We report on the experimental observation of stable dark solitons in an all normal dispersion fiber laser. We found experimentally that dark soliton formation is a generic feature of the fiber laser under strong continuous wave (CW) emission. However, only under appropriate pump strength and negative cavity feedback, stable single or multiple dark soliton could be achieved. Furthermore, we show that the features of the observed dark solitons could be well understood based on the nonlinear Schrodinger equation (NLSE).
The nonlinear propagation of light pulses in liquid-filled photonic crystal fibers is considered. Due to the slow reorientational nonlinearity of some molecular liquids, the nonlinear modes propagating inside such structures can be approximated, for pulse durations much shorter than the molecular relaxation time, by temporally highly-nonlocal solitons, analytical solutions of a linear Schroedinger equation. The physical relevance of these novel solitary structures, which may have a broad range of applications, is discussed and supported by detailed numerical simulations.
Vector soliton operation of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated. Either the polarization rotation or polarization locked vector dissipative solitons were experimentally obtained in a dispersion-managed cavity fiber laser with large net cavity dispersion, while in the anomalous dispersion cavity fiber laser, the phase locked NLSE solitons and induced NLSE soliton were experimentally observed. The vector soliton operation of the fiber lasers unambiguously confirms the polarization insensitive saturable absorption of the atomic layer gr…
Solitons, as stable localized wave packets that can propagate long distance in dispersive media without changing their shapes, are ubiquitous in nonlinear physical systems. Since the first experimental realization of optical bright solitons in the anomalous dispersion single mode fibers (SMF) by Mollenauer et al. in 1980 and optical dark solitons in the normal dispersion SMFs by P. Emplit et al. in 1987, optical solitons in SMFs had been extensively investigated. In reality a SMF always supports two orthogonal polarization modes. Taking fiber birefringence into account, it was later theoretica…
Solitons are non-dispersing localized waves that occur in diverse physical settings. A variety of optical solitons have been observed, but versions that involve both spatial and temporal degrees of freedom are rare. Optical fibers designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between single-mode fiber and free-space propagation. Here we report the observation of optical solitons and soliton self-frequency shifting in graded-index multimode fiber. These wave packets can be modeled as multi-component solitons, or as …
Experimental and numerical studies of spatiotemporal femtosecond soliton propagation over up to 1 km spans of parabolic graded-index (GRIN) fibers reveal that initial multimode soliton pulses naturally and irreversibly evolve into a singlemode soliton. This is carried by the fundamental mode of the fiber, which acts as a dynamical attractor of the multimode system for up to the record value (for multimode fibers) of 5600 chromatic dispersion distances. This experimental evidence invalidates the use of variational approaches, which intrinsically require that the initial multimode propagation of…
We report on the observation of various bound states of dispersion-managed (DM) solitons in a passively mode-locked Erbium-doped fiber ring laser at near zero net cavity group velocity dispersion (GVD). The generated DM solitons are characterized by their Gaussian-like spectral profile with no sidebands, which is distinct from those of the conventional solitons generated in fiber lasers with large net negative cavity GVD, of the parabolic pulses generated in fiber lasers with positive cavity GVD and negligible gain saturation and bandwidth limiting, and of the gain-guided solitons generated in…
Soliton-soliton collisions have a crucial role in enhancing the spectrum of dispersive waves in optical fibers and collisions among in-phase solitons lead to a dramatic enhancement of the dispersive wave power, as well as to its significant spectral reshaping. We obtained a simple analytical model to estimate the spectral position, width and amplitude of the dispersive waves induced by a collision of two in-phase solitons. We tested our theory in the case of a dual concentric core microstructured fiber.
We experimentally isolate and directly observe multimode solitons in few-mode graded-index fiber. By varying the input energy and modal composition of the launched pulse, we observe a continuous variation of multimode solitons with different spatiotemporal properties. They exhibit an energy-volume relation that is distinct from those of single-mode and fully spatiotemporal solitons.
We report on the experimental observation of two types of phase-locked vector soliton in weakly birefringent cavity erbium-doped fiber lasers. While a phase-locked dark-dark vector soliton was only observed in fiber lasers of positive dispersion, a phase-locked dark-bright vector soliton was obtained in fiber lasers of either positive or negative dispersion. Numerical simulations confirmed the experimental observations, and further showed that the observed vector solitons are the two types of phase-locked polarization domain-wall solitons theoretically predicted.
