Plasmonic Optical Antenna Research Articles

All-plasmonic optical leaky-wave antenna with a low sidelobe level

Optical antennas have received considerable attention in recent years due to their unique ability to convert localized energy to freely propagating radiation and vice versa. Sidelobe level (SLL) is one of the most crucial parameters in antenna design. A low SLL is beneficial to minimize the antenna interference with other optical components. Here a plasmonic optical leaky-wave antenna with low SLL is reported. Shifting spatial frequency by periodically modulating the electric-field amplitude in a plasmonic gap waveguide enables a free-space coupled wave out of the antenna. At the same time, precise control of the aperture fields by the modulation depth allows for reducing SLL. Simulation results indicate that the proposed design can achieve a high directivity of 15.8 dB and a low SLL of −20 dB at the wavelength of 1550 nm. A low SLL below −15 dB is experimentally demonstrated within the wavelength range from 1527 to 1570 nm. In addition, the low-SLL property is further verified by comparing it with a uniformly modulated antenna. By modulating the guided waves in the plasmonic gap waveguide in different forms, the aperture fields can be flexibly arranged to achieve arbitrary wavefront shaping. It bridges the gap between guided and free-space waves and empowers plasmonic integrated devices to control free-space light, thus enabling various free-space functions.

Tailoring the directional dependent emitter interaction based plasmonic antenna character of Ag–Au heterodimer

Based on the concept of optical nanoantennas, light-matter interaction between metal heterodimer (Ag and Au spherical nanoparticles) and single dipole emitter system are numerically simulated utilizing a MATLAB toolbox MNPBEM17 based on boundary element method (BEM). The precise position and orientation of the dipole emitter systematically controls not only the (non)radiative losses, but also the efficiency of excitation (absorption) and respective emission processes in the vicinity of the plasmonic optical antenna system. The overall (non)radiative decay rates and associated surface charge distributions help estimate the spatio-directional dependency of dipole emitter emission, analogous to that of the SERS enhancement. Furthermore, the Poynting vector analysis of our present hybrid plasmonic antenna system effectively assesses the flow of electromagnetic energy, thus accounting for improvement in both near- and far-field propagation modes. The calculation of Purcell factor and coupling strength along with quantum yield evaluate the detailed optical response of a nanoantenna characteristics simultaneously based on the dipole emitter position and orientation, offering better scope for understanding the underlying mechanisms governing such intriguing interactions in complex geometries as well.

Promoting 2D Material Photodetectors by Optical Antennas beyond Noble Metals

AbstractThe distinctive layered crystal structures and diverse properties of 2D layered materials (2DLMs) have established them as prospective building blocks for implementing next‐generation optoelectronics. One critical predicament in terms of light sensing is the weak absorption caused by the atomic‐scale thickness, as well as the limited effective wavelength range/low spectral selectivity constrained by the intrinsic band structures. Despite the fact that numerous noble metal antennas are harnessed for enhancing the light–matter coupling, they suffer from exorbitant cost and narrow resonant optical windows. To this end, a number of non‐noble plasmonic optical antennas have been developed to improve the light‐sensing properties of 2DLM photodetectors, and tremendous advances have been accomplished. Herein, a comprehensive overview of this subject is provided based on four aspects; namely, non‐noble metal antenna promoted 2DLM photodetectors, heteroatom doped semiconductor antenna promoted 2DLM photodetectors, non‐stoichiometric semiconductor antenna promoted 2DLM photodetectors, and MXene antenna promoted 2DLM photodetectors. The focus is on the device structures, preparation, and underlying mechanisms. In the end, the challenges are highlighted, and potential strategies addressing them are proposed, which aim to navigate the upcoming exploration in the related domains and fully exert the pivotal role of non‐noble plasmonic optical antennas toward advancing 2DLM photodetectors.

Metasurface-based Fourier lens fed by compact plasmonic optical antennas for wide-angle beam steering

