On spatial beam self-cleaning from the perspective of optical wave thermalization in multimode graded-index fibers

Ferraro, Mario; Mangini, Fabio; Zitelli, Mario; Wabnitz, Stefan

doi:10.1080/23746149.2023.2228018

Cited by 10 publications

(2 citation statements)

References 61 publications

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“…For this reason, SCF turned out to be extremely powerful in fundamental science. For instance, phase-only SLM devices were used for the MD of MM RFL beams, as well as for investigating the so-called Kerr beam self-cleaning effect [9][10][11], and validating its description in the framework of optical thermodynamics [12].…”

Section: Introductionmentioning

confidence: 99%

Accuracy of Holographic Real-Time Mode Decomposition Methods Used for Multimode Fiber Laser Emission

Kharenko,

Revyakin,

Gervaziev

et al. 2023

Photonics

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Mode decomposition is a powerful tool for analyzing the modal content of optical multimode radiation. There are several basic principles on which this tool can be implemented, including near-field intensity analysis, machine learning, and spatial correlation filtering (SCF). The latter is meant to be applied to a spatial light modulator and allows one to obtain information on the mode amplitudes and phases of temporally stable beams by only analyzing experimental data. As a matter of fact, techniques based on SCF have already been successfully used in several studies, e.g., for investigating the Kerr beam self-cleaning effect and determining the modal content of Raman fiber lasers. Still, such techniques have a major drawback, i.e., they require acquisition times as long as several minutes, thus being unfit for the investigation of fast mode distribution dynamics. In this paper, we numerically study three types of digital holograms, which permits us to determine, at the same time, the parameters of a set of modes of multimode beams. Because all modes are simultaneously characterized, the processing speed of these real-time mode decomposition methods in experimental realizations will be limited only by the acquisition rate of imaging devices, e.g., state-of-the-art CCD camera performance may provide decomposing rates above 1 kHz. Here, we compare the accuracy of conjugate symmetric extension (CSE), double-phase holograms (DPH), and phase correlation filtering (PCF) methods in retrieving the mode amplitudes of optical beams composed of either three, six, or ten modes. In order to provide a statistical analysis of the outcomes of these three methods, we propose a novel algorithm for the effective enumeration of mode parameters, which covers all possible beam modal compositions. Our results show that the best accuracy is achieved when the amplitude-phase mode distribution associated with multiple frequency PCF techniques is encoded by Jacobi–Anger expansion.

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Section: Introductionmentioning

confidence: 99%

Accuracy of Holographic Real-Time Mode Decomposition Methods Used for Multimode Fiber Laser Emission

Kharenko,

Revyakin,

Gervaziev

et al. 2023

Photonics

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“…An interesting approach based on the statistical mechanics of a photon gas permits a simplified description, based on a few thermodynamic parameters that obey an equation of state. Within this approach, BSC represents a state of thermal equilibrium, that is obtained from spatial four-wave-mixinginduced energy exchanges between modes, which play the role of particle collisions [8], [9], [10], [11]. The thermodynamic description is grounded on the existence of basic conservation laws, involving optical power and momentum (both linear and angular) of the beam.…”

mentioning

confidence: 99%

Spatial Beam Cleaning in Multimode GRIN Fibers: Polarization Effects

Ferraro,

Mangini,

Zitelli

et al. 2023

IEEE Photonics J.

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The beam self-cleaning effect in graded-index multimode optical fibers has several interesting potential applications, such as high-resolution nonlinear imaging and mode-locked fiber lasers. Most experimental and theoretical studies of beam selfcleaning have neglected the role of the state of polarization of light. In this work, we fill this gap by reporting extensive experimental investigations of beam self-cleaning in multimode fibers, for beams with different input states of light polarization. We found that the state of polarization undergoes a complex evolution, which may lead either to full conservation of the input state of polarization, or nearly complete light depolarization at the fiber output. The former outcome is compelling for applications based on the beam self-cleaning effect, such as multimode mode-locked fiber lasers for micromachining, and multimode devices for microscopy and endoscopy. The latter result, instead, permits to test the limits of validity of current purely scalar theoretical approaches for describing nonlinear propagation in multimode fibers.

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Pattern formation by turbulent cascades

de Wit,

Fruchart,

Khain

et al. 2024

Nature

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Fully developed turbulence is a universal and scale-invariant chaotic state characterized by an energy cascade from large to small scales at which the cascade is eventually arrested by dissipation1–6. Here we show how to harness these seemingly structureless turbulent cascades to generate patterns. Pattern formation entails a process of wavelength selection, which can usually be traced to the linear instability of a homogeneous state7. By contrast, the mechanism we propose here is fully nonlinear. It is triggered by the non-dissipative arrest of turbulent cascades: energy piles up at an intermediate scale, which is neither the system size nor the smallest scales at which energy is usually dissipated. Using a combination of theory and large-scale simulations, we show that the tunable wavelength of these cascade-induced patterns can be set by a non-dissipative transport coefficient called odd viscosity, ubiquitous in chiral fluids ranging from bioactive to quantum systems8–12. Odd viscosity, which acts as a scale-dependent Coriolis-like force, leads to a two-dimensionalization of the flow at small scales, in contrast with rotating fluids in which a two-dimensionalization occurs at large scales4. Apart from odd viscosity fluids, we discuss how cascade-induced patterns can arise in natural systems, including atmospheric flows13–19, stellar plasma such as the solar wind20–22, or the pulverization and coagulation of objects or droplets in which mass rather than energy cascades23–25.

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On spatial beam self-cleaning from the perspective of optical wave thermalization in multimode graded-index fibers

Cited by 10 publications

References 61 publications

Accuracy of Holographic Real-Time Mode Decomposition Methods Used for Multimode Fiber Laser Emission

Accuracy of Holographic Real-Time Mode Decomposition Methods Used for Multimode Fiber Laser Emission

Spatial Beam Cleaning in Multimode GRIN Fibers: Polarization Effects

Pattern formation by turbulent cascades

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