Extraordinary Optical Transmission Property of X-Shaped Plasmonic Nanohole Arrays

Optical transmission properties of periodic X-shaped plasmonic nanohole arrays in a silver film are investigated by performing the finite element method. Obvious peaks appear in the transmission spectra due to surface plasmon polaritons (SPPs) on the top surface of the silver film, to the Fabry–Ferot resonance effect of SPPs in the nanohole, and to the localized surface plasmon resonance of the nanohole. Besides the topologic shape parameters of the X-shaped nanohole, transmission properties strongly depend on incident polarization. The results of this study not only present a tunable plasmonic filter, but also aid in the understanding of the mechanisms of the extraordinary optical transmission phenomenon.     

Plasmonic Filter Using Metal-Insulator-Metal Waveguide with Phase Shifts and its Transmission Characteristics

Plasmonics - A plasmonic filter based on metal-insulator-metal (MIM) waveguide with phase shifts is proposed, and the corresponding transmission characteristics are investigated. Since the...     

Electromagnetically Induced Transparency and Refractive Index Sensing for a Plasmonic Waveguide with a Stub Coupled Ring Resonator

A plasmonic refractive index sensor based on electromagnetically induced transparency (EIT) composed of a metal-insulator-metal (MIM) waveguide with stub resonators and a ring resonator is presented. The transmission properties and the refractive index sensitivity are numerically studied with the finite element method (FEM). The results revealed an EIT-like transmission spectrum with an asymmetric line profile and a refractive index sensitivity of 1057 nm/RIU are obtained. The coupled mode theory (CMT) based on transmission line theory is adopted to illustrate the EIT-like phenomenon. Multiple EIT-like peaks are observed in the transmission spectrum of the derived structures based on the MIM waveguide with stub resonator coupled ring resonator. To analyze the multiple EIT-like modes of the derived structures, the H _z field distribution is calculated. In addition, the effect of the structural parameters on the EIT-like effect is also studied. These results provide a new method for the dynamic control of light in the nanoscale.     

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.     

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.

     

A Plasmonic Wavelength-Selected Intersection Structure

A subwavelength intersection structure with wavelength filtering functionality is proposed by using an open loop which consists of four slot cavities and four metal-insulator-metal (MIM) drop waveguides. The slot cavities are used as the resonators while the MIM waveguides serve as the input/output ports. The SPPs propagations and the transmission wavelengths in two pairs of matched input/output ports are immune to each other, which satisfy the intersection characters. The results based on finite difference time domain (FDTD) method demonstrate that high transmittance for the expected output port and high isolation for other ports have been achieved. Specifically, the transmittance and isolation is larger than 0.64 and 14 dB, respectively. In addition, a transmission peak, whose wavelength can be modulated by adjusting the length of the slot cavities, is available for the output port. Such a device can find applications in various optical systems, such as the wavelength filtering area and the optical intersection area.     

Propagation Properties of Nanoscale Three-Dimensional Plasmonic Waveguide Based on Hybrid of Two Fundamental Planar Optical Metal Waveguides

In this paper, a nanoscale three-dimensional plasmonic waveguide (TDPW), created by depositing an Ag stripe on a SiO₂ layer with an Ag substrate, is introduced and theoretically investigated at visible and telecom wavelengths. By applying the effective index method and finite-difference time-domain numerical simulations, the authors find that the propagation properties of surface plasmon polaritons (SPPs) in the TDPW, including the propagation length and beam width, are mainly decided by the core (the SiO₂ layer just under the Ag stripe) itself, due to the much stronger localization of SPPs in the core than in the two side claddings (the SiO₂ layer without the covered Ag stripe). And propagating SPPs in the TDPW are strongly confined in the core region, even with a very small waveguide cross section. Furthermore, based on the stronger localization of propagation SPPs in the TDPW, two kinds of bending waveguides, oblique bending and 90° circular bending waveguides, are also investigated. For wavelength of 1550 nm, the 90° circular bending guide with a minimum radius as small as 2.6 μm show nearly zero radiation loss, even with a small waveguide cross section of 70?×?80 nm². The proposed TDPW is suitable for planar integration and provides a possible way for constructing various nanoscale counterparts of conventional integrated devices such as splitter, resonator, sensor, and optical switch.     

Direct Coupling Strategy in Plasmonic Nanocircuits for Low Loss and Easy Fabrication

Plasmonic nanocircuits can deliver light in subwavelength scale, however, require state-of-the-art fabrication process due to the ultra-small footprints. Here, we introduce direct coupling strategy based on metal-insulator-metal (MIM) waveguide systems to reduce the system loss as well as the fabrication difficulty and increase the structural stability. Following this strategy, the coupling between the input waveguide and square ring resonator (SRR) can be realized via an aperture, and for the coupling between SRRs, the metal gap can be removed. The numerical results show that such direct coupling can produce similar effects with conventional indirect coupling in MIM waveguide systems, and the physics mechanism behind as well as influences of geometric parameters on transmission spectrum is also investigated. This work provides a simpler approach to realize on-chip plasmonic nanodevices, such as filters, sensors, and optical delay lines, in practice.

     

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.     

Guiding Terahertz Waves by a Single Row of Periodic Holes on a Planar Metal Surface

In this paper, we show that surface plasmon polaritons (SPPs) can be sustained by a single row of holes periodically drilled on a perfect electric conductor surface. These SPPs can be strongly confined in the transverse plane and they possess an excellent modal shape. In the terahertz regime, large propagation length is available for highly confined SPPs on a real-metal surface waveguide. As the dispersion characteristics of such SPPs can be controlled by the surface geometry, unusual total reflection phenomenon occurs when waves travel along a nonuniform surface waveguide with gradually increasing hole depths.     

