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Examinando por Materia "OPTICA NO LINEAL"

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Characteristics and stability of soliton crystals in optical fibres for the purpose of optical frequency comb generation
(2017-06) Zajnulina, Marina; Böhm, M.; Bodenmüller, D.; Blow, K.; Chavez Boggioa, J. M.; Rieznik, Andrés; Roth, M. M.
"We study the properties of a soliton crystal, a bound state of several optical pulses that propagate with a fixed temporal separation through the optical fibres of the proposed approach for generation of optical frequency combs (OFC) for astronomical spectrograph calibration. This approach - also being suitable for subpicosecond pulse generation for other applications - consists of a conventional single-mode fibre and a suitably pumped Erbium-doped fibre. Two continuous-wave lasers are used as light source. The soliton crystal arises out of the initial deeply modulated laser field at low input powers; for higher input powers, it dissolves into free solitons. We study the soliton crystal build-up in the first fibre stage with respect to different fibre parameters (group-velocity dispersion, nonlinearity, and optical losses) and to the light source characteristics (laser frequency separation and intensity difference). We show that the soliton crystal can be described by two quantities, its fundamental frequency and the laser power-threshold at which the crystal dissolves into free solitons. The soliton crystal exhibits features of a linear and nonlinear optical pattern at the same time and is insensitive to the initial laser power fluctuations. We perform our studies using the numerical technique called Soliton Radiation Beat Analysis."
A direct method for the simultaneous estimation of self-steepening and the fractional Raman contribution in fiber optics
(2021-06) Linale, N.; Bonetti, Juan I.; Fierens, Pablo Ignacio; Hernández, Santiago M.; Grosz, Diego
"We propose an original, simple, and direct method for the simultaneous estimation of the selfsteepening parameter and the fractional Raman contribution in fiber optics. Our proposal is based on the dependence of the modulation instability gain on both parameters, as obtained from a linear stability analysis of the newly introduced photon-conserving generalized nonlinear Schrödinger equation (pcGNLSE), and requires only the CW or quasi-CW pumping of the waveguide under test and a few direct spectral measurements. Further, we demonstrate the feasibility of the estimation procedure by means of detailed simulations for typical waveguide parameters in relevant spectral ranges. Last, we discuss the range of applicability of the proposed method and compare its results, advantages, and disadvantages with a recently introduced method based on short-pulse dynamics."
A geometrical view of scalar modulation instability in optical fibers
(2017) Hernández, Santiago M.; Fierens, Pablo Ignacio; Sánchez, Alfredo D.; Grosz, Diego; Bonetti, Juan I.
"Full models of scalar modulation instability (MI) in optical fibers available in the literature usually involve complex formulations. In this paper, we present a novel approach to the analysis of MI in optical fibers by means of a simple geometrical description in the power versus frequency plane. This formulation allows us to relate the shape of the MI gain to any arbitrary dispersion profile of the medium, thus providing a simple insight. As a result, we derive a straightforward explanation of the nontrivial dependence of the cutoff power on high-order dispersion and explicitly derive the power that maximizes the gain. Our approach puts forth a tool to synthesize a desired MI gain with the potential application to a number of parametric-amplification and supercontinuum-generation devices whose initialstage dynamics rely upon MI."
Model for frequency-dependent nonlinear propagation in 2D-decorated nanowires
(2021-03) Linale, N.; Bonetti, Juan I.; Sánchez, Alfredo D.; Fierens, Pablo Ignacio; Grosz, Diego
"We show that 2D-decorated silicon nanowires exhibit a strong frequency dependence of the real (Kerr) and imaginary (two-photon absorption) nonlinear coefficients. In this setting, we demonstrate that the usual extension of the nonlinear Schr¨odinger equation used to model propagation in this type of waveguides is rendered inadequate. Hence, we introduce a new modeling framework to tackle the frequency dependence of the nonlinear coefficients in 2D-decorated." nanowires, and present an example of its application to the relevant case of supercontinuum generation in graphene- and graphene-oxide decorated silicon nanowires
Modified nonlinear Schrödinger equation for frequency-dependent nonlinear profiles of arbitrary sign
(2019) Bonetti, Juan I.; Linale, N.; Sánchez, Alfredo D.; Hernández, Santiago M.; Fierens, Pablo Ignacio; Grosz, Diego
In recent times, materials exhibiting frequency-dependent optical nonlinearities, such as nanoparticle-doped glasses and other metamaterials, have gathered significant interest. The simulation of the propagation of intense light pulses in such media, by means of the nonlinear Schrödinger equation (NLSE), poses the problem in that straightforward inclusion of a frequency-dependent nonlinearity may lead to unphysical results, namely, neither the energy nor the photon number is conserved in general. Inspired by a simple quantum-mechanical argument, we derive an energy- and photon-conserving NLSE (pcNLSE). Unlike others, our approach relies only on the knowledge of the frequency-dependent nonlinearity profile and a generalization of Miller’s rule for nonlinear susceptibility, enabling the simulation of nonlinear profiles of arbitrary frequency dependence and sign. Moreover, the proposed pcNLSE can be efficiently solved by the same numerical techniques commonly used to deal with the NLSE. Relevant simulation results supporting our theoretical approach are presented.