Rapid progress in passively mode-locked fiber lasers is currently driven by the recent discovery of vector feature of mode-locking pulses, namely, the group velocity-locked vector solitons, the phase locked vector solitons, and the high-order vector solitons. Those vector solitons are fundamentally different from the previously known scalar solitons. Here, we report a fiber laser where the mode-locked pulse evolves as a vector soliton in the strong birefringent segment and is transformed into a regular scalar soliton after the polarizer within the laser cavity. The existence of solutions in a …
We show that gap-acoustic solitons, i.e., optical gap solitons with electrostrictive coupling to sound modes, can be produced with velocities down to less than 2.5% of the speed of light using a fiber Bragg grating that is linearly coupled to a non-Bragg fiber over a finite domain. Forward- and backward-moving light pulses in the non-Bragg fiber that reach the coupling region simultaneously couple into the Bragg fiber and form a moving soliton, which then propagates beyond the coupling region.
Experimental study on the soliton dynamics of a passively mode locked fiber ring laser firstly revealed a state of bound soliton operation in the laser, where two solitons bind together tightly with fixed pulse separation. We further report on the properties of the bound-soliton emission of the laser. In particular, we demonstrate both experimentally and numerically that, like the single pulse soliton operation of the laser, the bound soliton emission is another intrinsic feature of the laser.
We experimentally observe soliton self-organization and pulsation in a passively mode-locked fiber laser. The optomechanical interaction in the optical fiber is key to the formation of equidistant soliton bunches. These solitons simultaneously undergo a pulsation process with a period corresponding to tens of the cavity round trip time. Using the dispersive Fourier transformation technique, we find that the Kelly sidebands in the shot-to-shot spectra appear periodically, synchronizing with the pulsation.
Pure solitons are for the first time distilled from the resonant continuous wave (CW) background in a fiber laser by utilizing nonlinear Fourier transform (NFT). It is identified that the soliton and the resonant CW background have different eigenvalue distributions in the nonlinear frequency domain. Similar to water distillation, we propose the approach of soliton distillation, by making NFT on a steady pulse generated from a fiber laser, then filtering out the eigenvalues of the resonant CW background in the nonlinear frequency domain, and finally recovering the soliton by inverse NFT (INFT)…
We report on the experimental observation of temporal cavity soliton destabilization via spatiotemporal chaos in a coherently-driven optical fiber ring resonator. Numerical simulations and theoretical analyses are in good agreement with experimental observations.
We report on the observation of dispersion-managed (DM) dark soliton emission in a net-normal dispersion erbium-doped fiber laser. We found experimentally that dispersion management could not only reduce the pump threshold for the dark soliton formation in a fiber laser, but also stabilize the single dark soliton evolution in the cavity. Numerical simulations have also confirmed the DM dark soliton formation in a fiber laser.
We report on the experimental observation of a novel type of polarization locked vector soliton in a passively mode-locked fiber laser. The vector soliton is characterized by that not only the two orthogonally polarized soliton components are phase locked, but also one of the components has a double-humped intensity profile. Multiple such phase-locked high order vector solitons with identical soliton parameters and harmonic mode-locking of the vector solitons were also obtained in the laser. Numerical simulations confirmed the existence of stable high-order vector solitons in fiber lasers.
The red shifted solitonic resonant radiation is a fascinating phase matching phenomenon that occurs when an optical pulse, launched in the normal dispersion regime of photonic crystal fiber, radiates across the zero dispersion wavelength. The formation of such phase-matched radiation is independent of the generation of any optical soliton and mainly governed by the leading edge of input pump which forms a shock front. The radiation is generated at the anomalous dispersion regime and found to be confined both in time and frequency domain. We experimentally investigate the formation of such radi…
The process of high-energy soliton fission is experimentally and numerically investigated in a graded-index multimode fiber. Fission dynamics is analyzed by comparing numerical observations and simulations. A novel regime is observed, where solitons produced by the fission have a nearly constant Raman wavelength shift and same pulse width over a wide range of soliton energies.
