Dissipative Solitons Research Articles

Soliton rain in all-polarization-maintaining mode locked fiber laser.

For the first time the phenomenon of soliton rain is observed in a mode-locked fiber laser with all-polarization-maintaining (all-PM) architecture. The laser is mode-locked using a semiconductor saturable absorber mirror (SESAM) and operates in the all-normal dispersion (ANDi) regime. The operation state of the laser can be switched from dissipative soliton to soliton rain by simply raising the pump power, without any manipulation of the intracavity polarization state given that all components of the resonator are made of PM fibers. The soliton rain generated in the laser is self-starting and replicable, since it occurs in every individual operation of the laser as the pump power is increased to an approximately invariant value.

Quiet point engineering for low-noise microwave generation with soliton microcombs

Low-noise microwave signals can be efficiently generated with microresonator-based dissipative Kerr solitons (microcombs). However, the phase noise level in integrated microcombs is presently several orders of magnitude above the limit imposed by fundamental thermorefractive noise, resulting from residual pump laser frequency noise transduction to the soliton repetition rate. This effect can be substantially reduced by accessing a quiet point (QP) in the parameter space, where the transduction is compensated by the dispersive wave (DW) recoil, which conventionally relies on accidental mode crossings. Here we present a method to deterministically engineer the QP, both in terms of spectral width and position, and we discover a continuum of possible QPs within the soliton existence region. Using two controlled mode crossings, we obtain regions where the QPs interact with each other, extending the noise suppression range. Our work demonstrates a promising way to reach the fundamental limit of low-noise microwave generation in integrated microcombs.

Nonlinear dynamics and Kerr frequency comb formation in lattices of coupled microresonators

Recently, substantial progress has been made in the understanding of microresonators frequency combs based on dissipative Kerr solitons (DKSs). However, most of the studies have focused on the single-resonator level. Coupled resonator systems can open new avenues in dispersion engineering and exhibit unconventional four-wave mixing (FWM) pathways. However, these systems still lack theoretical treatment. Here, starting from general considerations for the N-(spatial) dimensional case, we derive a model for a one-dimensional lattice of microresonators having the form of the two-dimensional Lugiato-Lefever equation (LLE) with a complex dispersion surface. Two fundamentally different dynamical regimes can be identified in this system: elliptic and hyperbolic. Considering both regimes, we investigate Turing patterns, regularized wave collapse, and 2D (i.e., spatio-temporal) DKSs. Extending the system to the Su-Schrieffer-Heeger model, we show that the edge-state dynamics can be approximated by the conventional LLE and demonstrate the edge-bulk interactions initiated by the edge-state DKS.

Research on wideband dissipative soliton generation and the dynamics process

Research on wideband dissipative soliton generation and the dynamics process

Solitary waves in ultrafast fiber lasers: From solitons to dissipative solitons

The development of the connections between ultrafast laser dynamics and solitary waves concepts is presented, with an attempt to emphasize on important research milestones and conceptual advances. At various stages, the concepts of conventional and dissipative solitons are found to echo, oppose, or complement each other. The pivotal role of fiber lasers is highlighted, which multiplied the investigation of ultrafast laser dynamics since the 90s, and lead to the widespread usage of dissipative soliton concepts that were instrumental in understanding original dynamical regimes and related optical waveforms, such as the generation of bright solitons in the normal dispersion regime and the self-assembly of optical soliton molecules within laser cavities.

Ultrafast dissipative soliton generation in anomalous dispersion achieving high peak power beyond the limitation of cubic nonlinearity

The maximum peak power of ultrafast mode-locked lasers has been limited by cubic nonlinearity, which collapses the mode-locked pulses and consequently leads to noisy operation or satellite pulses. In this paper, we propose a concept to achieve mode-locked pulses with high peak power beyond the limitation of cubic nonlinearity with the help of dissipative resonance between quintic nonlinear phase shifts and anomalous group velocity dispersion. We first conducted a numerical study to investigate the existence of high peak power ultrafast dissipative solitons in a fiber cavity with anomalous group velocity dispersion (U-DSAD) and found four unique characteristics. We then built long cavity ultrafast thulium-doped fiber lasers and verified that the properties of the generated mode-locked pulses match well with the U-DSAD characteristics found in the numerical study. The best-performing laser generated a peak power of 330 kW and a maximum pulse energy of 80 nJ with a pulse duration of 249 fs at a repetition rate of 428 kHz. Such a high peak power exceeds that of any previous mode-locked pulses generated from a single-mode fiber laser without post-treatment. We anticipate that the means to overcome cubic nonlinearity presented in this paper can give insight in various optical fields dealing with nonlinearity to find solutions beyond the inherent limitations.

