Low phase noise self-injection-locked diode laser with a high-Q fiber resonator: model and experiment.

Low phase noise and narrow linewidth lasers are achieved by implementing self-injection locking of a DFB laser on two distinct fiber Fabry-Perot resonators. More than 45 dB improvement of the laser phase or frequency noise is observed when the laser is locked. In both cases, a frequency noise floor below 1 Hz2/Hz is measured. The integrated linewidth of the best of the two lasers is computed to be in the range of 400 Hz and appears to be dominated by vibration noise close to the carrier. The results are then compared with a model based on the retro-injected power and the Q factors ratio between the DFB laser and the resonator. This straightforward model facilitates the extraction of the theoretical performance of these sources close to the carrier, a characteristic still hidden by vibration noise.

Low phase noise self-injection-locked diode laser with a high-Q fiber resonator: model and experiment: publisher's note.

This publisher's note contains a correction to Opt. Lett.49, 1933 (2024)10.1364/OL.514778.

Optimization of a fiber Fabry-Perot resonator for low-threshold modulation instability Kerr frequency combs.

We report a theoretical and experimental investigation of fiber Fabry-Perot cavities aimed at enhancing Kerr frequency comb generation. The modulation instability (MI) power threshold is derived from the linear stability analysis of a generalized Lugiato-Lefever equation. By combining this analysis with the concepts of power enhancement factor (PEF) and optimal coupling, we predict the ideal manufacturing parameters of fiber Fabry-Perot (FFP) cavities for the MI Kerr frequency comb generation. Our findings reveal a distinction between the optimal coupling for modulation instability and that of the cold cavity. Consequently, mirror reflectivity must be adjusted to suit the specific application. We verified the predictions of our theory by measuring the MI power threshold as a function of detuning for three different cavities.

"Extraordinary" modulation instability in optics and hydrodynamics.

The classical theory of modulation instability (MI) attributed to Bespalov-Talanov in optics and Benjamin-Feir for water waves is just a linear approximation of nonlinear effects and has limitations that have been corrected using the exact weakly nonlinear theory of wave propagation. We report results of experiments in both optics and hydrodynamics, which are in excellent agreement with nonlinear theory. These observations clearly demonstrate that MI has a wider band of unstable frequencies than predicted by the linear stability analysis. The range of areas where the nonlinear theory of MI can be applied is actually much larger than considered here.

Intra-envelope four-wave mixing in optical fibers.

We report experimentally on the phenomenon of intra-envelope four-wave mixing (FWM) in optical fibers. We demonstrate that the non-linear interaction between two pulse trains operating at the same repetition rate, but with slightly different carrier frequencies, leads by FWM to the generation of new components within their spectral envelops. The frequency differences between the FWM components and the pump lines are in the RF domain, making it almost impossible to observe the process using a standard optical spectrum analyzer. We show that using a third light source as a multi-line local oscillator makes the analysis of these new spectral components accessible. It enables to extract these FWM components from the spectra of the initial light sources by converting optical frequencies into radio frequencies. The experimental results are in excellent agreement with the numerical simulations.

Coexistence of gain-through-filtering and parametric instability in a fiber ring cavity.

We experimentally and numerically investigate the dynamics of a fiber ring cavity in which two different instability can be excited: gain-through-filtering and parametric instability. We demonstrate that they can be triggered individually or collectively depending on the two main control parameters offered by the cavity, namely the pump power and the cavity detuning. The experimental observations are in good agreement with numerical simulations.

Measurement of the nonlinear parametric instability gain in dispersion oscillating fibers.

We report the observation of the parametric gain band distortion in the nonlinear (depleted) regime of modulation instability in dispersion oscillating fibers. We show that the maximum gain is shifted even outside the boundaries of the linear parametric gain band. Experimental observations are confirmed by numerical simulations.

Impact of pump pulse duration on modulation instability Kerr frequency combs in fiber Fabry-Pérot resonators.

We report an experimental investigation on the impact of the pump pulse duration on the modulation instability process in fiber Fabry-Pérot resonators. We demonstrate that cross-phase modulation between the forward and the backward waves alters significantly the modulation instability process. By varying the pump pulse duration, we show the modification of the modulation instability threshold and frequency. These experimental observations are in excellent agreement with theoretical predictions.

Observation of modulation instability Kerr frequency combs in a fiber Fabry-Pérot resonator.

We report the experimental observation of a modulation instability induced Kerr frequency comb in an all fiber Fabry-Pérot resonator. We fully characterized, in intensity and phase, the frequency comb using a commercial 10 MHz resolution heterodyne detection system to reveal more than 125 comb teeth within each of the modulation instability sidelobes. Moreover, we were able to reveal the fine temporal structure in phase and intensity of the output Turing patterns. The experimental results are generally in good agreement with numerical simulations.

Experimental investigation of short pulse Raman amplification with backward pumping.

We report an experimental study on the backward-pumped Raman amplification of short pulses into a 20.3 km long optical fiber. We demonstrate that the gain and the pump saturation depend on the pulse duration. We also reveal that for short enough pulses, the amplification process remains linear, and very high peak powers, even larger than the Raman pump, are achievable. Numerical simulations reproduce the experimental results with excellent agreement.

