Examinando por Materia "GUIAS DE ONDAS"
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- Artículo de Publicación PeriódicaAnti-stokes Raman gain enabled by modulation instability in mid-IR waveguides(2018-11) Sánchez, Alfredo D.; Fierens, Pablo Ignacio; Hernández, Santiago M.; Bonetti, Juan I.; Brambilla, Gilberto; Grosz, Diego"The inclusion of self-steepening in the linear stability analysis of modulation instability (MI) leads to a power cutoff above which the MI gain vanishes. Under these conditions, MI in mid-IR waveguides is shown to give rise to the usual double-sideband spectrum but with Raman-shaped sidelobes. This results from the energy transfer of a CW laser simultaneously to both stokes and anti-stokes bands in pseudo-parametric fashion. As such, the anti-stokes gain matches completely the stokes profile over the entire gain bandwidth. This remarkable behavior, not expected from an unexcited medium, is shown not to follow from a conventional four-wave mixing interaction between the pump and the Stokes band. We believe this observation to be of relevance in the area of Raman-based sensors, which, in several instances, rely on monitoring small power variations of the anti-stokes spectral component."
- Capítulo de libroEnhanced anti-stokes Raman gain in nonlinear waveguides(2019) Sánchez, Alfredo D.; Hernández, Santiago M.; Bonetti, Juan I.; Grosz, Diego; Fierens, Pablo Ignacio"We show that, under certain conditions, modulation instability in nonlinear waveguides gives rise to the usual double-sideband spectral structure, but with a Raman gain profile. This process is enabled by the energy transfer from a strong laser pump to both Stokes and antiStokes sidebands in a pseudo-parametric fashion. We believe this striking behavior to be of particular value in the area of Raman-based sensors which rely on sensitive measurements of the anti-Stokes component".
- Artículo de Publicación PeriódicaMeasuring self-steepening with the photon-conserving nonlinear Schrödinger equation(2020-08-15) Linale, N.; Fierens, Pablo Ignacio; Bonetti, Juan I.; Sánchez, Alfredo D.; Hernández, Santiago M.; Grosz, Diego"We propose an original, simple, and direct method to measure self-steepening (SS) in nonlinear waveguides. Our proposal is based on results derived from the recently introduced photon-conserving nonlinear Schrödinger equation (NLSE) and relies on the time shift experienced by soliton-like pulses due to SS upon propagation. In particular, a direct measurement of this time shift allows for a precise estimation of the SS parameter. Furthermore, we show that such an approach cannot be tackled by resorting to the NLSE. The proposed method is validated through numerical simulations, in excellent agreement with the analytical model, and results are presented for relevant spectral regions in the near infrared, the telecommunication band, and the mid infrared, and for realistic parameters of available laser sources and waveguides. Finally, we demonstrate the robustness of the proposed scheme against deviations expected in real-life experimental conditions, such as pulse shape, pulse peak power, pulsewidth, and/or higher-order linear and nonlinear dispersion."
- Artículo de Publicación PeriódicaModulation instability in waveguides with an arbitrary frequency-dependent nonlinear coefficient(2020-05) Linale, N.; Bonetti, Juan I.; Sánchez, Alfredo D.; Hernández, Santiago M.; Fierens, Pablo Ignacio; Grosz, Diego"In this Letter, we present, for the first time, to the best of our knowledge, the modulation instability (MI) gain spectrum of waveguides with an arbitrary frequency-dependent nonlinear coefficient ensuring strict energy and photon-number conservation of the parametric process. This is achieved by starting from a linear stability analysis of the recently introduced photon-conserving nonlinear Schrödinger equation. The derived MI gain is shown to predict some unique features, such as a nonzero gain extending beyond a zero-nonlinearity wavelength and a complex structure of the MI gain spectrum. Analytical results are shown to be in excellent agreement with numerical simulations."
- Artículo de Publicación PeriódicaNarrowband and ultra-wideband modulation instability in nonlinear metamaterial waveguides(2020-11-01) Linale, N.; Fierens, Pablo Ignacio; Hernández, Santiago M.; Bonetti, Juan I.; Grosz, Diego"Waveguides based on metamaterials may exhibit strongly frequency-dependent nonlinearities. In this work, we focus on the phenomenon of modulation instability in this type of waveguide, departing from a new modeling equation that ensures strict conservation of both the energy and photon number of the parametric process. In particular, we analyse the case of a waveguide with a linearly frequency-dependent nonlinear coefficient, revealing unique features such as narrowband and ultra-wideband gain spectra and the suppression of the power cutoff giving rise to an ever-growing MI gain. These markedly distinct regimes are enabled by self-steepening (SS) and manifest themselves depending upon the magnitude and sign of the SS parameter.We believe these findings to be most relevant in the context of mid-IR supercontinuum sources."
- Ponencia en CongresoNonlinear 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."
- Artículo de Publicación PeriódicaPhoton-conserving generalized nonlinear Schrödinger equation for frequency-dependent nonlinearities(2020) Bonetti, Juan I.; Linale, N.; Sánchez, Alfredo D.; Hernández, Santiago M.; Fierens, Pablo Ignacio; Grosz, Diego"Pulse propagation in nonlinear waveguides is most frequently modeled by resorting to the generalized nonlinear Schrödinger equation (GNLSE). In recent times, exciting new materials with peculiar nonlinear properties, such as negative nonlinear coefficients and a zero-nonlinearity wavelength, have been demonstrated. Unfortunately, the GNLSE may lead to unphysical results in these cases since, in general, it does not preserve the number of photons and, in the presence of a negative nonlinearity, predicts a blue shift due to Raman scattering. In this paper, we put forth a modified GNLSE that can be used to model the propagation in media with an arbitrary, even negative, nonlinear coefficient. This novel photon-conserving GNLSE (pcGNLSE) ensures preservation of the photon number and can be solved by the same tried and trusted numerical algorithms used for the standard GNLSE. Finally, we compare results for soliton dynamics in fibers with different nonlinear coefficients obtained with the pcGNLSE and the GNLSE."
- Artículo de Publicación PeriódicaSimple method for estimating the fractional Raman contribution(2019-02) Sánchez, Alfredo D.; Linale, N.; Bonetti, Juan I.; Hernández, Santiago M.; Fierens, Pablo Ignacio; Brambilla, Gilberto; Grosz, Diego"We propose a novel and simple method for estimating the fractional Raman contribution, fR, based on an analysis of a full model of modulation instability (MI) in waveguides. An analytical expression relating fR to the MI peak gain beyond the cutoff power is explicitly derived, allowing for an accurate estimation of fR from a single measurement of the Raman gain spectrum."
- Artículo de Publicación PeriódicaTunable Raman gain in mid-IR waveguides(2018) Sánchez, Alfredo D.; Hernández, Santiago M.; Bonetti, Juan I.; Fierens, Pablo Ignacio; Grosz, Diego"By means of theoretical analysis and numerical simulations, we show a tunable Raman gain which may find applications in a variety of fields, ranging from mid-IR fiber Raman lasers and supercontinuum generation to ultra-wideband slow-light Raman-based devices. In particular, by analyzing the interplay among Raman gain, dispersion, and self-steeping (SE) in a full model of modulation instability (MI) in waveguides, we show that there exists a range of pump powers where the gain spectrum is not only dominated by the Raman contribution, but also, most strikingly, it can be fine-tuned at will. We present analytical and numerical results, in excellent agreement, confirming this observation. "