Plasmonic Waveguide Filters Based on Tunneling and Cavity Effects

This work presents a bandstop plasmonic filter that comprises a metal–insulator–metal (MIM) waveguide and a few pairs of strip cavities that are embedded in the metal. The strip cavity acts as both a near-field antenna and an MIM resonator. The central frequency and the bandwidth of the forbidden band are inversely related to the cavity length and the cavity-to-waveguide distance, respectively. These results correlate with the predictions of the ring resonator model but only under the resonant condition that double the effective length of cavity is an integer multiple of the guiding wavelength in the cavity.     

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...     

Plasmonically Induced Absorption and Transparency Based on Stub Waveguide with Nanodisk and Fabry-Perot Resonator

A novel metal-insulator-metal (MIM) plasmonic waveguides structure, which is composed by stub waveguide with nanodisk and Fabry-Perot (F-P) resonator, has been proposed and numerically simulated with the finite-difference time-domain (FDTD). Based on the three-level system, the extreme destructive interference between bright and dark resonators gives rise to the distinct plasmonically induced absorption (PIA) response with the abnormal dispersion and novel fast-light feature. Simultaneously, the dramatic double plasmonically induced transparency (PIT) effect with slow-light characteristic can also be achieved in the system. The relationship between the transmission characteristics and the geometric parameters is studied in detail. By optimum design, the modulation depth of the PIA transmission spectrum of 90 % with 0.145 and 0.14 ps fast-light effect can be gained simultaneously, and the peak transmissivity of the double PIT system of 75.2 and 72.8 % with ?0.38 ps slow light-effect can be achieved. The simulated transmission features are in agreement with the temporal-coupled mode theory (CMT). The characteristics of the system indicate an important potential application in integrated optical circuits such as slow-light and fast-light devices, high-performance filter, and optical storage.     

The Tunability of Surface Plasmon Polaritons in Graphene Waveguide Structures

The tunability of propagation properties of surface plasmon polariton (SPP) modes in a waveguide formed by two parallel graphene layers separated by a dielectric layer is studied. For this purpose, the dispersion equation of the structure is numerically solved and the effects of applied bias voltage, the role of effective structural parameters, and electron–phonon scattering rate on the propagation of symmetric and antisymmetric SPP waves are investigated. The results of calculations show that considering the electron–phonon scattering rate as a function of Fermi energy and temperature leads to a considerable decrease in the propagation length of SPPs. As the main result of this work, tuning the propagation characteristics of SPPs is possible by varying any of the parameters such as applied voltage, thickness of insulating layer between two graphene layers and permittivities of dielectric layers, and finally the temperature. It is found that antisymmetric mode benefits from a larger propagation length in comparison with that of the symmetric mode.

     

Plasmonic Photonic Bloch Oscillations in Composite Metal–Insulator–Metal Waveguide Structure

This study proposes the time-evolved plasmonic photonic Bloch oscillations (PBOs) in a composite metal–insulator–metal (CMIM) waveguide structure. This device contains two kinds of MIM waveguide with different thickness of the insulator gaps. The time-resolved plasmonic PBO motion in this CMIM waveguide can be observed by introducing a linearly graded dielectric material. The ray trajectory results from the Hamiltonian optics are consistent with the finite-difference time-domain simulation results.     

Coated Drop-Shaped Nanowires for Guiding THz Surface Plasmon Polaritons with Nanoscale Confinement and Ultra-Long Propagation Distances

Focusing far beyond the diffraction limit is very important for terahertz (THz) wave applications due to its much longer wavelength compared with optical wave. Surface plasmon polaritons (SPPs) on metal wires are frequently used to attain this focusing. However, when the mode width is reduced down to the nanometer scale, the mode loss is very high. Here, a coated drop-shaped nanowire (CDSN) is proposed for guiding THz SPPs with both ultra-strong mode confinement (10 nm) and extreme-long propagation length (1~15 mm), which result from the distinctive mode fields around the top and bottom arcs, respectively, of the metal wire. The fantastic mode properties make the waveguide very useful in nanophotonics, bio-photonics, and highly integrated photonic circuits.     

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.

     

Imaging and Characterizing Long-Range Surface Plasmon Polaritons Propagating in a Submillimeter Scale by Two-Color Two-Photon Photoelectron Emission Microscopy

Long-range surface plasmon polaritons (SPPs), which propagate along metal/dielectric interfaces to submillimeter distances in the range of near-infrared (NIR) excitation wavelength, were examined by two-color two-photon photoelectron emission microscopy (2P-PEEM). Interferences between incident NIR photons and SPPs excited by the NIR photons at surface defects were imaged by detecting photoelectrons emitted from a gold surface, assisted by simultaneously irradiated ultraviolet photons which are to overcome the workfunction of the surface. The wavelength of the interference beat depends sensitively on the NIR wavelength. By analyzing the interference beat, the dispersion curve as well as phase and group velocities of SPP’s were experimentally obtained. The results closely match the theoretical one based on the Drude free electron model, indicating that two-color 2P-PEEM is applicable not only to the visualization of NIR-excited SPPs but also to the quantitative analysis of its physical properties. This method will be widely used to observe SPPs for various artificial plasmonic devices.