Nonlinear optics in waveguides doped with dimers of metal nanoparticles
(2020-09-14) Sánchez, Alfredo D.; Linale, N.; Grosz, Diego; Fierens, Pablo Ignacio
"We investigate the nonlinear response of waveguides doped with dimers of noble-metal nanoparticles using a simple effective model. Our results show a markedly distinctive response depending on the dimer gap."
Revisiting soliton dynamics in fiber optics under strict photon-number conservation
(2021) Linale, N.; Fierens, Pablo Ignacio; Grosz, Diego F.
"We revisit the complex interplay between the Raman-induced frequency shift (RIFS) and the effect of selfsteepening (SS) in the propagation of solitons, and in the framework of an equation that ensures strict conservation of the number of photons. The generalized nonlinear Schrödinger equation (GNLSE) is shown to severely fail in preserving the number of photons for sub-100-fs solitons, leading to a large overestimation of the frequency shift. Furthermore, when considering the case of a frequency-dependent nonlinear coefficient, the GNLSE also fails to provide a good estimation of the time shift experienced by the soliton. We tackle these shortcomings of the GNLSE by resorting to the recently introduced photon-conserving GNLSE (pcGNLSE) and study the interplay between the RIFS and selfsteepening. As a result, we make apparent the impact of higherorder nonlinearities on short-soliton propagation and propose an original and direct method for the estimation of the second-order nonlinear coefficient."
Revisiting soliton dynamics in fiber optics under strict photon-number conservation
(2021) Linale, N.; Fierens, Pablo Ignacio; Grosz, Diego
"We revisit the complex interplay between the Raman-induced frequency shift (RIFS) and the effect of self steepening (SS) in the propagation of solitons, and in the frame work of an equation that ensures strict conservation of the num ber of photons. The generalized nonlinear Schrodinger equation (GNLSE) is shown to severely fail in preserving the number of photons for sub-100-fs solitons, leading to a large overestimation of the frequency shift. Furthermore, when considering the case of a frequency-dependent nonlinear coefficient, the GNLSE also fails to provide a good estimation of the time shift experienced by the soliton. We tackle these shortcomings of the GNLSE by resorting to the recently introduced photon-conserving GNLSE (pcGNLSE) and study the interplay between the RIFS and self steepening. As a result, we make apparent the impact of higher order nonlinearities on short-soliton propagation and propose an original and direct method for the estimation of the second-order nonlinear coefficient."
Soliton solutions and self-steepening in the photon-conserving nonlinear Schrödinger equation
(2020-12-09) Hernández, Santiago M.; Bonetti, Juan I.; Linale, N.; Grosz, Diego; Fierens, Pablo Ignacio
"We have recently introduced a new modeling equation for the propagation of pulses in optical waveguides, the photon-conserving Nonlinear Schrödinger Equation (pcNLSE) which, unlike the canonical NLSE, guarantees strict conservation of both the energy and the number of photons for any arbitrary frequency-dependent nonlinearity. In this paper, we analyze some properties of this new equation in the familiar case where the nonlinear coefficient of the waveguide does not change sign. We show that the pcNLSE effectively adds a correction term to the NLSE proportional to the deviation of the self-steepening (SS) parameter from the photon-conserving condition in the NLSE. Furthermore, we describe the role of the self-steepening parameter in the context of the conservation of the number of photons and derive an analytical expression for the relation of the SS parameter with the time delay experienced by pulses upon propagation. Finally, we put forth soliton-like solutions of the pcNLSE that, unlike NLSE solitons, conserve the number of photons for any arbitrary SS parameter. "
Uncertainty relation for the optimization of optical-fiber transmission systems simulations
(2005) Tolisano, T.; Callegari, Fulvio A.; Grosz, Diego; Fragnito, Hugo L.; Rieznik, Andrés
“The mathematical inequality which in quantum mechanics gives rise to the uncertainty principle between two non commuting operators is used to develop a spatial step-size selection algorithm for the Split-Step Fourier Method (SSFM) for solving Generalized Non-Linear Schrödinger Equations (G-NLSEs). Numerical experiments are performed to analyze the efficiency of the method in modeling optical-fiber communications systems, showing its advantages relative to other algorithms.”

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