arXiv subjects

Kiyanoush Goudarzi

Publications and source records attributed to Kiyanoush Goudarzi.

7 recordsLinked to original sources

arXiv2025

In-situ tuning of cavity dissipation and a topological transition in an atom-nanotip-cavity system

We theoretically investigate a method for tuning a dissipation rate in an atom-cavity system. By inserting a nanotip into the cavity mode, we estimate that the cavity dissipation rate increases by a factor of approximately 20, due to the scattering loss at the tip. As applications of our in-situ technique, we demonstrate that an exceptional line can be obtained when a single atom or ion is coupled to the resonator. Moreover, the position of an exceptional point is tuned by adjusting the decay rate, enabling a topological transition through dissipation control alone.

quant-ph↗

arXiv2025

Single-defect mode lasing in a non-Hermitian 1D trivial SSH lattice

We demonstrate robust single-mode lasing in a non-Hermitian 1D trivial Su-Schrieffer-Heeger defective lattice. This structure exhibits a significantly lower threshold power compared to the non-defective lattice, with single-mode lasing sustained across a wide range of pump powers. Notably, our proposed device requires pumping of only the defect ring, leading to minimal required pump power. Moreover, lasing is not confined to the edges but can occur at any point within the lattice.

physics.optics↗

arXiv2023

Tolerance and breakdown of topological protection in a disordered waveguide

We consider a disordered waveguide consisting of trivial dielectric and non-trivial magnetically anisotropic material. A topologically-protected edge mode appears owing to the broken time-reversal symmetry of the non-trivial lattice. While the edge mode maintains under other position and radius disorders, the protection is immediately broken by applying a radius disorder to the non-trivial lattice. This breakdown originates from donor and acceptor modes occupying the topological bandgap. Furthermore, via the calculation of the Bott index, we show that Anderson localization occurs as a metal conducting gap changes to a topological gap along with increasing disorders.

cond-mat.dis-nn↗

arXiv2021

Inverse design of an all-dielectric digitized terahertz optical power splitter by particle swarm optimization method

This letter proposes a 50:50 TE terahertz (THz) power splitter based on digitized metamaterials. The device is optimized using particle swarm optimization algorithm. The structure of the digitized metamaterials contains circular air holes in silicon slab which are deposited on silicon dioxide substrate. The optimized structure shows insertion loss (IL) of less than 3.9 dB over the frequency range of 0.9-1.1 THz. The proposed device has the footprint of 400 $\times$ 350 $μ$m$^2$. The proposed device has excellent merits such as compactness, efficient, all-dielectric, and compatible with CMOS fabrication technologies. This device can be used as a vital component in most of the THz circuits to route THz waves.

physics.optics↗

arXiv2021

Highly-efficient broadband TE/TM polarization beam splitter

Highly-efficient broadband polarization beam splitters with small footprint and based on silicon photonics technology are of great importance in optical integrated circuits. In this paper, a crucially applicable optical component of a TE/TM polarization beam splitter has been designed and simulated using the inverse design of adjoint method. The mentioned device has ultra-high transmission efficiency (about 96% for TM$_{00}$ and 93% for TE$_{00}$ modes) and high extinction ratio of more than 16 dB over the bandwidth of 200 nm. Small footprint (2.2 $\times$ 2.1 $μ$m$^2$), broad bandwidth (200 nm), and compatibility with CMOS technology fabrication indicate the eligibility of this device.

physics.optics↗

arXiv2020

Design of a Broadband and Polarization Insensitive THz Absorber Based on Two Layers of Periodic Arrays of Graphene Disks

In this paper, we analytically design a simple configuration of a broadband THz and polarization-insensitive absorber. The mentioned absorber consists of two layers of graphene disks, and the transmission line model is considered for the whole of the proposed absorber's structure to design it accurately. Therefore, the input admittance of the designed absorber is obtained by the transmission line model. Also, the real part of the input admittance is approximately tuned to be matched to the free space admittance. In contrast, the imaginary part of it is closely adjusted to zero around the central frequency of the THz absorber. Using only just two layers of Periodic Arrays of Graphene Disks (PAGDs) with one kind of dielectric as the material of substrates, it causes that the absorption of the structure can be achieved higher than 90% by the Finite Element Method (FEM). Normalized bandwidth has reached up to 75.4% in 5 THz as the central frequency of the device. As the next step, we use the CST studio software to validate our designed absorber, and it will show that the numerical results will have the best matching with the analytical method.

physics.optics↗

arXiv2019

Ultra-High Normalized Bandwidth TE and TM Polarization Insensitive Terahertz Absorber with Graphene Disks Configuration

In this paper, we have proposed ultra-broadband terahertz absorber with three layers of periodic graphene disks arrays (PGDAs). A gold layer was utilized as backside reflector and TOPAS as dielectric spacers. Circuit model of PGDAs and the developed Transmission Line Model (TLM) for the absorber is utilized to design the structure using impedance matching concept. The validity of the results of the device was confirmed by Finite Element Method (FEM). The structure absorbs both TE and TM polarizations. Furthermore, the obtained normalized absorption bandwidth is 148% with a bandwidth of 2.64 THz in 1.78 THz central frequency which is to best of our knowledge the best report in two-dimensional graphene-based structures.

physics.optics↗