Multicolor Continuous‐Variable Quantum Entanglement in the Kerr Frequency Comb

AbstractIn a traveling wave microresonator, the cascaded four‐wave mixing (FWM) between optical modes allows the generation of frequency combs, including intriguing dissipative Kerr solitons (DKS). This study explores the quantum fluctuations of frequency combs and reveal the continuous‐variable quantum entanglement between different comb lines of the DKS states. The entanglement of DKS exhibits two distinct characteristics. For modes located at the spectral edge with a small number of excitations, different comb modes with multiple colors become entangled due to photon‐pair generation and coherent photon conversion stimulated by the FWM. Notably, a sudden disappearance of quantum entanglement in the center of the DKS spectrum is observed, which is attributed to the self‐locking phenomena in the FWM network. These findings demonstrate the prominent quantum nature of DKS, which is of fundamental significance in quantum optics and has the potential to be utilized in quantum networking and distributed quantum sensing applications.

Coupling dynamics of dissipative localized structures: From polarized vector solitons to soliton molecules

Dissipative solitons are well known as representative nonlinear localized wave packets resulting from the composite balance of dispersion, nonlinearity, gain and loss in optical cavities. Since the last three decades, dissipative solitons keep as one of the most active research topics in the framework of nonlinear physics, not only for fundamental researches but also for various industrial applications. From one hand, due to the rich nonlinear dynamics, dissipative solitons have been considered as an ideal testbed to study the pumping-dissipation-bifurcation complexities. On the other hand, the emergences of dissipative solitons are tightly linked with the emission of ultrashort laser pulses, as well as the formation of broadband optical frequency combs. Compared with single-soliton counterpart, the multi-component dissipative solitons have exhibited even more fascinating properties and much wider range of applications, therefore the coupling dynamics of dissipative solitons is the blooming and emergent research area in the last decade. From this point of view, this review article covers the latest developments of compound dissipative solitons, not only in passive Kerr resonators, but also in mode-locked laser cavities. Ranging from polarized vector solitons to soliton molecules, the rising degree of freedom of these multi-component localized structures is boosting the discovery of novel nonlinear dynamics and underpin the various photonic applications in light science.

Ultrashort dissipative Raman solitons in Kerr resonators driven with phase-coherent optical pulses

Ultrashort dissipative Raman solitons in Kerr resonators driven with phase-coherent optical pulses

Raman dissipative soliton source of ultrashort pulses in NIR-III spectral window.

We present a novel fiber source of ultrashort pulses at the wavelength of 1660 nm based on the technique of external cavity Raman dissipative soliton generation. The output energy of the generated 30 ps chirped pulses is in the range of 0.5-3.6 nJ with a slope efficiency of 57%. Numerical simulations are in excellent agreement with the experimental results and the shape of the compressed pulses. The compressed pulses consist of a central part with a duration of 300 fs and a weak pedestal. Our results clearly demonstrate the potential to extend the spectral range of the Raman-assisted technique for generating ultra-short pulses to new frequency regions, including biomedical windows. This paves the way for the development of new dissipative soliton sources in these bands.

Dynamics of dissipative structures in coherently-driven Kerr cavities with a parabolic potential

By means of a modified Lugiato–Lefever equation model, we investigate the nonlinear dynamics of dissipative wave structures in coherently-driven Kerr cavities with a parabolic potential. This potential stabilizes the system dynamics, leading to the generation of robust dissipative solitons in the positive detuning regime, and of higher-order solitons in the negative detuning regime. In order to understand the underlying mechanisms which are responsible for these high-order states, we decompose the field on the basis of linear eigenmodes of the system. This permits to investigate the resulting nonlinear mode coupling processes. By increasing the external pumping, one observes the emergence of high-order breathers and chaoticons. Our modal content analysis reveals that breathers are dominated by modes of corresponding orders, while chaoticons exhibit proper chaotic dynamics. We characterize the evolution of dissipative structures by using bifurcation diagrams, and confirm their stability by combining linear stability analysis results with numerical simulations. Finally, we draw phase diagrams that summarize the complex dynamics landscape, obtained by varying the pump, the detuning, and the strength of the potential.

