Continuous-wave driving elucidates the desynchronization dynamics of ultrashort dissipative Raman solitons generated in dispersive Kerr resonators.

Phase-coherent pulsed driving of passive optical fiber resonators enables the generation of ultrashort dissipative Raman solitons with durations well below 100 fs. The existence and characteristics of such solitons critically depend on the desynchronization between the pulsed driving source and the resonator round trip time, yet the full mechanism through which these dependencies arise remains unclear. Here, we numerically demonstrate that Raman solitons can exist even under conditions of continuous-wave (CW) driving, and by numerically examining the existence and characteristics of Raman solitons under such conditions, we elucidate the role of desynchronization in pulse-driven systems.

Nonlinear topological symmetry protection in a dissipative system.

We investigate experimentally and theoretically a system ruled by an intricate interplay between topology, nonlinearity, and spontaneous symmetry breaking. The experiment is based on a two-mode coherently-driven optical resonator where photons interact through the Kerr nonlinearity. In presence of a phase defect, the modal structure acquires a synthetic Möbius topology enabling the realization of spontaneous symmetry breaking in inherently bias-free conditions without fine tuning of parameters.

Kerr microresonator dual-comb source with adjustable line-spacing.

Optical microresonators offer a highly-attractive new platform for the generation of optical frequency combs. Recently, several groups have been able to demonstrate the generation of dual-frequency combs in a single microresonator driven by two optical pumps. This opens the possibility for microresonator-based dual-comb systems suitable for measurement applications such as spectroscopy, ranging and imaging.

Temporal characteristics of stationary switching waves in a normal dispersion pulsed-pump fiber cavity.

Kerr cavities driven in the normal dispersion regime are known to host switching waves. These consist of a traveling wavefront that connects separate regions associated with high- and low-intensity steady states of the cavity. In this Letter, we drive a 230-m custom built fiber ring cavity with strong normal dispersion using nanosecond pulses, allowing us to directly resolve the fine structure of individual switching waves, including resonant oscillations occurring over periods of the order of ∼10 ps.

Random number generation using spontaneous symmetry breaking in a Kerr resonator.

We demonstrate an all-optical random number generator based on spontaneous symmetry breaking in a coherently driven Kerr resonator. Random bit sequences are generated by repeatedly tuning a control parameter across a symmetry-breaking bifurcation that enacts random selection between two possible steady-states of the system. Experiments are performed in a fiber ring resonator, where the two symmetry-broken steady-states are associated with orthogonal polarization modes.

Inter-mode soliton linear-wave scattering in a Kerr microresonator.

Soliton microresonator frequency combs (microcombs) have recently emerged as an attractive new type of optical comb source with a wide range applications proposed and demonstrated. To extend the optical bandwidth of these microresonator sources, several previous studies have proposed and studied the injection of an additional optical probe wave into the resonator. In this case, nonlinear scattering between the injected probe and the original soliton enables the formation of new comb frequencies through a phase-matched cascade of four-wave mixing processes.

Wideband multimode optical parametric oscillation in a Kerr microresonator.

Parametric oscillation in Kerr microresonators provides an attractive pathway for the generation of new optical frequencies in a low-power, small-footprint device. The frequency shift of the newly generated parametric sidebands is set by the phasematching of the underlying four-wave-mixing process, with the generation of large frequency shift sidebands typically placing exacting requirements on a resonator's dispersion profile. In practice, this limits the range of viable pump wavelengths, and ultimately the range of output frequencies.

Optical frequency combs in dispersion-controlled doubly resonant second-harmonic generation.

We report on the experimental realization and a systematic study of optical frequency comb generation in doubly resonant intracavity second harmonic generation (SHG). The efficiency of intracavity nonlinear processes usually benefits from the increasing number of resonating fields. Yet, achieving the simultaneous resonance of different fields may be technically complicated, all the more when a phase matching condition must be fulfilled as well.

Breathing dynamics of symmetry-broken temporal cavity solitons in Kerr ring resonators.

