Metal-insulator-metal Plasmonic Waveguide Research Articles

Multiple ultra-narrow band-stop filters based on MIM plasmonic waveguide with nanoring cavities

In this work, multiple ultra-narrow band-stop filters based on metal–insulator–metal (MIM) plasmonic waveguide filters with high efficiency are designed and analyzed numerically. The relationship between incident radiation and transmission spectra is investigated between 0.45 μm and 1.5 μm in the electromagnetic spectrum by finite-difference time-domain (FDTD) method. The designed structures have a bus waveguide coupled with nanoring cavity resonators of different sizes. Minimum transmission is 1.3% at 622 nm. The full width at half maximum (FWHM) is 8.64 nm and the quality factor is obtained as 72.33 in this wavelength. The highest quality factor is 185.48 and the lowest FWHM is 4.2 nm at 779 nm. The designed waveguide-based filters can be used for integrated optical devices from visible to near-infrared regimes.

Hybrid MIM plasmonic waveguide by triangular grooves

This paper introduces a hybrid Metal-Insulator-Metal (MIM) plasmonic waveguide. The proposed MIM waveguide has triangular grooves that are periodically placed along the broad wall. The waveguide is analyzed and simulated in a 3-D model. The results show this structure operates as a suitable filter with high transmission amplitude at operational bandwidth of Hz. This waveguide size is 0.5μm×0.44μm with seven triangular grooves and the track length is 3.35μm. The short track length and a small number of grooves are the main advantages of the proposed waveguide. It has a more acceptable transmission amplitude and compact size compared to the previously reported designs.

Optical biosensors using plasmonic and photonic crystal band-gap structures for the detection of basal cell cancer

One of the most interesting topics in bio-optics is measuring the refractive index of tissues. Accordingly, two novel optical biosensor configurations for cancer cell detections have been proposed in this paper. These structures are composed of one-dimensional photonic crystal (PC) lattices coupled to two metal–insulator–metal (MIM) plasmonic waveguides. Also, the tapering method is used to improve the matching between the MIM plasmonic waveguides and PC structure in the second proposed topology. The PC lattices at the central part of the structures generate photonic bandgaps (PBGs) with sharp edges in the transmission spectra of the biosensors. These sharp edges are suitable candidates for sensing applications. On the other hand, the long distance between two PBG edges causes that when the low PBG edge is used for sensing mechanism, it does not have an overlapping with the high PBG edge by changing the refractive index of the analyte. Therefore, the proposed biosensors can be used for a wide wavelength range. The maximum obtained sensitivities and FOM values of the designed biosensors are equal to 718.6, 714.3 nm/RIU, and 156.217, 60.1 RIU−1, respectively. The metal and insulator materials which are used in the designed structures are silver, air, and GaAs, respectively. The finite-difference time-domain (FDTD) method is used for the numerical investigation of the proposed structures. Furthermore, the initial structure of the proposed biosensors is analyzed using the transmission line method to verify the FDTD simulations. The attractive and simple topologies of the proposed biosensors and their high sensitivities make them suitable candidates for biosensing applications.

Formation Laws of Direction of Fano Line-Shape in a Ring MIM Plasmonic Waveguide Side-Coupled with a Rectangular Resonator and Nano-Sensing Analysis of Multiple Fano Resonances

Plasmonic MIM (metal-insulator-metal) waveguides based on Fano resonance have been widely researched. However, the regulation of the direction of the line shape of Fano resonance is rarely mentioned. In order to study the regulation of the direction of the Fano line-shape, a Fano resonant plasmonic system, which consists of a MIM waveguide coupled with a ring resonator and a rectangle resonator, is proposed and investigated numerically via FEM (finite element method). We find the influencing factors and formation laws of the ‘direction’ of the Fano line-shape, and the optimal condition for the generation of multiple Fano resonances; and the application in refractive index sensing is also well studied. The conclusions can provide a clear theoretical reference for the regulation of the direction of the line shape of Fano resonance and the generation of multi Fano resonances in the designs of plasmonic nanodevices.

Strong plasmon-exciton coupling in MIM waveguide-resonator systems with WS2 monolayer.

