arXiv subjects

Regina Gumenyuk

Publications and source records attributed to Regina Gumenyuk.

12 recordsLinked to original sources

arXiv2026

Stability of Orbital Angular Momentum Modes in Conventional and Ring-Core Optical Fibers

Modal dynamics in multimode optical fibers are fundamentally governed by the inter- play between phase matching and intermodal coupling. In this work, we investigate the fundamental coupling mechanisms in ring-core fibers and identify a geometry-induced cou- pling suppression that significantly reduces coupling coefficients between orbital angular momentum modes compared to conventional multimode step-index fibers. This mechanism provides a clear physical explanation for the superior transmission stability of orbital angular momentum modes in ring-core fibers and establishes specific geometric constraints for the design of ring-core fiber-based mode converters.

physics.optics↗

arXiv2026

Noise-like pulse laser source with ultrabroadband tunability and coherence-limited sub-structure

High brightness and low coherence laser sources with wideband tunability are essential for many full-field imaging applications aiming for high contrast and speckle free performance. However, this combination of parameters is challenging to achieve. The current solutions focus on decreasing spatial coherence or generation of time-varying speckle patterns, while suppression of temporal coherence typically compromises brightness. Here we demonstrate a wideband pulsed laser source with low temporal coherence and the absence of phase correlation between pulses as an alternative approach with simultaneous time and frequency diversity. The full gain spectrum of a Tm doped fiber laser (1650 nm 2000 nm) is operated in a tunable noise like pulse regime, which by nature is composed of countless structured elementary events with uncorrelated phases randomly varying from bunch to bunch. The measured spectral widths range from 13.8 nm to 18.8 nm, while the average output power varies between 63.3 mW and 213 mW. Numerical simulations reveal that temporal coherence decreases significantly with increasing optical gain, dropping from near unity at low gain to approximately 0.2 at high gain. The startup dynamics of the noise like pulse laser are experimentally studied using the dispersive Fourier transformation (DFT) method. Based on single shot spectra and frequency resolved optical gating traces, the coherence properties of the laser are further analyzed by calculating the mutual coherence function and cross-spectral density. The noise like pulse laser exhibits a coherence time of approximately 100 fs and an average pulse burst duration of about 40 ps in the high-gain regime.

physics.optics↗

arXiv2025

Power-Scalable Generation of High-Order Optical Vortices Via Coherent Beam Combining

Structured light beams, such as optical vortices carrying orbital angular momentum, are essential for applications ranging from low-power optical communications to high-intensity laser-matter interactions. However, scaling their power and energy while preserving complex phase and spatial structures remains a fundamental challenge. In this work, we demonstrate coherent beam combining as a versatile and scalable method for generating high-power structured beams without limitations on topological charge or spatial structure, while maintaining exceptionally high modal purity. We experimentally implement coherent beam combining for optical vortex beams with topological charges l = 1, 5, and 8, achieving a combined average power of 100 W and a peak power of 100 kW, with combining efficiencies of 95.0%, 93.9%, and 91.2%, respectively. Off-axis digital holography confirms that the phase and intensity profiles of the combined beams retain high modal purity, even at high topological charges. These results establish coherent beam combining as an effective route to high modal purity structured light at high power levels, unlocking new opportunities for advanced photonics and high-intensity light-matter interaction studies.

physics.optics↗

arXiv2025

High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber

Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.

physics.optics↗

arXiv2025

Optical Vortex Dynamics in non-uniform twisted Ring-Core Fibers

In this work, we present a thorough analysis of the propagation of fiber modes carrying orbital angular momentum in twisted, tapered, ring-core optical fibers. In particular, by generalizing the usual coupled-mode approach to include the effect of twisting and tapering, we discuss how it is possible to achieve efficient power transfer between modes carrying different amounts of orbital angular momentum. Our simulation allows us to get a clear insight into the dynamics of vortex modes propagating through twisted ring core fibers.

physics.optics↗

arXiv2025

High-power monolithic narrow-linewidth 1.6 mJ/8 ns fiber laser system based on all-glass spun tapered double-clad fiber amplifier

High-energy, narrow-linewidth nanosecond pulses are highly demanding for many applications that require high temporal and spatial coherence. However, the amplification of narrow-linewidth pulses is primarily limited by stimulated Brillouin scattering, which causes pulse instabilities, back-reflected pulses, and catastrophic damage effects on optical components. In this work, we present a 1.6 mJ narrow-linewidth nanosecond pulsed fiber laser system based on all-glass spun tapered double-clad fibers without employing any mitigating technique for the stimulated Brillouin scattering effect. The system delivers pulses with an 8 ns duration at a 100 kHz repetition rate, over 97.5% degree of polarization, a beam quality factor of M2 = 1.3, a spectral linewidth of 53.8 MHz, a 160 W average power, and 188 kW peak power with a slope efficiency of 97.6%. The degree of spatial coherence of the amplified signal was measured to be 0.94. Our results are highly valued in applications requiring high-energy, high-coherence pulses with spectral, spatial, and polarization characteristics in a compact system.

physics.optics↗

arXiv2024

Versatile High-Power Monolithic All-Glass Fiber Amplifier for Pulsed Signals with a Wide Range of Repetition Rates

