Metal-dielectric Waveguide Research Articles

Review of Innovative Cavity Designs in Metal–Insulator-Metal Waveguide-Based Plasmonic Sensors

AbstractPlasmonic sensors utilizing metal–insulator-metal (MIM) waveguides represent a significant advancement in sensing technology due to their high sensitivity and versatility. These sensors leverage surface plasmon polaritons to detect minute changes in the surrounding environment, making them highly effective for a range of applications. For instance, they can precisely measure variations in the Refractive Index, which is crucial for monitoring chemical concentrations and biological interactions. Additionally, MIM waveguides can be adapted to sense temperature fluctuations, pressure changes, and the presence of specific gases, providing valuable insights in fields such as environmental surveillance, medical diagnostics, and industrial processes. In recent years, a variety of sensor cavity shapes have been proposed to enhance sensor performance. This review examines how these innovative geometries optimize sensor cavities to achieve unprecedented levels of resolution and sensitivity, underscoring their transformative potential across a broad spectrum of scientific and practical applications.

Plasmonic MIM waveguide based FR sensors for refractive index sensing of human hemoglobin

Fano resonance (FR) is a universal phenomenon that is used to attain electromagnetic-induced transparency (EIT), high absorption and sensitivity, and low-power photonic devices. This work presents dual FR refractive index (RI) sensor models on a plasmonic metal-insulator-metal (MIM) waveguide system. The FR phenomenon is attained by including circular and elliptic nanorod defects in the bus waveguides. The resonances originate from the defect's narrow discreteness and the rectangular resonator's broad state. Analytical methods such as finite difference time domain (FDTD) and multimode interference coupled mode theory are adopted to analyze the FRs. The shapes of the Fano line and resonance peak amplitude can be tuned independently by controlling the diameter of the defects, the separation between the defects, and the coupling (between the resonator and the bus waveguide) distance. Moreover, the proposed structures detect the RI (human hemoglobin) variation in the bus waveguide and resonator. The obtained results with circular nanorod defect verify the autocorrelation coefficient of 99.92 %, ensuring the device's linearity and high performance. However, an autocorrelation of 99.7 % is attained by using two elliptic nanorod defects.

Nanoscale temperature sensors based on MIM waveguide coupling and ring-embedded nanostructures

This study presents a novel refractive index sensor based on Fano resonance, incorporating a metal-insulator-metal (MIM) waveguide coupled with a circular ring structure (CRC). Using finite element method analysis, we investigated the propagation properties of the sensor. To evaluate their influence on sensor performance, we systematically varied the parameters of each Circular Resonant Cavity structure component, including the refractive index, employing a controlled variable approach. At its optimal configuration, the sensor achieves a maximum sensitivity of 3,240 nm/RIU and a figure of merit (FOM) of 57.9. With its high sensitivity, straightforward design, and suitability for temperature detection, the refractive index sensor holds promise for diverse applications.

Electrically driven cavity plasmons in Au nanowire over Au film

Light emission via inelastic tunneling electrons is appealing for integrated optoelectronic devices due to its femtosecond time scale that can in principle allow terahertz modulation bandwidth. It has gained renewed interest since 2015 due to the improved quantum efficiency, highly tunable emission wavelength, linewidth, or directionality once the electrodes are designed as a plasmonic nanocavity. However, efficient construction of stable tunnel junctions with desired plasmonic resonances is still technically challenging because of the subnanometer precision required in the electrical and optical design. Here, we demonstrate an easily accessible electrically driven cavity plasmon in metal-insulator-metal (MIM) tunnel junctions, comprised by a Au nanowire (NW) across two separate ultrasmooth Au electrodes. Two layers of self-assembled thiol molecule defines a reliable tunneling barrier. The contribution from the localized cavity plasmons to the total light emission is found to be dominant over that from the propagating surface plasmon polariton in the MIM waveguide, different from the traditional explanations. This work introduces a simplified method for constructing electrically driven cavity plasmons using crystalline metals, which holds promise for applications in in situ chemical or biosensing and the development of flexible light-emitting metasurfaces.