A Fourier lens can perform the Fourier transform of an incident wavefront at the focal plane. This paper reports a metasurface-based Fourier lens fed by compact plasmonic optical antennas for wide-angle beam steering. The metasurface, composed of six elements with different configurations covering the 2π phase range, features a large field-of-view (FOV) of ±50°. A novel plasmonic optical antenna for broadside radiation is then designed as the feed source of the metasurface. The proposed antenna has ultra-compact size of 0.77λ × 1.4λ, and achieves a high directivity of 9.6 dB and radiation efficiency of over 80% at the wavelength of 1550 nm. Full-wave simulations are carried out to evaluate the performances of the designed metasurface-assisted beam steering device. The results show that this device can achieve a maximum directivity of 21.5 dB at broadside radiation. Compared to conventional Yagi-Uda antenna feed, a directivity enhancement of about 2.7 dB can be obtained, exhibiting a great superiority of the proposed feed antenna. In addition, a large beam steering range of ±50° can be achieved with an acceptable gain drop of 2.83 dB. With the advantages of wide beam steering range, good radiation characteristics, small footprint, and ease of integration, the proposed metasurface-assisted beam steering device would be a promising candidate for integrated photonic applications, including wireless optical communications, light detection and ranging, and augmented reality.

Resonance Photoluminescence Enhancement of Monolayer MoS2 via a Plasmonic Nanowire Dimer Optical Antenna.

Two-dimensional transition-metal dichalcogenides (TMDs) such as monolayer MoS2 exhibit remarkable optical properties. However, the intrinsic absorption and emission rates of MoS2 are very low, thus severely hindering its application in electronics and photonics. Combining MoS2 with a plasmonic optical antenna is an alternative solution to enhance the emission rates of the 2D semiconductor, and this can drastically increase the photoresponsivity of the corresponding photodetector. Herein, we have constructed a plasmonic gap cavity of a nanowire dimer (NWD) system as an optical antenna to brighten the emission of MoS2 off the hot spot. Different from the conventional enhancement concept which occurred in the plasmonic hot spot, the light emission off the nanogap hot spot was thoroughly investigated. We demonstrate that this new plasmonic optical nanostructure leads to a strong enhancement due to the Purcell effect. The NWD optical antenna can trap light to the near field through a high-efficiency plasmonic gap mode (PGM); then the PL emission was enhanced drastically up to 14.5-fold due to the resonance of the plasmonic gap mode (PGM) in the NWD with the excitonic band of monolayer MoS2. Theoretical simulations reveal that this NWD can alter the efficiency of convergence and excitation, which was consistent with our experimental results. This study can provide a pathway toward enhancing and controlling PGM-enhanced light emission of TMD materials beyond the plasmonic hot spot.

High‐Frequency Light Rectification by Nanoscale Plasmonic Conical Antenna in Point‐Contact‐Insulator‐Metal Architecture

AbstractNumerous efforts have been undertaken to develop rectifying antennas operating at high frequencies, especially dedicated to light harvesting and photodetection applications. However, the development of efficient high frequency rectifying antennas has been a major technological challenge both due to a lack of comprehension of the underlying physics and limitations in the fabrication techniques. Various rectification strategies have been implemented, including metal‐insulator‐metal traveling‐wave diodes, plasmonic nanogap optical antennas, and whisker diodes, although all show limited high‐frequency operation and modest conversion efficiencies. Here a new type of rectifying antenna based on plasmonic carrier generation is demonstrated. The proposed structure consists of a resonant metallic conical nano‐antenna tip in contact with the oxide surface of an oxide/metal bilayer. The conical shape allows for an improved current generation based on plasmon‐mediated electromagnetic‐to‐electron conversion, an effect exploiting the nanoscale‐tip contact of the rectifying antenna, and proportional to the antenna resonance and to the surface‐electron scattering. Importantly, this solution provides rectification operation at 280 THz (1064 nm) with a 100‐fold increase in efficiency compared to previously reported results. Finally, the conical rectifying antenna is also demonstrated to operate at 384 THz (780 nm), hence paving a way toward efficient rectennas toward the visible range.

Circular disk plasmonic optical antenna array-enhanced avalanche photodiode with simultaneously enhanced gain and detection speed

Avalanche photodiodes (APDs) are critical photodetection devices for high sensitivity and high-speed sensing. Great efforts in bandgap engineering and impact-ionization engineering have been put to achieve high gain-bandwidth products. Plasmonic optical antenna (POA) techniques can change the near-field distributions of the illumination light and thus provide an effective approach to achieve simultaneous enhancement of the gain and the detection speed. We report a metallic circular disk POA array-enhanced APD, where the circular disk POA array was fabricated on top of the p-doped side of the GaAs p-i-n APD. The electric field (E-field) distribution were simulated. The gain and the frequency response of the APD POA-enhanced APD were measured and compared with a reference APD without the POA array. The POA-enhanced APD shows a simultaneous enhancement in the gain and the detection speed.