Generation of dual large energy pulses in Er3+-doped fiber lasers based on ZrTe2 saturable absorber via polarization manipulation

We report on the generation of dual large energy pulses in a passively mode-locked Er-doped fiber laser based on ZrTe2 as saturable absorber. When the pump power is 100.4 mW, dissipative soliton resonance mode-locked operation with an output power of 9.1 mW is generated. With the increase of pump power, its average output power increased from 9.1 to 52 mW, and its corresponding fundamental repetition rate and maximum single-pulse energy are 1.22 MHz and 42.6 nJ, respectively. By properly adjusting the polarization controller, stable large energy mode-locked pulse is obtained at the same pump power. At the maximum pump power of 617.5 mW, the maximum average output power, and single-pulse energy are 55.8 mW and 45.7 nJ, respectively. Our experimental results proved that ZrTe2 has good performance in obtaining large energy pulse operations, which promotes the development of ZrTe2 nanosheets as an effective saturable absorber in the future.

Dynamics of solitons in NOLM based all-normal dispersion Yb-doped mode-locked fiber laser

The properties of the saturable absorber are critical to the soliton dynamics in the all-normal dispersion Yb-doped mode-locked fiber laser based on the nonlinear optical loop mirror (NOLM). In this paper, it is found that by adjusting the splitting ratio f and cavity length L of the NOLM, self-similar pulse (SSP), soliton molecule (SM), dissipative soliton resonance (DSR), dissipative soliton (DS) and dissipative soliton pair (DSP) can be obtained in such fiber laser system. In addition, the mechanisms and characteristics of these solitons are discussed. These findings will facilitate the in-depth understanding of the characteristics of nonlinear pulses generated by NOLM-based all-normal dispersion Yb-doped mode-locked fiber laser.

Surpassing the nonlinear conversion efficiency of soliton microcombs

Laser frequency combs are enabling some of the most exciting scientific endeavours in the twenty-first century, ranging from the development of optical clocks to the calibration of the astronomical spectrographs used for discovering Earth-like exoplanets. Dissipative Kerr solitons generated in microresonators currently offer the prospect of attaining frequency combs in miniaturized systems by capitalizing on advances in photonic integration. Most of the applications based on soliton microcombs rely on tuning a continuous-wave laser into a longitudinal mode of a microresonator engineered to display anomalous dispersion. In this configuration, however, nonlinear physics precludes one from attaining dissipative Kerr solitons with high power conversion efficiency, with typical comb powers amounting to ~1% of the available laser power. Here we demonstrate that this fundamental limitation can be overcome by inducing a controllable frequency shift to a selected cavity resonance. Experimentally, we realize this shift using two linearly coupled anomalous-dispersion microresonators, resulting in a coherent dissipative Kerr soliton with a conversion efficiency exceeding 50% and excellent line spacing stability. We describe the soliton dynamics in this configuration and find vastly modified characteristics. By optimizing the microcomb power available on-chip, these results facilitate the practical implementation of a scalable integrated photonic architecture for energy-efficient applications.

Recent advances in optical solitons via low-dimensional materials in mode-locking fiber lasers

The year 2023 marks the 50th anniversary of the first theoretical prediction for optical solitons forming in optical fibers. In the past decades, optical soliton has attracted intense interest in the field of laser communications, ultrafast spectroscopy, and optics imaging in the past decades for its stably propagating a long distance in dispersive media with no change in their shapes. The most important generation method of optical solitons is passively mode-locking in which saturable absorbers (SAs) are a crucial device for optical solitons generation. Recently, low-dimensional (LD) nanomaterials-based SAs have received significant attention in fiber lasers owing to their unique electronic structures and exceptional nonlinear optical characteristics. Various optical solitons are explored based on LD nanomaterials. In this review, research on optical solitons via LD nanomaterials-based SAs is discussed by the bibliometric method. This analysis sample includes articles from 2002 to the present. In addition, the research status of LD nanomaterials-based SAs is discussed. A detailed overview of optical solitons based on LD SAs fiber lasers is presented, including conventional solitons (CSs), dispersion-managed solitons (DMSs), dissipative solitons (DSs), etc. Through the discussion in the review, we will gain a new understanding of optical solitons and propose ideas for future development.

