Surface Plasmon Resonance Intensification by Cavity-Ring Plasma Structure in the Giga-Hertz Regime

In this paper, we propose a novel sub-wavelength plasma structure that can effectively enhance surface plasmon resonance (SPR) to achieve a significant local field. On the basis of a plasma ring structure, we add a slit and two thin plasma layers, working as a metal-insulator-metal (MIM) waveguide at a specific incident wave frequency and generate the Fabry-Perot resonance (FPR). The structure thus couples the incident wave energy to the vicinity of the slit and intensifies the SPR inside the plasma ring. In addition, we also find the coupling and competing between SPR and FPR. For the coupling mode, the average field enhancement in the ring is up to a factor of 9.7. Moreover, the optimized thickness of the plasma layer is much thinner than the skin depth of the plasma to ensure the incident wave easily entering the MIM waveguide. We further calculate the dispersion relationship of surface plasmon polaritons in the waveguide cavity. The simulation results and theoretical dispersion function are in good agreements.

     

A Wavelength Demultiplexing Structure Based on the Multi-Teeth-Shaped Plasmonic Waveguide Structure

In this paper, a wavelength demultiplexing structure based on multi-teeth-shaped metal-insulator-metal (MIM) plasmonic waveguide is designed and numerically studied using the finite-difference time-domain (FDTD) method. Investigating the characteristics of a multi-teeth-shaped plasmonic waveguide structure reveals that with the design of the structure, it was possible to create a mode inside the bandgap of the filter. Based on the created mode inside the bandgap of the filter, the demultiplexer structure has been proposed and investigated. By changing the geometric parameters of the structure, the transmission wavelength of the demultiplexer channel can be adjusted. The proposed demultiplexer can be used in integrated optical circuits.

     

Design of Plasmonic Comb-Like Filters Using Loop-Based Resonators

A subwavelength plasmonic comb-like filter is proposed by using dual symmetric slot cavities which are placed between two parallel metal–insulator–metal (MIM) structure waveguides. The structure can be considered as a resonance loop which consists of slot cavity resonators and MIM waveguide resonators. The reflective wavelength range and channel spacing are determined by the lengths of slot cavities and MIM waveguides, respectively. Three, four, and five reflective channels with high reflection are achieved in a small wavelength range. Higher channel count can be available by increasing the length or the real part of effective index of MIM waveguides. Such a device can find applications in various optical systems such as wavelength demultiplexing components.     

Dynamically Switchable Multispectral Plasmon-Induced Transparency in Stretchable Metamaterials

We propose dynamically switchable multispectral plasmon-induced transparency (PIT) with high modulation depth in a three-dimensional metamaterial standing on a flexible substrate. The proposed metamaterial is composed of a pair of metal–insulator–metal (MIM) nano-cut-wires and a pair of insulator–metal–insulator (IMI) nano-cut-wires. Results show that two PIT windows can be achieved because of the near-field coupling between the dipole supported by the IMI nano-cut-wire and two quadrupoles supported by the MIM structures. These two PIT windows can be blue-shifted or even flipped over by stretching the substrate along one direction, or be switched off by stretching along the other direction. A classical coupled oscillator model is developed to quantitatively describe and explain these results. We expect this work will find promising applications in multispectral sensors, slow light devices and nonlinear optical devices.

     

Dynamically Tunable by Kerr Effect Multichannel Filter Based on Plasmon Induced Transparencies at Optical Communication Range

Dynamically tunable multichannel filter based on plasmon-induced transparencies (PITs) is proposed in a plasmonic waveguide side-coupled to slot and rectangle resonators system at optical communication range. The slot and rectangle resonators in this system can be regarded as radiative or dark resonators as same as the radiative or dark elements in the metamaterial structure with the help of the evanescent coupling. The multiple PIT responses which can enable the realization of nanoscale filter with four channels are originated from the direct near-field coupling and indirect phase couple through a plasmonic waveguide simultaneously. Moreover, the magnitudes and bandwidths of the filter can be efficiently tuned by controlling of the geometric parameters such as the coupling distances and the pump light-induced refractive index change of the Kerr material which is embedded into the metal-dielectric-metal waveguide between the radiative resonators.     

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1?×?10³ nm/RIU and its figure of merit is as high as 2?×?10⁵ at λ?=?980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm² may find important applications in the on-chip nano-sensors.     

A High Performance Plasmonic Sensor Based on Metal-Insulator-Metal Waveguide Coupled with a Double-Cavity Structure

A high performance plasmonic sensor based on a metal-insulator-metal (MIM) waveguide coupled with a double-cavity structure consisting of a side-coupled rectangular cavity and a disk cavity is proposed. The transmission characteristics of the rectangular cavity and disk cavity are analyzed theoretically and the improvements of performance for the double-cavity structure compared with a single cavity are studied. The influence of structural parameters on the transmission spectra and sensing performance are investigated in detail. A sensitivity of 1136 nm/RIU with a high figure of merit of 51,275 can be achieved at the resonant wavelength of 1148.5 nm. Due to the high performance and easy fabrication, the proposed structure may be applied in integrated optical circuits and on-chip nanosensors.     