Design and Simulation of a Three-Channel Plasmonic Demultiplexer in an MIM Waveguide

This study proposes a structure for optical plasmonic demultiplexers based on nanodisk/nanoring resonators in metal-insulator-metal (MIM) plasmonic waveguides. The proposed structure can transmit the desired wavelength spectra, including telecommunication and visible waves. It consists of a bus waveguide, several nanodisks and nanorings, and three drop waveguides, consisting of several filters that can be extended to N×1 channels. The FWHM of the designed structure was calculated to be approximately 18 nm. The transmission spectrum of each demultiplexer channel can be easily adjusted by changing the geometric parameters and refractive index. As the waveguide refractive index increases, the transmission spectrum shifts to higher wavelengths, and its amplitude decreases due to internal structural losses. Therefore, the differences between the waveguide and metal refractive indices gradually decrease, and the light confinement decreases in the waveguide, leading to an increase in FWHM. The outputs of each channel have two sharp resonance modes, resulting from the coupling of two interacting cavities (ring and disk) due to the Fano resonance phenomenon. This study employed a two-dimensional (2D) finite difference time domain (FDTD) numerical method and simulation by FDTD Lumerical software to evaluate the transmission properties.

Features of the modern development of metal‐insulator‐metal waveguide based plasmonic sensors

AbstractPlasmonic sensors based on metal‐insulator‐metal (MIM) waveguides are renowned for their miniaturization and high sensitivity in various sensing applications. A broad spectrum of researchers is numerically investigating the characteristics of MIM waveguide‐based plasmonic sensors with diverse cavity shapes. However, practical demonstrations of these sensors have not yet been realized, primarily due to the overlooked aspect of the light coupling mechanism into these waveguides. In this context, two distinct methods for coupling light into and out of plasmonic chips based on MIM waveguides are presented.

Double tunable Fano resonance based on a metal–insulator–metal waveguide with double coupled cavities and its application

A metal–insulator–metal (MIM) waveguide with a ring cavity (RC) and a half ring cavity (HRC) is proposed to realize the detection of two mediums simultaneously based on independently tunable double Fano resonances. Utilizing numerical simulation of the finite element method, the transmission characteristics and magnetic field distribution are investigated. The simulation findings indicate that the structure is capable of generating double Fano resonances, and the two Fano resonances are tuning independently. The maximum sensitivity and figure of merit (FOM) are 2385 nm/RIU (refractive index unit) and 31886RIU−1, respectively, and these values are achieved by changing the structural parameters and the refractive index of the insulator. Moreover, the sugar content in flavor and the concentration of ethanol solution can be detected at the same time, which indicates the high efficiency of the sensor. Therefore, these performances demonstrate that the tunable double Fano resonance based on a MIM waveguide is a hopeful method for chemical detection.

Design and analysis of high performance 1×N optical wavelength demultiplexers based on MIM waveguide with polygon resonators

Confinement of the light at the subwavelength scale makes photonic devices more efficient in applications such as optical filtering, switching, and sensing with their low dimensions. Metal-insulator- metal waveguide-based configurations present many paths for manipulating light at the wide range of the electromagnetic spectrum. For that purpose, in this study, a wavelength demultiplexer (WDM) based on a metal-insulator-metal (MIM) waveguide is numerically investigated by finite difference time domain (FDTD) method. Proposed WDMs have cascade polygon resonators. After optimizing the fundamental filter, this structure is formed as 1×N demultiplexers. The proposed demultiplexers have two- and three channels. The minimum full width at half-maximum (FWHM) value for these channels is 20.02 nm and the maximum quality factor value is 47.7 at 954.9 nm wavelength. The minimum crosstalk value is obtained as -30.37 dB for this study. The proposed 1×N demultiplexers have potential tools to design low-cost integrated optical circuits for specific wavelengths.

MIM waveguide refractive index sensor with graphene enhanced three-ring nested resonator Fano resonance

In this paper, a metal-insulator-metal (MIM) waveguide featuring a three-ring nested cavity structure is proposed. We enhance and optimize this design by integrating graphene nanostructures into the ferrule resonance cavity, resulting in a hybrid graphene-MIM waveguide structure. The transmission spectra and electric fields generated by the structure are analyzed by using the finite element method (FEM), shedding light on the formation mechanism of various Fano resonance peaks. The validity of our theoretical analysis is confirmed using multimode interference coupled mode theory (MICMT), and the simulation results are largely aligning with the theoretical verification results. Next, by manipulating the chemical potential of graphene, the Fano resonance can be tuned across a wide range of wavelength bands. And this capability enables the realization of a dynamically tunable refractive index sensor for transmission spectroscopy. Under optimized parameter settings, the refractive index sensor achieves a maximum sensitivity of 1266.67nm/RIU, and a maximum figure of merit (FOM) value of 199.67RIU−1. Compared with conventional MIM waveguide devices, this design overcomes the difficulty of conventional MIM waveguide structures that cannot be dynamically tunable. Notably, the wavelength of the Fano resonance formed by the transmission spectrum can be dramatically altered when the refractive index of the medium in the surrounding environment is slightly changed. Therefore, this structure expands the repertoire of integrated optical devices with potential applications, particularly in the field of optical sensors.

