We present a theoretical approach for a terahertz graphene-based plasmonic waveguide (TGPW) structure. TGPW is combination of two silicon micro-wires located in a SiO2 surroundings on both sides of graphene layers where each one supports two independent propagating surface plasmon polariton waves on both surfaces. It also investigates properties of TGPW and how sub-terahertz frequency impact them. In this structure, we employed two graphene plates and a silver layer. The results show that the structure under study can confine light in the wavelength ranging from λ = 300 μm to λ = 3000 μm with a propagation length ranging from 0.5 to 8.2 μm. The highly compact configuration can be chiefly applicable in areas such as trapping optical force, transporting biomolecules and also in high-density integrated circuits.

A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection. A quantitative theoretical model is also developed for performance prediction and validated with a finite element method. The numerical results show that the Mach-Zehnder interferometer sensor possesses an RI sensitivity as high as 140000  nm/RIU (or 0.42  THz/RIU) and a relative intensity sensitivity of 1200%RIU-1. In addition, a temperature sensitivity of 1470  nm/K (or 4.7×10-3  THz/K) is determined. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure. The proposed sensing scheme may pave the way for applications in terahertz sensing and integrated terahertz circuits.

A novel plasmonic Mach-Zehnder interferometer (MZI) biosensor, which is based on a simple slit-groove microstructure, is reported in the terahertz (THz) regime. The permittivity-sensitive phase difference between the two propagating SPPs waves gives rise to the modulation of the transmitted intensity. The results show that the MZI biosensor possesses a sensitivity as high as 140000 nm/RIU (refractive index unit). The highly compact configuration may find important applications in areas of sensing and integrated THz circuits (ITCs).

A plasmonic Mach-Zehnder interferometer (MZI) for temperature sensing is reported in the terahertz (THz) regime. The MZI is formed by embedding a semiconductor (SC) layer into a silicon membrane, where the SC layer supports two independent propagating surface plasmon polariton (SPP) waves on both surfaces. The temperature-sensitive phase difference between these two SPP waves gives rise to the modulation of the transmitted intensity. The results show that the MZI sensor possesses a sensitivity and a figure of merit as high as 8.9 x 10(-3) THz/K and 117, respectively. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure Moreover, an investigation of structural perturbations indicates that the MZI has a good tolerance to the fabrication errors. The compact MZI-based waveguide structure may find important applications in areas of sensing and integrated THz circuits.

In this letter, a novel waveguide based on semiconductor THz hybrid surface plasmon polariton (STHSPP) is proposed and numerically analyzed. The structure under study can confine light in the ultradeep-subwavelength region (ranging from λ 2 /360 to λ 2 /156) with a large propagation length ranging from 374 to 506 µm. Compared with a conventional hybrid SPP (HSPP) waveguide without a ridge, our proposed structure with the same propagation length has a much higher mode confinement with a one order of magnitude smaller normalized mode area.

The simultaneous realization of low propagation loss and subwavelength mode localization remains one of the critical challenges in plasmonics. Aiming to simultaneously realize low propagation loss and subwavelength mode localization in plasmonics, we introduce a class of low-loss and deeply confined guiding schemes utilizing an alternative plasmonic material, i.e., a superconductor (SC). The optical properties of a SC–insulator–SC (SCISC) waveguide are analyzed both at terahertz (THz) and telecommunication (TC) frequencies. The SCISC waveguide features a deep-subwavelength confinement with a mode length as small as λ/6000 (λ/18) for THz (TC) frequency, while the propagation length can be extended up to 400 mm (1 mm).

Numerical solutions are obtained for the proposed novel hybrid terahertz plasmonic waveguide structure, namely the silicon metal silicon (SMS) waveguide. It is shown that the SMS waveguide can overcome the diffraction limit while still maintaining a sizeable propagation length. The geometric dependence of the mode characteristics of this structure is analyzed in detail, showing strong confinement and low loss with propagation lengths exceeding 14mm at normalized mode areas of 1.72×10−2. By using the FEM method (Comsol), the guiding properties of the hybrid terahertz surface plasmon polariton (HTSPP) waveguide are numerically analyzed at the THz frequency, and a combination of double-structured comparisons of the best features of the terahertz plasmonic waveguide is made. Depending on the height used and how the mode confinement is measured, various modal designs, such as double microwire structures, are developed. The structures indicate that we verified the possibility of low attenuation loss of hybrid THz plasmonics propagation. The effective mode area Aeff, energy distribution, and propagation length Lp versus height for waveguides with Si microwire and SiO2 are shown. The numerical calculation results reveal a potential for use in applications such as optical force in trapping and transporting biomolecules, and in high-density integrated circuits.

