97 research outputs found
Instabilities, pattern formation, localized solutions, mode-locking and stochastic effects in nonlinear optical systems and beyond
No full textIn this thesis the results of scientific research about dierent nonlinear phenomena with particular emphasis to photonic systems are presented. Works about dissipation induced modulation instabilities with applications for signal amplification in nonlinear optics and mode-locking in lasers constitute the main part of the thesis. The dissipa-tive instabilities studied are of two kinds, parametric instabilities induced by a periodic variation of spectral losses and instabilities induced by non varying but spectrally asym-metric losses. Although the main achievements are theoretical successful collaboration with experimentalists are reported too. Other results presented in this thesis concern a new fundamental theory of active mode-locking in lasers having a more general validity than Haus’ one and hence useful for describing mode-locked lasers with a fast gain dynamics such as semiconductor or quantum cascade lasers; the prediction of the novel theoretical model have been successfully compared with experimental findings. Theo-retical studies are also presented about collective phenomena, such as synchronization and localization, in coupled excitable lasers with saturable absorber and localized so-lutions on the non-vanishing background of the two-dimensional nonlinear Schr¨odinger equation with periodic potential: the Bogoliubov-de Gennes bullets
Nonlinear Optical Effects and Their Applications: From Parametric Amplification in Coupled Waveguides to Modulation Instabilities in Fibre Ring Resonators
No full textThis thesis investigates nonlinear optical phenomena in two coupled waveguides and fibre ring resonators, with a particular emphasis on optical parametric amplification (OPA), modulation instability (MI), and optical frequency comb (OFC) generation. The work is divided into two parts. The first part investigates OPA in dual-core waveguide systems. By exploiting coupling-induced dispersion, we demonstrate flexible dispersion engineering that enables broadband gain, even in normally dispersive waveguides. Analytical and numerical models are developed to assess the impact of pump power and phase fluctuations on system stability. Additionally, we explore intermodal four-wave mixing in dual-core fibres, revealing how frequency-dependent coupling and power imbalance between the waveguides lead to asymmetric gain and signal–idler separation into distinct supermodes. These findings offer design strategies for efficient, robust, and tunable amplifiers in both fibre and integrated photonic platforms. The second part focuses on MI in nonlinear optical resonators. We study filter-induced MI in a fibre ring cavity with an intracavity amplifier, demonstrating enhanced MI and efficient energy transfer to spectral sidebands. In parametrically driven resonators with quadratic nonlinearity, we analyse filter-induced MI and show its role in enabling tunable OFC generation. Furthermore, we uncover a new dynamical regime in Kerr resonators: period-4 MI, characterised by temporal patterns repeating every four cavity round trips. Analytical gain expressions are derived and validated through numerical simulations. Together, these results advance the understanding and control of nonlinear wave dynamics in optical systems, providing novel mechanisms for amplification, frequency conversion, and complex temporal pattern formation, with implications for both fundamental science and practical photonic technologies
Optical frequency combs applications for synchronous transmission
No full textThis chapter focuses on exploring optical frequency comb technology for synchronised clock, radio-frequency (RF) carrier, and optical carrier distribution in radio access networks and optical access networks. Largescale clock distribution can be realised by detecting the entire optical frequency comb. The coherence between neighbouring comb lines results in low phase noise photo-mixing terms and the fundamental term can be used for clock distribution, which enables timing-sensitive application. In a radio access network, a similar concept can be applied, the higher order photo-mixing terms between comb lines can be naturally used as frequency synchronised low phase noise RF carriers, which facilitates wideband high-capacity wireless data transmission. On the other hand, in optical access network, optical frequency combs are used as optical frequency reference to lock multiple free-running lasers at user end, which enables dense frequency-division-multiplexing upstream communication with low cost and power consumption. More importantly, compared to conventional time-division–multiplexing, this approach ensures stable and low latency between user and cloud by allowing all users to transmit within dedicated bandwidth instead of time-sharing, which is critical for latency sensitive applications
