arXiv subjects

Humeyra Caglayan

Publications and source records attributed to Humeyra Caglayan.

At least 19 recordsLinked to original sources

arXiv2026

Meta-optical processors for broadband complex-field image operations

All-optical image processing provides a fast and energy-efficient alternative to conventional electronic systems by directly manipulating optical wavefronts. However, metasurface-based optical processors reported to date are often limited in functionality, operating bandwidth, or input modality, which restricts their adaptability across different image processing tasks. Here, we demonstrate a broadband metasurface platform capable of performing diverse analog image processing operations on both amplitude- and phase-encoded inputs. This platform is realized using a single-layer dielectric metasurface designed through an end-to-end, task-driven inverse design framework. By tailoring the spatial-frequency components of incident image wavefronts, the metasurface implements analog operations such as edge detection and pattern recognition across a 200nm wavelength bandwidth in the visible spectrum. Furthermore, we develop a compact processor architecture that integrates imaging and computation within a reduced optical footprint. These results establish a flexible and compact metasurface-based optical processor with strong potential for integration into practical imaging and optical computing systems.

physics.optics↗

arXiv2026

Disorder-Engineered Hybrid Plasmonic Cavities for Emission Control of Defects in hBN

Defect-based quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for scalable quantum photonics due to their stable single-photon emission at room temperature. However, enhancing their emission intensity and controlling the decay dynamics remain significant challenges. This study demonstrates a low-cost, scalable fabrication approach to integrate plasmonic nanocavities with defect-based quantum emitters in hBN nanoflakes. Using the thermal dewetting process, we realize two distinct configurations: stochastic Ag nanoparticles (AgNPs) on hBN flakes and hybrid plasmonic nanocavities formed by AgNPs on top of hBN flakes supported on gold/silicon dioxide (Au/SiO2) substrates. While AgNPs on bare hBN yield up to a two-fold photoluminescence (PL) enhancement with reduced emitter lifetimes, the hybrid nanocavity architecture provides a dramatic, up to 100-fold PL enhancement and improved uniformity across multiple. emitters, all without requiring deterministic positioning. Finite-difference time-domain (FDTD) simulations and time-resolved PL measurements confirm size-dependent control over decay dynamics and cavity-emitter interactions. Our versatile solution overcomes key quantum photonic device development challenges, including material integration, emission intensity optimization, and spectral multiplexity. Future work will explore potential applications in integrated photonic circuits hosting on-chip quantum systems and hBN-based label-free single-molecule detection through such quantum nanoantennas.

physics.optics↗

arXiv2025

Phase-shifting structured illumination with polarization-encoded metasurface

Phase-shifting structured illumination is a powerful technique used across diverse imaging modalities, including 3D surface measurement, quantitative phase imaging, and super-resolution microscopy. However, conventional implementations often rely on mechanically driven or optoelectronically complex systems, limiting their compactness, stability, and integration. Here, we present a polarization-controlled dielectric metasurface that generates phase-shifting fringe patterns in the visible spectrum, enabling compact and robust structured light projection. The metasurface encodes distinct phase gratings for orthogonal polarizations, producing fringe patterns with relative lateral displacements that vary according to the polarization of the transmitted light. We experimentally demonstrate high-quality fringe generation and apply the structured illumination in a fringe projection profilometry system for 3D surface measurement of different objects. The metasurface integrates multiple phase-shifting steps into a single static device, offering a millimeter-scale footprint and compatibility with polarization multiplexing. This approach introduces a compact, passive solution for structured light generation with broad potential in next-generation optical metrology and advanced computational imaging.

physics.optics↗

arXiv2025

Optical Wireless Communications: Enabling the Next Generation Network of Networks

Optical wireless communication (OWC) is a promising technology anticipated to play a key role in the next-generation network of networks, especially as a complementary technology to traditional radio frequency communications, for enhancing networking capabilities beyond conventional terrestrial networks. OWC is already a mature technology with diverse usage scenarios, and can enable integrated applications via wireless access and backhaul networks, dynamic drone and satellite networks, underwater networks, inter- and intra-system interconnecting networks, and vehicular communication networks. Furthermore, novel and emerging technological opportunities such as photovoltaic cells, orbital angular momentum-based modulation, optical reconfigurable intelligent surfaces, organic light-emitting and photo diodes, and recent advances in ultraviolet communications can help enhance future OWC capabilities even further. Moreover, OWC networks can also support value-added services such as enhanced positioning and gesture recognition. Hence, OWC provides unique functionalities that can play a crucial role in building convergent and resilient future network of networks alongside radio frequency and optical fiber technologies.

