Fluctuations of nonequilibrium localized waves are shaped not only by direct stochastic forcing but also by deterministic transfer among coupled collective degrees of freedom. We develop a pathway-resolved stochastic collective-coordinate theory that makes this transfer explicit for stationary driven-dissipative solitons of the generalized Lugiato–Lefever equation with Raman response. The reduction yields a refined stationary phase-locking relation, providing a fixed point for the subsequent stochastic theory. Projecting field-level fluctuations onto four soliton coordinates: amplitude, frequency shift, temporal position, and global phase, yields a reduced Langevin model and, after linearization about a stable stationary state, an analytic power-spectral-density matrix. This framework separates direct stochastic injection from deterministic inter-coordinate conversion and thereby resolves how each observable spectrum is assembled from distinct internal fluctuation pathways. It shows that timing jitter is governed primarily by Gordon–Haus-type frequency-to-timing conversion, while phase noise is often dominated by amplitude-to-phase transfer rather than by direct phase diffusion. Raman response opens additional cascaded pathways, and the low-detuning hump in the intensity and phase spectra is traced to the driven response of an underdamped amplitude–phase subsystem preceding the breathing instability. Comparisons with stochastic simulations of both the reduced model and the full generalized Lugiato–Lefever equation show good agreement throughout most of the stable stationary single-soliton regime, with systematic deviations mainly near the Hopf boundary. The theory provides a general route for connecting internal fluctuation-transfer mechanisms of dissipative solitons to measurable noise observables.

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.

We demonstrate temporal pattern formation in a coherently driven fiber ring cavity whose effective finesse is continuously reconfigured using distributed Raman amplification. We achieve an effective finesse of up to Feff≈800, corresponding to a linewidth of ∼725 Hz (Qeff ≈ 2.7 × 1011) at 1555 nm. By exploiting the resulting increase in effective photon lifetime, we excite stable temporal cavity solitons and generate a low-repetition-rate frequency comb with a spacing of 580 kHz. Finally, we analyze the impact of the Raman loss-compensation mechanism, particularly its associated noise, and show that a trade-off exists between soliton excitation threshold and stability.

We report ultradense optical frequency combs generated via dissipative Kerr cavity solitons in a 357.7 m fiber ring. By utilizing distributed Raman amplification to compensate for roundtrip losses, we boost the effective finesse from F approximate to 17 to F approximate to 800 (loaded effective Q approximate to 2.7 x 10(11)), enabling stable soliton formation when the driving power is 80 mW. Although the 580.25 kHz spectral spacing recludes direct optical resolution of individual comb lines, the temporal periodicity establishes a precise sub-MHz spectral ruler.

We demonstrate temporal pattern formation in a coherently driven fiber ring cavity whose effective finesse is continuously reconfigured using distributed Raman amplification. We achieve an effective finesse of up to ℱ_eff≈800, corresponding to a linewidth of approximately 725 Hz (Q≈2.7×10^11) at 1555 nm. By exploiting the resulting increase in effective photon lifetime, we excite stable temporal cavity solitons and generate a low-repetition-rate frequency comb with a spacing of 580 kHz. Finally, we analyze the impact of the Raman loss-compensation mechanism, particularly its associated noise and show that a trade-off exists between soliton excitation threshold and stability.

We study parametrically driven soliton crystals in doubly resonant chi((2))-chi((3)) cavities. Using numerical continuation, we map multi-soliton solution families versus driving strength and identify stability changes mediated by fold and Hopf bifurcations. Direct time-domain simulations confirm robust phase-locked soliton crystals at higher drive and reveal a Hopf-induced oscillatory regime that we term the soliton-pursuing state, where circulating solitons periodically exchange power and group velocity, producing slow oscillations of their separations. Increasing the drive shortens the pursuing period and quenches the oscillations, recovering stationary soliton crystals.

Reservoir computing leverages the nonlinear dynamics of physical systems to process temporal information with minimal training cost. Here, we demonstrate that cavity solitons sustained in a fiber optical cavity provide an optical platform for photonic reservoir computing. Our methodology employs a phase-modulated drive laser to encode the input, while the reservoir states are accessed through a frequency-resolved readout. Numerical simulations indicate that the emission of Kelly waves enriches the dynamics and enhances performance for machine learning tasks. We evaluated the performance of the cavity-soliton reservoir computer on several standard benchmark tasks.

