arXiv subjects

Matteo Conforti

Publications and source records attributed to Matteo Conforti.

At least 19 recordsLinked to original sources

arXiv2026

Three-core fiber Fabry-Perot resonator for dual-frequency comb generation

Fiber Fabry-Perot resonators have proven their ability to generate broad and stable optical frequency combs, and are ideal devices for fiber systems as they are high-Q, compact, and easily integrated with FC/PC connectors. Here, we present an advanced fiber Fabry-Perot resonator designed for multi-frequency comb generation and spatial multiplexing. The resonator is fabricated using a three-core optical fiber and is able to generate two mutually coherent frequency combs while being locked to a driving laser. Multiplexing of the combs is achieved with a fan-in/fan-out system, enabling a fully fiber-based experimental setup. The generated combs, induced by cavity solitons, feature a 1.27 GHz repetition rate and a bandwidth above 40 nm. A slight difference in the group index of each core leads to a 112 kHz repetition rate offset between the combs, enabling dual-comb spectroscopy proof-of-concept measurement of a 0.1 nm absorption band.

physics.optics↗

arXiv2026

Self-organization of cavity solitons in Brillouin-Kerr ring resonators

We report on the interaction between stimulated Brillouin scattering and temporal cavity solitons in doubly resonant ring resonators. Our experiments are performed in coherently driven passive optical-fibre resonators. We demonstrate that the interplay between four-wave mixing and cascade Brillouin lasing spontaneously generates patterns of CSs on a temporal grid at twice the Brillouin-shift. These patterns are shown to be highly stable owing to a long-range locking mechanism mediated by the acoustic oscillation generated by the solitons. We introduce a unified mean-field model of the cavity to describe the dynamics between the coupled forward and backward waves under coherent driving. This model reproduces very well the experiments and explains the paracrystalline structures of the soliton pattern. Our findings significantly advance the understanding of hybrid Brillouin-Kerr optical frequency combs.

physics.optics↗

arXiv2025

Roadmap: Emerging Platforms and Applications of Optical Frequency Combs and Dissipative Solitons

The discovery of optical frequency combs (OFCs) has revolutionised science and technology by bridging electronics and photonics, driving major advances in precision measurements, atomic clocks, spectroscopy, telecommunications, and astronomy. However, current OFC systems still require further development to enable broader adoption in fields such as communication, aerospace, defence, and healthcare. There is a growing need for compact, portable OFCs that deliver high output power, robust self-referencing, and application-specific spectral coverage. On the conceptual side, progress toward such systems is hindered by an incomplete understanding of the fundamental principles governing OFC generation in emerging devices and materials, as well as evolving insights into the interplay between soliton and mode-locking effects. This roadmap presents the vision of a diverse group of academic and industry researchers and educators from Europe, along with their collaborators, on the current status and future directions of OFC science. It highlights a multidisciplinary approach that integrates novel physics, engineering innovation, and advanced researcher training. Topics include advances in soliton science as it relates to OFCs, the extension of OFC spectra into the visible and mid-infrared ranges, metrology applications and noise performance of integrated OFC sources, new fibre-based OFC modules, OFC lasers and OFC applications in astronomy.

physics.optics↗

arXiv2025

Laser self-injection locking to fiber Fabry-Perot resonator for frequency comb generation

This study demonstrates that self-injection locking (SIL) of a distributed feedback (DFB) laser to a high-Q fiber Fabry Perot (FFP) resonator, fabricated with highly nonlinear fiber, allows optical frequency combs (OFC) generation with a laser power as low as 100 mW. More precisely, cavity soliton (CS) regime has been observed in this configuration, along with other types of combs. The laser stabilization using SIL is described. Then the system's behavior is analyzed through modeling the laser's dynamics and comparing the model results to experimental tuning curve measurements. Our findings highlight the critical role of the initial phase of the fiber link between laser and FFP in determining the stability and effectiveness of the locking process. We explore the dynamics of the nonlinear SIL process while varying the laser current, revealing the transition from modulation instability to chaotic comb states, and eventually to soliton formation as the system moves from an effective blue-detuned to an effective red-detuned regime. Notably, the inclusion of self-phase modulation (SPM) in the SIL model predicts accessibility of the narrow soliton existence range. These results highlight the potential of SIL in FFP resonators for low-power, stable OFC generation, offering a promising path forward for practical applications.

