Plasmonic Sources Research Articles

Polarization of the edge emission from Ag/InGaAsP Schottky plasmonic diode

Electrical plasmonic sources with compact sizes are a fundamental component in plasmonics. Here, we report a simple plasmonic diode having an Ag/InGaAsP quantum well Schottky structure. The polarization ratio (TM:TE) of the edge-emission photoluminescence for the quantum wells is about 2:1 and increases to about 3:1 after covered by Ag. As contrast, the electroluminescence polarization ratio exceeds 10:1 at a low current, indicating a high plasmon generation efficiency but drops gradually as current increasing; simultaneously, the peak wavelength red shifts evidently, which are attributed to the recombination zone shift and quantum confinement Stark effect.

Generation of a periodic array of radially polarized Plasmonic focal spots

This paper demonstrates experimentally the tight focusing of a 3X3 array of radially polarized diffraction orders, and the coupling of this array of spots to surface plasmon polaritons (SPPs), propagating on a uniform metal film, and effectively generating a periodic structure of plasmonic sources by the use of structured illumination pattern, rather than by structuring the plasmonic sample. Using near field measurements, we observed coherent interactions between these multiple plasmonic sources as they propagate towards each other. The demonstrated setup exploits the previously demonstrated advantages of radially polarized light in coupling to SPPs and in generating sharper plasmonic hot spots and expends its use towards mitigating parallel processing challenges. The experimental results are in good agreement with the theory, showing interference fringes having periodicity compatible with the plasmonic SPP wavelength. The demonstrated approach of generating array of hot spots on flat metallic films is expected to play a role in variety of applications, e.g. microscopy, lithography, sensing and optical memories.

Subwavelength coherent control and coupling of light in plasmonic nanoresonators on dielectric waveguides

We report results on the possibility of subwavelength coherent control of light in coupled plasmonic nanoresonators on dielectric waveguides. Our calculations show that subwavelength regions of the plasmonic structure, spatially separated by a few nanometers, can be individually addressed by controlling the relative phase of the injected fields. We also show the complementary possibility to efficiently inject a guided mode into a planar dielectric waveguide by collecting the radiation emitted by wire-like and/or point-like sources, placed into the resonators. For example, this configuration provides a useful and powerful tool to control the emission of the localized sources such as stripes of fluorescent molecules or quantum dots placed in the gaps between the plasmonic structures. Possible applications of the considered study include plasmonic logic gates, integrated sensors for single-molecule fluorescence, and ready-to-use devices based on plasmonic single-photon sources.

Mode recombination and alternation of surface plasmons in anisotropic mediums

Dispersion relations of surface plasmon polaritons with transverse-magnetic- and transverse-electric-polarized waves coexisting in insulator-metal-anisotropic planar waveguides are analytically derived. Aligned nematic liquid crystal, as an anisotropic medium, is employed to manipulate the mode properties. By varying its optical axis, two kinds of mode transformation are found: one is mode recombination, accompanied by dramatically extended propagation lengths at the cutoff angles, and the other is mode alternation, associated with an obvious shift of the electromagnetic energy flux from one insulator to the other. The results may have applications in actively modulated plasmon-based nanodevices and tunable surface plasmon sources.

一种基于布拉格反射波导的表面等离子体激光光源

We designed a new type of plasmonic laser source based on the Bragg reflection waveguide. This laser source is simple in structure and convenient for integration. It works under room temperature electrical pumping condition and outputs plasmonic laser with more than milliwatt power, which is much larger than those demonstrated plasmonic laser sources with power of nano-watt scale. The proposed laser works at 808 nm. The tilted light beam offered by Bragg reflection waveguide directly couples into surface plasmon polaritons in our quasi-Otto configuration.

