Plasmonic Logic Gates Research Articles

Plasmonic Mid-Infrared Wavelength Selector and Linear Logic Gates Based on Graphene Cylindrical Resonator

In this paper, we report the design, simulation, and some applications of a tunable graphene-based cylindrical resonator by analytical and numerical two-dimensional finite-difference time-domain methods. The base structure operates as a bandpass filter in the mid-infrared region. The tunability of the filter is achieved by changing the radius and/or the chemical potential of the graphene cylinder. Based on the proposed cylindrical resonator, a two-channel wavelength selector and some novel linear plasmonic logic gates are designed and proposed. The even- and the odd-order resonance modes are separated in the two-channel wavelength selector and are transmitted to the output graphene waveguides. Moreover, the plasmonic logic gates including XOR, XNOR, NAND, and NOT having the significant features such as linearity, compact size, and low loss are proposed. The analytical approach and the numerical simulations prove the excellent performance of the logic gates in comparison to the reported ones in the literature. The simulation results demonstrate that the maximum ON/OFF ratios for these plasmonic logic gates are 29.09, 28.78, 28.78, and 29.09 dB, respectively. The proposed functional ultra-compact nano-scale graphene-based structures offer potential basic blocks for mid-infrared optical computing and signal processing.

Edge mode graphene plasmons based all-optical logic gates

Graphene plasmonic logic gates (GPLGs) with high compaction and simple structure are presented and investigated in this paper. Due to the strong confinement of edge mode graphene surface plasmon polaritons (EGSPPs), it can process optical signal on nanoscale ribbons with both straight and flexible shapes. Three eigen modes of graphene surface plasmon polaritons (GSPPs) are studied from the aspect of their propagation properties, indicating that the symmetric edge-mode (SEM) is an optimal choice for designing the GPLGs. Finally, some basic logic gates, i.e., the XOR and XNOR gates, are demonstrated by employing the SEM. More kind of GPLGs and functional devices are expected to be realized by cascading these basic logic gates.

All-Optical NOT Gate Based on Nanoring Silver-Air Plasmonic Waveguide

In this work, all-optical plasmonic NOT logic gate was proposed by using metal-insulator-metal (MIM) plasmonic waveguides design. This logic gate is numerically analyzed by COMSOL Multiphysics 5.3a. Recently, plasmonics have attracted more attention due to its huge applications in all optical signal processing. Due to it’s highly localization to metallic surfaces, surface plasmon (SP) may have many applications in sub wavelength to guide the optical signal in waveguides to overcome the diffraction limit which considered a big problem in conventional optics. The proposed design of MIM structure is consist of a dielectric waveguides plus metallic claddings, which guide the incident light strongly in the insulator region. Strong localization and relatively simple fabrication make the MIM waveguides the potential key design of Nano-scale all optical devices. Our design consists of symmetric ring structures with straight waveguides which based on MIM structure. All-optical logic gate (NOT gate) behavior is achieved from utilizing the interface between straight waveguides and ring structure waveguides. By switching the activation of the control port, the propagation of the outgoing field in the output waveguide will be changed. As the simulation results show, the proposed structure could operate as an all-optical NOT logic gate. This gate would be a potential component in many applications of all-optical signals processing.

Ring-Shaped Plasmonic Logic Gates

Ring-shaped one-, two-, and three-bit plasmonic logic gate configurations and circuits have been proposed, which, besides being compact, are also versatile and can be easily cascaded, the output logic values being controlled by both the geometry of the multi-port rings and the phase of the incident beams. This latter degree of freedom, not fully exploited up to now in plasmonic circuits, offers a high degree of flexibility of logic gate configurations.

Broadband Multifunctional Plasmonic Logic Gates

AbstractPlasmonic logic gates provide a promising platform to realize diffraction‐unlimited all‐optical logic circuits. However, previous plasmonic logic gates suffer from narrow bandwidth and high loss. Here, broadband plasmonic logic gates are proposed and demonstrated using a unique design based on curved silver gratings. These logic gates can maintain a high intensity contrast ratio (29 dB) under front optical illumination. And, the broadband feature is achieved due to the feature of zero optical path difference from different positions of the curved grating to the output port. All the seven fundamental logic gates are demonstrated. In addition, different types of logic gates can be realized using the same device configuration. The possibility of multifunctionality makes these logic gates easy for device fabrication and system integration.

Reconfigurable Plasmonic Logic Gates

Reconfigurable one-, two-, and three-bit plasmonic logic gate configurations have been proposed, which work by covering a straight slot waveguide with materials with tunable dielectric constants, such as graphene. By encoding the logic states in the values of dielectric constants as opposed to different waveguides, the plasmon excitation problems are minimized and the simplified logic gate configurations could be easily implemented.