physics.optics↗

arXiv2025

Experimental observation of self-frequency-shifting Raman quasi-solitons in a fiber Fabry-Perot resonator

We report the generation of self-frequency-shifting Raman quasi-solitons in a pulse-pumped high-Q fiber Fabry-Perot resonator in the weak normal dispersion regime. They are induced by modulation instability mediated by fourth-order dispersion in a regime where the Raman gain overwhelms the cavity losses. The resulting spectrum, spanning over 50 THz, is reminiscent of the supercontinuum generated in single-pass waveguides. For the first time to our knowledge, we clearly identify this process using a dispersive Fourier transform experiment. Additionally, we demonstrate the suppression of modulation instability by tuning the synchronization mismatch between the pump repetition rate and the cavity roundtrip time, enabling the generation of a standard dissipative Kerr soliton in this system. These observations align remarkably well with numerical simulations based on a generalized Lugiato-Lefever equation, incorporating the Raman response of the optical fiber.

physics.optics↗

arXiv2025

Fast and accurate modelling of Kerr-Brillouin combs in Fabry-Perot resonators

We introduce a new mean-field equation for modeling Fabry-Perot resonators filled with a dispersive medium exhibiting both Brillouin and Kerr nonlinearities, e.g. an optical fiber. This model is derived from a unified framework that accounts for Brillouin scattering and four-wave mixing. It involves two coupled nonlinear Schr\"odinger equations for the forward and backward propagating fields, alongside a single equation governing the acoustic oscillation. Under the standard assumptions for the mean-field approach (high finesse, weak nonlinearity, and weak dispersion) we demonstrate that our model closely matches the original system. The simplified and elegant mathematical structure of our equation provides valuable physical insights. As a key example, we derive an expression for the growth rate of harmonic perturbations to the steady states. Additionally, our model facilitates fast and accurate numerical simulations using standard Fourier split-step methods. We highlight the effectiveness of this approach by simulating frequency comb generation in state-of-the-art high-Q fiber Fabry-Perot resonators.

physics.optics↗

arXiv2025

Dual-Frequency Comb in Fiber Fabry-Perot Resonator

This paper presents a novel approach to dual-frequency comb generation utilizing a single fiber Fabry-Perot resonator, advancing the implementation of these sources in fiber-based systems. Dual-comb applications such as spectroscopy, ranging, and imaging, known for their high-resolution and rapid data acquisition capabilities, benefit significantly from the stability and coherence of optical frequency comb sources. Our method leverages the birefringent property of the resonator induced by the optical fiber to generate two orthogonally polarized optical frequency combs in a monolitic resonator. This approach allows for the generation of two different frequency combs with slightly different repetition rates, exhibiting excellent mutual coherence, making it highly relevant for dual-comb applications. The 40 nm bandwidth generated combs are induced by switching-waves in a normal dispersion fiber Fabry-Perot resonator. These comb types have the advantage of being easily generated by a pulse pumping scheme, which is employed in this study. Finally, the potential of the source is demonstrated by a proof-of-concept spectroscopy measurement.

physics.optics↗

arXiv2025

Brillouin-Induced Kerr Frequency Comb in normal dispersion fiber Fabry Perot resonators

We report the generation of a stable, broadband frequency comb, covering more than 10 THz, using a normal dispersion fiber Fabry-Perot resonator with a high quality factor of 69 millions. This platform ensures robust and easy integration into photonic devices via FC/PC connectors, and feature quality factors comparable to those of microresonators. We demonstrate a passive mode-locking phenomenon induced by the coherent interaction of the Kerr effect and Brillouin scattering, which generates a frequency comb with a repetition rate exceeding the free spectral range of the cavity. This parametric process modulates the continuous wave (CW) pump and can then be transformed into a train of almost square-wave pulses thanks to the generation of switching waves. Our results are supported by advanced numerical simulations, and theoretical derivations that include the Brillouin effect in the Fabry-Perot configuration. The very high stable feature of this optical frequency comb lying in the GHz range is critical to several applications ranging from telecommunication, spectroscopy and advanced microwave generation.

