V-shaped Nanoantennas Research Articles

Functionality Expansion of Guided Mode Radiation via On-Chip Metasurfaces.

On-chip metasurfaces play a crucial role in bridging the guided mode and free-space light, enabling full control over the wavefront of scattered free-space light in an optimally compact manner. Recently, researchers have introduced various methods and on-chip metasurfaces to engineer the radiation of guided modes, but the total functions that a single metasurface can achieve are still relatively limited. In this work, we propose a novel on-chip metasurface design that can multiplex up to four distinct functions. We can efficiently control the polarization state, phase, angular momentum, and beam profile of the radiated waves by tailoring the geometry of V-shaped nanoantennas integrated on a slab waveguide. We demonstrate several innovative on-chip metasurfaces for switchable focusing/defocusing and for multifunctional generators of orbital angular momentum beams. Our on-chip metasurface design is expected to advance modern integrated photonics, offering applications in optical data storage, optical interconnection, augmented reality, and virtual reality.

Far-field mapping and efficient beaming of second harmonic by a plasmonic metagrating

Abstract We study numerically and experimentally the second-harmonic generation (SHG) from rectangular metagratings of V-shaped gold nanoantennas. We show that by carefully engineering the array pitch to steer the diffraction orders toward the single antenna emission, the extracted signal is maximized. This enhancement is attributed to the angular overlap between the radiation pattern and array factor and is comparable to the improvement yielded by the coupling of surface lattice resonances (SLRs) with local modes. Moreover, we demonstrate a simple technique to experimentally reconstruct the emission diagram of an antenna from measurements of the collective grating response as a function of the excitation angle. Excellent agreement is obtained with simulations when the sample is immersed either in air or in water, which is crucial in view of future sensing application. Thanks to the high signal-to-noise ratio and low dependence on the statistical particle dispersity, this method constitutes an effective alternative to back-focal plane imaging when very weak signals such as SHG are involved.

Broadband unidirectional transverse light scattering in a V-shaped silicon nanoantenna

The efficient manipulation of light-matter interactions in subwavelength all-dielectric nanostructures offers a unique opportunity for the design of novel low-loss visible- and telecom-range nanoantennas for light routing applications. Several studies have achieved longitudinal and transverse light scattering with a proper amplitude and phase balance among the multipole moments excited in dielectric nanoantennas. However, they only involve the interaction between electric dipole, magnetic dipole, and up to the electric quadrupole. Here, we extend and demonstrate a unidirectional transverse light scattering in a V-shaped silicon nanoantenna that involves the balance up to the magnetic quadrupole moment. Based on the long-wavelength approximation and exact multipole decomposition analysis, we find the interference conditions needed for near-unity unidirectional transverse light scattering along with near-zero scattering in the opposite direction. These interference conditions involve relative amplitude and phases of the electromagnetic dipoles and quadrupoles supported by the silicon nanoantenna. The conditions can be applied for the development of either polarization- or wavelength- dependent light routing on a V-shaped silicon and plasmonic nanoantennas.

A high gain and wideband on-chip hybrid plasmonic V-shaped nano-antenna

In this paper, a wideband hybrid plasmonic V-shaped nano-antenna is proposed based on coupled hybrid plasmonic waveguide (CHPW) feeding to increase the surface plasmon propagation length. The CHPW specifications are investigated analytically and numerically to obtain the dispersion relation and propagation length using the genetic algorithm and the finite element method, respectively. Moreover, the proposed V-shaped nano-antenna, with a fractional bandwidth of ∼86% and a maximum efficiency of 98%, is able to receive/transmit optical signals at three telecommunication wavelengths of 850, 1310, and 1550 nm with high realized gains of 10.5, 9.39, and 9.05 dB, respectively. The shape of the radiation pattern, with a main lobe along the antenna axis, makes this antenna appropriate for point-to-point connections in inter- or intra-chip optical wireless links and networks, which is studied comprehensively in this article. Furthermore, to obtain a high optical power signal and tune the antenna orientation, the performance of the antenna is investigated with two different types of array structure, single row and square, and its applications for energy harvesting and beam steering are studied. The fabrication feasibility of the nano-antenna is realizable based on complementary metal-oxide-semiconductor technology.

Reconfigurable metasurface hologram by utilizing addressable dynamic pixels.