We theoretically investigate the dynamics of parametrically driven soliton crystals (PDSC) and their associated frequency combs in doubly resonant cavities with quadratic and cubic nonlinearities. We show that, with significant pump-signal walk-off, PDSCs emerge as robust attractors in a monostable regime, and the soliton number is set primarily by the driving strength. Pump-signal walk-off extends pump depletion from a local perturbation to a global constraint, enabling long-range soliton interactions; in combination with the pump phase, this mechanism stabilizes the crystal’s equal spacing and preserves comb coherence. Additionally, we identify a novel nonlinear state in parametric soliton crystals in which circulating solitons periodically alternate their intensities and group velocities, a phenomenon we term the soliton-pursuing state. Furthermore, due to the phase-selective nature of the optical parametric process, we show how different configurations of soliton phases determine the optical frequency combs, enabling odd-harmonic and subharmonic-like combs.

Temporal cavity solitons are ultrashort optical pulses circulating in driven Kerr resonators. Their intrinsic stability and ability to generate coherent broadband frequency combs have led to breakthroughs in fields such as sensing, metrology, and signal synthesis. However, this robustness limits control over soliton dynamics and constrains comb characteristics. Here, we demonstrate that stationary and moving trapping potentials, generated through intracavity phase modulation, provide unprecedented control over cavity soliton properties. We theoretically show that, for deep potentials, the soliton spectral shift and repetition rate tuning range are primarily limited by a Hopf bifurcation, and reveal the role of dissipation in soliton dynamics. Using a fibre resonator, we observe stable blue- and red-shifted solitons up to 0.4 times their spectral width, at least an order of magnitude larger than with external phase modulation of the drive. We also investigate the interplay between the trapping potential and stimulated Raman scattering, showing that Raman self-frequency shift can be fully compensated, extending the existence range of cavity solitons. Our results provide a new means for stabilising or rapidly tuning the repetition rate of Kerr combs over a wide range, broadening the applications of Kerr frequency combs.

The generation of optically coherent ultrashort pulses by mode-locked lasers has revolutionized advancements in modern science and technology. These pulses often arise from the formation of dissipative solitons, which emerge due to a balance between energy excitation and dissipation. Harnessing the concept of parity-time (PT) symmetry to control this balance, we demonstrate a new type of laser dissipative soliton hosted in linearly coupled ring cavities. Our experiments are performed in a laser where the linear hybridized modes are in the PT-symmetric phase. Here we experimentally observe the formation of short pulses, stabilized by the selective breaking of the PT symmetry by Kerr nonlinearity. Our results unlock new possibilities for passive mode-locking by demonstrating spontaneous pulse formation in PT-symmetric lasers, which hold the potential for simple cavity designs.

Temporal cavity solitons (CSs) are ultra-stable self-sustaining light pulses circulating indefinitely within a resonator [1]. They are sustained through a balance between the anomalous chromatic dispersion, cavity loss, Kerr nonlinearity and a coherent drive, detuned relative to a cavity resonance. CSs have been demonstrated across various platforms, with fiber ring resonators [1] and integrated microcombs [2] being the most common. Recent studies have explored the interaction between CSs-based frequency combs and stimulated Brillouin scattering (SBS), with the aim of developing hybrid combs. SBS arises from photon scattering onto an acoustic wave generated by the beating between two mutually coherent counter-propagating beams. For a single beam, this interaction results in an ultranarrow backward gain, enabling the generation of a highly coherent Brillouin laser from a lower coherence source. The combination of Brillouin laser coherence and high bandwidth of CSs-based combs motivates the development of hybrid CS-Brillouin frequency combs. Recent developments include using a Brillouin laser driven by a low-coherence external pump to drive counterpropagating CSs within the same cavity, in both a singly resonant fiber resonator [3] and a doubly resonant microcomb [4]. Brillouin dual-comb sources have also been demonstrated to generate both backward and forward microcombs [5]. Brillouin-enhanced Kerr frequency combs were also unexpectedly observed in a Fabry-Perot fiber resonator [6].

We discuss the formation of dissipative structures in active parity-time symmetric cavities made by directly coupling an active and a lossy resonator. We report on coherently driven temporal cavity solitons and on mode-locked solitons. Our experimental demonstrations are performed using fiber ring cavities.