This study presents a compact, high-power monolithic all-glass spun tapered double-clad fiber amplifier for single-stage amplification of narrow linewidth picosecond pulsed signals from a few tens of mW to several hundred Watts of average power and MW level of peak power, covering a wide range of repetition rates. The absence of free-space elements in the amplifier module enhances its overall reliability by omitting the dependency on the pump alignment and internal back reflections. The versatile all-glass amplifier module delivers 50 ps pulses with over 2 MW peak power at 1 MHz, 50 ps pulses with over 625 W average power at 20 MHz, and 20 ps pulses with over 645 W average power at 1 GHz, all exhibiting excellent spectral, spatial, and polarization characteristics. This monolithic all-glass ultra-large mode area fiber amplifier is verified as a robust solution for direct amplification of short pulses attaining high peak/average power laser systems with excellent spectral, spatial, and polarization characteristics.

physics.optics↗

arXiv2023

Coherent beam combining of optical vortices

We experimentally demonstrate the power scaling of optical vortices by the coherent beam combining, encompassing topological charges ranging from l=1 to l=5 realized on the basis of a Yb-doped fiber short-pulsed laser system. The combining efficiency varies from 83.2 to 96.9% depending on the topological charge and beam pattern quality generated by the spatial light modulators. These results open a pathway to high-intensity optical vortices with enormous potential applications in science and industry by utilizing advances in light-matter interactions.

physics.optics↗

arXiv2023

1720nm-1800nm tunable chirped pulse amplification based on thulium-doped fiber

Chirped pulse amplification (CPA) has been adopted as a commonly used methodology to obtain powerful ultrashort laser pulses since its first demonstration. However, wavelength-tunable CPA systems are rarely reported. Wavelength-tunable ultrashort and intense laser pulses are desired in various fields like nonlinear spectroscopy and optical parametric amplification. In this work, we report a 1720 nm -1800 nm tunable CPA system based on a single-mode Tm-doped fiber covering the middle wavelength band of the third biological window. The tunable CPA system delivers ultrashort pulses varied between ~300 to 500 fs depending on the central wavelength emission at the fixed repetition rate of 22.7 MHz. The maximum average power ranges from 126 mW at 1720 nm to 294 mW at 1800 nm following the gain shape of Tm-doped fiber. Considering the specific wave-length range, this tunable CPA system is highly desired for biomedical imaging, sensing and parametric amplifiers for mid-infrared light generation.

physics.optics↗

arXiv2023

Predicting mode-locked fiber laser output using feed-forward neural network

With a great ability to solve regression problems, the artificial neural network has become a powerful tool to facilitate advancing ultrafast laser research. In this contribution, we demonstrate the capability of a feed-forward neural network (FNN) to predict the output parameters of a mode-locked fiber laser, which mutually depend on multiple intracavity parameters, with high speed and accuracy. A direct mapping between cavity parameters and laser output is realized through the FNN-trained models, bypassing tedious iterative numerical simulation as a common approach to get a converged solution for a laser cavity. We show that the laser output spectrum and temporal pulse profiles can be accurately predicted with the normalized root mean square error (NRMSE) of less than 0.032 within only a 5 ms time frame for scenarios inside and outside the training data. We investigate the influence of FNN configuration on prediction performance. Both gain and spectral filter parameters are explored to test the prediction capability of the trained FNN models at high speed. Straightforward and fast prediction of the laser output performance for varying laser intracavity parameters paves the way to intelligent short-pulsed lasers with inversed design or autonomous operation maintenance.

physics.optics↗

arXiv2023

A double-clad ytterbium-doped tapered fiber with circular birefringence as a gain medium for structured light

Amplifying radially and azimuthally polarized beams is a significant challenge due to the instability of the complex beam shape and polarization in inhomogeneous environment. In this Letter, we demonstrated experimentally an efficient approach to directly amplify cylindrical-vector beams with axially symmetric polarization and doughnut-shaped intensity profile in a picosecond MOPA system based on a double-clad ytterbium-doped tapered fiber. To prevent polarization and beam shape distortion during amplification, for the first time to the best of our knowledge, we proposed using the spun architecture of the tapered fiber. In contrast to an isotropic fiber architecture, a spun configuration possessing nearly-circular polarization eigenstates supports stable wavefront propagation. Applying this technique, we amplified the cylindrical-vector beam up to 22 W of average power with 10 ps pulses at a central wavelength of 1030 nm and a repetition rate of 15 MHz, maintaining both mode and polarization stability.

physics.optics↗

arXiv2021

Talbot self-imaging and two-photon interference in ring-core fibers

Wave propagation on the surface of cylinders exhibits interferometric self imaging, much like the Talbot effect in the near-field diffraction at periodic gratings. We report the experimental observation of the cylindrical Talbot carpet in weakly-guiding ring-core fibers for classical light fields. We further show that the ring-core fiber acts as a high-order optical beamsplitter for single photons, whose output can be controlled by the relative phase between the input light fields. By also demonstrating high-quality two-photon interference between indistinguishable photons sent into the ring-core fiber, our findings open the door to applications in optical telecommunications as a compact beam multiplexer as well as in quantum information processing tasks as a scalable realization of a linear optical network.

physics.optics↗