arXiv subjects

Khondokar Zahin

Publications and source records attributed to Khondokar Zahin.

5 recordsLinked to original sources

arXiv2026

An Integrated DFT-FDTD Design of Plasmon-Enhanced Lead-Free $CsSn$$_x$$Ge$$_{1-x}$$I$$_3$ Perovskite LEDs

CsSn$_x$Ge$_{1-x}$I$_3$ as lead-free perovskites are promising for next generation NIR emitting perovskite LEDs due to their tunable bandgaps and stability. However, they suffer from poor light extraction efficiency, and accurate composition-specific optical data for these materials remain scarce. This study presents a DFT-FDTD framework to optimize light extraction via compositional tuning and plasmonic enhancement. First, DFT calculations were performed to obtain composition-specific complex refractive index and extinction coefficient values for $x = 0, 0.25, 0.5, 0.75$, and $1$. Results show bandgap increased from 1.331 eV for CsSnI$_3$ to 1.927 eV for CsGeI$_3$ with increasing Ge content, while refractive index ranges from 2.2 to 2.6 across compositions. These optical constants were then used as inputs for FDTD simulations of a PeLED structure with optimized Au/SiO$_2$ core-shell nanorods for plasmonic enhancement. A 12.1-fold Purcell enhancement was achieved for CsSn$_{0.25}$Ge$_{0.75}$I$_3$, while light extraction efficiency reached 25% for CsSn$_{0.5}$Ge$_{0.5}$I$_3$. LEE enhancement of 36% was obtained for CsSnI$_3$, and spectral overlap between emitter and plasmon resonance reached 96% for Sn-rich compositions. Design guidelines indicate CsSn$_{0.5}$Ge$_{0.5}$I$_3$ offers optimal balance of extraction efficiency (25%), Purcell enhancement (5.3$\times$), spectral overlap (93%), and oxidation stability for wearable and flexible optoelectronic applications, while CsSn$_{0.25}$Ge$_{0.75}$I$_3$ is recommended for applications prioritizing spontaneous emission rate.

physics.optics↗

arXiv2026

Toward Scalable Heterogeneous Quantum Networks: Microwave-Optical Transduction Across Platforms

The development of scalable quantum networks requires coherent interfaces capable of converting microwave photons used in superconducting quantum processors into optical photons suitable for long-distance fiber transmission. This review surveys recent progress in microwave-to-optical quantum transduction across optomechanical, electro-optic, and magneto-optic platforms, with emphasis on conversion efficiency, bandwidth, added noise, and operating temperature. In addition to standard metrics, we propose the internal efficiency eta_in and the magnon decay rate kappa_m/2pi as normalized parameters that enable fairer comparison across heterogeneous implementations. Optomechanical systems achieve internal phonon-to-photon efficiencies of 93% with sub-quantum added noise of 0.25 quanta at millikelvin temperatures. Electro-optic devices based on LiNbO3 and AlN have advanced from room-temperature efficiencies below 1% to millikelvin systems with internal efficiencies approaching 99.5%, added noise as low as 0.16 quanta at 60 mK, and bandwidths extending to several tens of megahertz. Magneto-optic (optomagnonic) platforms exhibit the lowest efficiencies (typically $10^{-10}$ to $10^{-8})$, but offer intrinsic non-reciprocity and broadband magnonic operation, with emerging approaches based on topological heterostructures and magnon squeezing predicting enhancements up to $10^{-4}$. Optomechanical systems appear promising for high-fidelity quantum state transfer, electro-optic transducers for high-bandwidth coherent links, and magneto-optic devices for non-reciprocal network components. We discuss the fundamental trade-off between efficiency and added noise across all three platforms, and argue that heterogeneous microwave-optical transduction is emerging as a key enabling technology for distributed quantum computing and large-scale quantum networks.

quant-ph↗

arXiv2026

Composition-Dependent Plasmon-Enhanced Emission in Lead-Free Cs$_3$Cu$_2$X$_5$ Halides: A DFT--FDTD Study