Microcomb-Driven Optical Convolution for Car Plate Recognition

The great success of artificial intelligence (AI) calls for higher-performance computing accelerators, and optical neural networks (ONNs) with the advantages of high speed and low power consumption have become competitive candidates. However, most of the reported ONN architectures have demonstrated simple MNIST handwritten digit classification tasks due to relatively low precision. A microring resonator (MRR) weight bank can achieve a high-precision weight matrix and can increase computing density with the assistance of wavelength division multiplexing (WDM) technology offered by dissipative Kerr soliton (DKS) microcomb sources. Here, we implement a car plate recognition task based on an optical convolutional neural network (CNN). An integrated DKS microcomb was used to drive an MRR weight-bank-based photonic processor, and the computing precision of one optical convolution operation could reach 7 bits. The first convolutional layer was realized in the optical domain, and the remaining layers were performed in the electrical domain. Totally, the optoelectronic computing system (OCS) could achieve a comparable performance with a 64-bit digital computer for character classification. The error distribution obtained from the experiment was used to emulate the optical convolution operation of other layers. The probabilities of the softmax layer were slightly degraded, and the robustness of the CNN was reduced, but the recognition results were still acceptable. This work explores an MRR weight-bank-based OCS driven by a soliton microcomb to realize a real-life neural network task for the first time and provides a promising computational acceleration scheme for complex AI tasks.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

Wavelength-tunable soliton molecule in spatiotemporal mode-locked Yb-doped fiber laser

Spatiotemporal mode-locking (STML) fiber lasers could realize the synchronized locked of multiple transverse and longitudinal modes, which could be regarded as an ideal platform to investigate high-dimensional nonlinear dynamics. The observation of STML in the soliton molecule state could offer a unique opportunity to reveal the mechanism of molecular complexity. Due to the distinctive spatiotemporal characteristics, realizing the wavelength tunable of soliton molecule in STML fiber laser is still challenging. In this letter, we report wavelength-tunable soliton molecules in an STML Yb-doped fiber laser. By rotating the wave plates at a fixed pump power, both single dissipative soliton (SDS) and various soliton molecules, including loose bounded dissipative soliton pairs (BDSPs), tight BDSPs, soliton molecules of triplet pulses or soliton molecules of quadruplets pulses, have all realized wavelength tunable with a tuning range of ∼25 nm. The realization of the wavelength tunable and the formation of the soliton molecule can all be attributed to the tunable comb filter and saturable absorber induced by the nonlinear polarization rotation technique. The formation of SDS and BDSPs was further confirmed by the numerical simulations. And the numerical results contribute to further comprehending the nonlinear dynamics of the STML fiber laser.

Nonlinear-Fourier-Transform-Based Dynamic Analyses on the Multiple Cavity Solitons in Kerr Microresonators

The Kerr microresonators have aroused widespread interests for their ultrahigh integration, compatible fabrication and ultralow energy consumption. Similar to the traditional mode-locked fiber lasers, the microresontors can sustain the generation of dissipative solitons called cavity solitons relying on the double balance of gain and loss as well as nonlinearity and dispersion. The state of multiple solitons is common in the microresonator with anomalous dispersion. In particular, an ideal state named as soliton crystals is obtained when the multiple solitons have a equidistant arrangement. And recent experiments have successfullly observed soliton crystals in the Kerr microresonators. To intuitively reveal the formation and evolution dynamics of the multiple solitons and get insight into the underlying physical mechanisms of soliton crystals, we applied the nonlinear Fourier transform to project these states into nonlinear discrete spectrum. The discrete spectra of single soliton with different modulated background waves have been displayed, which can help distinguish different optical components. Then, the nonlinear spectrum evolution of normal multiple solitons state shows the typical nonlinear states of the intracavity field. And the equidistant solitons have the effects of power enhancement, whose spectral intensity is several times that of a single soliton state. Comparing with the discrete spectrum of the equidistant solitons, the solitons inside the soliton crystals interact with each other by the modulated background. Our results suggest that the nonlinear Fourier transform is a powerful technique to characterize soliton dynamics in the Kerr microresonator, which provides a new perspective to understand the interactions of cavity solitons.

Transient behaviors of pulse breaking and recovering in a dispersion-managed mode-locked Yb fiber laser

Various pulse regimes have been discovered in mode-locked fiber lasers with carefully designed cavity setups. However, the transitions between different types of stable pulse solutions are rarely observed in a laser with the same cavity configuration. Here, we report on the experimental observation of the transformation from stretched pulses (SPs) to dissipative solitons (DSs) in an all-polarization-maintaining dispersion-managed mode-locked Yb fiber laser for the first time. By means of the time-stretch dispersive Fourier transform technique, the temporal and spectral dynamics of transient behaviors from pulse breaking to pulse recovering are identified in real time. It is revealed that the overdriven nonlinear effect induced by pump increase triggers the wave breaking of SPs, and the improved net-cavity dispersion originated from wavelength shift helps the self-recovering of DSs. Numerical simulations validate the experimental observations and bring insights to the understanding of transient nonlinear dynamics in ultrafast fiber lasers.