The room-temperature strong plasmon-exciton coupling is first investigated in a metal-insulator-metal (MIM) waveguide-resonator system with WS2 monolayer. Finite-difference time-domain (FDTD) simulated results exhibit that the Fabry-Pérot (F-P) cavity is realized by the MIM plasmonic waveguide with two separated metal bars. When the F-P resonance is tuned to overlap with the A-exciton absorption peak of WS2 monolayer, the strong plasmon-exciton coupling is obtained at visible wavelengths. As a result, the spectral splitting response confirmed by the coupled-mode theory (CMT) appears in the transmission spectrum. Intriguingly, the switching response is handily witnessed by tuning the orientation of WS2 monolayer along the cavity, and the coupling strength is dynamically tuned by changing the position of the WS2 monolayer. Simultaneously, the anticrossing behavior with the Rabi splitting up to 109 meV is achieved by small changes in the length of the F-P cavity and the refractive index of dielectric in the cavity, respectively. The underlying physics is further revealed by the coupled oscillator model (COM). The proposed strong plasmon-exciton coupling can find utility in highly integrated plasmonic circuits for optical switching.

Unidirectional Reflectionless Propagation in Plasmonic Waveguide System Based on Phase Coupling Between Two Stub Resonators

A scheme on unidirectional reflectionless propagation is theoretically investigated in a plasmonic waveguide system which consists of two metal–insulator–metal (MIM) stub resonators side coupled to an MIM plasmonic waveguide. By appropriately tuning the phase difference between two stub resonators, unidirectional reflectionless propagation at exceptional point, phase transition, and coherent perfect absorber are realized. Moreover, in both directions, reflectivity for one side is close to 0 and for the other side approximates to 0.8.

Unidirectional reflectionless phenomenon in ultracompact non-Hermitian plasmonic waveguide system based on phase coupling

Unidirectional reflectionless phenomenon is theoretically investigated based on phase coupling in an ultracompact non-Hermitian plasmonic waveguide system, which consists of two metal-insulator-metal (MIM) stub resonators side coupled to a MIM plasmonic waveguide. By appropriately tuning the phase difference between two stub resonators, the reflectivity for forward direction reaches to 0.91 and backward direction is close to 0 at the exception point (EP), while the backward absorption reaches to 0.98 and the forward absorption is close to 0.05. Hence, the unidirectional coherent perfect absorption (CPA) is realized at the vicinity of EP. This work will provide potential applications in the filter, sensor, plasmonic diode-like device, and so on.

Transmission characteristics of a Y-shaped MIM plasmonic waveguide with side-coupled cavities

A plasmonic Y-shaped metal-insulator-metal (MIM) plasmonic waveguide with two side-coupled Fabry–Perot (FP) resonant cavities is proposed. Simulation results show that there is a stopband existing in the transmission spectrum of each output port. When the lengths of the two cavities are equal, the transmission spectra of the two output ports are almost coincident. But if they are not equal, the two stopbands are not in the same place. Meanwhile, the transmission dip of one output port corresponds to the transmission peak of another port. By ad-justing the length, width and refractive index of the two FP cavities, one can control the resonant wavelength of each cavity to further achieve functions of filtering, power splitting, switching and refractive index sensing. Results show that the sensing sensitivity is up to 1280 nm/RIU with its figure of merit above 200 when the waveguide is used as a refractive sensor. The proposed waveguide structure has potential applications in the fields of integrated optical filter, nano-optic switch, power splitter and refractive sensor in subwavelength scale.

Dual-band unidirectional reflectionless phenomena in an ultracompact non-Hermitian plasmonic waveguide system based on near-field coupling

Dual-band unidirectional reflectionlessness and coherent perfect absorption (CPA) are demonstrated in a non-Hermitian plasmonic waveguide system based on near-field coupling between a single resonator and the resonant modes of two resonators showing an electromagnetically induced-transparency-like (EIT-like) effect. The non-Hermitian plasmonic system consists of three metal-insulator-metal (MIM) resonators coupled to a MIM plasmonic waveguide.

Design of Full-Adder and Full-Subtractor Using Metal-Insulator-Metal Plasmonic Waveguides

The metal-insulator-metal (MIM) waveguides are considered best among all plasmonic waveguides for propagation of optical signal to deep sub-wavelength scale. In this paper, MIM plasmonic waveguides based Mach-Zehnder interferometer (MZI) is developed. It possesses nonlinear Kerr material in one of its linear arm for controlling of optical signal with light intensity. Self phase modulation (SPM) and cross phase modulation (XPM) processes inside nonlinear MZI are used to design novel and compact full-adder and full-subtractor. Analysis and verification of proposed devices are carried out using FDTD and MATLAB simulations.

