arXiv subjects

Abdullah Alabbadi

Publications and source records attributed to Abdullah Alabbadi.

9 recordsLinked to original sources

arXiv2026

Demonstration of a Single-Laser-Diode-Pumped Ti:Sapphire Astrocomb on the Southern African Large Telescope

Astrocombs -- broadband lasers comprising thousands of narrow, uniformly spaced and atomically-referenced spectral lines -- offer gold-standard wavelength calibration for ground-based optical telescopes, with the potential for the cm/s precision needed for radial-velocity follow-ups of exoplanet candidates from photometric space missions like Kepler, TESS and PLATO. Current astrocombs, particularly those operating in the visible spectrum, are complex and expensive, putting them beyond the reach of many observatories. Here, we present the first on-instrument demonstration of a new and simple astrocomb concept, providing calibration light across nearly the entire 550 nm to 890 nm red channel of the Southern African Large Telescope's High Resolution Spectrograph (SALT-HRS). An octave-spanning supercontinuum generated in a silicon nitride waveguide by a GPS-referenced diode-pumped Ti:sapphire laser is filtered to 21 GHz before fibre delivery to the spectrograph. Using the astrocomb, we obtain the wavelength solution for one order of SALT-HRS and the wavelength-dependent line-spread function of the instrument. With potential for further extension into the blue spectral region, this uniquely simple architecture brings visible-to-infrared astrocomb technology within the reach of a wider range of astronomical observatories.

astro-ph.IM↗

arXiv2026

Cavity-enhanced superconducting response in an underdoped cuprate

Superconductors carry electrical current without resistance when paired electrons condense into a coherent macroscopic quantum state. In underdoped cuprates, evidence suggests that pairing-related correlations and superconducting fluctuations can survive above the temperature at which global coherence is lost, pointing to phase fluctuations as a key limitation on superconductivity in this regime. Motivated by recent demonstrations of cavity-modified collective states in quantum materials, we investigate whether superconducting coherence can be stabilized by engineering the electromagnetic environment of the superconductor. We study an underdoped YBa$_2$Cu$_3$O$_{7-\delta}$ thin film in a tunable terahertz cavity formed with a semi-transparent gold mirror. From temperature-dependent terahertz transmission measurements, we find that the cavity enhances the superconducting response below the critical temperature, with an increase of the inferred superfluid weight. The effect becomes more pronounced at smaller cavity lengths and is accompanied by an upward shift of the superconducting onset temperature. Calculations based on a cavity-coupled model for phase-fluctuating superconductors capture these trends and support an interpretation in terms of cavity-enhanced phase stiffness. These results showcase the potential of cavity engineering for designing emergent functionalities in correlated systems.

cond-mat.supr-con↗

arXiv2026

Magnon-mediated microwave to optical time dynamics

Optomagnonic modulation techniques are an emerging platform for information transfer from the microwave to the optical domain. However, these techniques focus largely on the spectral domain of the transduced signal. Given the potential of the field to bridge the gap between microwave and optical signals, analyzing and studying the interactions real-time in temporal domain becomes equally essential. In this work, we exploit the optomagnonic modulation in a YIG microsphere to demonstrate and study microwave to optical real-time dynamic transfer on a time scale comparable to the decay of magnons. We inductively excite magnons in the microwave domain and use magnon-based Brillouin light scattering to transduce the signature of excited magnonic waveforms to the optical domain. The square type modulation of the magnons is retrieved in the corresponding optical sidebands. Our work enables real-time measurement of the magnonic dynamics and therefore direct access to lifetime measurements of the magnonic mode. Providing insight into the temporal dynamics of magnons, this work can open up new promising research directions such as in magnon coupled superconducting qubits or magnon-based Brillouin memory.

physics.optics↗

arXiv2026

Symmetry-Broken Cavity Solitons and Collective Polarization Conformity in Fabry-Perot Kerr Resonators

We report on the experimental generation of polarization symmetry-broken cavity solitons (CSs) in a passive, fiber-based, coherently-driven, Fabry-Perot (FP) Kerr resonator. Polarization resolved measurements reveal the spontaneous transition of initially symmetric CSs into asymmetrical vectorial states, triggered by a cross-phase modulation-induced polarization bifurcation. Most notably, due to counter-propagation of light occurring in FP resonators, we unveil a collective polarization conformity effect, whereby multiple CSs circulating in the cavity converge to the same asymmetric polarization state once their number exceeds a certain threshold. These results demonstrate that Fabry-Perot resonators support novel collective soliton dynamics that are absent in ring architectures.

physics.optics↗

arXiv2026

Visible octave frequency combs in silicon nitride nanophotonic waveguides driven by Ti:sapphire lasers