We have experimentally investigated the soliton interaction in a passively mode-locked fiber ring laser and revealed the existence of three types of strong soliton interaction: a global type of soliton interaction caused by the existence of unstable CW components; a local type of soliton interaction mediated through the radiative dispersive waves; and the direct soliton interaction. We found that the appearance of the various soliton operation modes observed in the passively mode locked fiber soliton lasers are the direct consequences of these three types of soliton interaction. The soliton in…
We have developed an analytical model based on the perturbation theory in order to study the optical propagation of two successive intense solitons in hollow-core photonic crystal fibers filled with Raman-active gases. Based on the time delay between the two solitons, we have found that the trailing soliton dynamics can experience unusual nonlinear phenomena such as spectral and temporal soliton oscillations and transport towards the leading soliton. The overall dynamics can lead to a spatiotemporal modulation of the refractive index with a uniform temporal period and a uniform or chirped spat…
Physics phenomena of multi-soliton complexes have enriched the life of dissipative solitons in fiber lasers. By developing a birefringence-enhanced fiber laser, we report the first experimental observation of group-velocity-locked vector soliton (GVLVS) molecules. The birefringence-enhanced fiber laser facilitates the generation of GVLVSs, where the two orthogonally polarized components are coupled together to form a multi-soliton complex. Moreover, the interaction of repulsive and attractive forces between multiple pulses binds the particle-like GVLVSs together in time domain to further form …
We report experimental observation of incoherently coupled dark-bright vector solitons in single-mode fibers. Properties of the vector solitons agree well with those predicted by the respective systems of incoherently coupled nonlinear Schroedinger equations. To the best of our knowledge, this is the first experimental observation of temporal incoherently coupled dark-bright solitons in single-mode fibers.
We report on the experimental observation of incoherently coupled dark vector soliton trapping in a fiber laser. Dark vector solitons along the two orthogonal polarization directions though with large difference in central frequency, energy and darkness could be still synchronously trapped as a group velocity locked dark vector soliton in virtue of the incoherent interactions. Our numerical simulation could well rebirth the experimental observations and confirm the existence of incoherently coupled dark vector soliton under certain conditions.
We study numerically and experimentally supercontinuum generation in optical fibers with dark and bright solitons simultaneously contributing into the spectral broadening and dispersive wave generation. We report a novel type of weak trapped radiation arising due to interaction of bright solitons with the dark soliton background. This radiation expresses itself as two pulses with the continuously shifting spectra constituting the short and long wavelength limits of the continuum. Our theoretical and experimental results are in good agreement.
We report results of numerical simulations on the multiple soliton generation and soliton energy quantization in a soliton fiber ring laser passively mode-locked by using the nonlinear polarization rotation technique. We found numerically that the formation of multiple solitons in the laser is caused by a peak power limiting effect of the laser cavity. It is also the same effect that suppresses the soliton pulse collapse, an intrinsic feature of solitons propagating in the gain media, and makes the solitons stable in the laser. Furthermore, we show that the soliton energy quantization observed…
Recently, in addition to exploring the application of new saturable absorber devices in fiber lasers, soliton dynamics has also become a focus of current research. In this article, we report an ultrashort pulse fiber laser based on VSe2/GO nanocomposite and verify the formation process of soliton and soliton molecules by the numerical simulation. The prepared VSe2/GO-based device shows excellent saturable absorption characteristics with a modulation depth of 14.3% and a saturation absorption intensity of 0.93MW/cm2. The conventional soliton is obtained with pulse width of 573fs, which is curre…
Ultrafast fiber lasers play important roles in many aspects of our life for their various applications in fields ranging from fundamental sciences to industrial purposes. Passive mode-locking technique is a key step to realize the ultrafast soliton fiber lasers. However, the booting dynamics of the soliton fiber lasers have not yet been well understood. Herein, we reveal the soliton buildup dynamics of ultrafast fiber lasers operating both in anomalous and net-normal dispersion regimes. Based on the advanced experimental methodologies of spatio-temporal reconstruction and dispersive Fourier tr…
In this work, we unveil the unique complex dynamics of multimode soliton interactions in graded-index optical fibers through simulations and experiments. By generating two multimode solitons from the fission of an input femtosecond pulse, we examine the evolution of their Raman-induced red-shift when the input pulse energy grows larger. Remarkably, we find that the output red-shift of the trailing multimode soliton may be reduced, so that it accelerates until it collides with the leading multimode soliton. As a result of the inelastic collision, a significant energy transfer occurs between the…
Soliton fusion is a fascinating and delicate phenomenon that manifests itself in optical fibers in case of interaction between co-propagating solitons with small temporal and wavelengths separation. We show that the mechanism of acceleration of trailing soliton by dispersive waves radiated from the preceding one provides necessary conditions for soliton fusion at the advanced stage of supercontinuum generation in photonic crystal fibers. As a result of fusion large intensity robust light structures arise and propagate over significant distances. In presence of small random noise the delicate c…
We propose an optical trapping technique in which a fundamental soliton traps an ultrashort small amplitude radiation in a symmetric hollow-core photonic crystal fiber filled with a noble gas, preventing its dispersion. The system is Raman- and plasma-free. Trapping is due to the cross phase modulation effect between the two pulses. The trapped radiation inside the soliton-induced potential will oscillate periodically due to the shock effect, similar to the motion of a mechanical pendulum.
