Plasmonic Switch Research Articles

Light coupling structures and switches for plasmonic coaxial waveguides

We introduce wavelength-scale light coupling structures and switches for plasmonic coaxial waveguides. We first consider single-slit structures optimized for a wavelength of 1550 nm and find that, when the slit is on resonance, the coupling to the plasmonic coaxial waveguide is maximized. We also observe that for optimized double- and triple-slit structures, the coupling efficiency is enhanced compared to the single-slit structure by factors of ∼3.02 and ∼4.21, respectively. We find that, in the case of double- and triple-slit structures, the surface plasmons excited at the metal–air interface enhance light coupling to the plasmonic coaxial waveguide via the slits. In addition, we investigate slit-based outcoupling structures for light extraction from the waveguide into a free space. We observe that while the far-field radiation pattern of single-slit structures is symmetric, double- and triple-slit structures have asymmetric radiation patterns. We also show that by exciting the incoupling slit structures at proper angles, we can excite only the right- or the left-propagating mode of the plasmonic coaxial waveguide. We finally design compact plasmonic switches consisting of a plasmonic coaxial waveguide side-coupled to a periodic array of two open-circuited coaxial stub resonators. Such a structure is based on a plasmonic analog of electromagnetically induced transparency and supports a slow-light mode. The space between the metallic parts is filled with an active material with a tunable refractive index. We show that the modulation depth of this structure is large enough for optical switching applications.

PH-Driven Reversible Assembly and Disassembly of Colloidal Gold Nanoparticles.

Owing to the localized surface plasmon resonance (LSPR), dynamic manipulation of optical properties through the structure evolution of plasmonic nanoparticles has been intensively studied for practical applications. This paper describes a novel method for direct reversible self-assembly and dis-assembly of Au nanoparticles (AuNPs) in water driven by pH stimuli. Using 3-aminopropyltriethoxysilane (APTES) as the capping ligand and pH-responsive agent, the APTES hydrolyzes rapidly in response to acid and then condenses into silicon. On the contrary, the condensed silicon can be broken down into silicate by base, which subsequently deprotonates the APTES on AuNPs. By controlling condensation and decomposition of APTES, the plasmonic coupling among adjacent AuNPs could be reversible tuned to display the plasmonic color switching. This study provides a facile and distinctive strategy to regulate the reversible self-assembly of AuNPs, and it also offers a new avenue for other plasmonic nanoparticles to adjust plasmonic properties via reversible self-assembly.

Active tunable plasmonic switch designed by metal–insulator–metal waveguides connected to a nanodisk cavity enabled by a phase-change material ring

Phase-change materials, such as vanadium dioxide (VO2), exhibit high contrast in their optical properties upon transitions between their insulator and metallic phases, providing an interesting tool to design active devices. A cavity structure consisting of a VO2 ring within a nanodisk is proposed to control the propagation of light through a metal–insulator–metal plasmonic waveguide. Numerical simulations indicate that the transmission of the designed structure is higher than 0.56 in the wavelength range of 1500 to 1600 nm in the insulating phase of the VO2 rings. However, transition of the VO2 rings to the metallic phase considerably increases their absorption coefficient. Then the transmission of the structure falls to lower than 0.0034 in the 1500- to 1600-nm wavelength range. Therefore, the achieved extinction ratio is higher than 22.1 dB in this wavelength range. We demonstrate that the central wavelength of the transmission band of the structure can be tuned by changing the geometrical parameters of the VO2 ring. The influence of partial phase transition on the transmission level is also studied by effective medium theory.

Manipulation of Plasmon Dephasing Time in Nanostructure Arrays Via the Far-Field Coupling

On-demand manipulation of the plasmon dephasing time plays critical roles in many important applications of localized surface plasmon resonance. Here, we systemically investigate the influence of the far-field coupling on plasmon dephasing time in different nanostructure arrays supporting single or multiple modes by for the first time applying the harmonic oscillator analysis model combined with the finite-difference time-domain numerical simulation. The results show that the dephasing time of a bright mode in the nanodisk array can be well on-demand manipulated based on the far-field coupling through varying the individual nanodisk size and array period. In particular, the dephasing time of nanodisk array with adjusting periods exhibits the behavior of first increasing and then decreasing, and it is also modified to different extents under different nanodisk sizes. Furthermore, for the heptamer array supporting multiple modes, we demonstrate that the influence of array period on dephasing time also exists for a bright mode, but a negligible effect appears for dark mode due to the negligible far-field coupling. These findings provide a potential solution to manipulate the dephasing time of plasmonic nanostructure and thereby offer flexible controllability of the ultrafast on-off process of plasmonic switching and photocatalytic efficiency.

