Metal-dielectric Waveguide Research Articles

Liquid crystal based tunable plasmonic induced reflection in MIM waveguide coupled with a disk resonator

In this paper, plasmon induced reflection effect is achieved in a simple structure, which composed of a rectangle resonator and a disk resonator coupled to the metal-insulator-metal (MIM) waveguide. Liquid crystal (LC) material is incorporated in the rectangular resonator to tune the plasmon resonance. The transmission properties and field distribution are simulated by two dimensional finite difference time domain (FDTD) method and theoretically explained by coupled mode theory (CMT). The result of FDTD and CMT agrees well and it show that the plasmon induced reflection resonance can be tuned by geometrical parameters or the director angles of LC. The proposed plasmonic structure may have application in slow light device, optical switch, highly integrated optical circuit and other related plasmonic devices.

Nonlinear signal processing in a chalcogenide plasmonic nanoresonator

We have numerically studied the quasi pulse evaluation in a nonlinear metal-dielectric-metal (MDM) plasmonic nanoresonator at telecom wavelength. In this system a MDM waveguide, vertically coupled to stub filled with nonlinear chalcogenide glasses to make a nonlinear plasmonic nanoresonator (NPNR). NPNR shows two kinds of optical bistability i.e. S-type and Z-type. The effect of S-type and Z-type bistability on the Gaussian input pulse is studied numerically and showed that the output pulses are square pulse for S-type and nearly dark soliton shape for Z-type pulse if the peak input intensity larger than critical intensity. The output shape of pulse is strongly depending on the input peak power of pulse so such signal processing refers to all optical self-signal processing.

Selective magnetic responses of silicon nanoparticles modulated by waveguide structures.

High-refractive-index nanoparticles (NPs), such as silicon NPs, were considered as effective carriers in their response to a magnetic field at optical frequencies. Such NPs play an important role in many state-of-the-art technologies in nano-optics. Although the resonance properties of these NPs when varying their structural parameters have been studied intensely in the past few years, their interaction with the underlying substrate has seldom been discussed, in particular, when the substrate is a waveguide structure that significantly modulates the optical responses of the NPs. We proposed and studied a selective magnetic coupling system comprising a Si-NP on a metal-dielectric waveguide (MDW). The MDW structure supports either a transverse electric (TE) or a transverse magnetic (TM) mode that induces a large polarization dependence in the magnetic resonance. A new manifestation of the optical spin Hall effect was demonstrated in which a vertical rotating magnetic dipole excites a TE-type waveguide mode with a specific unidirectional emission. Making use of this polarization response, we developed a scanning imaging system that can selectively map the transverse or longitudinal magnetic field component of a focused beam depending on the type of MDW used in the system. This selective magnetic resonance coupling system is expected to be valuable for studying the fundamental interactions between the magnetic field and matter and for developing related nano-applications.

MATHEMATICAL THEORY OF NORMAL WAVES IN AN OPEN METAL-DIELECTRIC REGULAR WAVEGUIDE OF ARBITRARY CROSS SECTION

The problem of normal waves in an open metal-dielectric regular waveguide of arbitrary cross-section is considered. This problem is reduced to the boundary eigenvalue problem for longitudinal components of electromagnetic field in Sobolev spaces. To find the solution, we use the variational formulation of the problem. The variational problem is reduced to study of an operator-function. Discreteness of the spectrum is proved and distribution of the characteristic numbers of the operatorfunction on the complex plane is found.

Wakefields in conducting waveguides with a lossy dielectric channel

The resonant properties of the impedance of a two-layer circular metal-dielectric waveguide are investigated by taking into account the finite conductivity of the metallic pipe and the dissipation of the radiated energy in the dielectric layer. The dispersion relations for azimuthally symmetric monopole TM modes are analyzed. It is shown that, for an outer metallic layer with finite conductivity and a thin internal dielectric cover, the waveguide has only a single slowly propagating ${\mathrm{TM}}_{01}$ mode. The point charge longitudinal wake potentials are evaluated for thin and thick internal layers.

