Optical Waveguides and Terahertz Signal by Finite Element Method: A Survey

This paper examines the use of the Finite Element Method (FEM) in the field of optical waveguides and terahertz signals, with the main goal of explaining how this method aids in recent advances in this field. The basics of FEM are briefly reviewed, and the technique's application to waveguide discontinuity analysis is observed. Second-order and higher-order derivatives result from optical waveguide modeling, which is significant for information exchange and many other nonlinear phenomena. The use of FEM in the improvised design of hexagonal sort air hole porous core microstructure fibers, which produces hexagonal structure cladding and rectangular-shaped air holes in the fiber core for excellent terahertz signal transmission, was also observed. These modifications were intended to improve the fiber's properties in comparison to other structures. This approach verifies that the fiber has high birefringence, low material loss, a high-power fraction, and minimal dispersion varia-tion. The features of square-type microstructure fiber are investigated. A folded-shaped po-rous cladding design is recognized for sensing applications. This type of photonic crystal fiber is also known as FP-PCF since it features circular air holes. The most approximate findings of this application are obtained using FEM. In comparison to many other approach-es for various applications, it is evident that FEM is a powerful and numerically efficient tool. This work does a survey of optical waveguides and terahertz signals using the Finite Element Method. Terahertz signals can be used in conjunction with electromagnetic waves to identify viruses. Thus, Terahertz signals are employed in real-world applications such as fuel adulteration, liquid metal synthesis, and virus detection.

Electrically controllable active plasmonic directional coupler of terahertz signal based on a periodical dual grating gate graphene structure

We propose a concept of an electrically controllable plasmonic directional coupler of terahertz signal based on a periodical structure with an active (with inversion of the population of free charge carriers) graphene with a dual grating gate and numerically calculate its characteristics. Proposed concept of plasmon excitation by using the grating gate offers highly effective coupling of incident electromagnetic wave to plasmons as compared with the excitation of plasmons by a single diffraction element. The coefficient which characterizes the efficiency of transformation of the electromagnetic wave into the propagating plasmon has been calculated. This transformation coefficient substantially exceeds the unity (exceeding 6 in value) due to amplification of plasmons in the studied structure by using pumped active graphene. We have shown that applying different dc voltages to different subgratings of the dual grating gate allows for exciting the surface plasmon in graphene, which can propagate along or opposite the direction of the structure periodicity, or can be a standing plasma wave for the same frequency of the incident terahertz wave. The coefficient of unidirectionality, which is the ratio of the plasmon power flux propagating along (opposite) the direction of the structure periodicity to the sum of the absolute values of plasmon power fluxes propagating in both directions, could reach up to 80 percent. Two different methods of the plasmon propagation direction switching are studied and possible application of the found effects are suggested.

Electrically Controllable Active Plasmonic Directional Coupler of Terahertz Signal based on a Periodical Dual Grating Gate Graphene Structure

We propose a concept of an electrically controllable plasmonic directional coupler of terahertz signal based on a periodical structure with an active (with inversion of the population of free charge carriers) graphene with a dual grating gate and numerically calculate its characteristics. Proposed concept of plasmon excitation by using the grating gate offers highly effective coupling of incident electromagnetic wave to plasmons as compared with the excitation of plasmons by a single diffraction element. The coefficient which characterizes the efficiency of transformation of the electromagnetic wave into the propagating plasmon has been calculated. This transformation coefficient substantially exceeds the unity (exceeding 6 in value) due to amplification of plasmons in the studied structure by using pumped active graphene. We have shown that applying different dc voltages to different subgratings of the dual grating gate allows for exciting the surface plasmon in graphene, which can propagate along or opposite the direction of the structure periodicity, or can be a standing plasma wave for the same frequency of the incident terahertz wave. The coefficient of unidirectionality, which is the ratio of the plasmon power flux propagating along (opposite) the direction of the structure periodicity to the sum of the absolute values of plasmon power fluxes propagating in both directions, could reach up to 80 percent. Two different methods of the plasmon propagation direction switching are studied and possible application of the found effects are suggested.

Детектирование терагерцевых электромагнитных волн с помощью проводящих антиферромагнетиков

We investigate a mathematical model of a terahertz electromagnetic wave detector based on a conducting antiferromagnet and a heavy metal. The mechanism of resonant straightening of oscillations is based on the inverse spin Hall effect in a heavy metal under spin pumping from an antiferromagnet. It is shown that the frequency dependence of the constant voltage of the detector has a resonant character with a peak corresponding to the frequency of antiferromagnetic resonance. The sensitivity to an alternating terahertz signal of the proposed detector structure is comparable to the sensitivity of modern detectors based on Schottky and Gunn diodes.