eess.SP↗

arXiv2025

Analytical Framework of Orbital Angular Momentum Beam under Misaligned Detection

This work presents an analytical framework for modeling a detected orbital angular momentum (OAM) spectrum of an optical beam subject to tilt and lateral displacement. Firstly, we demonstrate that both types of misalignment generate OAM sidebands governed by the same functional form, each characterized by a distinct dimensionless parameter that depends on the beam's size and wavelength. Secondly, our analysis reveals that increasing the beam's topological charge broadens the detected OAM spectrum. Lastly, we show that when both tilt and lateral displacement are present, the contribution of the original OAM mode can be tuned: specifically, by orienting the tilt and displacement in perpendicular directions, the resulting misalignment effects interfere destructively, thereby reducing crosstalk.

physics.optics↗

arXiv2025

Meta-operators for all-optical image processing

All-optical image processing offers a high-speed, energy-efficient alternative to conventional electronic systems by leveraging the wave nature of light for parallel computation. However, traditional optical processors rely on bulky components, limiting scalability and integration. Here, we demonstrate a compact metasurface-based platform for analog optical computing. By employing double-phase encoding and polarization multiplexing, our approach enables arbitrary image transformations within a single passive nanophotonic device, eliminating the need for complex optical setups or digital post-processing. We experimentally showcase key computational operations, including first-order differentiation, cross-correlation, vertex detection, and Laplacian differentiation. Additionally, we extend this framework to high-resolution 3D holography, achieving subwavelength-scale volumetric wavefront control for depth-resolved reconstructions with high fidelity. Our results establish a scalable and versatile approach to computational optics, with applications including real-time image processing, energy-efficient computing, biomedical imaging, high-fidelity holographic displays, and optical data storage, driving the advancement of intelligent optical processors.

physics.optics↗

arXiv2025

Multifunctional meta-optic azimuthal shear interferometer

Azimuthal shear interferometry is a versatile tool for analyzing wavefront asymmetries. However, conventional systems are bulky, alignment-sensitive, and prone to nonuniform shear. We present a broadband, compact, and robust meta-optics-based azimuthal shear interferometer in a common-path configuration, reducing the system size to the millimeter scale. Unlike conventional designs, the meta-optic azimuthal shear interferometer utilizes the localized wavefront modulation capabilities of meta-optics to achieve uniform azimuthal shear displacement independent of radial position, significantly enhancing accuracy and stability. Our approach eliminates the need for bulky optical components and precise multi-path alignment, making it more resilient to environmental disturbances. Its multifunctionality is demonstrated through applications in all-optical edge detection, differential interference contrast microscopy, and aberrated wavefront sensing. These results underscore its potential for real-time analog image processing, advanced optical imaging, and optical testing.

physics.optics↗

arXiv2024

Fractional Dimensional Approach to Dielectric Tuning Effects on Excitonic Parameters in 2D semiconductor materials

We demonstrated the potential of the fractional dimensional approach to understand exciton parameters in the exemplary atomically thin semiconductor material, a monolayer of WS$_2$. This approach has proved to be successful in finding the exciton binding energy and quasiparticle bandgap for the WS$_2$ monolayer in varying dielectric environments. A tuning of the quasiparticle bandgap and binding energy by 141 meV and 188 meV, respectively, has been achieved by varying the dielectric of the environment from 1.52 to 8.1. The approach is justified by comparing the changes in the binding energy with the computational results from the Quantum Electrostatic Heterostructures model. The fractional dimension found through the excitonic Rydberg series is close to 2.8 for WS$_2$ monolayer in all different dielectric surroundings. Thus, this approach provides a rapid and robust method for determining the binding energy of excitons in 2D semiconductors independent of the particular dielectric environment.

cond-mat.mes-hall↗

arXiv2023

Ultrafast optical properties of stoichiometric and non-stoichiometric refractory metal nitrides TiNx, ZrNx, and HfNx