The flatness, compactness and high-capacity data storage capability make metasurfaces well-suited for holographic information recording and generation. However, most of the metasurface holograms are static, not allowing a dynamic modification of the phase profile after fabrication. Here, we propose and demonstrate a dynamic metasurface hologram by utilizing hierarchical reaction kinetics of magnesium upon a hydrogenation/dehydrogenation process. The metasurface is composed of composite gold/magnesium V-shaped nanoantennas as building blocks, leading to a reconfigurable phase profile in a hydrogen/oxygen environment. We have developed an iterative hologram algorithm based on the Fidoc method to build up a quantified phase relation, which allows the reconfigurable phase profile to reshape the reconstructed image. Such a strategy introduces actively controllable dynamic pixels through a hydrogen-regulated chemical process, showing unprecedented potentials for optical encryption, information processing and dynamic holographic image alteration.

Deep-Subwavelength Resolving and Manipulating of Hidden Chirality in Achiral Nanostructures.

The chiral state of light plays a vital role in light-matter interactions and the consequent revolution of nanophotonic devices and advanced modern chiroptics. As the light-matter interaction goes into the nano- and quantum world, numerous chiroptical technologies and quantum devices require precise knowledge of chiral electromagnetic modes and chiral radiative local density of states (LDOS) distributions in detail, which directly determine the chiral light-matter interaction for applications such as chiral light detection and emission. With classical optical techniques failing to directly measure the chiral radiative LDOS, deep-subwavelength imaging and control of circular polarization (CP) light associated phenomena are introduced into the agenda. Here, we simultaneously reveal the hidden chiral electromagnetic mode and acquire its chiral radiative LDOS distribution of a single symmetric nanostructure at the deep-subwavelength scale by using CP-resolved cathodoluminescence (CL) microscopy. The chirality of the symmetric nanostructure under normally incident light excitation, resulting from the interference between the symmetric and antisymmetric modes of the V-shaped nanoantenna, is hidden in the near field with a giant chiral distribution (∼99%) at the arm-ends, which enables the circularly polarized CL emission from the radiative LDOS hot-spot and the following active helicity control at the deep-subwavelength scale. The proposed V-shaped nanostructure as a functional unit is further applied to the helicity-dependent binary encoding and the two-dimensional display applications. The proposed physical principle and experimental configuration can promote the future chiral characterization and manipulation at the deep-subwavelength scale and provide direct guidelines for the optimization of chiral light-matter interactions for future quantum studies.

Theoretical investigations on a class of double-focus planar lens on the anisotropic material

We study a double-focus lens constituted of V-shaped plasmonic nano-antennas (VSPNAs) on the anisotropic TiO2 thin film. The phase and amplitude variations of cross-polarized scattered wave from a unit cell are computed by the developed fast Method of Moments (MoM) in which the dyadic Green's function is evaluated with the transmission line model in the spectral domain. Using the calculated phase and amplitude diagrams, a double-focus lens on the anisotropic thin film is designed in 2µm. To validate the numerical results, the designed lens is analysed using a full-wave EM-solver. The obtained results show a tunable asymmetric behavior in the focusing intensity of the focal spots for different incident polarizations. It is shown that changing the thickness of anisotropic thin film leads to the changing in such an asymmetric behavior and also the intensity ratio of two focal spots. In addition, the lens performance is examined in the broadband wavelength range from 1.76 to 2.86µm. It is achieved that the increasing the wavelength leads to decreasing the focal distances of the designed lens and increasing its numerical aperture (NA).

基于V形纳米天线的平面透镜设计与制备

基于V形纳米天线的平面透镜设计与制备

Anisotropic Surface Plasmon Polariton Generation Using Bimodal V-Antenna Based Metastructures

V-shaped nanoantennas are among the popular choices for the unit element of a metasurface, a nanostructured surface used for its ability to mold and control the wavefront of light. In general, the motivation for choosing the V-antenna as the unit element comes from its bimodal nature, where the introduction of the second mode offers extra control over the scattered wavefronts. Here, through near-field scanning optical microscopy, we study a 1D metastructure comprised of V-antennas in the context of generating asymmetric surface plasmon polariton (SPP) wavefronts. The key point is that the use of the V-antenna allows for the creation of a two-dimensional phase gradient with a single line of antennas, where the extra phase dimension offers additional control and allows for asymmetric features. Two different asymmetries are created: (1) SPP wavefronts that have different propagation directions on either side of the metastructure, and (2) SPP wavefront asymmetry through focusing: one side of the metastructure focuses SPP wavefronts, while the other side has diverging SPP wavefronts.

Study on focusing properties of broadband range and oblique incidence on the basis of V-shaped nanoantenna

A V-shaped nanoantenna lens capable to realize effective focusing is designed by numerical simulation on the basis of theories pertinent to surface plasmon. The focusing of lens within the scope of broadband and its broad angles of view are also explored. The lens can realize focusing while the wavelength of incident light ranges from 432 to 632 nm. Focusing with equal focal distance can be achieved while the incident angle ranges from −30° to 30°. These research works give great potential to promote the use of metallic nanostructures in the fields of laser direct writing, superdiffraction lithography, high-density optical storage, and optical integrated devices.