Lead-free Cs$_3$Cu$_2$X$_5$ (X = Cl, Br, I) halides exhibit high photoluminescence quantum yields and excellent ambient stability, yet light-emitting devices based on these materials remain limited by poor optical outcoupling. In this work, we develop an integrated density functional theory (DFT) and finite-difference time-domain (FDTD) framework to establish quantitative links between halide composition, wavelength-dependent optical constants, and plasmonic enhancement. First-principles calculations are used to obtain composition-specific refractive index (n) and extinction coefficient (k) spectra, which are directly implemented into three-dimensional FDTD simulations of a complete PeLED stack incorporating Ag/SiO$_2$ core--shell nanostructures. Among the investigated compositions, Cs$_3$Cu$_2$Cl$_5$ demonstrates the strongest plasmonic response, achieving a 4.4$\times$ Purcell enhancement and 30\% light extraction efficiency (LEE) using optimized nanorods. The superior performance originates from its lower refractive index, which reduces dielectric screening and improves near-field coupling. Cs$_3$Cu$_2$Br$_5$ exhibits the highest spectral overlap ($J_{\mathrm{cos}} = 0.955$) but yields moderate extraction (26%) due to increased optical confinement. Cs$_3$Cu$_2$I$_5$ requires a nanosphere geometry and shows limited enhancement, with LEE restricted to 10%. Distance-ependent analysis reveals composition-specific optimal emitter--plasmon separations, ranging from 8--12 nm for Cs$_3$Cu$_2$Br$_5$ to approximately 15 nm for Cs$_3$Cu$_2$Cl$_5$. These results provide composition-dependent design guidelines for plasmon-enhanced lead-free PeLEDs and highlight the critical role of accurate optical constants in predictive device optimization.

physics.optics↗

arXiv2025

Compact Plasmonic Logic Gates Enabled by Magnetoelectric Light Funneling for On-Chip Optical Computing in the Telecom Band

The realization of all-optical logic gates (AOLGs) is important for advancing photonic integrated circuit (PIC) design and optical data communication. Various photonic structures and design techniques, including two-dimensional photonic crystals, silicon waveguides, plasmonic waveguides, diffractive neural networks, and inverse design techniques, are actively being explored to achieve multifunctional, high-performance optical logic gates with fast data processing capabilities. Among these, plasmonic structure-based AOLGs often face challenges such as fabrication complexity and large device footprints when integrating multiple logic operations within a single structure. In this work, a planar and compact metal-insulator-metal (MIM) plasmonic waveguide structure is proposed for AOLG design, utilizing the light funneling effect in grooved metasurfaces. The designed device, with dimensions of 700 nm X 460 nm, successfully implements three fundamental logic gates (NOT, AND, OR) with a high contrast ratio of 18.69 dB. The device operates within the wavelength range of 1400 nm to 1450 nm, making it suitable for the telecommunications field. Its planar architecture offers fabrication feasibility and all logic gates can be controlled using a single light source incident from one specific direction, which facilitates its integration into photonic circuits with fast operational speed. This work contributes to the advancement of scalable and high-speed photonic computing platforms.

physics.optics↗

arXiv2025

Inverse Design Optimization of MIS Nanorod Array to Enhance Wavelength-Selective Light Extraction of OLED through Guided SPCE

One of the primary causes of low light extraction efficiency (LEE) in conventional OLEDs is the trapping of light within the substrate layer. To overcome this limitation, various nanostructures have recently been investigated for integration into different OLED layers, aiming to convert the trapped loss modes into out-coupled light and thereby improve LEE. In this work, we propose a simple yet innovative nanorod array design composed of metal, insulator, and semiconductor-oxide layers, integrated on the bottom surface of the OLED structure. This configuration enhances light extraction through guided surface plasmon-coupled emission (SPCE). Using an inverse design-based optimization approach, the structural parameters of the nanorods were optimized to achieve wavelength-selective LEE enhancement. The periodic MIS nanorod array was optimized via the Particle Swarm Optimization (PSO) algorithm for different emission wavelengths, yielding improvements of 29\%, 30\%, and 51\% at 440 nm, 550 nm, and 540 nm, respectively, compared with conventional OLEDs. In addition, the optimized arrays demonstrate high spectral luminous efficiency (SLE), reduced UV transmittance, and uniform emission directionality. These enhancements have significant potential to advance OLED-based display technologies.

physics.optics↗