We investigate theoretically and experimentally the instabilities of symmetry-broken, vectorial, bright cavity solitons (CSs) of two-mode nonlinear passive Kerr resonators. Through comprehensive theoretical analyses of coupled Lugiato-Lefever equations, we identify two different breathing regimes where the two components of the vectorial CSs breathe respectively in-phase and out-of-phase. Moreover, we find that deep out-of-phase breathing can lead to intermittent self-switching of the two components, spontaneously transforming a soliton into its mirror-symmetric state.

Dual-microcomb generation in a synchronously driven waveguide ring resonator.

Microcombs-optical frequency combs generated in coherently driven nonlinear microresonators-have attracted significant attention over the last decade. The ability to generate two such combs in a single resonator device has, in particular, enabled a host of applications from spectroscopy to imaging. Concurrently, novel comb generation techniques such as synchronous pulsed driving have been developed to enhance the efficiency and flexibility of microcomb generation.

Nonlinear Localization of Dissipative Modulation Instability.

Modulation instability (MI) in the presence of noise typically leads to an irreversible and complete disintegration of a plane wave background. Here we report on experiments performed in a coherently driven nonlinear optical resonator that demonstrate nonlinear localization of dissipative MI: formation of persisting domains of MI-driven spatiotemporal chaos surrounded by a stable quasi-plane-wave background. The persisting localization ensues from a combination of bistability and complex spatiotemporal nonlinear dynamics that together permit a locally induced domain of MI to be pinned by a shallow modulation on the plane wave background.

Spontaneous symmetry breaking of dissipative optical solitons in a two-component Kerr resonator.

Dissipative solitons are self-localized structures that can persist indefinitely in open systems driven out of equilibrium. They play a key role in photonics, underpinning technologies from mode-locked lasers to microresonator optical frequency combs. Here we report on experimental observations of spontaneous symmetry breaking of dissipative optical solitons.

Frequency comb generation in a pulse-pumped normal dispersion Kerr mini-resonator.

Kerr microresonators driven in the normal dispersion regime typically require the presence of localized dispersion perturbations, such as those induced by avoided mode crossings, to initiate the formation of optical frequency combs. In this work, we experimentally demonstrate that this requirement can be lifted by driving the resonator with a pulsed pump source. We also show that controlling the desynchronization between the pump repetition rate and the cavity free-spectral range (FSR) provides a simple mechanism to tune the center frequency of the output comb.

Dissipative Polarization Domain Walls in a Passive Coherently Driven Kerr Resonator.

Using a passive, coherently driven nonlinear optical fiber ring resonator, we report the experimental realization of dissipative polarization domain walls. The domain walls arise through a symmetry breaking bifurcation and consist of temporally localized structures where the amplitudes of the two polarization modes of the resonator interchange, segregating domains of orthogonal polarization states. We show that dissipative polarization domain walls can persist in the resonator without changing shape.

Polarization modulation instability in a nonlinear fiber Kerr resonator.

We report on the experimental and numerical observation of polarization modulation instability (PMI) in a nonlinear fiber Kerr resonator. This phenomenon is phased-matched through the relative phase detuning between the intracavity fields associated with the two principal polarization modes of the cavity. Our experimental investigation is based on a 12 m long fiber ring resonator in which a polarization controller is inserted to finely control the level of intracavity birefringence.

Experimental observation of internally pumped parametric oscillation and quadratic comb generation in a χ whispering-gallery-mode microresonator.

We report on the experimental observation of internally pumped parametric oscillation in a high-$\!Q$Q lithium niobate microresonator under conditions of natural phase matching. Specifically, launching near-infrared pump light around 1060 nm into a $ z $z-cut congruent lithium niobate microresonator, we observe the generation of optical sidebands around the input pump under conditions where second-harmonic generation is close to natural phase matching. We find that a wide range of different sideband frequency shifts can be generated by varying the experimental parameters.

Optical Frequency Combs in Quadratically Nonlinear Resonators.

Optical frequency combs are one of the most remarkable inventions in recent decades. Originally conceived as the spectral counterpart of the train of short pulses emitted by mode-locked lasers, frequency combs have also been subsequently generated in continuously pumped microresonators, through third-order parametric processes. Quite recently, direct generation of optical frequency combs has been demonstrated in continuous-wave laser-pumped optical resonators with a second-order nonlinear medium inside.