Bending Gold Nanorods with Light.

V-shaped gold nanoantennas are the functional components of plasmonic metasurfaces, which are capable of manipulating light in unprecedented ways. Designing a metasurface requires the custom arrangement of individual antennas with controlled shape and orientation. Here, we show how highly crystalline gold nanorods in solution can be bent, one-by-one, into a V-shaped geometry and printed to the surface of a solid support through a combination of plasmonic heating and optical force. Significantly, we demonstrate that both the bending angle and the orientation of each rod-antenna can be adjusted independent from each other by tuning the laser intensity and polarization. This approach is applicable for the patterning of V-shaped plasmonic antennas on almost any substrate, which holds great potential for the fabrication of ultrathin optical components and devices.

Enhanced tunability of V-shaped plasmonic structures using ionic liquid gating and graphene

Graphene is a strong candidate for active optoelectronic devices because of its electrostatically tunable optical response. Current substrate back-gating methods are unable to sustain high fields through graphene unless a high gate voltage is applied. In order to solve this problem, ionic liquid gating is used which allows substrate front side gating, thus eliminating the major loss factors such as a dielectric layer and a thick substrate layer. On the other hand, due to its two dimensional nature, graphene interacts weakly with light and this interaction limits its efficiency in optoelectronic devices. However, V-shaped plasmonic antennas can be used to enhance the incident electric field intensity and confine the electric field near graphene thus allowing further interaction with graphene. Combining V-shaped nanoantennas with the tunable response of graphene, the operation wavelength of the devices that utilize V-shaped antennas can be tuned in situ. In the present paper, we demonstrate a graphene-based device with ionic liquid gating and V- shaped plasmonic antennas to both enhance and more effectively tune the total optical response. We are able to tune the transmission response of the device for up to 389 nm by changing the gate voltage by 3.8 V in the mid-infrared regime.

Polarization-independent characteristics of the metasurfaces with the symmetrical axis’s orientation angle of 45° or 135°

A series of symmetrical nanoantennas with a symmetrical axis orientation angle of 45° or 135°, which are suitable for both X/Y linear and circular polarizations incidences simultaneously, have been designed and investigated in detail. We have deduced the transmitted matrix of the metasurface structure by rigorous mathematical theory, and found that the essential reason for the polarization-independence characteristics is that there are the same transmitted amplitudes and phases under the incidences of X/Y linear and circular polarization lights due to metasurface structure with the symmetrical axis’s orientation angles of 45° or 135°. Based on the V-shaped, C-shaped, U-shaped and elliptical slit nanoantennas, we have verified the proposed theory fully by numerical simulations. The independence of the incident polarizations is very important for the practical applications and developments of the metasurfaces.

Tunable directional coupling of surface plasmon polaritons with linearly polarized light

A tunable directional surface plasmon polaritons (SPP) coupler, which utilizes the polarization direction of linearly polarized incident light to control the SPP coupling direction, is proposed. The SPP coupler consists of a column of V-shaped slot nanoantennas, which can support two kinds of plasmon resonant modes that have opposite symmetries. By controlling the polarization direction of linearly polarized incident light, the power flow of SPP coupled to the two opposite directions perpendicular to the column is continuously tuned. For 45° and 135° polarized incidence, SPP are unidirectional coupled to the two opposite directions, respectively. A highest extinction ratio of 31.6 dB is achieved, and the extinction ratio keeps larger than 10 dB within a wavelength of 135 nm.

Tunable Unidirectional Coupling of Surface Plasmon Polaritons Utilizing a V-Shaped Slot Nanoantenna Column

A polarization-sensitive V-shaped slot nanoantenna column is utilized to realize tunable unidirectional coupling of surface plasmon polaritons (SPP). Two plasmon resonant modes are excited in the V-shaped slot nanoantennas with x- and y-polarized incident light, respectively. The electric fields of coupled SPP show different symmetries corresponding to that of the two resonant modes. Linear combinations of the two resonant modes result in asymmetric SPP intensity distributions. As a result, by controlling the incident polarizations, tunable unidirectional coupling of SPP to two opposite directions perpendicular to the column at different wavelengths are realized. A highest extinction ratio of 36.7 dB is achieved, and the extinction ratio keeps larger than 7 dB within a wavelength of 149 nm.