A Consistent Scheme for the Precise FDTD Modeling of the Graphene Interband Contribution

The conductivity of graphene, due to interband electron transitions, is evaluated, in this article, as rational functions through an efficient iterative optimization of Padé polynomials. Then, the latter are straightforwardly imported in the text finite-difference text time-domain algorithm, as an equivalent surface current, by means of precise recursive convolution schemes. Numerical examples, considering an incident plane wave toward graphene, the extraction of the corresponding surface wave propagation attributes, and a plasmonic switch, successfully validate the consistent modeling of interband conductivity through the proposed technique.

Ultrafast spatiotemporal control of directional launching of surface plasmon polaritons in a plasmonic nano coupler

Ultrafast spatiotemporal control of a surface plasmon polariton (SPP) launch direction is a prerequisite for ultrafast information processing in plasmonic nanocircuit components such as ultrafast on–off of plasmonic switching and information recording. Here we realize for the first time, to the best of our knowledge, ultrafast spatiotemporal control of the preferential launch direction of an SPP at the nano-femtosecond scale via a plasmonic nano directional coupler. The spatiotemporal switching of the SPP field was revealed using time-resolved photoemission electron microscopy (TR-PEEM). Experimental results show that the extinction ratio of the SPP directional coupler can be substantially optimized by properly selecting the amplitude and time delay of the two incident light pulses in the experiment. More importantly, we demonstrate a solution for the launch direction of the SPP field, switched in a plasmonic nano directional coupler on the femtosecond timescale, by adjusting the instantaneous polarization state of the excitation light. The TR-PEEM images are supported by finite-difference time-domain (FDTD) simulations. We believe the results of this study can be used to develop high-speed, miniaturized signal processing systems.

Optical Fiber Delivered Ultrafast Plasmonic Optical Switch.

Ultrafast optical switch based on plasmonic nanostructures has large application potentials in optical logic circuits and optical communication systems. Integration of plasmonic optical switching devices with optical fibers is a breakthrough for realizing practical applications in long‐range optical data transmission or communication techniques. Here, the incorporation of plasmonic optical switch devices onto the end facets of optical fibers is reported, so that the switched optical signals are generated by interaction between femtosecond laser pulses and plasmonic nanostructures on one end of the fiber, and are delivered via the fiber waveguide to the other end for detection or decoding. “Quenching” of localized surface plasmon in the gold nanowires by its interaction with band‐edge modulation in gold through strong optical excitation is the responsible photophysics. This work accomplishes for the first time the implementation of ultrafast plasmonic optical switch device on optical fiber tips for logic data transmission.

Surface plasmon resonances between silver nanoribbons and anisotropic black phosphorus to light confinement

Two-dimensional plasmonic materials generally use patterned structural design to enhance the intensity of interaction with light near the resonance wavelength. We propose a non-patterned monolayer black phosphorus (BP) and patterned silver periodic nanostructures. The surface plasmon resonances (SPRs) between the upper metal silver nanoribbons or silver nano-square matrix and the BP sheet are used to achieve effective light confinement. Since the BP sheet is continuous in the structural design, the absorption response of the system can be dynamically adjusted by voltage-controlled Fermi level of BP. We also discussed two structural parameters closely related to the local size of SPR, the width of silver nanoribbons w 1, and the distance d 1 between silver and BP. The crystal structure of the BP puckered shows a strong in-plane anisotropy. When the silver in the system is a nanoribbon and a nano-square matrix, we research the anisotropy of the system by placing the BP in different directions relative to the structure and change the polarization angle of the incident light. The proposed anisotropic structure has the ability to achieve light confinement, which provides the basis for the construction of plasmonic sensors and polarization switches.

Tunable Plasmon-Induced-Transparency Effect in a Simple Planar Composite Structure

A planar metamaterial structure has been designed to obtain surface plasmon-induced-transparency (PIT) effect, which is composed of a nanodisk sandwiched between double rods. From theoretical perspective, the three-level plasmonic system has been utilized to analyze the near-field coupling mechanism. Besides, the simulation results show that PIT resonance can be tailored by structure parameters. Particularly, when the length of the rods is more than twice of the diameter of the disk, two PIT windows are generated simultaneously, based on the coupling between the bright mode of the nanodisk and two multipole dark modes of rods. Furthermore, a metamaterial structure, composed by a disk and two pairs of nanorods, is suggested to achieve the polarization-independent plasmon-induced-transparency effect. As a result, this work shows great application prospect in the area of compact optical devices, such as multiband tunable filters, plasmonic switches, and slow light devices.

