for multi-directional cloaking purposes. And to obtain the multi-directional effect of the cloaking structure, an optimized slice is mirror symmetrized through a radial perimeter. Three-dimensional (3D) finite-difference time-domain method is integrated with genetic optim…
In this paper we describe a methodology for tailoring the design of metamaterial dielectric resonators, which represent a promising path toward low-loss metamaterials at optical frequencies. We first describe a procedure to decompose the far field scattered by subwavelength resonators in terms of multipolar field components, providing explicit expressions for the multipolar far fields. We apply this formulation to confirm that an isolated high-permittivity cube resonator possesses frequency separated electric and magnetic dipole resonances, as well as a magnetic quadrupole resonance in close p…
For the purpose of using plasmonics in an integrated scheme where single emitters can be probed efficiently, we experimentally and theoretically study the scattering properties of single nano-rod gold antennas as well as antenna arrays placed on one-dimensional dielectric silicon nitride waveguides. Using real space and Fourier microscopy correlated with waveguide transmission measurements, we quantify the spectral properties, absolute strength and directivity of scattering. The scattering processes can be well understood in the framework of the physics of dipolar objects placed on a planar la…
The concept of the broadband epsilon-near-zero meta-atom consisting of layered stacks with specified metallic filling ratio and thickness is proposed based on the Bergman spectral representation of the effective permittivity. The step-like metal-dielectric multilayer structures are designed to achieve realistic broadband epsilon-near-zero meta-atoms in optical frequency range. These meta-atoms can be integrated as building blocks for unconventional optical components with exotic electromagnetic properties over a wide frequency range, such as the demonstrated broadband directional emission and …
Nanoantennas for highly efficient excitation and manipulation of surface waves at nanoscale are key elements of compact photonic circuits. However, previously implemented designs employ plasmonic nanoantennas with high Ohmic losses, relatively low spectral resolution, and complicated lithographically made architectures. Here we propose an ultracompact and simple dielectric nanoantenna (silicon nanosphere) allowing for both directional launching of surface plasmon polaritons on a thin gold film and their demultiplexing with a high spectral resolution. We show experimentally that mutual interfer…
We report a novel design of a compact wavelength add-drop multiplexer utilizing dielectric-loaded surface plasmon-polariton waveguides (DLSPPWs). The DLSPPW-based configuration exploits routing properties of directional couplers and filtering abilities of Bragg gratings. We present practical realization of a 20-$μ$m-long device operating at telecom wavelengths that can reroute optical signals separated by approximately 70 nm in the wavelength band. We characterize the performance of the fabricated structures using scanning near-field optical microscopy as well as leakage-radiation microscopy a…
Optical microdisk cavities with certain asymmetric shapes are known to possess unidirectional far-field emission properties. Here, we investigate arrays of these dielectric microresonators with respect to their emission properties resulting from the coherent behaviour of the coupled constituents. This approach is inspired by electronic mesoscopic physics where the additional interference effects are known to enhance the properties of the individual system. As an example we study the linear arrangement of nominally identical Limaçon-shaped cavities and find mostly an increase of the portion of …
The far-field emission of two dimensional (2D) stadium-shaped dielectric cavities is investigated. Micro-lasers with such shape present a highly directional emission. We provide experimental evidence of the dependance of the emission directionality on the shape of the stadium, in good agreement with ray numerical simulations. We develop a simple geometrical optics model which permits to explain analytically main observed features. Wave numerical calculations confirm the results.