Broadband anomalous reflector based on cross-polarized version phase gradient metasurface

Phase gradient meatsurface (PGM) is a new way to control reflective beam and refractive beam. By means of PGM, wave-fronts can be controlled in a more freedom way. The generalized Snell's law was put forward first by Nanfang Yu et al. [Yu N F, Genevet P, Kats M A, Aieta F, Tetienne J P, Capasso F, Gaburro Z 2011 Science 333 334] to describe the anomalous refraction on PGM. Anomalous refraction and out-of-plane reflection were then demonstrated using PGM composed of V-shaped nanoantennas. As deeper research about PGM, many reflective PGMs are also proposed. Typical examples are the reflective PGM using H-shaped resonators by Lei Zhou's group and using split-ring resonators by Shaobo Qu's group, both acting as high-efficiency surface wave couplers. However phase gradient of most PGMs above are achieved in a narrow-band and cannot change the polarizations. Anomalous reflection can only be realized in a certain narrow-band, and anomalous reflective angles cannot be precisely predicted. In this paper, a polarized conversion metasurface based on double-circular metallic resonator is first designed. The conversion successfully achieves ultra-wideband cross-polarization for linearly-polarized waves within a broadband of 12.2 GHz (from 7.9-20.1 GHz) with more than 99% cross-polarized reflectance. On the premise of high efficiency, reflective phase can be regulated by changing geometrical parameter of double-circular metallic structure. Then a broadband one-dimensional dispersive phase gradient metasurface comprised of six unit cells periodically arrayed above substrate is designed and fabricated. The PGM can perfectly achieve anomalous reflection. Measured result about its specular reflectivity is in good agreement with simulated result. Moreover, the measurement results of E-field distribution and anomalous reflective angle nearly accord with simulation results. Anomalous reflective angle is precisely predicted based on the generalized Snell's law. Both simulation and experiment verify that the PGM can make incident waves efficiently coupled as surface waves from 8.9-10 GHz and anomalously reflected in a range from 10 GHz to 18.1 GHz.

Enhancement of focusing energy of ultra-thin planar lens through plasmonic resonance and coupling.

A metal-insulator-metal (MIM) structure which is used to enhance the focusing energy of planar lens is developed in this work. The top of the MIM structure is formed by circularly arranged V-shaped nanoantennas whose double resonance effect makes it possible for light to obtain great phase changes within an ultra-thin area. The middle and bottom of the structure is medium and gold film layer respectively. This structure produces plasmonic coupling between the antenna layer and gold film, thus reducing Ohmic loss and enhancing the effect of plasmonic excitation. When the distance between the antenna layer with a thickness of 30 nm and gold film is 88 nm, and the thickness of gold film is 20 nm, the enhancement of plasmonic coupling reaches to the strongest when the focusing intensity is 1.33 times higher than the lens only. With the advantages of small size, ultra-thin, great phase changes and high-efficient focusing ability, the enhanced plasmonic coupling lens structure can be widely applied in photoetching, and integrated optics.

Tailorable optical scattering properties of V-shaped plasmonic nanoantennas: a computationally efficient and fast analysis.

In this work, we introduce an efficient computational scheme, based on the macro basis function method, to analyze the scattering of a plane wave by V-shaped plasmonic optical nanoantennas. The polarization currents and scattered fields for the both symmetric and antisymmetric excitations are investigated. We investigate how the resonant frequency of the plasmonic V-shaped nanoantenna is tailored by engineering the geometrical parameters and by changing the polarization state of the incident plane wave. The computational model presented herein is faster by many orders of magnitude than commercially available finite methods, and is capable of characterizing all nanoantennas comprised of junctions and bends of nanorods.

Plasmonic holographic imaging with V-shaped nanoantenna array

In this article, a novel method of holographic imaging with Au nanoantenna array is presented. In order to obtain the plasmonic holographic plate for a preset letter "NANO", the phase distribution of the hologram is firstly generated by the weighted Gerchberg-Saxton (GSW) algorithm, and then 16 kinds of V-shaped nanoantennas with different geometric parameters are designed to evenly cover the phase shift of 0 to 2π by finite-difference time-domain (FDTD) method. Through orienting these nanoantennas according to the phase distribution of the hologram, the plasmonic array hologram is obtained. Very good imaging quality is observed with our nanoantenna array hologram plate. This method can be used for holographic imaging of arbitrary shape, and may find potential applications in holographic memory, printing and holographic display.

Aberration-Free Ultrathin Flat Lenses and Axicons at Telecom Wavelengths Based on Plasmonic Metasurfaces

The concept of optical phase discontinuities is applied to the design and demonstration of aberration-free planar lenses and axicons, comprising a phased array of ultrathin subwavelength-spaced optical antennas. The lenses and axicons consist of V-shaped nanoantennas that introduce a radial distribution of phase discontinuities, thereby generating respectively spherical wavefronts and nondiffracting Bessel beams at telecom wavelengths. Simulations are also presented to show that our aberration-free designs are applicable to high-numerical aperture lenses such as flat microscope objectives.