DIELECTRIC OPTICAL ANTENNA: A NEW CONCEPT FOR MICROWAVE FREQUENCIES

The dielectric optical antenna operating band is used to enhance bandwidth of operation band. The dielectric resonator antenna has high permittivity. The capabilities of antenna depend on made-up materials. Antenna range plays very important role for transmission of radio-signals. The properties of antenna play very important role in any technical or communicational devices. Current communication system requires high level portable communicational devices. Nanoantenna has high level configurable conductor power to help to change specific feature. Optical antenna has great capability to connect one network another network . The specific feature of optical antenna moving around development of our life to give convenient life. Only advanced generation technology has power to change our simple life to advanced technological life. In this research paper we have introduced new technical idea to develop our brain to gain high level efficiency to controlled our system with helps of antenna full usability for human being .The antenna characteristics depends on permittivity , dimension, properties limiting factors, geometrical properties, shape, model, wavelength scale and intensity of antenna aperture wavelength, which incident radiation relates to its design . In this paper we apply maxwell equations for free space propagation, as well as solve its amplitude of phase future plasmonic integrated circuits will be capable to extremely high range data processing at optical domain, the optical frequencies will be controlled by efficient optical emission of plasmonic antenna. In this project the new concept of microwave range arrays is applied to convert plasmonic optical antenna array, with nano-coupled plasmonic wave guide, as a spatial filter to absorb a specific wave length at particular specified incident angle. Nanoantenna transmits optical signals on nanometre scale. Optical nanoantenna are expected to radiate in THZ or GHZ frequency range. Optical DRA antenna has very unique and key application for such types of device based configuration .The optical DRA –antenna has unique spectral ability to optimize as well as design in nanometre scale.

Accurately Predicting the Radiation Enhancement Factor in Plasmonic Optical Antenna Emitters.

Plasmonic optical antennas (POAs), often constructed from gold or silver nanostructures, can enhance the radiation efficiency of emitters coupled to POAs and are applied in surface-enhanced Raman spectroscopy (SERS) and light-emitting devices. Over the past four decades, radiation enhancement factors (REFs) of POA-emitter systems were considered to be difficult to calculate directly and have been predicted indirectly and approximately, assuming POAs are illuminated by electromagnetic plane waves without emitters. The validity of this approximation remains a significant open problem in SERS theory. Herein, we develop a method based on the rigorous optical reciprocity theorem for accurately calculating the REFs of emitters in nanoparticle-substrate nanogaps for single-molecule SERS and scanning probe-substrate nanogaps for tip-enhanced Raman spectroscopy. We show that the validity of the plane wave approximation breaks down if high-order plasmonic modes are excited. The as-developed method paves the way toward designing high-REF POA nanostructures for luminescence-related devices.

Study of frequency-dependent plasmonic enhancement of a circular disk nano-optical antenna array using a femtosecond laser frequency comb

In this paper, we report the study of the frequency-dependent plasmonic enhancement of a circular disk nano-optical antenna array and the photo-response of the optical antenna enhanced photodetector at different frequencies using a femtosecond (fs) laser frequency comb. A fs-laser frequency comb can provide hundreds of evenly spaced harmonic frequencies and thus allows simultaneous measurement of the plasmonic optical antenna enhancement effect at these harmonic frequencies. This offers a highly efficient frequency-dependent measurement approach compared to the conventional method of modulating of a c.w. laser, which measures the frequency response at each frequency. The impulse response of the circular disk nano-optical antenna array and the electric-field (E-field) distribution profile are simulated under a fs laser illumination. The light intensity spectrum is simulated and verified to have uniform intensities on the harmonic frequencies within the ±5 GHz frequency range. The photocurrent densities in different regions of a GaAs p-i-n photodetector are analyzed together with their frequency dependence at the harmonic frequencies of the fs laser frequency comb with a repetition rate of MHz. A circular disk nano-optical antenna array enhanced GaAs p-i-n photodetector was fabricated and measured using a fs laser frequency comb with the same repetition rate. The nano-optical antenna can provide ~20 dB enhancement for the harmonic frequencies and extend the detector cut-off frequency from 2.4 GHz to 4.2 GHz.

Unidirectional emission in an all-dielectric nanoantenna

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 nearly-unidirectional emission can be realized by the interference of two modes, which can be spectrally tuned via the geometric parameters in an easy way. More importantly, the emission directions for the magnetic and electric dipole emitters are shown as opposite to each other through control of the phase difference between the induced magnetic and electric dipole modes of the antenna. Meanwhile, the Purcell factors can be enhanced by more than one order of magnitude and high quantum efficiencies can be maintained at the visible spectrum for both kinds of dipole emitters. We further show that these unidirectional emission phenomena can withstand small disorder effects of in-plane dipole orientation and location. Our study provides a simple yet versatile platform that can shape the emission of both magnetic and electric dipole emitters.