Coexistence and Interactions between Nonlinear States with Different Polarizations in a Monochromatically Driven Passive Kerr Resonator.

We report on experimental observations of coexistence and interactions between nonlinear states with different polarizations in a passive Kerr resonator driven at a single carrier frequency. Using a fiber ring resonator with adjustable birefringence, we partially overlap nonlinear resonances of two orthogonal polarization modes, achieving coexistence between different nonlinear states by locking the driving laser frequency at various points within the overlap region. In particular, we observe coexistence between temporal cavity solitons and modulation instability patterns, as well as coexistence between two nonidentical cavity solitons with different polarizations.

Modulation Instability Induced Frequency Comb Generation in a Continuously Pumped Optical Parametric Oscillator.

Continuously pumped passive nonlinear cavities can be harnessed for the creation of novel optical frequency combs. While most research has focused on third-order "Kerr" nonlinear interactions, recent studies have shown that frequency comb formation can also occur via second-order nonlinear effects. Here, we report on the formation of quadratic combs in optical parametric oscillator (OPO) configurations.

Origins of clustered frequency combs in Kerr microresonators.

Recent experiments have demonstrated the generation of widely spaced parametric sidebands that can evolve into "clustered" optical frequency combs in Kerr microresonators. Here we describe the physics that underpins the formation of such clustered comb states. In particular, we show that the phase matching required for the initial sideband generation is such that (at least) one of the sidebands experiences anomalous dispersion, enabling the sideband to drive frequency comb formation via degenerate and non-degenerate four-wave mixing.

Experimental observations of breathing Kerr temporal cavity solitons at large detunings.

It was recently predicted that, due to stimulated Raman scattering, temporal Kerr cavity solitons may exhibit oscillatory instabilities at large cavity detunings [Phys. Rev. Lett.

Addressing temporal Kerr cavity solitons with a single pulse of intensity modulation.

We experimentally and numerically study the use of intensity modulation for the controlled addressing of temporal Kerr cavity solitons (CSs). Using a coherently driven fiber ring resonator, we demonstrate that a single temporally broad intensity modulation pulse applied on the cavity driving field permits systematic and efficient writing and erasing of ultrashort cavity solitons. We use numerical simulations based on the mean-field Lugiato-Lefever model to investigate the addressing dynamics, and present a simple physical description of the underlying physics.

Stimulated Raman Scattering Imposes Fundamental Limits to the Duration and Bandwidth of Temporal Cavity Solitons.

Temporal cavity solitons (CS) are optical pulses that can persist in passive resonators, and they play a key role in the generation of coherent microresonator frequency combs. In resonators made of amorphous materials, such as fused silica, they can exhibit a spectral redshift due to stimulated Raman scattering. Here we show that this Raman-induced self-frequency-shift imposes a fundamental limit on the duration and bandwidth of temporal CSs.

Widely tunable optical parametric oscillation in a Kerr microresonator.

We report on the first experimental demonstration of widely tunable parametric sideband generation in a Kerr microresonator. Specifically, by pumping a silica microsphere in the normal dispersion regime, we achieve the generation of phase-matched four-wave mixing sidebands at large frequency detunings from the pump. Thanks to the role of higher-order dispersion in enabling phase matching, small variations of the pump wavelength translate into very large and controllable changes in the wavelengths of the generated sidebands: we experimentally demonstrate over 720 nm of tunability using a low-power continuous-wave pump laser in the C-band.

Second-harmonic-assisted four-wave mixing in chip-based microresonator frequency comb generation.

Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology. Moreover, the presence of both second- and third-order nonlinearities results in complex cavity dynamics that is of high scientific interest but is still far from being well-understood. Here, we demonstrate that the interaction between the fundamental and the second-harmonic waves can provide an entirely new way of phase matching for four-wave mixing in optical microresonators, enabling the generation of optical frequency combs in the normal dispersion regime under conditions where comb creation is ordinarily prohibited.