Plasmon induced absorption in a graphene-based nanoribbon waveguide system and its applications in logic gate and sensor

In this article, nanoscale integrated logic gates and a refractive index sensor both based on the tunable plasmon induced absorption (PIA) effect are proposed and investigated by employing a plasmonic waveguide nanostructure. Except for the direct and indirect coupling mechanism which is employed to explain the single PIA effect, the transmission of a three-resonators-coupled waveguide system is deduced theoretically to explain the dual PIA effects. Our calculated results prove that high tunability in wavelength and amplitude of the PIA effect can be achieved by tuning the Fermi levels of the graphene nanoribbons. By taking advantage of the interferometric effect, the logic gates are realized in this ultracompact structure based on the PIA effect in the mid-infrared region. The numerical results reveal that, for the plasmonic logic gate with coupling length of 60 nm, a high extinction ratio (>23.5 dB) can be achieved within a footprint of <0.06 µm2. Moreover, a plasmonic refractive index sensor with sensitivity as high as 1870 nm/RIU is also numerically predicted in this graphene-based waveguide system.

Lithographically fabricated gold nanowire waveguides for plasmonic routers and logic gates.

Fabricating plasmonic nanowire waveguides and circuits by lithographic fabrication methods is highly desired for nanophotonic circuitry applications. Here we report an approach for fabricating metal nanowire networks by using electron beam lithography and metal film deposition techniques. The gold nanowire structures are fabricated on quartz substrates without using any adhesion layer but coated with a thin layer of Al2O3 film for immobilization. The thermal annealing during the Al2O3 deposition process decreases the surface plasmon loss. In a Y-shaped gold nanowire network, the surface plasmons can be routed to different branches by controlling the polarization of the excitation light, and the routing behavior is dependent on the length of the main nanowire. Simulated electric field distributions show that the zigzag distribution of the electric field in the nanowire network determines the surface plasmon routing. By using two laser beams to excite surface plasmons in a Y-shaped nanowire network, the output intensity can be modulated by the interference of surface plasmons, which can be used to design Boolean logic gates. We experimentally demonstrate that AND, OR, XOR and NOT gates can be realized in three-terminal nanowire networks, and NAND, NOR and XNOR gates can be realized in four-terminal nanowire networks. This work takes a step toward the fabrication of on-chip integrated plasmonic circuits.

Correction: Lithographically fabricated gold nanowire waveguides for plasmonic routers and logic gates.

Correction for 'Lithographically fabricated gold nanowire waveguides for plasmonic routers and logic gates' by Long Gao et al., Nanoscale, 2018, 10, 11923-11929.

Proposal for nanoscale cascaded plasmonic majority gates for non-Boolean computation

Surface-plasmon-polariton waves propagating at the interface between a metal and a dielectric, hold the key to future high-bandwidth, dense on-chip integrated logic circuits overcoming the diffraction limitation of photonics. While recent advances in plasmonic logic have witnessed the demonstration of basic and universal logic gates, these CMOS oriented digital logic gates cannot fully utilize the expressive power of this novel technology. Here, we aim at unraveling the true potential of plasmonics by exploiting an enhanced native functionality - the majority voter. Contrary to the state-of-the-art plasmonic logic devices, we use the phase of the wave instead of the intensity as the state or computational variable. We propose and demonstrate, via numerical simulations, a comprehensive scheme for building a nanoscale cascadable plasmonic majority logic gate along with a novel referencing scheme that can directly translate the information encoded in the amplitude and phase of the wave into electric field intensity at the output. Our MIM-based 3-input majority gate displays a highly improved overall area of only 0.636 μm2 for a single-stage compared with previous works on plasmonic logic. The proposed device demonstrates non-Boolean computational capability and can find direct utility in highly parallel real-time signal processing applications like pattern recognition.

Ag nanoprism metamaterial based tunable plasmonic logic gate

A metamaterial comprised of asymmetrically arranged Ag nanoprisms has been proposed and investigated in this paper. The metamaterial shows a polarization dependent PIT effect. The metamaterial with its periodic length along a y-axis less than 400 nm shows two tunable transmission dips. When the periodicity is increased above 400 nm, the metamaterial shows three adjustable transmission dips against the polarization state. By choosing different wavelengths of incident light, the metamaterial can be used as plasmonic Boolean logic gates. The working wavelengths of these plasmonic devices can then be adjusted by controlling the fillet radius of Ag nanoprism in metamaterial. These results offer great potential in developing polarization dependent tunable plasmonic information processing devices.

Ultrafast surface plasmon-polariton logic gates and half-adder.