Observation of four Fermi-Pasta-Ulam-Tsingou recurrences in an ultra-low-loss optical fiber.

We report the experimental observation of more than four Fermi-Pasta-Ulam-Tsingou recurrences in an optical fiber thanks to an ultra-low loss optical fiber and to an active loss compensation system. We observe both regular (in-phase) and symmetry-broken (phase-shifted) recurrences, triggered by the input phase. Experimental results are confirmed by numerical simulations.

Observation of doubly periodic solutions of the nonlinear Schrödinger equation in optical fibers.

We report the first, to the best of our knowledge, experimental observation of doubly periodic first-order solutions of the nonlinear Schrödinger equation in optical fibers. We confirm, experimentally, the existence of A-type and B-type solutions. This is done by using the initial conditions that consist of a strong pump and two weak sidebands. The evolution of power and phase of the main spectral components is recorded using heterodyne time-domain reflectometry. Another important part of our experiment is active loss compensation. We reach a good agreement between theory and experiment.

Quantitative approach to breather pair appearance in nonlinear modulational instability.

We investigate the generation of symmetric and asymmetric pairs of breathers from localized disturbances in the nonlinear stage of modulational instability governed by the nonlinear Schrödinger equation. An asymptotic matching approach allows us to predict with great accuracy how their emergence and evolution depend on the parameters of the perturbation. The same approach turns out to be applicable to other classes of perturbations which, due to their different decays in time, do not give rise to breathers.

Experimental characterization of recurrences and separatrix crossing in modulational instability.

We experimentally investigate two cycles of Fermi-Pasta-Ulam-Tsingou recurrence in optical fibers. Using three waves input, we characterize the distance of maximum compression points against the sideband amplitude and relative phase, outlining the qualitative changes of the dynamics due to separatrix crossing. Experimental results are in good agreement with numerical simulations and analytical predictions.

Full-field characterization of breather dynamics over the whole length of an optical fiber.

Full-field longitudinal characterization of picosecond pulse train formation in optical fibers is reported. The spatio-temporal evolution is obtained via fast and non-invasive distributed measurements in phase and intensity of the main spectral components of the pulses. To illustrate the performance of the setup, we report, to the best of our knowledge, the first time-domain experimental observation of the symmetry breaking of Fermi-Pasta-Ulam recurrences. The experimental results are in good agreement with numerical simulations.

Auto-modulation versus breathers in the nonlinear stage of modulational instability.

The nonlinear stage of modulational instability in optical fibers induced by a wide and easily accessible class of localized perturbations is studied using the nonlinear Schrödinger equation. It is shown that the development of associated spatio-temporal patterns is strongly affected by the shape and the parameters of the perturbation. Different scenarios are presented that involve an auto-modulation developing in a characteristic wedge, possibly coexisting with breathers which lie inside or outside the wedge.

Modulation instability in the weak dispersion regime of a dispersion modulated passive fiber-ring cavity.

We present a theoretical and experimental study of the modulation instability process in a dispersion oscillating passive fiber-ring resonator in the low dispersion region. Generally, the modulation of the dispersion along the cavity length is responsible for the emergence of a regime characterised by multiple parametric resonances (or Faraday instabilities). We show that, under weak dispersion conditions, a huge number of Faraday sidebands can grow under the influence of fourth order dispersion. We specifically designed a piecewise uniform fiber-ring cavity and report on experiments that confirm our theoretical predictions. We recorded the dynamics of this system revealing strong interactions between the different sidebands in agreement with numerical simulations.

Multi-resonant Lugiato-Lefever model.

We introduce a new model that extends the Lugiato-Lefever equation to the description of multiple resonances in Kerr optical cavities. It perfectly agrees quantitatively (in both stationary and dynamical regimes) with the exact Ikeda map, even when using a small number of resonances. Our model predicts the onset of complex phenomena such as the recently observed super-cavity solitons and the coexistence of multiple nonlinear states. It will be of crucial importance for the analytical understanding of new nonlinear phenomena in Kerr cavities when the intensities or nonlinearities are high enough to be able to excite more than one cavity resonance.

Fast and accurate modeling of nonlinear pulse propagation in graded-index multimode fibers.

We develop a model for the description of nonlinear pulse propagation in multimode optical fibers with a parabolic refractive index profile. It consists of a 1+1D generalized nonlinear Schrödinger equation with a periodic nonlinear coefficient, which can be solved in an extremely fast and efficient way. The model is able to quantitatively reproduce recently observed phenomena like geometric parametric instability and broadband dispersive wave emission. We envisage that our equation will represent a valuable tool for the study of spatiotemporal nonlinear dynamics in the growing field of multimode fiber optics.

Dispersive Dam-Break Flow of a Photon Fluid.

We investigate the temporal photonic analogue of the dam-break phenomenon for shallow water by exploiting a fiber optics setup. We clearly observe the decay of the steplike input (photonic dam) into a pair of oppositely propagating rarefaction wave and dispersive shock wave. Our results show evidence for a critical transition of the dispersive shock into a self-cavitating state. The detailed observation of the cavitating state dynamics allows for a fully quantitative test of the Whitham modulation theory applied to the universal defocusing nonlinear Schrödinger equation.