Design optimization and fabrication of Mach- Zehnder interferometer based on MIM plasmonic waveguides.

We proposed and designed a compact unbalanced Mach-Zehnder interferometer (MZI) based on metal/insulator/metal (MIM) plasmonic waveguides for ultrafast optical signal processing. The MZI was fabricated by a lithography technique and we provide, for the first time experimental evaluation of the transmission performance of the MZI using MIM PWGs. The experimental results were in good agreement with the numerical simulations. The proposed structure could be considered as a key device for on-chip optical integrated circuits.

Enhancement of photorefractive effect in asymmetric metal-insulator-metal plasmonic waveguides

The photorefractive effect in metal-insulator-metal (MIM) plasmonic waveguides is modeled and investigated for both symmetric and asymmetric structures. A metal-LiNbO3-metal nanostructure with different top and bottom metals is proposed as a plasmonic waveguide. Three different metals, aluminum, gold, and silver, are used as the metals of the plasmonic waveguide and the photorefractive effect is investigated in different structures. The interaction between interfering surface plasmonic polariton modes is studied. It is shown that a strong mode can be coupled to a weak mode by means of the photorefractive effect. It is found that compared with conventional symmetric MIM plasmonic waveguides, an asymmetric structure with different metals, silver-LiNbO3-gold for example, has a higher photorefractive gain and longer propagation distance, and there is a net photorefractive gain. The effect of the crystal thickness and amplitude inputs is also analyzed. It is found that there is an optimum crystal thickness that yields the maximum photorefractive gain.

Nonlinear tuning techniques of plasmonic nano-filters

In this paper, a fitting model to the propagation constant and the losses of Metal–Insulator–Metal (MIM) plasmonic waveguide is proposed. Using this model, the modal characteristics of MIM plasmonic waveguide can be solved directly without solving Maxwell's equations from scratch. As a consequence, the simulation time and the computational cost that are needed to predict the response of different plasmonic structures can be reduced significantly. This fitting model is used to develop a closed form model that describes the behavior of a plasmonic nano-filter. Easy and accurate mechanisms to tune the filter are investigated and analyzed. The filter tunability is based on using a nonlinear dielectric material with Pockels or Kerr effect. The tunability is achieved by applying an external voltage or through controlling the input light intensity. The proposed nano-filter supports both red and blue shift in the resonance response depending on the type of the used non-linear material. A new approach to control the input light intensity by applying an external voltage to a previous stage is investigated. Therefore, the filter tunability to a stage that has Kerr material can be achieved by applying voltage to a previous stage that has Pockels material. Using this method, the Kerr effect can be achieved electrically instead of varying the intensity of the input source. This technique enhances the ability of the device integration for on-chip applications. Tuning the resonance wavelength with high accuracy, minimum insertion loss and high quality factor is obtained using these approaches.

Wideband slow light achievement in MIM plasmonic waveguide by controlling Fano resonance

In this paper, we have investigated the characteristics of an asymmetric shaped Fano line in a metal–insulator–metal (MIM) plasmonic waveguide side coupled to two resonating stub structures. The spectral properties of Fano resonance are quite distinct due to the destructive interference between a two propagating plasmon modes. Two structural parameters are carefully adjusted: physical separation between both the resonating stubs and length of resonating stubs. By tailoring the separation between both the resonating structures, coupling between both the plasmon modes is controlled, and hence asymmetric nature of Fano line can be shaped accordingly. Resonance condition of Fano line can be tuned by scaling the length of stubs. A strong red shift in resonating wavelength with varying degree of asymmetry is observed, when length of resonating structures is increased. The sharp resonant peak, due to an asymmetric shaped Fano resonance is generally accompanied by large dispersion that results in reduction of group velocity of light near Fano resonance. By controlling the coupling between resonating stub, or by scaling the length of lower resonating stub, large value of group index (ng=75) and delay bandwidth product (DBP=0.2533) is obtained. The structure can be modified to suit different applications in optical buffers, optical switches and nonlinear optics devices.

Significantly increased surface plasmon polariton mode excitation using a multilayer insulation structure in a metal-insulator-metal plasmonic waveguide.