A back side configured pointed dipole plasmonic optical antenna array enhanced quantum dot infrared photodetector

In this paper, we report a back side configured pointed dipole optical antenna array enhanced quantum dot infrared photodetector (QDIP). In this configuration, the light illumination is from the substrate side (i.e. back side illumination), goes through the QDIP and then reaches the optical antenna array. The near-field electric fields (E-fields) are simulated for both top and back side illuminations. The back side configured pointed dipole antenna array gives stronger E-fields than the top side configuration. The physical mechanism for the difference is analyzed. A longwave infrared QDIP with the back side configured pointed dipole optical antenna array was fabricated and tested. The measurements agree well with the simulation. Compared with the top side configured optical antenna array, the back side configured optical antenna array allows easier fabrication of large format (e.g. 640 × 512 or 1024 × 1024) focal plane arrays and provides higher plasmonic enhancement.

Ultrathin Au film on polymer surface for surface plasmon polariton waveguide application

Formation of laterally continuous ultrathin gold films on polymer substrates is a technological challenge. In this work, the vacuum thermal evaporation method is adopted to form continuous Au films in the thickness range of 7–17 nm on polymers of Poly(methyl-methacrylate-glycidly-methacrylate) and SU-8 film surface without using the adhesion or metallic seeding layers. Absorption spectrum, scanning electron microscope and atomic force microscope images are used to characterize the Au film thickness, roughness and optical loss. The result shows that molecular-scale structure, surface energy and electronegativity have impacts on the Au film morphology on polymers. Wet chemical etching is used to fabricate 7-nm thick Au stripes embedded in polymer claddings. These long-range surface plasmon polariton waveguides demonstrate the favorable morphological configurations and cross-sectional states. Through the end-fire excitation method, propagation losses of 6-[Formula: see text] wide Au stripes are compared to theoretical values and analyzed from practical film status. The smooth, patternable gold films on polymer provide potential applications to plasmonic waveguides, biosensing, metamaterials and optical antennas.

Concentric circular ring and nanodisk optical antenna enhanced multispectral quantum dot infrared photodetector with spectral localization

In this paper, we report a concentric circular ring and nanodisk plasmonic optical antenna (POA) enhanced multispectral quantum dot infrared photodetector (QDIP). The circular ring and the nanodisk POA structures are designed to have plasmonic resonant wavelengths in the longwave infrared (LWIR) and the midwave infrared (MWIR) spectral regimes, respectively. The electric field (E-field) distributions are simulated and show spectral localization due to the distinct plasmonic resonant wavelengths of the POA structures. The circular ring is found to enhance the E-fields in the nanodisk regions due to the mutual coupling. A concentric circular ring and nanodisk POA enhanced multispectral QDIP was fabricated and tested. Multispectral enhancement was observed. The enhancement is compared to that of a QDIP with only the circular ring POA structure. The experiment data agree with the simulation. The concentric circular ring and nanodisk POA provides a compact planar structure for multispectral QDIP enhancement.

Analysis of mutual couplings in a concentric circular ring plasmonic optical antenna array

In this paper, we report the analysis of a concentric circular ring plasmonic optical antenna (POA) array using a simple lumped coupled circuit (LCC) model. The currents in the circular rings of the POA array and their mutual couplings are analyzed using the LCC model. The results agree well with the numerical simulation using CST’s Microwave Studio®. The LCC model reveals the mutual couplings between the antenna rings. It is found that the mutual couplings are not only between the adjacent antenna rings, but also involve their second (2nd) nearest or farther neighbors. Since the near-fields of the optical antennas are related to the currents in the optical antennas, the LCC model provides a useful tool for the analysis of the near-field and their mutual interactions in the circular ring POA array.

Enabling inter- and intra-chip optical wireless interconnect by the aid of hybrid plasmonic leaky-wave optical antennas

In this paper, we propose a new method to provide optical link in Photonic Integrated Circuits (PICs). The proposed method uses two hybrid plasmonic leaky-wave optical antennas, operating at the standard optical telecommunication wavelength of 1.55μm, to provide inter-chip interconnect between two layers in a photonic chip and also intra-chip interconnect between two different photonic ICs. Linearly tapered couplers are designed to couple the optical signal from the silicon waveguide to the hybrid plasmonic antennas. The performance of the proposed optical link is verified using numerical full wave simulation. The proposed structure is planar, and can be fabricated using standard CMOS technology which makes it the superior candidate for realization of future multi-layered Photonic Integrated Circuits.