Novel high performance Fano resonance sensor with circular split ring resonance

This study conducts an in-depth discussion on the Fano resonance phenomenon and its application in optical sensors. A circular split ring was proposed. By designing a metal-insulator-metal (MIM) waveguide structure with specific geometric parameters, we successfully excited the Fano resonance, which produced a unique asymmetric Fano through the coupling of discrete and continuous states. Resonance transmission spectroscopy. The sensitivity of Fano resonance is extremely sensitive to changes in structural parameters. This characteristic provides a theoretical basis for the development of highly sensitive optical sensors. The simulation results show that by optimizing the structural parameters, high sensitivity Fano resonance characteristics can be obtained, further enhancing the performance of the optical sensor. The calculated sensitivity is as high as 1250 nm/RIU, and the figure of merit (FOM) reaches 54, indicating that the designed MIM waveguide structure has excellent sensing capabilities. This study not only demonstrates the potential of Fano resonance in improving sensor sensitivity, but also provides valuable guidance for the design and development of future optical sensors.

MIM waveguide based nano refractive index sensor for hemoglobin and glucose concentration detection in human body

In this study, a nanoscale refractive index sensor structure is proposed, which is realised using a metal-insulator-metal (MIM) waveguide and a grooved circular ring with double disk cavity (GRDD) structure coupled to each other. The finite element method (FEM) was used to analyze and investigate the effects of the variations of each structural parameter on the transmittance spectra and the comprehensive performance of the sensor. Based on the simulation results, the optimum sensitivity parameter of the sensor structure is 2800 nm R−1IU−1 with a figure of merit (FOM) value of 51.9 RIU−1. The sensor structure is capable of being used in biomedical field with sensitivities of 3.895 nm g−L−1, 4.870 nm/gL−1, and 4.955 nm/gL−1, respectively, for detecting hemoglobin of blood types A, B, and O, and 4.48 nm/gL−1, for detecting glucose concentration.

Multiple Fano resonances by MIM waveguide coupling whispering gallery mode resonator and application in Refractive index sensing

In this study, a baffled metal–insulator–metal (MIM) waveguide coupled with a whispering gallery mode resonator (WGMR) is proposed. This structure could excite quadruple Fano resonances. The asymmetric Fano resonance transmittance spectrum and the electric field at the resonance peak were numerically simulated using the finite difference time domain method. The obtained data were fitted using the multimode interference coupled mode theory. The number of Fano resonance peaks was tuned by the outer radius of the WGMR. With other geometric parameters unchanged, the number of Fano resonance peaks increased with increasing outer radius of the WGMR. Thus, it achieved multiple Fano resonances by adjusting solely the radius of the WGMR. When the ring width was fixed, the structure could excite multiple Fano resonances within a certain outer radius range. This structure was used for refractive index sensing and its sensitivity and figure of merit (FOM) were 3004 nm/RIU and 3.14 × 104 in a gas environment, respectively. Therefore, the proposed structure can excite multiple Fano resonances and achieve high sensitivity and FOM, providing a theoretical basis for micro and nano applications.

Propagation-Invariant Space-Time Plasmonic Pulse in Subwavelength MIM Waveguide.

The metal-insulator-metal (MIM) plasmonic waveguide has been highly anticipated for confining and guiding surface plasmon polaritons (SPPs) on the subwavelength scale. However, perennial drawbacks such as a short propagation length and an unbounded transverse field have set limits on the use of the MIM waveguide in various applications. Herein, diffraction- and dispersion-free MIM modes are synthesized by using space-time wave packets (STWPs) and are therefore referred to as space-time MIM (ST-MIM) waveguide modes. Compared to a Gaussian pulse of the same duration and spectral bandwidth, the ST-MIM demonstrates enhanced propagation lengths of about 2.4 times for the symmetric mode and about 6.3 times for the antisymmetric mode. In the simulations, the ST-MIMs are confined in all transverse dimensions, thereby overriding the diffraction limits. In addition, the group velocities of the ST-MIMs can be arbitrarily designed, which makes it possible to synchronize the pulse propagation speeds of the symmetric and antisymmetric MIM modes.