In this paper, we propose a novel multilayer insulation structure in a metal-insulator-metal (MIM) plasmonic waveguide to explore the possibility of increasing surface plasmon polariton (SPP) mode excitation. Numerical investigations show that the effective refractive index of the multilayer insulation structure affects symmetric SPP mode excitation. The significant enhancement of electric field intensity in horizontal and vertical profiles with a dipole in SiO2 compared with in Al2O3 is observed in the proposed MIM plasmonic waveguides due to a combination of the improved optical density and dipole radiation intensities under a low refractive index. The Au/SiO2/Al2O3/SiO2/Au geometry shows the best enhancement performances, which can serve as an excellent guideline for designing and optimizing a high-performance SPP source using a multilayer insulation structure.

MIM plasmonic waveguide splitter with tooth-shaped structures

A plasmonic splitter based on subwavelength metal–insulator–metal (MIM) waveguides with tooth-shaped structures is proposed and numerically researched by using the finite-difference time-domain (FDTD) method in visible and near infrared frequencies. The splitter is regarded as two zigzag-shaped MIM waveguides, which naturally stretch out two tooth structures in bending corners. Each tooth forms a resonant cavity. The transmission of the zigzag-shaped waveguide is close to zero at some resonant wavelength of the tooth cavity. The same-order resonant wavelength has an approximately linear relationship with the depth of the tooth. When the geometric parameters of the two zigzag-shaped waveguides of teeth are suitably initialized, both frequency splitter and power splitter can be simply achieved.

New design of triplexer based on metal–insulator–metal plasmonic ring resonators

In this work, we propose a new design of all-optical triplexer based on of metal-insulator-metal (MIM) plasmonic waveguide structures and ring resonators. By adjusting the radii of ring resonators and the gap distance, certain wavelengths can be filtered out and the crosstalk of each channel can also be reduced. The numerical results show that the proposed MIM plasmonic waveguide structure can really function as an ­optical triplexer with respect to the three wavelengths, that is, 1310, 1490, and 1550 nm, respectively. It can be widely used as the fiber access network element for multiplexer-demultiplexer wavelength selective in ­fiber-to-the-home communication systems with transmission efficiency higher than 90%. It can also be a potential key component in the applications of the biosensing systems.

Efficient transition between photonic and plasmonic guided modes at abrupt junction of MIM plasmonic waveguide

We propose a novel metal-insulator-metal (MIM) waveguide mode transition scheme by the use of the abrupt junction of MIM plasmonic waveguide. Power coupling between anti-symmetric plasmonic mode and fundamental photonic mode can be easily done by reflection at the waveguide junction with an oblique MIM mode incidence due to the field intersection between those modes. With numerical simulation we find that mode conversion efficiency can be obtained up to 60% for single junction geometry, and it can be further increased up to 82% with the suppression of non-transited mode by adapting Bragg grating structure composed of periodical arranges of MIM junctions.

Manipulation of light in MIM plasmonic waveguide systems

Plasmonic waveguides that allow deeply subwavelength confinement of light provide an effective platform for the design of ultra-compact photonic devices. As an important plasmonic waveguide, metal-insulator-metal (MIM) structure supports the propagation of light in the nanoscale regime at the visible and near-infrared ranges. Here, we focus on our work in MIM plasmonic waveguide devices for manipulating light, and review some of the recent development of this topic. We introduce MIM plasmonic wavelength filtering and demultiplexing devices, and present the electromagnetic induced transparency (EIT)-like and Fano resonance effects in MIM waveguide systems. The slow-light and rainbow trapping effects are demonstrated theoretically. These results pave a way toward dynamic control of the special and useful optical responses, which actualize some new plasmonic waveguide-integrated devices such as nanoscale filters, demultiplexers, sensors, slow light waveguides, and buffers.

A subwavelength MIM waveguide filter with single-cavity and multi-cavity structures

We present a systematical study of a subwavelength MIM (metal⿿insulator⿿metal) plasmonic waveguide filter with single-cavity and multi-cavity shaped structures by using the finite difference time domain (FDTD) method with perfectly matched layer (PML) absorbing boundary conditions. Both their similar and different characteristics are analyzed, and we find both structures can realize the function of filter, in which several wavelengths are stopped while others can pass through. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the length of the cavity, inversely proportional to the gap between the two slits. Finally, a wideband filter is demonstrated with the multi-cavity structure.