Plasmonic all-optical metal–insulator–metal switches based on silver nano-rods, comprehensive theoretical analysis and design guidelines

In this paper, all-optical plasmonic switches are proposed and analyzed. These structures consist of a rectangular resonator filled with a Kerr-type material (AuSiO2) which is coupled to isolated metal–insulator–metal plasmonic waveguides. The resonators contain periodic arrays of nano-rods with rectangular and triangular patterns. The horizontal and vertical waveguides are used for data and control signals, respectively. Using two separate paths for the data and control signals results in suitable isolation between the signals. The finite difference time domain (FDTD) method is used for numerical investigation of the designed structures. To provide more insight, the FDTD results of the building blocks of the switches are compared with transmission line method results. The most important benefits of the proposed topologies are requiring lower pump intensities, needing smaller footprints and having isolated data and control ports. The proposed switch needs a pump intensity equal to 193.2 mW/μm2 and requires a 0.593 μm2 footprint area. A 11.3 dB contrast ratio exists between the On and Off states of the switch. Based on the mentioned advantages, these switches have the potential to be used in complex integrated optical circuits.

Plasmon switching of gold nanoparticles through thermo-responsive terminal breathing of surface-grafted DNA in hydrated ionic liquids.

Self-assembly performed in ionic liquids (ILs) as a unique solvent promises distinct functions and applications in sensors, therapeutics, and optoelectronic devices due to the rich interactions between nanoparticle building blocks and ILs. However, the general consideration that common nanoparticles are readily destabilized by counterions in an IL has largely prevented researchers from investigating controlled nanoparticle assembly in IL-based systems. This study explores the assembling behaviour of double-stranded (ds) DNA-functionalized gold nanoparticles (dsDNA-AuNPs) in hydrated ionic liquids. The DNA base pair stacking assembly of dsDNA-AuNPs occurs at a low IL concentration (<5%). However, a moderate ionic liquid concentration (5-40%) can de-hybridize dsDNA and leaves single-stranded (ss) DNA stabilizing the AuNPs. In concentrated ionic liquids (>40%), interestingly, the higher ionic strength leads to the assembly of DNA-AuNPs. The triphasic assembly trend is also generally observed regardless of the type of IL. By down-regulation of DNA's melting temperature with the IL, the assembly of DNA-AuNPs affords robust response to a lower temperature range, promising applications in plasmonic devices and range-tunable temperature sensors.

A new cobalt(II) complex nanosheet as an electroactive medium for plasmonic switching on Au nanoparticles.

2D metal-organic complex nanosheets with the merits of high stability and structure tunability are an emerging topic in recent years. To extend the promising ultrathin architectures, a new Co(II) complex nanosheet (Co-nanosheet) is designed and prepared via a readily operated interface-assisted coordination reaction between the ligand 4,4'',4'''-(2,4,6-trimethylbenzene-1,3,5-triyl)tris(2,2':6',2''-terpyridyl) (L) and Co2+ ions. The as-formed Co(II) complex nanosheet exhibits both a uniform layered structure and good thermostability as proposed, which were verified by various chemical and physical analytical methods. Moreover, it is first utilized as an electroresponsive medium to tune the surface plasmon resonance behavior of Au nanoparticles, expanding the applicable fields of this type of 2D materials.

Range-tunable plasmon switching of gold nanorods by terminal breathing of surface-grafted DNA in alcoholic solvents

A smart thermal plasmon switch of Au nanorods featured with tunable response temperature is developed by thermal-responsive terminal breathing of surface-grafted DNA in alcoholic solvents.

Whispering-gallery mode resonance-assisted plasmonic sensing and switching in subwavelength nanostructures

Whispering-gallery modes (WGMs), confining the resonant photons in nanoscale volumes, have been known to exhibit high-quality factor and sensitivity for electromagnetic waves in the field of nanophotonics. Here, we numerically demonstrate that a metasurface, which consists of periodic arrays with concentrically hybrid rectangular-slot (RS) and circular-ring-aperture (CRA) unit cells, supports polarization-dependent plasmonic sensing and switching in the visible and near-infrared regions. In particular, it is shown that the magnetic plasmon-induced transparency (PIT) effect arises from the coupling between a wideband WGM resonance and a narrowband magnetic dipole resonance mode in the hybrid metasurface. It is of great interest to find that the resonance mode broadening and mode shift sensing can be realized by varying the polarization angle of incident light and the length of the RS structure, respectively. Moreover, a novel and easy-fabricated plasmonic switching can be implemented in the visible and near-infrared regions. By changing the inner radius of the CRA structure, we reveal that the operating wavelength of the plasmonic switching can be extended to the telecom O- or E-band with an optimal ON/OFF ratio being 18.35 dB. Our results provide a path toward designing compact and tunable PIT device and could expand the application range of subwavelength nanostructures to the realm of optical communications and information process.

