Temporal reflection and refraction in the presence of a zero-nonlinearity wavelength.

We put forth a theoretical model allowing for the analysis of short-pulse interactions at time boundaries in waveguides with arbitrary frequency-dependent nonlinear profiles, in particular those exhibiting a zero-nonlinearity wavelength. Moreover, this is performed within a photon-conserving framework, thus circumventing use of the nonlinear Schrödinger equation in such scenarios, as it may lead to unphysical outcomes. Results indicate that the waveguide zero-nonlinearity wavelength has a great influence on said interactions, specifically by defining spectral bands where either signal total reflection or signal transmission can occur. We believe these findings to be of relevance in the area of all-optical switching schemes based on the interaction of short pulses in nonlinear media.

Measuring self-steepening with the photon-conserving nonlinear Schrödinger equation.

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.

Modulation instability in waveguides with an arbitrary frequency-dependent nonlinear coefficient.

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.

Simple method for estimating the fractional Raman contribution.

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.

Clogging Transition of Vibration-Driven Vehicles Passing through Constrictions.

We report experimental results on the competitive passage of elongated self-propelled vehicles rushing through a constriction. For the chosen experimental conditions, we observe the emergence of intermittencies similar to those reported previously for active matter passing through narrow doors. Noteworthy, we find that, when the number of individuals crowding in front of the bottleneck increases, there is a transition from an unclogged to a clogged state characterized by a lack of convergence of the mean clog duration as the measuring time increases. It is demonstrated that this transition-which was reported previously only for externally vibrated systems such as colloids or granulars-appears also for self-propelled agents. This suggests that the transition should also occur for the flow through constrictions of living agents (e.g., humans and sheep), an issue that has been elusive so far in experiments due to safety risks.

Numerical and experimental study of stochastic resistive switching.

In this paper we study the role of noise in the context of resistive switching phenomena by means of experiments and numerical simulations. Experiments are conducted on a manganite sample. We show that the addition of external Gaussian noise to a small amplitude driving signal yields a contrast ratio between low- and high-resistance states, comparable to that obtained by the application of a large amplitude noiseless signal. Furthermore, excellent agreement between numerical simulation and measurement allows us to study resistive switching under varying input conditions and, thus, properly characterize the beneficial role of noise. We believe these results might be of relevance in the area of memory devices where the large scale of electronic integration renders the presence of noise unavoidable.