We consider the surface plasma polariton dispersion in inhomogeneous semiconductor/ air interface. The plasma permittivity in a two-layer compound is studied by inclusion of an inhomogeneous plasma density. Numerical solutions were obtained for the plasma dispersion curve of an inhomogeneous semiconductor/dielectric structure. A detailed analysis was carried out to derive an expression for the dispersion of a silicon/air interface, or other [1], by applying our new original approach [2]. This approach takes into account the free-charge carrier concentration profile effect.

Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs).

Numerical solutions are obtained for a novel inhomogeneous semiconductor hybrid plasmonic waveguide structure by using Finite Element Method (FEM) method (Comsol). The guiding properties of an inhomogeneous semiconductor hybrid surface plasmon polaritons (ISHSPPs) slot waveguide was numerically analyzed at an optical frequency, which shows the ISHSPPs waveguide could surpass the diffraction limit while still maintaining long polariton's propagation lengths. The geometric dependence of the mode characteristics of the proposed structure is analyzed in detail, showing strong confinement with long propagation lengths. Numerical results offer a potential for use in several applications such as biosensors.

We present a novel theoretical approach for analytically solving wave propagation through two-dimensional (2D) inhomogeneous slab waveguides. The validity and reliability of our analytical approach is verified by its application to electrical field distribution in 2D waveguides, when compared with numerically exact solution. The main advantage of this theoretical treatment is that the obtained solution is global and can be presented in an analytical form. The effects of the refractive index profile on the guided modes are analyzed by introducing the field distributions of the guided modes. Our analytical calculations show significant potential for use in various applications.

Optical waveguides have been a subject of an intensive theoretical research, resulting in applications in several fields, and stimulated research in integrated optics. Homogeneous dielectric waveguides and their properties are covered in detail in many articles and textbooks. However, in waveguides loaded with arbitrary inhomogeneous dielectrics, analytical solutions are possible only for a limited number of permittivity profiles in simple geometries. The analysis of longitudinally inhomogeneous waveguides has been already proposed, but the main drawback of this approach is that it requires cumbersome and time-consuming integration. We therefore suggest to take this a step further by applying our new original analytical approach that does not require integration. The aim of this work is to establish a different method that is generally applicable to any vectorial time-dependent, anisotropic, non-linear, inhomogeneous, dissipative and dispersive media to analyze the field distribution of inhomogeneous 1-D and 2-D waveguides with symmetric and asymmetric permittivity profiles. Our initial consideration of slab problems with arbitrary profiles by means of analytical method shows a great deal of potential for use in applications in fields such as physics, and engineering.

Theoretical solutions are obtained for the propagation of electromagnetic waves at optical frequencies along a semiconductor/dielectric interface when losses are taken into account in the form of a complex dielectric function. A combination method for the dielectric function, comprised of the best features of the Drude and Lorentz models, is herein proposed. By including the loss term in both models, we were able to obtain numerical solutions for the Plasma dispersion curve of the semiconductor/dielectric interface. The surface plasmon waves, when excited, become short wavelength waves in the Optical frequency or THz region. A silicon/air structure was used as our semiconductor/dielectric material combination, and comparisons were made to optical plasmons generated without losses. Our initial numerical calculation results show enormous potential for use in several applications.

Theoretical solutions are obtained for the propagation of electromagnetic waves at optical frequencies along a semiconductor/dielectric interface when losses are taken into account in the form of a complex dielectric function. A combination method for the dielectric function, comprised of the best features of the Drude and Lorentz models, is herein proposed. By including the loss term in both models, we were able to obtain numerical solutions for the plasma dispersion curve of the semiconductor/dielectric interface. The surface plasmon waves, when excited, become short wavelength waves in the optical frequency or THz region. A silicon/air structure was used as our semiconductor/dielectric material combination, and comparisons were made to optical plasmons generated without losses. Our initial numerical calculation results show enormous potential for use in several applications.