Orthogonal mode couplers for plasmonic chip based on metal–insulator–metal waveguide for temperature sensing application

In this work, a plasmonic sensor based on metal–insulator–metal (MIM) waveguide for temperature sensing application is numerically investigated via finite element method (FEM). The resonant cavity filled with PDMS polymer is side-coupled to the MIM bus waveguide. The sensitivity of the proposed device is ~ − 0.44 nm/°C which can be further enhanced to − 0.63 nm/°C by embedding a period array of metallic nanoblocks in the center of the cavity. We comprehend the existence of numerous highly attractive and sensitive plasmonic sensor designs, yet a notable gap exists in the exploration of light coupling mechanisms to these nanoscale waveguides. Consequently, we introduced an attractive approach: orthogonal mode couplers designed for plasmonic chips, which leverage MIM waveguide-based sensors. The optimized transmission of the hybrid system including silicon couplers and MIM waveguide is in the range of − 1.73 dB to − 2.93 dB for a broad wavelength range of 1450–1650 nm. The skillful integration of these couplers not only distinguishes our plasmonic sensor but also positions it as a highly promising solution for an extensive array of sensing applications.

A HORN-LENS ANTENNA FOR THE TERAHERTZ RANGE BASED ON THE “HOLLOW DIELECTRIC CHANNEL” CLASS WAVEGUIDE

In the antenna-feeder paths of the terahertz (THz) range, waveguides of increased cross sections, the so-called "oversized waveguides", have found wide application. This term refers to a waveguide whose transverse dimensions are much greater than the length of the propagating wave in it. A feature of such a waveguide is the possibility of propaga-tion in it of waves of higher types, which are excited on homogeneity of this waveguide and can have a significant impact on the operation of the entire antenna-feeder path. This can lead to resonances at the transcendental section of the oversized waveguide. This phe-nomenon has been studied in detail in quasi-optical paths for radio relay systems. Indeed, since the inputs and outputs of most active components of microwave transceiver systems use a standard single-mode waveguide, to excite an oversized waveguide, waveguide tran-sitions are widely used. In antenna-feeder paths of the THz range oversize section waveguides the so called “oversize waveguides” are widely used. By an “oversize waveguide” we mean a waveguide whose transverse dimensions are much longer than those of the wave propadating in it. A wave type converter for excitation of an oversized waveguide is an important ele-ment of a quasi-optical antenna-feeder path, since it allows matching the output (input) channel of the active components of the transceiver device (generators, amplifiers, etc.) with the quasi-optical path, which are usually made on the basis of waveguides of the main section. At the same time, the design of almost any type of transducers is based on the formation of a field distribution, the transverse structure of which coincides with the field of the working wave of the oversized waveguide, for example, when the field structure of the waveguide of the main section is smoothly transformed into the working type of the wave of the oversized waveguide. In this paper, waveguide transitions for the terahertz range are considered, which pro-vide minimal conversion losses when joining waveguides with different cross sections. A metal-dielectric waveguide of square cross section is used as the main waveguide. A copper-lens antenna of the terahertz range with high technical characteristics has been developed, which can be widely used in various fields of radio communication.

Nanoscale Refractive Index Sensor Based on an MIM Waveguide Coupled to U-Shaped Ring Resonator with Three Stubs for Alcohol Solution Concentration Detection

In this paper, a nano refractive index sensor consisting of a metal–insulator-metal (MIM) waveguide and a U-shaped ring resonator with three stubs (URRS) resonator is proposed. The transmittance performance of the sensor was theoretically analyzed using the finite element method (FEM). The effects of refractive index and different structural geometrical parameters on the sensor performance were evaluated. The optimal sensitivity of the designed refractive index sensor structure is 2900 nm/RIU, and the figure of merit (FOM) is 55.76. The suggested sensor shows promising potential for utilization in the study of alcohol solution concentration detection. In addition, we applied this sensor structure in the field of alcohol solution concentration detection, and its test results were good with a sensitivity up to 112.