We predict that a photonic crystal fiber whose strands are filled with a defocusing nonlinear medium can support stable bright and also vortex solitons if the strength of the defocusing nonlinearity grows toward the periphery of the fiber. The domains of soliton existence depend on the transverse growth rate of the filling nonlinearity and nonlinearity of the core. Remarkably, solitons exist even when the core material is linear.
Investigation of internal polarization dynamics of vector dissipative-soliton-resonance (DSR) pulses in a mode-locked fiber laser is presented. Stable vector DSR pulses are experimentally ob- served. Using a waveplate-analyzer configuration, we find that polarization is not uniform across a resonant dissipative soliton. Specifically, although the central plane wave of the resonant dissi- pative soliton acquires nearly a fixed polarization, the fronts feature polarization states that are different and spatially varying. This distinct polarizaiton distribution is maintained while the whole solit…
We report on trapped pulse generation in birefringent microstructured optical fiber. Linearly polarized fs pulses are injected into the microstructured fiber in anomalous dispersion regime. We observed experimentally that soliton pulse polarized along the fast fiber axis partially transfers its energy to the orthogonal polarization. The generated pulse is amplified through the orthogonal Raman gain. The two polarization components are located at group-velocity matched wavelengths. The experimental works are supported with numerical simulations. The obtained results are important for the light …
We report the experimental observation of multiple dispersive waves emitted in the anomalous dispersion region of an optical fiber from a train of dark solitons. Each individual dispersive wave can be associated to one particular dark soliton of the train, using phase-matching arguments involving higher-order dispersion and soliton velocity. For a large number of dark solitons (>10), we observe the formation of a continuum associated with the efficient emission of dispersive waves.
We report on the observation of bound states of gain-guided solitons (GGSs) in a dispersion-managed erbium-doped fiber laser operating in the normal net cavity dispersion regime. Despite of the fact that the GGS is a chirped soliton and there is strong pulse stretching and compression along the cavity in the laser, the bound solitons observed have a fixed pulse separation, which is invariant to the pump strength change. Numerical simulation confirmed the experimental observations.
We report on the experimental observation of a new type of dark soliton in a fiber laser made of all normal group velocity dispersion fibers. It was shown that the soliton is formed due to the cross coupling between two different wavelength laser beams and has the characteristic of separating the two different wavelength laser emissions. Moreover, we show experimentally that the dual-wavelength dark solitons have a much lower pump threshold than that of the nonlinear Schrödinger equation dark solitons formed in the same laser.
For the first time, we demonstrated alternative generation of dispersion-managed (DM) solitons or similaritons in an all-fiber Erbium-doped laser. DM solitons or similaritons can be chosen to emit at the same output port by controlling birefringence in the cavity. The pulse duration of 87-fs for DM solitons and 248-fs for similaritons have been observed. For proof of similaritons, we demonstrate that the spectral width depends exponentially on the pump power, consistent with theoretical studies. Besides, the phase profile measured by a frequency-resolved optical gating (FROG) is quadratic corr…
We report on the experimental evidence of four wave mixing (FWM) between the two polarization components of a vector soliton formed in a passively mode-locked fiber laser. Extra spectral sidebands with out-of-phase intensity variation between the polarization resolved soliton spectra was firstly observed, which was identified to be caused by the energy exchange between the two soliton polarization components. Other features of the FWM spectral sidebands and the soliton internal FWM were also experimentally investigated and numerically confirmed.