Electrical source of surface plasmon polaritons based on hybrid Au–GaAs QW structures

In this paper, the electrical excitation of surface plasmon polaritons (SPPs) based on a hybrid metal-semiconductor quantum well (QW) structure is investigated by finite-difference time-domain (FDTD) simulations and experiments. The metal-QW hybrid structure is made of a metal grating structure deposited on a semiconductor QW with small separation between them. When electron-hole pairs are excited using current injection into the QW, SPPs are generated and coupled out by a metal grating. The spectral and imaging measurements were performed to confirm the electrical excitation of SPPs. The hybrid structure could serve as a plasmonic source for integrated plasmonic circuits.

An Electrically-Driven GaAs Nanowire Surface Plasmon Source

Over the past decade, the properties of plasmonic waveguides have extensively been studied as key elements in important applications that include biosensors, optical communication systems, quantum plasmonics, plasmonic logic, and quantum-cascade lasers. Whereas their guiding properties are by now fairly well-understood, practical implementation in chipscale systems is hampered by the lack of convenient electrical excitation schemes. Recently, a variety of surface plasmon lasers have been realized, but they have not yet been waveguide-coupled. Planar incoherent plasmonic sources have recently been coupled to plasmonic guides but routing of plasmonic signals requires coupling to linear waveguides. Here, we present an experimental demonstration of electrically driven GaAs nanowire light sources integrated with plasmonic nanostrip waveguides with a physical cross-section of 0.08λ(2). The excitation and waveguiding of surface plasmon-polaritons (SPPs) is experimentally demonstrated and analyzed with the help of full-field electromagnetic simulations. Splitting and routing of the electrically generated SPP signals around 90° bends are also shown. The realization of integrated plasmon sources greatly increases the applicability range of plasmonic waveguides and routing elements.

Compact Magnetic Antennas for Directional Excitation of Surface Plasmons

Plasmonics is considered as one of the most promising candidates for implementing the next generation of ultrafast and ultracompact photonic circuits. Considerable effort has been made to scale down individual plasmonic components into the nanometer regime. However, a compact plasmonic source that can efficiently generate surface plasmon polaritons (SPPs) and deliver SPPs to the region of interest is yet to be realized. Here, bridging the optical antenna theory and the recently developed concept of metamaterials, we demonstrate a subwavelength, highly efficient plasmonic source for directional generation of SPPs. The designed device consists of two nanomagnetic resonators with detuned resonant frequencies. At the operating wavelength, incident photons can be efficiently channeled into SPP waves modulated by the electric field polarization. By tailoring the relative phase at resonance and the separation between the two nanoresonators, SPPs can be steered to predominantly propagate along one specific direction. This novel magnetic nanoantenna paves a new way to manipulate photons in the near-field, and also could be useful for SPP-based nonlinear applications, active modulations, and wireless optical communications.

Propagating anti-symmetrically coupled plasmons generation by electron beams

Propagating anti-symmetrically coupled plasmons that usually cannot be excited with incident light and radiate to far field can be efficiently generated by electron beams. An electron beam is proposed as a practical propagating anti-symmetrically coupled plasmon source due to that it couples differently to the surface plasmons than free radiation. Specifically, whispering-gallery anti-symmetrically coupled plasmons with the character of symmetrical coupled dipoles are excited by an electron beam in a nested ringlike waveguide, which is consistent with the dispersion of electron excited plasmons in an infinite-long nanowire pair.

Quantitative Modeling of the Third Harmonic Emission Spectrum of Plasmonic Nanoantennas

Plasmonic dimer nanoantennas are characterized by a strong enhancement of the optical field, leading to large nonlinear effects. The third harmonic emission spectrum thus depends strongly on the antenna shape and size as well as on its gap size. Despite the complex shape of the nanostructure, we find that for a large range of different geometries the nonlinear spectral properties are fully determined by the linear response of the antenna. We find excellent agreement between the measured spectra and predictions from a simple nonlinear oscillator model. We extract the oscillator parameters from the linear spectrum and use the amplitude of the nonlinear perturbation only as scaling parameter of the third harmonic spectra. Deviations from the model only occur for gap sizes below 20 nm, indicating that only for these small distances the antenna hot spot contributes noticeable to the third harmonic generation. Because of its simplicity and intuitiveness, our model allows for the rational design of efficient plasmonic nonlinear light sources and is thus crucial for the design of future plasmonic devices that give substantial enhancement of nonlinear processes such as higher harmonics generation as well as difference frequency mixing for plasmonically enhanced terahertz generation.