BACKGROUND:Infrared neural stimulation (INS) uses short optical pulses to activate nerves. While electrical stimulation (ES) activates large-diameter fibers first, light may preferentially activate small-diameter fibers first, which could be valuable for many clinical applications. NEW METHOD:This study used a compact diode laser of 1470 nm to perform INS. Conduction velocity (CV) measurements were performed to assess differences in fiber type activation between INS and ES in the rat sciatic nerve and the goat vagus nerve. The rat sciatic nerve was chosen as a standard model because of its well-characterized physiology and extensive use in studies of INS mechanisms. The goat vagus nerve was chosen because of its expected high proportion of small-diameter fibers and its larger size, which allows sufficient separation between recording units to optimize CNAP measurements. RESULTS:The results showed that in the rat sciatic nerve, ES-excited fibers had significantly higher CVs (9.81 ± 3.18 m/s) than INS-excited fibers (8.10 ± 2.82 m/s). In the goat vagus nerve, ES produced a mean CV of 6.47 ± 1.25 m/s, but INS did not produce clearly distinguishable compound nerve action potential, highlighting the challenges of applying INS to larger nerves. COMPARISON TO EXISTING METHODS:To the best of our knowledge, CV is, for the first time, measured to identify the type of nerve fiber excited by INS. CONCLUSION:These results suggest that INS may preferentially activate smaller diameter fibers, providing insight for potential neuromodulation applications.

Temporal solitons in coherently driven optical cavities have drawn considerable interest for their remarkable stability and promising applications such as in optical communications and spectroscopy [1]. These solitons arise in high-finesse cavities through a delicate balance between dispersion and Kerr nonlinearity, as well as gain and loss. In passive cavities, the coherent driving field provides the gain. Thus, in practice, only a small fraction of the soliton power can be extracted. Active cavity solitons (ACSs) [2], [3] overcome this limitation by integrating an intracavity amplifier to partially compensate for losses while keeping the cavity below lasing threshold. In this work, we leverage the active cavity scheme to theoretically and experimentally demonstrate the formation of stable ACSs with output coupling up to 90% under low power continuous-wave (CW) driving.

Infrared neural stimulation (INS) uses transient near-infrared light to activate neuronal activity, likely through heat-induced thermal gradients. However, neither the effect of basal temperature nor heat accumulation has specifically been investigated. This study examines how spatial temperature gradients, varied by different laser repetition rates and the addition of a continuous wave laser, affect the elicitation of compound nerve action potentials (CNAPs). In addition, we investigate the role of basal temperature. Overall, our results indicate that CNAP generation is more influenced by the induced spatial temperature gradients than by the increase in local or basal temperature, or temperature build-up. For instance, low-power continuous wave laser combined with low repetition rate pulsed laser stimulation successfully induced CNAPs, whereas increasing the basal nerve temperature did not facilitate CNAP generation. A heat transfer model, consistent with the experimental data, confirms that, while the volume exposed to rapid temperature changes remains constant, heat accumulation increases spatial gradients with the number of stimulation pulses. This likely explains the progressive recruitment of nerve fibers and the observed increase in CNAP amplitude. Taken together, these results highlight the critical role of spatial temperature gradients in effective infrared neural stimulation, while a temperature threshold does not appear to be the primary mechanism in CNAP triggering.

We experimentally observe signatures of 475-fs-long sech-squared-shaped solitons in a ps-pumped phase-mismatched parametric oscillator in the normal dispersion regime, purely due to cascaded quadratic nonlinearities. The results are in good agreement with our theoretical predictions.

Temporal cavity solitons (CSs) are stable, localized particle-like objects in the form of optical pulses that circulate indefinitely in coherently driven nonlinear resonators. In the spectral domain, they form highly coherent frequency combs. Owing to their remarkable stability, they are attracting attention for applications in sensing, metrology, or optical signal synthesis. In this work, we report on the dynamics of CSs interacting with a trapping potential. We demonstrate that this interaction provides a powerful means to control their properties such as position, speed, and central frequency. Our theoretical analysis predicts fundamental limitations on the spectral shift of CSs relative to the driving frequency. Specifically, it reveals that within a broad range of detunings, frequency-shifted CSs encounter destabilization through a Hopf bifurcation. Moreover, we find that with periodic potentials, the Kelly sidebands emitted by trapped solitons undergo Bloch oscillations. In our experiments, we use an intracavity phase modulator to create the equivalent of an external real potential. We observe stable blue- and red- shifted solitons up to a limit close to our theoretical predictions. We then show theoretically and experimentally that this unprecedented level of control over the CS spectrum can be leveraged to cancel the Raman-induced self-frequency shift and even to stabilize CSs beyond the limitation imposed by stimulated Raman scattering. Our results provide valuable insights for applications requiring robust and potentially rapid tunable control over the cavity soliton properties.

Active cavity solitons suffer from gain saturation preventing high average cavity power. We overcome this limitation by optical gain clamping and demonstrate the generation of numerous solitons, opening the way to high power soliton crystals.

We experimentally demonstrate mode-locking in a parity-time symmetric laser made of two coupled ring resonators, one experiencing loss and the other gain. This versatile concept opens the way to new laser architectures for pulse generation.