The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nielsen, S. G., Bekaert, D., V., Magna, T., Mezger, K., & Auro, M. The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system. Geochemical Perspectives Letters, 15, (2020): 35-39, doi:10.7185/geochemlet.2032.The V isotope composition of martian meteorites reveals that Bulk Silicate Mars (BSM) is characterised by δ51V = −1.026 ± 0.029 ‰ (2 s.e.) and is thus ∼0.06 ‰ heavier than chondrites and ∼0.17 ‰ lighter than Bulk Silicate Earth (BSE). Based on the invariant V isotope compositions of all chondrite groups, the heavier V isotope compositions of BSE and BSM relative to chondrites are unlikely to originate from mass independent isotope effects or evaporation/condensation processes in the early Solar System. These differences are best accounted for by mass dependent fractionation during core formation. Assuming that bulk Earth and Mars both have a chondritic V isotopic compostion, mass balance considerations reveal V isotope fractionation factors Δ51Vcore-mantle as substantial as −0.6 ‰ for both planets. This suggests that V isotope systematics in terrestrial and extraterrestrial rocks potentially constitutes a powerful new tracer of planetary differentiation processes accross the Solar System.This work was funded by NASA Emerging Worlds grant NNX16AD36G to SGN. Samples were acquired with funds from the Helmholtz Association through the research alliance HA 203 “Planetary Evolution and Life” to KM. TM contributed through the Strategic Research Plan of the Czech Geological Survey (DKRVO/ČGS 2018-2022). KM acknowledges support through NCCR PlanetS supported by the Swiss National Science Foundation. We thank Jurek Blusztajn for support in the WHOI Plasma Facility
Collective dynamics of evanescently coupled excitable lasers with saturable absorber
No full textWe present a numerical study of the collective dynamics in a population of coupled excitable lasers with saturable absorber. At variance with previous studies where real-valued (lossy) coupling was considered, we focus here on the purely imaginary coupling (evanescent wave coupling). We show that evanescently coupled excitable lasers exhibit synchronization like the lossy coupled ones. Furthermore, we show that out-of-diagonal disorder-induced localization of excitability takes place for imaginary coupling too, but it can be frustrated by nonvanishing linewidth enhancement factor. Graphical abstract: [Figure not available: see fulltext.]
Array-enhanced synchronization and coherence resonance in coupled excitable semiconductor lasers
No full textSummary form only given. We present a numerical study of the nonlinear dynamics of a population of coupled semiconductor lasers with saturable absorber operating in the excitable regime [1] and described by a set of coupled Yamada models [2]. In particular we have investigated the self-organized synchronization process taking place spontaneously among the lasers, showing significant correlations between the spike-like pulses emitted by different lasers. Our findings demonstrate that synchronization in time and also in intensity occurs in a large region of the parameter space and for different population sizes and furthermore it is robust with respect to random distribution of the lasers' pump parameter which is linked to the excitability threshol
Theory of filter-induced modulation instability in driven passive optical resonators
No full textWe present the theory of modulation instability induced by spectrally dependent losses (optical filters) in passive driven nonlinear fiber ring resonators. Starting from an Ikeda map description of the propagation equation and boundary conditions, we derive a mean-field model - a generalized Lugiato-Lefever equation - which reproduces with great accuracy the predictions of the map. The effects on instability gain and comb generation of the different control parameters such as dispersion, cavity detuning, filter spectral position, and bandwidth are discussed
Optical Darboux Transformer
No full textThe Optical Darboux Transformer is introduced as a photonic device which
performs the Darboux transformation directly in the optical domain. This
enables two major advances for signal processing based on the nonlinear Fourier
transform: (i) the multiplexing of different solitonic waveforms corresponding
to arbitrary number of discrete eigenvalues of the Zakharov-Shabat system in
the optical domain, and (ii) the selective filtering of an arbitrary number of
individual solitons too. The Optical Darboux Transformer can be built using
existing commercially available photonic technology components and constitutes
a universal tool for signal processing, optical communications, optical rogue
waves generation, and waveform shaping and control in the nonlinear Fourier
domain
Optical Darboux Transformer
No full textThe optical Darboux transformer for solitons is introduced as a photonic device that performs the Darboux transformation directly in the optical domain. This enables two major advances for optical signal processing based on the nonlinear Fourier transform: (i) the multiplexing of solitonic waveforms corresponding to different discrete eigenvalues of the Zakharov-Shabat system, and (ii) the selective filtering of an arbitrary number of individual solitons too. The optical Darboux transformer can be built using existing commercially available photonic technology components and constitutes a universal tool for signal processing, optical communications, optical rogue waves generation, and waveform shaping and control in the nonlinear Fourier domain
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