Enhancement of the Purcell effect for colloidal CdSe/ZnS quantum dots coupled to silver nanowires by a metallic tip

In this study, the Purcell effect for CdSe/ZnS quantum dots emission coupled to a silver nanowire cavity was investigated. We manipulated the interaction between colloidal quantum dots (QDs) and an Ag NW in the presence of a metallic tip. When a metal tip approaches the Ag NW, the Ag surface plasmon mode could be lifted away from the metallic NW so that a low optical loss could still be obtained. This work demonstrates enhancement of the spatial coupling between the plasmonic mode and light sources and reduction in metal Ohmic losses, resulting in an enhanced Purcell effect and coupling efficiency accompanied with increased fluorescence intensity.

Terahertz plasmon amplification using two-dimensional electron-gas layers

In this study, we present an analytical model to investigate the possibility of guiding and amplifying terahertz (THz) plasmons in a two dimensional electron gas (2DEG) layer of a hetero-structure by applying a bias electric field. This analytical model solves Maxwell equations and semi-classical electronic transport equations inside the biased hetero-structure simultaneously. It is shown that the two dimensional plasmon’s properties alter vastly as the electrons are accelerated by the bias field. Four asymmetric plasmonic modes can propagate inside the un-gated 2DEG layer of the biased hetero-structure. One of these modes in the un-gated 2DEG layer is a growing mode which can be useful in the implementation of THz amplifiers. Since the modes characteristics can be controlled via biasing, design of new plasmonic devices such as modulators and switches is possible by this approach. Similar analysis has been performed in a gated 2DEG layer that shows clear changes in the two dimensional plasmon properties due to the biasing. Unlike the un-gated 2DEG layer, our efforts to find a growing mode in the gated 2DEG layer have failed. These multi-physics models lead to a better understanding of THz plasmonic sources and detectors as well as proposals on new plasmonic devices. Besides, they provide a physical insight into the electron-wave interactions inside the biased hetero-structure.

Electrically generated unidirectional surface plasmon source

We experimentally demonstrated an electrically excited surface plasmon source, which was fulfilled in a silver coated light emitting diode (LED) with well-designed gratings. With a DC current supply, surface plasmon polariton (SPP) waves were generated directly from the illuminations of the LED via the grating coupler. By adjusting the grating to a tilted one, a unidirectional SPP beam was successfully attained with a high extinction ratio (ER~10) and an improved launching efficiency. Detailed analyses show that this electrically generated unidirectional SPP has a considerable long propagation distance (~14 μm), allowing for further manipulations in plasmonic integrations and sensors.

Localization of Light with Two Metallic Wedges: A Step Toward Surface Plasmon Sources

A new technique for localization of the light in subwavelength scale is proposed by using two adjacent metallic wedges, which are made by different metals, i.e., Al and Ag. Green’s function surface integral equation method is exploited to numerically calculate magnetic field at different points. The results illustrate that by controlling the phase difference between two surface plasmon polariton waves propagating on the sides of the first wedge and the distance between two wedges the amplitude and the phase of SPP waves generated on the sides of the second wedge can be adjusted.