Refractory metal nitrides have recently gained attention in various fields of modern photonics due to their cheap and robust production technology, silicon-technology compatibility, high thermal and mechanical resistance, and competitive optical characteristics in comparison to typical plasmonic materials like gold and silver. In this work, we demonstrate that by varying the stoichiometry of sputtered nitride films, both static and ultrafast optical responses of refractory metal nitrides can efficiently be controlled. We further prove that the spectral changes in ultrafast transient response are directly related to the position of the epsilon-near-zero region. At the same time, the analysis of the temporal dynamics allows us to identify three time components - the "fast" femtosecond one, the "moderate" picosecond one, and the "slow" at the nanosecond time scale. We also find out that the non-stoichiometry does not significantly decrease the recovery time of the reflectance value. Our results show the strong electron-phonon coupling and reveal the importance of both the electron and lattice temperature-induced changes in the permittivity near the ENZ region and the thermal origin of the long tail in the transient optical response of refractory nitrides.

physics.optics↗

arXiv2023

New horizons in near-zero refractive index photonics and hyperbolic metamaterials

The engineering of the spatial and temporal properties of both the electric permittivity and the refractive index of materials is at the core of photonics. When vanishing to zero, those two variables provide new knobs to control light-matter interactions. This perspective aims at providing an overview of the state of the art and the challenges in emerging research areas where the use of near-zero refractive index and hyperbolic metamaterials is pivotal, in particular light and thermal emission, nonlinear optics, sensing applications and time-varying photonics.

physics.optics↗

arXiv2023

Two-color all-optical switching in Si-compatible epsilon-near-zero hyperbolic metamaterials

All-optical ultrafast switches enabled by artificial materials are considered at the forefront of the next generation of photonic communications and data processing. During the last two decades, the photonic applications, impact, and interest have tremendously increased in the framework of epsilon-near-zero (ENZ) photonics. Here, we experimentally propose a novel multilayered metamaterial utilizing Si-compatible titanium nitride and indium-tin-oxide materials. The device exhibits two effective ENZ wavelengths in the visible and near-infrared spectrum, with switching times down to a few hundred femtoseconds at the corresponding ENZ regions. This novel approach will bring ENZ metamaterials towards new hybrid integrated CMOS photonic circuit components for ultrafast all-optical terahertz modulation.

physics.optics↗

arXiv2022

Dual-Band Metal-Insulator-Metasurface Absorber

We explored a metal-insulator-metasurface structure exhibiting dual-band absorption in the visible and infrared regions with almost perfect absorbance. We demonstrated that the existence of the dual peak absorbance is due to the excitation of propagating surface plasmon and localized surface plasmon mode. We further utilized the excited degenerate propagating surface plasmon to enhance the fluorescence emission of an emitter located on top of the metasurface. This was accomplished by engineering a metasurface that excites a degenerate mode with resonance absorption bands close to the emission wavelength of fluorescent material. This condition helps to increase the rate of excitation and emission of an emitter by generating additional electron configurations when coupled to such metal-insulator-metasurface structures. This approach offers relevant potential in radiative engineering techniques.

physics.optics↗

arXiv2022

Hot electron dynamics and relaxation in hyperbolic meta-antennas

Conventional plasmonic nanoantennas enable scattering and absorption bands at the same wavelength region, making their utilization to full potential impossible for both features simultaneously. In this regard, hyperbolic meta-antennas (HMA) offer independent, tunable and separate scattering and absorption resonance bands at different spectral ranges. Here, we take advantage of these separated spectral bands in HMA to enhance and modify the hot electron-based phenomena. On the one hand, we observed the photoexcited emission of particle plasmons by hot carriers; on the other, we utilized ultrafast transient absorption spectroscopy to characterize the dynamics of hot electrons. Compared to corresponding plasmonic nanodisk antennas (NDA), extended plasmon-modulated photoluminescence (PM-PL) spectrum in HMA is achieved, attributing to their particular scattering spectra. Furthermore, the absorption band at longer wavelengths in HMA enhances the excitation efficiency of plasmon-induced hot electrons (HEs) in the near-infrared region (NIR) with an extended lifetime. It broadens the utilization of the visible/NIR range that can not be observed in conventional NDAs. Our results further show that such meta-antennas can generate plasmon-induced hot carriers on demand and provide insight into the optimization and engineering of the hot-carrier-assisted photochemistry.