Modelling of Polarization-Dependent Loss in Plasmonic Nanowire Waveguides

We have investigated the potential of using gold nanowires embedded in a dielectric cladding environment as polarization-independent long-range surface plasmon polariton waveguides at telecom wavelengths. We performed finite-element analysis on various symmetric and close-to-symmetric cross-sectional geometries and evaluated the effects of cladding thickness on the propagation and coupling loss. The calculations confirm that fabrication of polarization-independent waveguides with reasonable tolerances is feasible and that straight-waveguide insertion losses around 1.5 dB for short (0.5 mm) devices can be realized when coupling to and from conventional dielectric waveguide geometries.     

Entanglement of Two Quantum Dots with Azimuthal Angle Difference in Plasmonic Waveguide System

We investigate the properties of entanglement between two quantum dots (QDs) with an azimuthal angle difference in two different plasmonic waveguide systems where a cavity coupled to the QDs is included or not. The real space formalism and the concurrence are used in solving the eigenvalue equation and calculating the entanglement, respectively. We analyze the influence of azimuthal angle difference on the entanglement and propose several effective ways to achieve high entanglement by adjusting the detuning, the QD-cavity coupling strength, and so on. Moreover, comparing the entanglement in the two models, we demonstrate that the addition of cavity can improve the entanglement of two QDs.

     

Liquid Phase Synthesis of Peptide Nucleic Acid (or Polyamide Nucleic Acid) Dimers

Abstract

The liquid phase synthesis of “polyamide nucleic acid” (PNA) dimers containing the purine nucleic acid bases adenine and guanine has been achieved in good yields. This strategy was elaborated in order to circumvent difficult direct coupling of protected PNA monomers. This method can be applied to the liquid phase synthesis of short protected polyPNAs fragments, which can then selectively be deprotected.     

Design and Optimization of Open-cladded Plasmonic Waveguides for CMOS Integration on Si3N4 Platform

Herein, we present a design analysis and optimization of open-cladded plasmonic waveguides on a Si₃N₄ photonic waveguide platform targeting CMOS-compatible manufacturing. For this purpose, two design approaches have been followed aiming to efficiently transfer light from the hosting photonic platform to the plasmonic waveguide and vice versa: (i) an in-plane, end-fire coupling configuration based on a thin-film plasmonic structure and (ii) an out-of-plane directional coupling scheme based on a hybrid slot waveguide. A comprehensive numerical study has been conducted, initially deploying gold as the reference metal material for validating the numerical models with already published experimental results, and then aluminum and copper have been investigated for CMOS manufacturing revealing similar performance. To further enhance coupling efficiency from the photonic to the plasmonic part, implementation of plasmonic tapering schemes was examined. After thorough investigation, plasmo-photonic structures with coupling losses per single interface in the order of 1 dB or even in the sub-dB level are proposed, which additionally exhibit increased tolerance to deviations of critical geometrical parameters and enable CMOS-compatible manufacturing.

     

High-extinction-ratio and low-insertion-loss Plasmonic Filter with Coherent Coupled Nano-cavity Array in a MIM Waveguide

In this paper, a novel plasmonic filter with very high extinction ratio and low insertion loss is proposed based on the coherent coupled nano-cavity array in a metal–insulator–metal (MIM) waveguide. The coherent coupling interactions among nano-cavities are investigated with an analytical model which is derived based on the temporal coupled-mode theory and transfer-matrix method. The destructive interference of the surface plasmon polaritons coupled from the nano-cavities at the resonant wavelength is achieved by suitably designing the period of the cavity array, which may be used for increasing the extinction ratio of the filter based on the nano-cavity array in the MIM waveguide. A plasmonic filter with an extinction ratio higher than 60 dB and an insertion loss less than 1.0 dB is obtained by applying the destructive interference in the design of a six-rectangular-cavity array in an Ag–air–Ag waveguide. And the correctness of the design for the filter is verified by the results obtained with the finite-difference time-domain simulation technique. This work may provide useful schemes and approaches for realization of various wavelength-sensitive devices in plasmonic integrated circuits.     

Fano Resonance in a Gear-Shaped Nanocavity of the Metal–Insulator–Metal Waveguide

The filter function of the metal–insulator–metal (MIM) waveguide with a gear-shaped nanocavity is investigated using the finite-difference time-domain method. Since the gear breaks the symmetric distribution of the resonance, Fano resonance occurs in the gear-shaped nanocavity. Fano resonance strongly depends on the structural parameters of the gear. Compared to the MIM waveguide with a disk-shaped nanocavity, the MIM waveguide with a gear-shaped nanocavity allows for a much more sensitive detection of small refractive index changes of the filled media inside the nanocavity, which reveals a potential sensor application of the MIM waveguide with a gear-shaped nanocavity.     