physics.optics↗

arXiv2024

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.

physics.optics↗

arXiv2024

Gain-controlled taming of recurrent modulation instability

We show how the recurrence phenomenon characteristic of the nonlinear stage of induced modulational instability in a passive fiber is affected by forcing. An additional linear amplification, even if extremely weak, induces separatrix crossing in correspondence of critical values of the gain around which the recurrence process considerably slows down, switching between dynamical orbits of different kind. We present evidence for such phenomenon in a fiber optics experiment where the gain is finely tuned by means of Raman amplification. A theoretical explanation is also provided that matches almost perfectly with our experimental results.

physics.optics↗

arXiv2024

Switching waves-induced broadband Kerr frequency comb in fiber Fabry-Perot resonators

We report the generation of broadband frequency combs in fiber Fabry-Perot resonators in the normal dispersion regime enabled by the excitation of switching waves. We theoretically characterise the process by means of a transverse linear stability analysis of the Lugiato-Lefever equation, enabling precise prediction of the switching waves' frequencies. Experimentally, we employed a pulsed-pump fiber Fabry-Perot resonator operating in the normal dispersion regime, integrated into an all-fiber experimental setup. The synchronisation mismatch and the influence of dispersion is thoroughly discussed, unveiling the potential to generate a frequency comb spanning over 15 THz bandwidth, specifically leveraging a flattened low dispersion cavity.

physics.optics↗

arXiv2024

28 THz soliton frequency comb in a continuous-wave pumped fiber Fabry-Perot resonator

We report the generation of an optical frequency comb featuring 28 THz bandwidth, sustained by a single 80 fs cavity soliton recirculating in a fiber Fabry-Perot resonator. This large spectrum is comparable to frequency combs obtained with microresonators operating in the anomalous dispersion regime. Thanks to the compact design and the easy coupling of the resonator, cavity solitons can be generated in an all-fiber experimental setup with a continuous wave pumping scheme. We also observe the generation of a dispersive wave at higher frequencies which is supported by higher-order dispersion. These observations align remarkably well with both numerical simulations and the established theory of cavity solitons.

physics.optics↗

arXiv2023

Random telegraph dispersion-management: modulational instability

We study modulational instability in a fiber system resembling a dispersion-managed link where the sign of the group-velocity dispersion varies randomly according to a telegraph process. We find that the instability gain of stochastic origin converges, for long fiber segment mean length (the inverse of the transition rate between the two values), to the conventional values found in a homogeneous anomalous dispersion fiber. For short fiber segments, the gain bands are broadened and the maximum gain decreases. By employing correlation splitting formulas, we obtain closed form equations that allow us to estimate the instability gain from the linearized nonlinear Schr\"odinger equation. We compare the analytical to the numerical results obtained in a Monte Carlo spirit. The analysis is proven to be correct not only for a fluctuating group-velocity dispersion, but also including fourth-order dispersion (both constant or varying according to a synchronous or independent telegraph process). These results may allow researchers to tailor and control modulational instability sidebands, with applications in telecommunications and parametric photon sources.

physics.optics↗

arXiv2023

Theory of modulation instability in Kerr Fabry-Perot resonators beyond the mean field limit