Competition between Förster Resonance Energy Transfer and Donor Photodynamics in Plasmonic Dimer Nanoantennas

Plasmonic optical antennas enhance and control the emission of quantum sources in the far-field. Interestingly, the antenna concept can also be applied to enhance the electric field produced by a quantum emitter in the near-field and increase the rate of Forster resonance energy transfer (FRET) between two nearby donor and acceptor dipole emitters. However, plasmonic antennas also influence numerous other photophysical processes such as the donor excitation intensity and decay dynamics and the acceptor emission yield, which compete with the observation of FRET. Understanding the balance between FRET and these processes and monitoring FRET under intense resonant optical confinement in plasmonic nanoantennas have remained challenging open questions. Here, we use DNA-driven self-assembly to accurately produce 40 and 60 nm gold nanoparticle dimer antennas containing a single FRET pair located in the center of a 14 nm gap. The spontaneous donor decay rate constants are increased by 2 orders of magnitude, creat...

Optical and Thermal Behaviors of Plasmonic Bowtie Aperture and Its NSOM Characterization for Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording has the potential to keep increasing the areal density in the next-generation hard disk drives using a nanoscale optical antenna, called a near-field transducer (NFT), to locally and temporally heat a sub-diffraction-limited region in the recording medium. The NFTs made of plasmonic nanoscale optical antennas provide the capability of sub-wavelength light manipulation at optical frequencies. These antennas are designed using both plasmonic resonance and localized plasmons to produce an enhanced field in an area far below the diffraction limit. To reduce the self-heating effect in the NFT, which could cause materials failure that leads to the degradation of the overall hard drive performance, the NFT must deliver sufficient power to the recording medium with as small as possible incident laser power. In this paper, using the bowtie aperture as an example, we present the effect of optical properties on field localization, absorption, and coupling efficiency. Computations of heat dissipation and the induced temperature rise in the NFT are carried out to study their dependence on materials’ properties. With the recent significant interests in alternative low-loss plasmonic materials in the visible and near-infrared range, the possibility of using alternative plasmonic materials for delivering higher power and simultaneously reducing heating in the NFT is investigated. The NFT characterization using scanning near-field scanning optical microscopy is also discussed.

Directional Light Extinction and Emission in a Metasurface of Tilted Plasmonic Nanopillars.

Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions for particular incidence or emission angles could find widespread use in solar harvesting, biophotonics, and in improving photon source performance at optical frequencies. However, directional plasmonic structures have generally large footprints or require complicated geometries and costly nanofabrication technologies. Here, we present a directional metasurface realized by breaking the out-of-plane symmetry of its individual elements: tilted subwavelength plasmonic gold nanopillars. Directionality is caused by the complex charge oscillation induced in each individual nanopillar, which essentially acts as a tilted dipole above a dielectric interface. The metasurface is homogeneous over a macroscopic area and it is fabricated by a combination of facile colloidal lithography and off-normal metal deposition. Fluorescence excitation and emission from dye molecules deposited on the metasurface is enhanced in specific directions determined by the tilt angle of the nanopillars. We envisage that these directional metasurfaces can be used as cost-effective substrates for surface-enhanced spectroscopies and a variety of nanophotonic applications.

A plasmonic dipole optical antenna coupled quantum dot infrared photodetector

In this paper, we report a full-wavelength plasmonic dipole optical antenna coupled quantum dot infrared photodetector (QDIP). The plasmonic dipole optical antenna can effectively modify the EM wave distribution and convert free-space propagation infrared light to localized surface plasmonic resonance (SPR) within the nanometer (nm) gap region of the full-wavelength dipole antenna. The plasmonic dipole optical antenna coupled QDIP shows incident-angle-dependent photocurrent enhancement. The angular dependence follows the far-field pattern of a full-wavelength dipole antenna. The directivity of the plasmonic dipole optical antenna is measured to be 1.8 dB, which agrees well with the antenna simulation. To our best knowledge, this is the first report of the antenna far-field and directivity measurement. The agreement of the detection pattern and the directivity with antenna theory confirms functions of an optical antenna are similar to that of a RF antenna.