A plasmonic nano-antenna with controllable resonance frequency: Cu1.94S–ZnS dimeric nanoheterostructure synthesized in solution

This work presents a strategy for fine control of the localized surface plasmonic resonance (LSPR) frequency of nano-antennas by constructing dimeric nanoheterostructures, in which the first phase serves as a plasmonic resonance source, while the second one as a tunable component for the fine-control of the LSPR frequency. Following this strategy, Cu1.94S–ZnS dimeric nanoheterostructures are synthesized in solution, with Cu1.94S being the plasmonic resonance source while ZnS the tunable dielectric component. An ideal equivalent electric circuit model is established to simulate the optical response of the nano-antennas. By managing the growth of the ZnS nanocrystals, the LSPR peak is proved designable and controllable in the range of 1390 nm–1680 nm, which renders the material potentially applicable in telecommunication. The reported results may provide new strategies for designing and fabricating various technologically important nano-devices.

On-chip silicon light source: from photonics to plasmonics

Practical silicon photonic interconnects become possible nowadays after the realization of the practical silicon light sources, where the hybrid integrations of III–V semiconductors and silicon by bonding play a fundamental role. Photonic interconnects dissipate substantially less power and offer a significantly greater information bandwidth than those of electronic interconnects; however, one emerging problem is the size mismatch between photonic and electronic components when integrated on a chip. Therefore, surface plasmonic source with deeply sub-wavelength size is under intense investigation as the next generation Si-based light source for on-chip interconnects. In this paper, we shall review some of the latest achievements on this topic.

Fabrication of nanoscale plasmonic structures and their applications to photonic devices and biosensors

In this review, we explored the fabrication and application of various metallic nanostructures that support localized surface plasmons. Principles and unique characteristics for individual nanopatterning technologies were demonstrated and relevant discussion focused on the process cost, throughput, and possibilities of large-area patterning and mass production. As a potential use of the nanoscale plasmonic structures, several applications such as plasmonic light sources, photovoltaic devices, and localized surface plasmon resonance biosensors were investigated. In conclusion, true realization of such promising applications could be accomplished through an advance in nanofabrication techniques, together with a better understanding of the underlying fundamentals and a greater collaboration in a variety of fields.

Direct observation of amplified spontaneous emission of surface plasmon polaritons at metal/dielectric interfaces

We report on direct observation of amplified spontaneous emission (ASE) of surface plasmon polaritons (SPPs) at the interface of a silver film and a gain medium. Based on a typical Kretschmann configuration incorporated with Rhodamine 6G molecules, the growing ASE spectra of SPPs have been clearly identified by carefully conducting a pump-dependent angle-resolved spectral measurement. Spectral narrowing effects induced by the SPP amplification are also demonstrated. The observed phenomena are helpful in understanding the fundamental interactions between SPPs and gain medium, which could enable wide applications on plasmonic sources and sensors.

Anomalous spectral scaling of light emission rates in low-dimensional metallic nanostructures

The strength of light emission near metallic nanostructures can scale anomalously with frequency and dimensionality. We find that light-matter interactions in plasmonic systems confined in two dimensions (e.g., near metal nanowires) strengthen with decreasing frequency owing to strong mode confinement away from the surface-plasmon frequency. The anomalous scaling also applies to the modulation speed of plasmonic light sources, including lasers, with modulation bandwidths growing at lower carrier frequencies. This allows developing optical devices that exhibit simultaneously femtosecond response times at the nanometer scale, even at longer wavelengths into the mid-IR, limited only by nonlocal effects and reversible light-matter coupling.

Generation of Surface Plasmon Polariton Using Plasmonic Resonant Cavity Based on Microdisk Laser

We study the generation of surface plasmon polariton and its extraction efficiency from a microdisk-based plasmonic source to a metal-insulator-metal (MIM) waveguide. The field distribution is no longer a whispering gallery mode commonly found in microdisk lasers but hybridized with surface plasmon polariton. We observe the steady-state intensity of the surface plasmon polariton mode inside the plasmonic microdisk structure at 1.47- μm wavelength. This field intensity is extracted efficiently to a MIM plasmonic waveguide through a nanometer gap. The extraction efficiency reaches 60%.