We analyse the nonlinear dynamics of Fabry-Perot cavities of arbitrary finesse filled by a dispersive Kerr medium, pumped by a continuous wave laser or a synchronous train of flat-top pulses. The combined action of feedback, group velocity dispersion and Kerr nonlinearity leads to temporal instability with respect to perturbations at specified frequencies. We characterise the generation of new spectral bands by deriving the exact dispersion relation and we find approximate analytical expressions for the instabilities threshold and gain spectrum of modulation instability (MI). We show that, in contrast to ring-resonators, both the stationary solutions and the gain spectrum are dramatically affected by the duration of the pump pulse. We derive the extended Lugiato-Lefever equation for the Fabry-Perot resonator (FP-LLE) starting from coupled nonlinear Schr\"odinger equations (rather than Maxwell-Bloch equations) and we compare the outcome of the stability analysis of the two models. While FP-LLE gives overall good results, we show regimes that are not captured by the mean-field limit, namely the period-two modulation instability, which may appear in highly detuned or nonlinear regimes. We report numerical simulations of the generation of MI-induced Kerr combs by solving FP-LLE and the coupled Schr\"odinger equations.

physics.optics↗

arXiv2022

Modulational instability in randomly dispersion-managed fiber links

We study modulational instability in a dispersion-managed system where the sign of the group-velocity dispersion is changed at uniformly distributed random distances around a reference length. An analytical technique is presented to estimate the instability gain from the linearized nonlinear Schr{\"o}dinger equation, which is also solved numerically. The comparison of numerical and analytical results confirms the validity of our approach. Modulational instability of purely stochastic origin appears. A competition between instability bands of periodic and stochastic origin is also discussed. We find an instability gain comparable to the conventional values found in a homogeneous anomalous dispersion fiber.

physics.optics↗

arXiv2022

Multiple symmetry breaking induced by weak damping in the Fermi-Pasta-Ulam-Tsingou recurrence process

We show that even small dissipation can strongly affect the Fermi-Pasta-Ulam-Tsingou recurrence phenomenon. Taking the fully nonlinear stage of modulational instability as an experimentally accessible example, we show that the linear attenuation induces the symmetry of the recurrence to be broken through separatrix crossing occurring at multiple critical values of the attenuation. We provide experimental evidence for this phenomenon in a fiber optics experiment designed in such a way that the effective losses can be carefully tailored by techniques based on Raman amplification.

nlin.PS↗

arXiv2022

Observation of the noise-driven thermalization of the Fermi-Pasta-Ulam-Tsingou recurrence in optical fibers

We report the observation of the thermalization of the Fermi-Pasta-Ulam-Tsingou recurrence process in optical fibers. We show the transition from a reversible regime to an irreversible one, revealing a spectrally thermalized state. To do so, we actively compensate the fiber loss to make the observation of several recurrences possible. We inject into the fiber a combination of three coherent continuous waves, which we call Fourier modes, and a random noise. We enhance the noise-driven modulation instability process against the coherent one by boosting the input noise power level to speed up the evolution to the thermalization. The distributions of the Fourier modes power along the fiber length are recorded thanks to a multi-heterodyne time-domain reflectometer. At low input noise levels, we observe up to four recurrences. Whereas, at higher noise levels, the Fourier modes fade into the noise-driven modulation instability spectrum revealing that the process reached an irreversible thermalized state.

nlin.PS↗

arXiv2021

Stochastic modulational instability in the nonlinear Schr\"odinger equation with colored random dispersion

We study modulational instability (MI) in optical fibers with random group-velocity dispersion (GVD). We consider Gaussian and dichotomous colored stochastic processes. We resort to different analytical methods (namely, the cumulant expansion and the functional approach) and assess their reliability in estimating the MI gain of stochastic origin. If the power spectral density (PSD) of the GVD fluctuations is centered at null wavenumber, we obtain low-frequency MI sidelobes which converge to those given by a white noise perturbation when the correlation length tends to 0. If instead the stochastic processes are modulated in space, one or more MI sidelobe pairs corresponding to the well-known parametric resonance (PR) condition can be found. A transition from small and broad sidelobes to peaks nearly indistinguishable from PR-MI is predicted, in the limit of large perturbation amplitudes and correlation lengths of the random process. We find that the cumulant expansion provides good analytical estimates for small PSD values and small correlation lengths, when the MI gain is very small. The functional approach is rigorous only for the dichotomous processes, but allows us to model a wider range of parameters and to predict the existence of MI sidelobes comparable to those observed in homogeneous fibers of anomalous GVD

nlin.PS↗