Plasmonic Wavelength Demultiplexer with Mode Conversion Capabilities

An efficient wavelength demultiplexer with its input as a metal-insulator-metal (MIM) waveguide mode and output an out of plane free-space mode is proposed. The proposed demultiplexer design is integrated on a MIM waveguide such that power is evanescently coupled into an array of appropriately designed cavity-groove combination. The demultiplexer design permits control of phase of the dropped wavelength to achieve a desired wavefront. We demonstrate this through generation of circular and plane wavefront. By controlling the evanescently coupled power into the cavity-groove combinations, it is possible to dramatically improve the efficiency of the proposed demultiplexer. Results are simulated using FEM technique.     

Tunable Multiple Fano Resonances and Stable Plasmonic Band-Stop Filter Based on a Metal-Insulator-Metal Waveguide

Plasmonics - A metal-insulator-metal (MIM) waveguide consisting of two stub resonators and a ring resonator is proposed, which can be used as refractive index sensor and stop-band filter at the...     

Tunable Fano Resonances in Mid-Infrared Waveguide-Coupled Otto Configuration

A planar silicon carbide/dielectric multilayer structure is investigated in Otto geometry, where surface phonon polaritons and planar waveguide mode can be coupled to realize Fano resonances under transverse magnetic polarization. The resonance coupling is analytically demonstrated using the coupled harmonic oscillator model and numerically presented through rigorous coupled-wave analysis calculations, which shows that the coupling strength between different resonances and the resonant wavelength matching condition plays an important role in the bandwidth and position of the Fano resonance (FR); the magnetic field distribution was also shown to explain the origin of FRs qualitatively.

     

Tunable Hybrid Gap Surface Plasmon Polariton Waveguides with Ultralow Loss Deep-Subwavelength Propagation

Exploring hybrid gap surface plasmon polariton waveguides (HGSPPWs) is an important milestone in developing the next-generation, nanoscale integrated photonic circuit technology. To advance their potential applications, HGSPPWs are required to have tunable capability, highly reliable, simple fabrication process, and feasible integration. In this paper, we propose two tunable HGSPPWs fulfilling the requirements. The proposed HGSPPWs consist of a metallic wedge laterally coupled with a dielectric waveguide. The modal characteristics of HGSPPWs are investigated at the optical telecommunication wavelength, which shows the modal characteristics could be effectively controlled by tuning the key geometry parameters and structure of HGSPPWs. The propagation length could achieve the centimeter scale while maintaining the propagation mode size at the deep-subwavelength scale (~ λ²/10⁵). The studies on fabrication tolerance and waveguide crosstalk show their robust property for practical implementations. The effective tunable mechanism is also proposed and studied, which shows remarkable feasibility to realize multifunctional plasmon-based photonic components. Compared with the conventional HGSPPWs, the proposed HGSPPWs exhibit superior features in ultralow loss deep-subwavelength light guiding, are highly reliable, and are easy to integrate.

     

High Sensitivity Nanoplasmonic Sensor Based on Plasmon-Induced Transparency in a Graphene Nanoribbon Waveguide Coupled with Detuned Graphene Square-Nanoring Resonators

A novel nanoscale structure for high sensitivity sensing which consists of a graphene nanoribbon waveguide coupled with detuned graphene square-nanoring resonators (GSNR) based on edge mode is investigated in detail. By altering the Fermi energy level of the graphene, the plasmon-induced transparency (PIT) window from the destructive interference between a radiative square-nanoring resonator and a dark square-nanoring resonator can be easily tailored. The coupled mode theory (CMT) is used to show that the theoretical results agree well with the finite difference time domain (FDTD) simulations. This nanosensor yields a ultrahigh sensitivity of ∼2600 nm/refractive index unit (RIU) and a figure of merit (FOM) of ∼54 in the mid-infrared (MIR) spectrum. The revealed results indicate that the Fermi energy level of the graphene and the coupling distance play important roles in optimizing the sensing properties. Our proposed structure exerts a peculiar fascination on the realization of ultra-compact graphene plasmonic nanosensor in the future.

     

Coupling Between Silicon Waveguide and Metal-Dielectric-Metal Plasmonic Waveguide with Lens-Funnel Structure

Various photonic integrated components have been implemented by ultra-thin silicon-on-insulator (SOI) waveguides; therefore, it is desirable to couple ultra-thin SOI waveguides to plasmonic waveguides. In this paper, we present an ultra-thin SOI waveguide to a metal-dielectric-metal plasmonic waveguide based on a lens-funnel structure consisting of truncated Luneburg lens and metallic parabolic funnel. The lens is implemented by varying the guiding layer thickness. The effect of different parameters of the coupler’s geometry is studied using the finite-difference time-domain method. The 1.13-μm-long coupler improves the average coupling efficiency in the C-band from 66.4 to 82.1%. The numerical simulations indicate that the coupling efficiency is higher than 69% in the entire O, E, S, C, L, and U bands of optical communication.