Observation of period-doubling bifurcations in a femtosecond fiber soliton laser with dispersion management cavity

Pulsating dynamics in a pure-quartic soliton fiber laser

We numerically investigate the pulsating dynamics of pure-quartic solitons (PQSs) in a passively mode-locked fiber laser. The bifurcation diagrams show that the PQS can alternate between the stable single soliton and pulsating regimes multiple times before transiting into the chaotic state. This multi-alternation behavior can be attributed to energy redistribution across the central part and the oscillating tails of the PQS, which is caused by an imperfect counterbalance between self-phase modulation (SPM)-induced and fourth-order dispersion (FOD)-induced phase shifts. Soliton creeping behavior can be observed during the pulsating process, accompanied by periodic asymmetric temporal profiles and central wavelength shifts of the PQS. These findings give new insights into the dynamics of PQSs in fiber lasers.

Transient soliton dynamics in a mode-locked fiber laser: from stationary to pulsation

We report the experimental observation of the transformation process from a stationary soliton to a pulsating soliton in a mode-locked fiber laser. The detailed soliton dynamics, including soliton parameter changings and sideband variation in the transition, are analyzed by the dispersive Fourier transformation technique. This Letter unveils the great enhancement of intracavity periodic perturbations resulting from the slight increase of soliton intensity induced soliton modulation instability, leading to the occurrence of parametric sidebands and multi-periodic pulsing instability. Our experimental results can shed some light on the intrinsic mechanism of soliton pulsation, as well as contribute to the study of soliton stability and laser dynamics.

Dynamic behaviors of multiple-soliton pulsation in an L-band passively mode-locked fiber laser with anomalous dispersion

As a universal phenomenon in nonlinear optical systems, the soliton pulsating behavior is useful to achieve high pulse energy and can further enrich the complex soliton dynamics. To the best of our knowledge, herein we have demonstrated the observation of multiple-soliton pulsations in an L-band mode-locked fiber laser based on a nonlinear amplifying loop mirror with anomalous dispersion for the first time. Based on the dispersive Fourier transform method, we find that the pulsations in the multi-soliton regime are accompanied with the pulse width breathing and spectrum oscillation. In addition, the corresponding number of pulsating solitons increases linearly from 8 to 16 with the pump power. Our findings can facilitate a better understanding of the complex mechanism of soliton pulsations.

Period doubling and merging of multiple dissipative-soliton-resonance pulses in a fiber laser

Period doubling (PD) and the merging of multiple dissipative-soliton-resonance (DSR) pulses are investigated in a fiber laser. Depending on the initial conditions and operation settings, various PDs of multiple DSR pulses are achieved. For two coexisting DSR pulses, we observe PD on both pulses or PD on a single pulse while the other pulse maintains period one. For three coexisting DSR pulses, PD on all pulses or PD on one/two pulse(s) are achieved when the other pulses maintain period one. It is observed that excessively increasing the pump power could destroy the PD behavior. Within certain parameters, PD behavior can be maintained by increasing the pump power. Apart from the appearance of PD, it is found that two DSR pulses may merge into a single DSR pulse if the pulse interval is small enough during pump power increase.

Vector features of pulsating soliton in an ultrafast fiber laser

Pulsating soliton in ultrafast fiber lasers has interesting non-stationary dynamics, which is one of the hot topics in field of nonlinear soliton. So far, most researchers only focused on the spectral and temporal characteristics of pulsating soliton. However, the vector features of pulsating soliton were rarely studied. In this work, we experimentally studied the pulsating vector solitons in an ultrafast fiber laser. Three categories of vector solitons with different polarization evolution characteristics could be obtained by adjusting the pump power and polarization controller, such as pulsating polarization-locked vector soliton (PLVS), pulsating polarization-rotation vector soliton (PRVS) and progressive pulsating PRVS. Interestingly, besides the basic polarization rotation with a period of 2 roundtrips, the polarization angle also evolves with progressive mode in the progressive pulsating PRVS state. The abundant results of pulsating vector solitons demonstrate that investigating vector features of nonlinear soliton dynamics is necessary and significant and would greatly enrich the research of soliton dynamics.