Tunable Plasmonic System Based on a Slotted Side-Coupled Disk Resonator and Its Multiple Applications on Chip-Scale Devices

In this letter, based on the subwavelength metal-insulator-metal (MIM) waveguide embodying a baffle and a slotted side-coupled disk resonator (SSCDR) inserted with a metallic block is designed. The proposed structure is numerically investigated and analyzed by FEM method. Two sharp transmission peaks with high transmittance and asymmetrical line-shaped Fano resonances, originating from the interferences between the width continuum state supported by the MIM waveguide embodying a baffle and the narrow discrete state from the SSCDR, arise in its transmission spectrum. And multimode interference coupled mode theory (MICMT) is employed to analyze the proposed structure theoretically, which is consistent with the simulation results. Additionally, by adjusting the parameters of the structure, the resonant wavelengths of Fano resonances can be manipulated. Finally, the proposed structure is applied to nano-filters, refractive index (RI) sensors, temperature sensors and slow light devices, all showing high performance. It is believed that the proposed system can boost the development of highly integrated photonics and support substantial applications for nano-sensors, filters and slow light devices.

High Sensitivity Refractive Index Sensor Based on the Excitation of Long-Range Surface Plasmon Polaritons in H-Shaped Optical Fiber.

In this paper, we propose and numerically analyze a novel design for a high sensitivity refractive index (RI) sensor based on long-range surface plasmon resonance in H-shaped microstructured optical fiber with symmetrical dielectric–metal–dielectric waveguide (DMDW). The influences of geometrical and optical characteristics of the DMDW on the sensor performance are investigated theoretically. A large RI analyte range from 1.33 to 1.39 is evaluated to study the sensing characteristics of the proposed structure. The obtained results show that the DMDW improves the coupling between the fiber core mode and the plasmonic mode. The best configuration shows 27 nm of full width at half maximum with a resolution close to 1.3 × 10 nm, a high sensitivity of 7540 nm/RIU and a figure of merit of 280 RIU. Additionally, the proposed device has potential for multi-analyte sensing and self-reference when dissimilar DMDWs are deposited on the inner walls of the side holes. The proposed sensor structure is simple and presents very competitive sensing parameters, which demonstrates that this device is a promising alternative and could be used in a wide range of application areas.

Symmetric and antisymmetric surface plasmon polariton solitons in a metal-dielectric-metal waveguide with incoherent pumping

We propose a scheme to realize stable linear and nonlinear propagation of symmetric and antisymmetric surface plasmon polaritons (SPPs) solitons by doping ladder-type three-level quantum emitters into the middle layer of a metal-dielectric-metal (MDM) waveguide. In linear propagation regime, we show that both symmetric and antisymmetric SPPs can acquire a gain from electromagnetically induced transparency (EIT) effect with an incoherent pumping. The EIT can be used not only to completely compensate the Ohmic loss in the metal but also to acquire a subluminal group velocity for the SPPs. We also show that in nonlinear propagation regime a huge enhancement of Kerr nonlinearity of the symmetric and antisymmetric SPPs can be obtained but with different incoherent pumping intensities. As a result, gain-assisted (1+1)-dimensional symmetric and antisymmetric subluminal surface polaritonic solitons may be produced based on the strong confinement of electric field in the MDM waveguide. Our study may have promising applications in light information processing and transmission at nanoscale level based on MDM waveguides.

Plasmonic refractive index sensor with multi-channel Fano resonances based on MIM waveguides

A multi-channel Fano resonant structure is proposed and analyzed based on subwavelength metal–insulator–metal (MIM) waveguides. First, two MIM output ports associated with specific side-coupled cavities are designed to locate at the center and quarter positions of an end-coupled cavity, respectively. Since the interference between the dark and bright modes, dual-channel Fano resonances with asymmetrical lines shapes are obtained at both ports, respectively. High sensitivity and figure of merits are investigated. Besides, phase shifts are also investigated leading to positive and negative group delays available at the Fano peaks and dips, respectively. Likewise, two extra output ports with identical resonant cavities are placed on the other side of the end-coupled cavity. In this case, four-channel Fano resonances with considerable performances are obtained. The proposed structure is analyzed by the coupled mode theory and the finite difference time domain method. It is believed this device can be used as a chip-scale refractive index sensor and optical filter.