Quantum emitters radiate light omni-directionally, making it hard to collect and use the generated photons. Here we propose a 3D metal-dielectric parabolic antenna surrounding an individual quantum dot as a source of collimated single photons which can then be easily extracted and manipulated. Our fabrication method relies on a single optically-induced polymerization step, once the selected emitter has been localized by confocal microscopy. Compared to conventional nano-antennas, our geometry does not require near-field coupling and it is therefore very robust against misalignment issues, and …
Metamaterials offer unprecedented flexibility for manipulating the optical properties of matter, including the ability to access negative index, ultra-high index and chiral optical properties. Recently, metamaterials with near-zero refractive index have drawn much attention. Light inside such materials experiences no spatial phase change and extremely large phase velocity, properties that can be applied for realizing directional emission, tunneling waveguides, large area single mode devices, and electromagnetic cloaks. However, at optical frequencies previously demonstrated zero- or negative-r…
Vertical cavity surface emitting lasers (VCSELs) have made indispensable contributions to the development of modern optoelectronic technologies. However, arbitrary beam shaping of VCSELs within a compact system still remains inaccessible till now. The emerging ultra-thin flat optical structures, namely metasurfaces, offer a powerful technique to manipulate electromagnetic fields with subwavelength spatial resolution. Here, we show that the monolithic integration of dielectric metasurfaces with VCSELs enables remarkable arbitrary control of the laser beam profiles, including self-collimation, B…
We present simulations of an efficient high numerical aperture solid immersion metalens concept for fluorescence microscopy. The technique exploits the preferential emission of interfacial dipoles into a high refractive index substrate combined with a metalens and a conventional tube lens for imaging them. We have thus simulated dipole emission and an all-dielectric metasurface on opposite sides of a high refractive index substrate. Our calculations predict dipole collection efficiencies of up to 87 percent. The simulated beam propagation through the imaging system shows excellent performance …
Optical microcavities have received much attention over the last decade from different research fields ranging from fundamental issues of cavity QED to specific applications such as microlasers and bio-sensors. A major issue in the latter applications is the difficulty to obtain directional emission of light in the far-field while keeping high energy densities inside the cavity (i.e. high quality factor). To improve our understanding of these systems, we have studied the annular cavity (a dielectric disk with a circular hole), where the distance cavity-hole centers, d, is used as a parameter t…
A leaky-wave antenna at optical frequencies is designed and integrated with a ring resonator at 1550 nm wavelength. The leaky wave is generated by using periodic perturbations in the integrated dielectric waveguide that excite the -1 spatial harmonic. The antenna consists of a dielectric waveguides with semiconductor corrugations, and it is compatible with CMOS fabrication technology. We show that integrating the leaky wave antenna in an optical ring resonator that is fed by directional couplers, we can improve the electronic control of the radiation through carrier injection into the semicond…
Semiconductor nanolasers based on micro disks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last decade for on-chip light source applications. However, practical realization of low threshold, room temperature operation of semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Also, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the…
Edge modes of a finite-size woodpile can appear within a complete bandgap on an <010> edge. The mode area is as small as 0.066 squared half-in-vacuum-wavelengths, and the propagation loss is small. The field maxima occur at a dielectric-vacuum interface, like at a metal-dielectric interface for surface plasmon modes. The edge mode is a subwavelength-scale 2D light localization mode in non-metallic materials. Analysis of two-mode co-directional coupling between identical surface Bloch modes suggests that a large photonic crystal or surface designing would be needed for suppressing the evanescen…
All-dielectric nanoantennas are a promising alternative to plasmonic optical antennas for engineering light emission because of their low-loss nature in the optical spectrum. Nevertheless, it is still challenging to manipulate directional light emission with subwavelength all-dielectric nanoantennas. Here, we propose and numerically demonstrate that a hollow silicon nanodisk can serve as a versatile antenna for directing and enhancing the emission from either an electric or magnetic dipole emitter. When primarily coupled to both electric and magnetic dipole modes of a nanoantenna, broadband ne…
We propose to use optical antennas made out of natural hyperbolic material hexagonal boron nitride (hBN), and we demonstrate that this medium is a promising alternative to plasmonic and all-dielectric materials for realizing efficient subwavelength scatterers and metasurfaces based on them. We theoretically show that particles out of hyperbolic medium possess different resonances enabled by the support of high-k waves and their reflection from the particle boundaries. Among those resonances, there are electric quadrupole excitations, which cause magnetic resonance of the particle similar to wh…
