arXiv subjects

Sevgi Ozdemir Kart

Publications and source records attributed to Sevgi Ozdemir Kart.

4 recordsLinked to original sources

arXiv2025

An Investigation of Thermal Properties of Cu-Au Janus Nanoparticles

In this paper, the thermal and structural properties of Cu-Au (Copper-Gold) Janus nanoparticles with a diameter of 5 nm are investigated by using molecular dynamics (MD) simulations within the interactions defined by the many-body embedded atom model (EAM). A set of nanoparticle models has been constructed, with varying Cu and Au ratios. MD method is carried out to calculate the melting temperature, heat capacity, radial distribution function (RDF), Lindemann index, mean square displacement (MSD), and diffusion coefficients of these models. The findings demonstrate that nanoparticles rich in Cu exhibit a higher melting temperature and more defined phase transitions. In contrast, structures rich in gold exhibited reduced melting temperatures and showed surface-initiated melting behaviours. MD study highlights that the thermal stability and atomic mobility of Cu-Au Janus nanoparticles depend on the composition ratio and the dispersion of materials.

cond-mat.mtrl-sci↗

arXiv2025

Geometric Optimization and IPA-Induced Dispersion Tuning in Solid-Core Photonic Crystal Fibers

This study presents a numerical investigation of solid-core photonic crystal fibers with circular and hexagonal cladding geometries. The goal is to optimize optical parameters for nonlinear photonics and environmental sensing. Full-vectorial simulations using FDTD, PWE, and FDE are used to analyze the effects of core diameter, pitch, and air filling fraction on the zero-dispersion wavelength, nonlinear coefficient, effective mode area, and confinement loss. Reducing the core diameter from 2.4 to 1.4 microns tunes the zero-dispersion wavelength from 791 to 646 nanometers and increases the nonlinear coefficient by 72 percent, from 72 to 124 inverse watts per kilometer. The study also examines the effect of isopropyl alcohol infiltration, which causes a red-shift in dispersion and degrades confinement. These results offer a design framework that balances nonlinear efficiency and environmental robustness for supercontinuum generation and chemical sensing.

physics.optics↗

arXiv2024

The Effect of Symmetry Breaking in Coupled Cavity Photonic Crystal Waveguide on Dispersion Characteristics

In this study, we explore the effect of integrated auxiliary rods at varying angles to the primary cavity rod on the dispersion characteristics of the photonic crystal coupled cavity waveguide (PC CCW). Here, it is intended to break the symmetry of the cavity region by introducing auxiliary rods which gives the degree of freedom for tuning effective index of the PC waveguide. Furthermore, rotational angle variations of auxiliary rods reveal slow light operation of the PC CCW where the group index is maximized and group velocity dispersion, as well as the third-order dispersion, are minimized. In addition, auxiliary rods with a broken symmetry increase not only group index but also operating bandwidth and accordingly increase group bandwidth product by 675\%. Leveraging these results, we demonstrate effective rainbow trapping by manipulating the auxiliary rod angles in photonic crystal coupled cavity waveguides. Our results have encouraging implications for optical buffering, multiplexing, demultiplexing, advanced time-domain and spatial signal processing.

physics.optics↗

arXiv2024

Enhanced self-collimation effect by low rotational symmetry in hexagonal lattice photonic crystals

In this study, we present the design of a photonic crystal (PC) structure with a hexagonal lattice, where adjustments to the PC unit cell symmetry reveal an all-angle self-collimation (SC) effect. By optimizing opto-geometric parameters, such as the rotational angle of auxiliary rods and adjacent distances, we analyze the SC property in detail, leveraging group velocity dispersion (GVD) and third-order dispersion (TOD) characteristics. We also investigate the relationship between symmetry properties and their influence on dispersion characteristics. Through symmetry manipulation, we gain a comprehensive understanding of the underlying mechanisms governing light collimation and confinement in the proposed configurations. The PC structure with a $C_1$ symmetry group exhibits all-angle SC effect within the range of $a/λ=0.652$ and $a/λ=0.668$ normalized frequencies, with a bandwidth of $Δω/ω_c = 2.4\%$. Further breaking the symmetry, transforming from $C_1$ to $C_2$ group symmetry, enhances the SC bandwidth to $Δω/ω_c = 6.5\%$ and reveals the perfect linear equi-frequency contours (EFC) at two different frequency bands: all-angle SC between $a/λ=0.616$ and $a/λ=0.656$ normalized frequencies in the \nth{4} transverse magnetic (TM) band and between $a/λ=0.712$ and $a/λ=0.760$ in the \nth{5} TM band. Additionally, we propose a composite/hybrid PC structure resembling $C_2$ group symmetry, where two auxiliary rods are replaced by rectangular photonic wires with the same refractive index and width equal to the diameter of auxiliary rods. This hybrid structure exhibits an all-angle SC effect with an operating bandwidth of $Δω/ω_c = 11.7\%$, displays near-zero GVD and TOD performance, and offers enhanced robustness against potential fabrication precision issues.

physics.optics↗