Numerical analysis of a metal-insulator-metal waveguide-integrated magnetic field sensor operating at sub-wavelength scales

This article introduces a novel plasmonic magnetic field sensor (MFS) that utilizes a Metal-Insulator-Metal (MIM) waveguide configuration with a W-shaped cavity filled with magnetic fluid (MF). The MFS's unique design combines the advantages of plasmonic sensing, offering a promising solution for the detection of magnetic field strength. It operates based on the inherent properties of surface plasmon polaritons and the magneto-optical properties of MF, resulting in a shift in resonant wavelength. The performance of the proposed MFS has been investigated through numerical calculation employing the finite element method (FEM). Remarkably, the MFS exhibits a maximum magnetic field sensitivity of 49.11 pm/Oe, covering a detection range from 33 Oe to 200 Oe. The recorded figure of merit (FOM) and Q-factor of the MFS are 18.39 and 18.4 respectively, attesting to its high performance and reliability. This innovation has the potential to revolutionize fields such as navigation, medical diagnostics, and robotics technologies by seamlessly integrating optical sensing into traditional devices. The proposed sensor's excellent performance, compact size, and cost-effectiveness position it as a promising technology for widespread adoption, contributing to advancements in magnetic field sensing across scientific, industrial, and technological domains.

On the Existence of an Infinite Spectrum of Damped Leaky TE-Polarized Waves in an Open Inhomogeneous Cylindrical Metal–Dielectric Waveguide Coated with a Graphene Layer

We consider the problem of leaky waves in an inhomogeneous waveguide structure covered with a layer of graphene, which is reduced to a boundary value problem for the longitudinal components of the electromagnetic field in Sobolev spaces. A variational statement of the problem is used to determine the solution. The variational problem is reduced to the study of an operator function. The properties of the operator function necessary for the analysis of its spectral properties are investigated. Theorems on the discreteness of the spectrum and on the distribution of the characteristic numbers of the operator function on the complex plane are proved.

A nano-refractive index sensor based on a MIM waveguide with a semicircular ring rectangular resonator

This paper proposes a novel nano-sensor structure consisting of the metal-insulator-metal (MIM) waveguide with two rectangular baffles and a semicircular ring rectangular resonator (SRRR). The sensor's transmission characteristics are investigated using the finite-difference time-domain (FDTD) method. The results show that the transmission spectrum of the sensor exhibits the Fano resonance shape. The influences of refractive index and structural parameters on transmission characteristics are systematically investigated. The maximum sensitivity (S) of the sensor can get up to 2560 nm/RIU (refractive index unit), and the figure of merit (FOM) is 1080. In addition, the potential application of the structure in temperature sensing is explored with a sensitivity of 0.87 nm/°C. The proposed structure has promising applications in nanoscale optical sensing.

Quasi-TPPs/Fano resonance systems based on an MDM waveguide structure and its sensing application.

In this paper, quasi-Tamm plasmon polaritons (TPPs)/Fano resonance systems based on metal-dielectric-metal (MDM) waveguides are proposed. TPPs are surface electromagnetic modes formed at the interface between a metal and a one-dimensional dielectric photonic crystal (PhC). A metal plasmonic Bragg reflector (PBR) in a MDM waveguide is equivalent to a dielectric PhC, which is realized by periodic MDM waveguide width modulation and leads to the photonic bandgap. By introducing a thin Ag baffle and a PBR in MDM waveguide core, the quasi-TPPs are excited at the interface between the Ag baffle and the PBR, when the phase-matching condition is met. The proposed structure can be fabricated with focused ion beam or electron beam direct-writing lithography, avoiding complex fabrication procedures of manufacturing dielectric PhC by filling the MDM waveguide core with different dielectric materials. Furthermore, an MDM waveguide side-coupled resonator system is constructed to generate Fano resonance by placing a PBR on the side of the MDM waveguide and an Ag baffle in the waveguide core. The Fano resonance originates from the interference between a broad continuum state provided by the Ag baffle and a discrete state provided by quasi-TPPs. The sensing performance of the Fano resonance system is investigated. In this design, the open PBR structure replaces the traditional closed resonant cavity, which makes it more convenient to contact with analytes. The numerical simulations demonstrate that a high sensitivity of 1500nm/RIU and figure of merit value of 4.08×105 are achieved.