Optical transmission characteristics in the MDM waveguide coupled with N-rectangular resonators

A metal–dielectric–metal (MDM) waveguide coupled with N-rectangular cavities is proposed and its spectral features are derived and described based on the coupled-mode and multi-oscillator theory for the first time. The results of theoretical calculation and numerical simulation indicate that resonant modes are proportionally increased with the number of cavities, surprisingly, the wavelength at 716 nm is an F–P resonant mode for n = 1 and those new modes occur on both sides of 716 nm, thus a plasmonic tunable multi-modes filter and slow light effect are achieved. According to the field distributions, the resonant modes can be divided into several types: dipole, quadrupole, hexapole, eighth-pole modes and so on. Moreover, we find that the resonant transmissions are sensitively dependent on the widths and lengths of cavities as well as the vertical and horizontal distances between two cavities. In addition, the phenomena including magnitude modification, redshift, blueshift, and the disappearance and fusion of modes are clearly observed. Compared with those conventional MDM waveguides side-coupled with single or double cavities, our proposed device can provide more channels to manipulate the resonance wavelengths flexibly. Therefore, it may be applied in optoelectronic devices.

Ag-SiO2-Ag based plasmonic waveguide for refractive index sensing

In this paper, an Ag-SiO2-Ag based Metal-Insulator-Metal (MIM) plasmonic waveguide is investigated for Refractive Index sensing based applications. Dual resonators coupled to MIM waveguide is filled with material under sensing and the refractive index of the material is varied in the steps of 0.02 refractive index unit (RIU). The sensor is numerically analyzed using Finite difference in Time domain (FDTD) method. The interaction between resonators is observed and the sensitivity is measured. The sensitivity which is defined as change in resonance condition for per unit change in Refractive index unit (RIU) is obtained as high as 1145 nm/RIU. Proposed sensor finds its applicability in different refractive index based chemical and biological sensing.

Surface plasmon generation and field intensification by sub-wavelength double-ring structure of plasmas

In this paper, we propose a plasma structure that can effectively enhance surface plasmon resonance and achieve significant local field enhancement. For specific incident wave frequencies, two plasma rings and a vacuum layer between them can form a metal-insulator-metal (MIM) waveguide, which can resonant as a Fabry–Perot cavity and couple the incident wave energy to the vicinity of the plasma ring slit, and thus effectively enhance the localized surface plasmon resonance inside the plasma ring. The simulation results show that, by adjusting the thickness and angle of the outer plasma ring, the average electric field of the incident wave inside the structure can be increased by a factor of 9. Moreover, at the same plasma frequency and incident wave band, the local field enhancement of the double-ring structure is better than that of a circular ring structure or a circular ring structure with a slit. We have also analyzed the physical mechanism of field enhancement and calculated the dispersion relation of surface plasmon polaritons in the Fabry–Perot cavity. The results are in good agreement with the theory of the MIM waveguide cavity.

Manipulation of Multiple Fano Resonances Based on a Novel Chip-Scale MDM Structure

A novel chip-scale metal-dielectric-metal (MDM) refractive-index sensor is proposed and investigated in this paper by using finite-difference time-domain (FDTD) method and multimode interference coupled-mode theory (MICMT), respectively. A slot cavity with an embedded tooth-shape cavity and a side-coupled semi-ring cavity are inserted between the input and output MDM waveguides. According to the simulation results, dual ultra-sharp and asymmetrical Fano peaks emerge in transmission spectrum with high performances. Besides, the transmission responses for the primary parameters of this structure are also investigated. To focus on developing integrated photonic devices, the original structure is successfully expanded by two additional semi-ring cavities through an innovative coupling approach, generating up to eight Fano peaks with outstanding characteristics. It is believed that this novel MDM structure will be a guideline for designing the chip-scale plasmonic devices.

Theoretical Investigation on Microcavity Coupler for Terahertz Quantum-Well Infrared Photodetectors

Resonant behaviors and absorption enhancement of metallic grating-dielectric-metal (GDM) microcavity are theoretically investigated. The GDM structure is treated as periodic unit cells of two serially-connected metal-dielectric-metal (MDM) and air-dielectric-metal (ADM) waveguide resonators. The resonant modes can be divided into three types: the LC mode, the TEM modes supported by the MDM waveguide resonator, and the TEM-TM hybrid modes supported by the whole GDM structure. The resonant frequencies of LC and TEM modes are independent on a small incident oblique angle. However, for the TEM-TM hybrid modes, each mode splits into two branches with non-zero incident angles. Based on the temporal coupled-mode theory, the intersubband absorption efficiency of multi quantum wells inserted into the GDM microcavity is calculated and discussed qualitatively. We point out that the condition of critical coupling is not the optimal condition for intersubband absorption efficiency when the metallic loss cannot be neglected. An optimization procedure is given for the design of high performance GDM-microcavity-coupled terahertz quantum-well infrared photodetectors.