physics.optics↗

arXiv2022

Epsilon-near-zero nanoparticles

In this work, we propose epsilon-near-zero (ENZ) nanoparticles formed of metal and dielectric bilayers and employ the effective medium approach for multilayered nanospheres to study their optical response. We obtained a passive tunable ENZ region by varying the radii of the proposed bilayer nanospheres, ranging from visible to near-IR. In addition, we present the absorption and scattering cross-section of ENZ nanoparticles using an open-source, transfer-matrix-based software (STRATIFY). %, and a commercial FDTD software (LUMERICAL). The proposed ENZ nanoparticle is envisioned to be experimentally realized using chemical synthesis techniques.

physics.optics↗

arXiv2021

All-optical switching via coherent control of plasmon resonances

A novel ultrafast all-optical switching mechanism is demonstrated theoretically and experimentally based on a plasmonic analog of the effect of \textit{Enhancement of Index of Refraction}(EIR) in quantum optics. In the quantum optical EIR the atomic systems are rendered by coherence and quantum interference to exhibit orders of magnitude higher index of refraction with vanishing or even negative absorption near their resonances. Similarly, in the plasmon-induced EIR, a probe signal can experience positive, zero or negative extinction while strongly interacting with a metallic nanorod in a metamolecule that is coherently excited by a control beam. The same mechanism is observed in the collective response of a square array of such metamolecules in the form of a metasurface to modulate the amplitude of a signal by coherent control of absorption from positive to negative values without implementing gain materials or nonlinear processes. This novel approach can be used for challenging the control of light by light at the extreme levels of space, time, and intensity by applying ultra-short pulses interacting with ultrafast surface plasmons or extremely low-intensity pulses at the level of single photon to a nanoscale single plasmonic metamolecule. The scheme also introduces an effective tool for improving the modulation strength of optical modulators and switches through the amplification of the input signal.

physics.optics↗

arXiv2021

Rolled-up Epsilon-near-zero Waveguide reservoir for long-range qubit entanglement

Preservation of the entangled state of a quantum system is relevant in quantum applications. However, the preservation of entangled states is constrained due to the energy dissipation of the quantum system arising from the environment. As a result, the design of the environment seen by quantum bits is relevant due to its relation to the final state of the quantum system. This work presents the concurrence measure of entanglement between two qubits coupled to a rolled-up epsilon-near-zero (ENZ) waveguide reservoir consisting of an alternating layer of metal and dielectric. Our numerical calculations demonstrate that the proposed rolled-up ENZ waveguide reservoir can preserve the entanglement of two qubits at the cutoff wavelength of the reservoir via enhanced energy transfer. This proposed rolled-up ENZ waveguide can serve as a unique reservoir for various quantum technologies such as quantum communication, quantum information processing, and single-photon generation. As a proof of concept, we also demonstrate that this novel structure can be fabricated using cost-effective self-rolling techniques.

quant-ph↗

arXiv2020

Metamaterials designed for enhanced ENZ properties]{Metamaterials designed for enhanced ENZ properties

We examine layered metamaterial structures consisting of alternating films of epsilon-near-zero (ENZ) and dielectric material, and show that for such a stack it is possible to enhance the refractive, reflective or absorptive properties of the ENZ. The proposed structure takes advantage of resonances from several interfaces, guided modes, and plasmon excitations to achieve the desired enhancement, and it is not an effective medium. We use analytical modeling tools to show how the different degrees of freedom affect the properties of the stack, and propose experimentally feasible parameters for such structures.

physics.optics↗

arXiv2020

Hot Electron Dynamics in Ultrafast Multilayer Epsilon-Near-Zero Metamaterial

Realizing remarkable tunability in optical properties without sacrificing speed is critical to obtain all optical ultrafast devices. In this work, we investigate the ultrafast temporal behavior of optically tunable epsilon-near-zero (ENZ) metamaterials, operating in the visible spectral range. To perform this the ultrafast dynamics of the hot electrons is acquired by femtosecond pump-probe spectroscopy and studied based on two-temperature model (2TM). We show that pumping with femtosecond pulses changes the effective permittivity of the metamaterial more than 400 %. This significant modulation is more pronounced in ENZ region and we confirm this by the 2TM. The realized ultrafast modulation in effective permittivity, along with the ultrashort relaxation time of 3.3 ps, opens a new avenue towards ultrafast photonic applications.

physics.optics↗