Mohamed Eldlio

Mach–Zehnder Interferometer-Based Integrated Terahertz Temperature Sensor

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 × 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.

Plasmonic properties of superconductor–insulator–superconductor waveguide

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).

Analytic solution to field distribution in two-dimensional inhomogeneous waveguides

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.

Drude-Lorentz Model of Semiconductor Optical Plasmons

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.

Semiconductor-based plasmonic interferometers for ultrasensitive sensing in a terahertz regime

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 THz semiconductor hybrid plasmonic waveguide with fabrication-error tolerance

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 λ2/360 to λ2/156) 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.

Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations

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).

Surface plasmon polariton dispersion in inhomogeneous semiconductors

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, by applying our new original approach. This approach takes into account the free-charge carrier concentration profile effect. A detailed theoretical treatment is applied of optical properties of doped semiconductors to find the dispersion relation, taking into account that the density profile depends on the x-coordinate. It is worth mentioning that the published work does not cover all aspects of such inhomogeneous structures. This work reviews the concept of the known model (Le., Drude model) and discusses its feasibility. Since an objective was a theoretical treatment of surface plasmon polaritons in inhomogeneous semiconductors, the dielectric permittivity was derived and described. Initial numerical calculations show a potential for use in several applications The described approach enables one to obtain a suitable model that can be applied to semiconductors. Mathematically, principal properties of propagating optical surface plasmon polaritons were shown, including an effect of a density profile of the plasma frequency in the Drude model.

Plasmonic semiconductor-based interferometers for ultrasensitive THz biosensing

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).

Analysis of inhomogeneous semiconductor-based hybrid plasmonic slot waveguide

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 polaritons 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.