Nonlinear nanophotonic waveguides have opened a route to compact frequency combs for precision metrology, spectroscopy and astronomy, yet broadband comb access to the visible remains challenging on CMOS-compatible platforms. Silicon nitride is widely accessible and low loss into the visible, but most demonstrations rely on telecom pumping and thick stress-managed films, where the large spectral gap to the visible dispersive wave raises the soliton order and power required for efficient conversion. Here we show that pumping closer to the visible provides a complementary route. Starting from crack-free 400 nm SiN films, we implement dispersion-engineering with air-clad nanophotonic waveguides whose enhanced geometric dispersion opens an anomalous-dispersion window across the Ti-sapphire tuning range. Femtosecond Ti-sapphire pulses then drive octave-spanning combs from the visible to the near-infrared, with the visible edge and overall bandwidth lithographically tuned by the waveguide width at pulse energies of only tens of picojoules. The air-clad geometry also produces strong polarization-dependent dispersion, enabling switching between all-normal and soliton-dominated broadening in the same device, and support octave-spanning combs at 1 GHz repetition rates directly driven by a compact diode-pumped Ti-sapphire oscillator. These results position air-clad SiN nanophotonic waveguides as an efficient interface between emerging short-wavelength integrated gain platforms and fully integrated visible frequency-comb engines.

physics.optics↗

arXiv2025

Simplified Aluminum Nitride Processing for Low-Loss Integrated Photonics and Nonlinear Optics

Aluminum nitride (AlN) is an extremely promising material for integrated photonics because of the combination of strong \c{hi}2 and \c{hi}3 nonlinearities. However, the intrinsic hardness of the material and charging effects during electron beam lithography make AlN nanofabrication a challenging process. Conventional approaches often require multiple hard masks and a metal mask to fabricate nanostructures. In this letter, we report a novel, simple method to fabricate AlN microresonators by using a single layer of silicon nitride mask combined with a thin conductive polymer layer. The conductive layer can be conveniently removed during developing without requiring an additional etching step. We achieve high intrinsic quality (Q) factors up to one million in AlN microresonators and demonstrate several nonlinear phenomena within our devices, including frequency comb generation, Raman lasing, third harmonic generation and supercontinuum generation.

physics.optics↗

arXiv2025

Inverse-Designed Silicon Nitride Nanophotonics

Silicon nitride photonics has enabled integration of a variety of components for applications in linear and nonlinear optics, including telecommunications, optical clocks, astrocombs, bio-sensing, and LiDAR. With the advent of inverse design - where desired device performance is specified and closely achieved through iterative, gradient-based optimization - and the increasing availability of silicon nitride photonics via foundries, it is now feasible to expand the photonic design library beyond the limits of traditional approaches and unlock new functionalities. In this work, we present inverse-designed photonics on a silicon nitride platform and demonstrate both the design capabilities and experimental validation of manipulating light in wavelength and spatial mode dimensions to high-Q resonators with controllable wavelength range and dispersion. Furthermore, we use these inverse-designed structures to form optical cavities that hold promise for on-chip nonlinear and quantum optics experiments.

physics.optics↗

arXiv2024

Linear and Nonlinear Coupling of Light in Twin-Resonators with Kerr Nonlinearity

Nonlinear effects in microresonators are efficient building blocks for all-optical computing and telecom systems. With the latest advances in microfabrication, coupled microresonators are used in a rapidly growing number of applications. In this work, we investigate the coupling between twin-resonators in the presence of Kerr-nonlinearity. We use an experimental setup with controllable coupling between two high-Q resonators and discuss the effects caused by the simultaneous presence of linear and non-linear coupling between the optical fields. Linear-coupling-induced mode splitting is observed at low input powers, with the controllable coupling leading to a tunable mode splitting. At high input powers, the hybridized resonances show spontaneous symmetry breaking (SSB) effects, in which the optical power is unevenly distributed between the resonators. Our experimental results are supported by a detailed theoretical model of nonlinear twin-resonators. With the recent interest in coupled resonator systems for neuromorphic computing, quantum systems, and optical frequency comb generation, our work provides important insights into the behavior of these systems at high circulating powers.

physics.optics↗

arXiv2024

Controlled light distribution with coupled microresonator chains via Kerr symmetry breaking

Within optical microresonators, the Kerr interaction of photons can lead to symmetry breaking of optical modes. In a ring resonator, this leads to the interesting effect that light preferably circulates in one direction or in one polarization state. Applications of this effect range from chip-integrated optical diodes to nonlinear polarization controllers and optical gyroscopes. In this work, we study Kerr-nonlinearity-induced symmetry breaking of light states in coupled resonator optical waveguides (CROWs). We discover a new type of controllable symmetry breaking that leads to emerging patterns of dark and bright resonators within the chains. Beyond stationary symmetry broken states, we observe periodic oscillations, switching and chaotic fluctuations of circulating powers in the resonators. Our findings are of interest for controlled multiplexing of light in photonic integrated circuits, neuromorphic computing, topological photonics and soliton frequency combs in coupled resonators.

physics.optics↗