Period multiplication in mode-locked figure-of-9 fiber lasers

Period multiplication is a bifurcation phenomenon, which depicts a typical roadmap from periodic steady-state to chaos. There has been particular interest in studying period multiplication properties in mode-locked lasers, but the mechanism behind is still not well-studied. Here, we experimentally demonstrate a figure-of-9 fiber laser which can generate period-multiplied pulses with long-term stability. Further theoretical insight is obtained by numerical simulations, which clearly shows that the ratio between the distances of each bifurcation point is approaching the Feigenbaum constant. We believe that the laser design presented here could be a stable and reliable ultrafast optical platform to study bifurcation and chaos, which also has potential applications in optical frequency comb and all-optical modulation.

Generation and observation of ultrafast spectro-temporal dynamics of different pulsating solitons from a fiber laser

As a universal phenomenon in nonlinear optical systems, pulsating behaviors of solitons have attracted increasingly more investigations. While pulsating solitons and their likely generation conditions had been widely theoretical studied, their detailed spectro-temporal dynamics had been hardly reported in experiments. Here, three types of pulsating solitons are experimentally generated and observed in a dispersion-managed, hybrid mode-locked fiber laser. By controllably generating such states through intracavity tuning and leveraging the dispersive Fourier transform technique that maps spectral information into the time domain, real-time ultrafast spectro-temporal evolutions of the pulsating behaviors are revealed. The numerical results further show the generation of the pulsating soliton could be caused by the intracavity spectral filtering effect, consistent with the experimental configurations. Our findings could provide further insights into the complex nonlinear dynamics in lasers and potential ways to the design such systems to deliver targeted soliton outputs for potential applications.

Period doubling eigenstates in a fiber laser mode-locked by nonlinear polarization rotation

Due to the weak birefringence of single mode fibers, solitons generated in fiber lasers are indeed vector pulses and exhibit periodic parameter change including polarization evolution even when there is a polarizer inside the cavity. Period doubling eigenstates of solitons generated in a fiber laser mode-locked by the nonlinear polarization rotation, i.e., period doubling of polarization components of the soliton, are numerically explored in detail. We found that, apart from the synchronous evolution between the two polarization components, there exists asynchronous development depending on the detailed operation conditions. In addition, period doubling of one polarization component together with period-one of another polarization component can be achieved. When the period tripling window is obtained, much complexed dynamics on the two polarization components could be observed.

Experimental study on polarization evolution locking in a stretched-pulse fiber laser

Polarization evolution locking (PEL) of a stretched-pulse fiber laser is experimentally investigated with a simple pulse selection method based on a fast electrooptic modulator, capable of revealing the temporal and spectrum evolution of the PEL pulses. Moreover, the wavelength dependence of PEL is observed by spectrally filtering the pulses and is further investigated for individual fiber laser comb lines through beat note measurements with narrow-linewidth cw lasers.

Optical frequency combs based on a period-doubling mode-locked Er-doped fiber laser

The phase-locking mechanism and results of a frequency comb based on a period-doubling mode-locked (PD-ML) fiber laser were investigated. A mode-locked fiber laser was designed to switch from fundamental mode locking (FML) to PD-ML with similar output pulses by simply changing the pump. Experimental results show that the new comb teeth generated in the PD-ML are strongly correlated with the original teeth and have a consistent carrier-envelope offset (CEO) frequency. Controlling the pump and cavity length is also suited for phase-locking the PD-ML laser. With the same f-to-2f heterodyne beat system and locking circuit, phase locking of both PD-ML and FML-based optical combs with two repetition rates, and switching between them, were obtained by changing the pump only.