Fano resonance and its application using a defective disk resonator coupled to an MDM plasmon waveguide with a nano-wall

A coupled plasmonic system for Fano resonance, of which a defective disk resonator is side coupled to an MDM (metal-dielectric-metal) waveguide with a nano-wall, is proposed and investigated numerically and theoretically via FEM (finite element method). Simulation results show that the system can generate double Fano resonances, which result from the interactions between two narrow discrete states induced by the defective disk resonator and one broad continuous state excited by the nano-wall inserted in the MDM waveguide. The peak wavelengths of the two Fano resonances can be easily adjusted by changing the structure parameters, which indicates that the proposed structure has better flexibility in design. Additionally, the properties of the designed structure in the applications of refractive index sensing, temperature sensing, and optical switch are studied in detail, which reveals that the proposed plasmonic system may have potential applications for the integrated optical circuits of nanoscale optical filters, sensors, optical switches, optical modulators, and so on.

Resonant transmission through periodic subwavelength terahertz metallic slits based on a quartz plate

This article proposes the resonant transmission characteristic through the periodic subwavelength metal-insulator-metal (MIM) waveguide on a quartz plate at terahertz frequencies. By applying the multiregion problem to the mode matching technique (MMT), the total reflection and transmission characteristics of the periodic MIM waveguide can be resolved as functions of the thickness of the MIM waveguide, the gap width of the MIM waveguide, the thickness of the quartz plate, and frequency. To validate the results of the proposed MMT, the transmission results are compared with the results using a commercial electromagnetic simulation software (XFdtd). The similar results demonstrate that the proposed MMT is proper to compute the reflection and transmission characteristics of the periodic MIM waveguide on the real quartz plate and providing in-depth intuition for resonant transmissions using the modal approach.

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.

Chipscale plasmonic modulators and switches based on metal–insulator–metal waveguides with Ge2Sb2Te5

We introduce phase-change material Ge2Sb2Te5 (GST) into metal-insulator-metal (MIM) waveguide systems to realize chipscale plasmonic modulators and switches in the telecommunication band. Benefitting from the high contrast of optical properties between amorphous and crystalline GST, the three proposed structures can act as reconfigurable and non-volatile modulators and switches with excellent modulation depth 14 dB and fast response time in nanosecond, meanwhile possessing small footprints, simple frameworks and easy fabrication. This work provides new solutions to design active devices in MIM waveguide systems, and can find potential applications in more compact all-optical circuits for information processing and storage.

Fano Resonance in a MIM Waveguide with Two Triangle Stubs Coupled with a Split-Ring Nanocavity for Sensing Application.

Herein, a compact refractive index nanosensor comprising a metal- insulator- metal (MIM) waveguide with symmetric two triangle stubs coupled with a circular split-ring resonance cavity (CSRRC) is theoretically presented. An analysis of the propagation characteristics of the designed structure is discussed employing the finite element method (FEM). The calculation results revealed that a Fano resonance outline emerged, which results from an interaction between the continuous broadband state of the waveguide with two symmetric triangle stubs and the discrete narrowband state of the CSRRC. The influence of geometric parameters on sensing properties was studied in detail. The maximum sensitivity reached 1500 nm/RIU with a high figure of merit of 65.2. The presented structure has great applications for on-chip plasmonic nanosensors.

Plasmon induced transparency like transmission properties in compact MIM waveguide side-coupled with U-cavity

Surface plasmon polaritons (SPPs) can overcome the limitation of diffraction and control light at nanoscale, thus becoming a hotspot in recent years. SPPs based metal-insulator-metal (MIM) plasmonic waveguides using U-cavity and slot cavity are designed. The transmission characteristics are numerically simulated and verified by the coupled mode theory (CMT). Meanwhile, the effects of changing the geometric parameters on the transmission characteristics are also studied. Single and double plasmon induced transparency (PIT) effects are realized through the coupling and the destructive interfering between the transmission paths. Furthermore, characteristics of the refractive index sensing as well as the slow light and fast light effects are also investigated. We hope the designed waveguide structures along with their transmission characteristics have potential application prospects in the area of nanoscale integrated optical devices, such as filters, sensors, switches, slow/fast light devices, and other optoelectronic circuits.