In this paper, we present a plasmonic model system for the realization of ultrafast all-optical NOT, AND, OR, and XOR gate operations using linear interference effects in dielectric crossed waveguide structures. The waveguides for the surface plasmon-polaritons are produced by a simple but highly accurate microscopic lithographic process and are optimized for single mode operation at an excitation laser wavelength of 800 nm. The functionality of the presented structures is demonstrated using sub-30 fs laser pulses from a mode locked titanium:sapphire laser. Using leakage radiation microscopy we show ultrafast SPP switching and logic operations of one basic structure consisting of two crossed waveguides with an additional output waveguide along the bisecting line of the input waveguides. The individual gates are realized on a footprint of 10 µm × 20 µm. Experimental investigations are supported by finite-difference time-domain simulations, where good agreement between experimental results and numerical simulations is obtained. To exploit the high precision of the fabrication method and its huge potential for realizing functional complex plasmonic circuitry we experimentally demonstrate a half-adder structure and its operation by combining and cascading several plasmonic waveguide components and logic gate elements on an area of only 10 µm × 28 µm.

Subwavelength Graphene-Based Plasmonic THz Switches and Logic Gates

In this paper, we report on the design procedure for developing subwavelength graphene-based plasmonic waveguide, performing as a THz switch or an AND/OR logic gate. The propagation length of the surface plasmons (SPs), stimulated by a 6 THz TM polarized incident wave along this waveguide with a top graphene layer whose chemical potential is held at $\mu_{\rm C}=300~{\hbox{meV}}$ (ON state) is more than 35 times larger than that in the waveguide with $\mu_{\rm C}= 0~{\hbox{eV}}$ (OFF state). Numerical results, obtained from full wave simulations using a finite element method, also show that the modulation depth density obtained for the straight plasmonic switching waveguide, whose length is just about 20% of the incident wavelength, is larger than those reported to date. Moreover, we also designed a logic AND gate composed of a straight waveguide, a Y-branch switch, and a logic OR gate composed of two face to face Y-branches, whose total lengths are ${\sim} {\hbox{37\%}}$ , ${\sim} {\hbox{45\%}}$ , and ${\sim} {\hbox{53\%}}$ of the incident wavelength, respectively. Simulations show that the maximum ON/OFF ratios for these subwavelength plasmonic waveguides that occur between their ‘1 1’ and ‘0 0’ logical states are ${\sim} {\hbox{41.37}}$ , ${\sim} {\hbox{39.87}}$ , and ${\sim} {\hbox{40.76}}~{\hbox{dB}}$ , respectively. These numerical data also show that the modulation depth densities obtained for these devices are also greater than those reported to date. The proposed graphene-based plasmonic switches and gates offer potential building blocks for the future digital plasmonic circuits operating around 6 THz.

Design and analysis of an all optical OR gate using surface plasmon hopping along metallic nanorods

This paper proposes a novel design technique for realization of plasmonic logic gates. A 2D plasmonic all optical OR gate with the miniaturized size of 5 μm × 3 μm is presented. Ag metallic reflectors form the input and output waveguides to confine the light inside the gate. The logic operations are realized through selective propagation of light in the gate through hopping of the surface plasmon resonances along the metallic nanorods. With this novel idea approximately 100% of input signal propagates through the output waveguide and no division occurs at the cross point. Due to its simplicity, the OR gate was chosen to be the first implemented logic gate to verify the performance of the proposed method. Our proposed optical gate works at the operating wavelength of 652 nm with input signals of a transverse magnetic (TM) (Hz, Ex, Ey) polarized continuous wave with near zero cross talk between two input waveguides.

Electro-optical graphene plasmonic logic gates

The versatile control of graphene's plasmonic modes via an external gate-voltage inspires us to design efficient electro-optical graphene plasmonic logic gates at the midinfrared wavelengths. We show that these devices are superior to the conventional optical logic gates because the former possess cut-off states and interferometric effects. Moreover, the designed six basic logic gates (i.e., NOR/AND, NAND/OR, XNOR/XOR) achieved not only ultracompact size lengths of less than λ/28 with respect to the operating wavelength of 10μm, but also a minimum extinction ratio as high as 15dB. These graphene plasmonic logic gates are potential building blocks for future nanoscale midinfrared photonic integrated circuits.

New progress of plasmonics in complex metal nanostructures

Noble metal nanostructures possess novel optical properties because of their collective electronic oscillations, known as surface plasmons (SPs). The resonance of SPs strongly depends on the material, surrounding environment, as well as the geometry of the nanostructures. Complex metal nanostructures have attracted research interest because of the degree of freedom in tailoring the plasmonic properties for more advanced applications that are unattainable by simple ones. In this review, we discuss the plasmonic properties of several typical types of complex metal nanostructures, that is, electromagnetically coupled nanoparticles (NPs), NPs/metal films, NPs/nanowires (NWs), NWs/NWs, and metal nanostructures supported or coated by dielectrics. The electromagnetic field enhancement and surface-enhanced Raman scattering applications are mainly discussed in the NPs systems where localized SPs have a key role. Propagating surface plasmon polaritons and relevant applications in plasmonic routers and logic gates using NWs network are also reviewed. The effect of dielectric substrates and surroundings of metal nanostructures to the plasmonic properties is also discussed.

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.