A stable polarization switching laser from a bidirectional passively mode-locked thulium-doped fiber oscillator

We report on a novel polarization switching laser from a bidirectional passively mode-locked thulium(Tm)-doped fiber oscillator, which was characterized by the periodical change of polarization state of every pulse. The switching laser was created by combing two orthogonally stable vector solitons, which were found to be wave-breaking-free pulses in the all-anomalous-dispersion regime. The measured repetition rates of switching laser and the corresponding vector solitons were 49.596 MHz, 24.798 MHz, and 24.798MHz. By controlling wave plates, either of the polarized pulse trains can be switched on or off. To our knowledge, this is the first report of polarization switching laser with vector solitons in Tm fiber oscillators.

Direct generation of all-optical random numbers from optical pulse amplitude chaos

We propose and theoretically demonstrate an all-optical method for directly generating all-optical random numbers from pulse amplitude chaos produced by a mode-locked fiber ring laser. Under an appropriate pump intensity, the mode-locked laser can experience a quasi-periodic route to chaos. Such a chaos consists of a stream of pulses with a fixed repetition frequency but random intensities. In this method, we do not require sampling procedure and external triggered clocks but directly quantize the chaotic pulses stream into random number sequence via an all-optical flip-flop. Moreover, our simulation results show that the pulse amplitude chaos has no periodicity and possesses a highly symmetric distribution of amplitude. Thus, in theory, the obtained random number sequence without post-processing has a high-quality randomness verified by industry-standard statistical tests.

Dissipative soliton trapping in normal dispersion-fiber lasers

We report on the dissipative soliton (DS) trapping in a fiber ring laser mode locked with a semiconductor saturable absorber mirror and operated in normal dispersion regime. It was shown that despite the fact that a DS is strongly frequency chirped, two DSs formed along the two orthogonal polarization directions of a birefringent cavity fiber laser can incoherently couple and travel with the same group velocity in the laser. Numerical simulations have well confirmed the experimental observations.

Optical clock division based on dual-wavelength mode-locked semiconductor fiber ring laser

We have reported the optical clock division utilizing an injected mode-locked fiber ring laser incorporating semiconductor optical amplifiers (SOAs) and a dispersion compensation fiber (DCF). The clock division is mainly caused by the modulation competition between two wavelength components while both of them satisfy the harmonic mode-locking condition at the newly generated frequency. Stable second, third, and fourth clock divisions are obtained by properly adjusting the polarization controllers inside the ring cavity when a 10-GHz clock signal without any sub-harmonic frequency component is injected into the cavity. The radio-frequency spectra show good qualities of the obtained clock division trains.

Soliton polarization dynamics in fiber lasers passively mode-locked by the nonlinear polarization rotation technique

By numerically solving the coupled laser Ginzburg-Landau equations and using the pulse tracing technique to incorporate the cavity effect in the simulation, we have explicitly calculated the soliton polarization ellipses throughout the cavity of a fiber-ring laser mode-locked by the nonlinear polarization rotation technique, and investigated the soliton polarization dynamics in laser cavities. It was found that in a conventional stable soliton operation state, although the soliton polarization varies as the pulse propagates, at a fixed position inside the laser cavity the soliton polarization is invariant with time. However, in the presence of laser dynamics, at a fixed location within the cavity the soliton could either have multiple alternating fixed polarization states or no fixed polarization state at all, depending on the soliton dynamics.

Chaotic dynamics of a passively mode-locked soliton fiber ring laser

We report on the experimental and numerical studies of the chaotic dynamics of a soliton fiber ring laser passively mode-locked by using the nonlinear polarization rotation (NPR) technique. Period-doubling route to chaos on the soliton repetition rate of either the single pulse soliton or the bound solitons of the laser was experimentally observed. Based on a coupled complex Ginzburg-Landau equation model and also taking into account the laser cavity effect, we further show numerically that the period-doubling bifurcations and route to chaos are intrinsic properties of the laser, whose appearance is independent of the details of the laser cavity design and the laser soliton operation. Property of the solitons under the dynamical bifurcations is also numerically investigated.