Near-infrared dual-wavelength plasmonic switching and digital metasurface unveiled by plasmonic Fano resonance

Abstract Plasmonic Fano resonance (FR) that contributes to multitudinous potential applications in subwavelength nanostructures can facilitate the realization of tunable wavelength selectivity for controlling light–matter interactions in metasurfaces. However, the plasmonic FR can be generated in metasurfaces with simple or complex geometries, and few of them can support flexible amplitude modulation and multiwavelength information transfer and processing. Here, we study the near-infrared plasmonic FR in a hybrid metasurface composed of concentrically hybridized parabolic-hole and circular-ring-aperture unit cells, which can induce polarization-dependent dual-wavelength passive plasmonic switching (PPS) and digital metasurface (DM). It is shown that the designable plasmonic FR can be realized by changing the geometric configurations of the unit cells. In particular, owing to the polarization-dependent characteristic of FR, it is possible to fulfill a compact dual-wavelength PPS with high ON/OFF ratios in the related optical communication bands. Moreover, such PPS that manipulates the amplitude response of the transmitted spectrum is an efficient way to reveal a 1-bit DM, which can also be rationally extended to a 2-bit DM or more. Our results suggest a pathway for studying polarization-dependent PPS and programmable metasurface devices, yielding possibilities for subwavelength nanostructures in optical communication and information processing.

Two-Way Fano Resonance Switch in Plasmonic Metamaterials

A two-way Fano resonance switch in the plasmonic metamaterials has been proposed and experimentally demonstrated. The electrical Fano switch is composed of two concentric spoof localized surface plasmons (LSPs) resonators. By adjusting the slit in the inner spoof LSPs resonator, two different Fano resonance modes could be supported. By loading a Schottky barrier diode (SBD) across the slit in the inner LSPs resonator, both Fano resonance modes can be simultaneously switched when the SBD diode is forward-biased or reverse-biased and their switch status is opposite. Both simulated and measured results agree well at microwave frequencies and verify the two-way Fano resonance switch. The devices could be applied in many applications such as plasmonic circuits, multi-way sensing or switching, and so on.

Electro-Ionic Control of Surface Plasmons in Graphene-Layered Heterostructures.

Precise control of light is indispensable to modern optical communication devices especially as the size of such devices approaches the subwavelength scale. Plasmonic devices are suitable for the development of these optical devices due to the extreme field confinement and its ability to be controlled by tuning the carrier density at the metal/dielectric interface. Here, an electro-ionic controlled plasmonic device consisting of Au/graphene/ion-gel is demonstrated as an optical switch, where an external electric field modulates the real part of the electrical conductivity. The graphene layer enhances charge penetration and charge separation at the Au/graphene interface resulting in an increased photoinduced voltage. The ion-gel immobilized on the Au/graphene further enables the electrical tunability of plasmons which modulates the intensity of the reflected laser light. This work paves the way for developing novel plasmonic electro-optic switches for potential applications such as integrated optical devices.

A tunable band-stop plasmonic waveguide filter and switch designing with triangular resonator based on Kerr non-linearity

A tuneable band-stop plasmonic waveguide filter including a triangular resonator is proposed and designed numerically. Geometric parameters of the structure including the base of the triangle resonator and its height, the cavity distance from the waveguide, and the thickness of the cavity are used to design a tenable band-stop filter. The finite – difference time – domain algorithm is utilized to the simulation of a two-dimensional filtering mechanism as well as a demonstration of switching effect (with enabled-low and high conditions: T (ON/OFF) = 32.01 and 57.61, respectively) by using pump-probe signals. The proposed tunable filter and the all-optical switch can be applied as building blocks in optical integrated circuits.

Reversible plasmonic switching in a graphene nanoresonator loaded with a core – shell quantum dot

A model of an all-plasmonic switch based on a graphene waveguide integrated with a stub nanoresonator loaded with a quantum dot is considered. Using the full-wave numerical simulation, it is shown that successive on/off switching of the control surface plasmon – polariton wave at the input of the waveguide leads to a change in the phase of the signal plasmon – polariton wave in the nanoresonator by π. This causes reversible switching of the device operation regime – from almost complete blocking to stable transmission of the signal plasmon – polariton wave through the waveguide. The effect is implemented at rates of ∼0.5 THz for infrared electromagnetic waves localised in a device with a switching region of 40 × 20 nm.

High performance vanadium dioxide based active nano plasmonic filter and switch

We have designed a compact active nano-plasmonic waveguide-based filter and switch in a Fabry Perot structure, in which Vanadium dioxide (VO2) is used as the active material to form an Au/VO2/Au tri-layer structure, which is based on the effect of the electrical-driven phase transformation from the VO2 layer. The largest modulation depth and lowest insertion loss of the Au/VO2/Au tri-layer based FP resonator are 44.77 dB and 1.43 dB respectively in the near-infrared wavelength range from 1400 nm to 2100 nm. In addition, a moderate quality factor of 146 and a high figure-of-merit of 33.31 can be achieved by using a short nano-plasmonic waveguide. The compact size, wavelength tunability, high modulation depth and low insertion loss indicate that the proposed active nano-plasmonic waveguide can be used in a high-density integrated optical circuit.