Gas-filled hollow-core photonic crystal fibers offer unprecedented opportunities to observe novel nonlinear phenomena. The various properties of gases that can be used to fill these fibers give additional degrees of freedom for investigating nonlinear pulse propagation in a wide range of different media. In this review, we will consider some of the the new nonlinear interactions that have been discovered in recent years, in particular those which are based on soliton dynamics.
We report on the experimental observation of induced solitons in a passively mode-locked fiber ring laser with birefringence cavity. Due to the cross coupling between the two orthogonal polarization components of the laser, it was found that if a soliton was formed along one cavity polarization axis, a weak soliton was also induced along the orthogonal polarization axis, and depending on the net cavity birefringence, the induced soliton could either have the same or different center wavelengths to that of the inducing soliton. Moreover, the induced soliton always had the same group velocity as…
Dissipative solitons are non-dispersive localized waves that exhibit intriguing dynamics. In optical systems, the discovery of new soliton dynamics and how to accurately manipulate dissipative solitons are still largely unexplored and challenging in the ultrafast fiber laser community. Herein, we unveil a new type of dissipative soliton behavior in a net-normal-dispersion bidirectional ultrafast fiber laser. That is, the bidirectional dissipative solitons will always reveal similar spectral and temporal characteristics through common gain and loss modulation, even if the transient instability …
New resonant emission of dispersive waves by oscillating solitary structures is considered analytically and numerically. The resonance condition for the radiation is derived and it is demonstrated that the predicted resonances match the spectral lines observed in numerical simulations perfectly. The complex recoil of the radiation on the soliton dynamics is discussed.
We propose and experimentally demonstrate the generation of pseudo-high-order group velocity locked vector solitons (GVLVS) in a fiber laser using a SESAM as the mode locker. With the help of an external all-fiber polarization resolved system, a GVLVS with a two-humped pulse along one polarization while a single-humped pulse along the orthogonal polarization could be obtained. The phase difference between the two humps is 180 degree.
We report a study of soliton self-frequency shifting in hydrogen-filled hollow-core fiber. The combination of hydrogen and short 40-fs input pulses underlies clean and efficient generation of Raman solitons between 1080 and 1600 nm. With 240-nJ input pulses, the Raman soliton energy ranges from 110 to 20 nJ over that wavelength range, and the pulse duration is approximately 45 fs. In particular, 70-nJ and 42-fs pulses are generated at 1300 nm. Numerical simulations agree reasonably well with experiments and predict that microjoule-energy tunable pulses should be possible with higher-energy inp…
We demonstrate self-started mode-locking in an Erbium-doped fiber ring laser by using the nonlinear polarization rotation mode-locking technique but without an isolator in cavity. We show that due to the intrinsic effective nonlinearity discrimination of the mode-locked pulse propagating along different cavity directions, the soliton operation of the laser is always unidirectional, and its features have no difference to that of the unidirectional lasers with an isolator in cavity.
We report on the generation of multi-wavelength dissipative soliton (DS) in an all normal dispersion fiber laser passively mode-locked with a semiconductor saturable absorber mirror (SESAM). We show that depending on the strength of the cavity birefringence, stable single-, dual- and triple-wavelength DSs can be formed in the laser. The multi-wavelength soliton operation of the laser was experimentally investigated, and the formation mechanisms of the multi-wavelength DSs are discussed.
Pulsating behavior is a universal phenomenon in versatile fields. In nonlinear dissipative systems, the solitons could also pulsate under proper conditions and show many interesting dynamics. However, the pulsation dynamics is generally concerned with single soliton case. Herein, by utilizing real-time spectroscopy technique, namely, dispersive Fourier-transform (DFT), we reveal the versatile categories of pulsating solitons in a fiber laser. In particular, the weak to strong explosive behaviors of pulsating soliton, as well as the rogue wave generation during explosions were observed. Moreove…
The possibility of soliton self-compression of ultrashort laser pulses down to the few-cycle regime in photonic crystal fibers is numerically investigated. We show that efficient sub-two-cycle temporal compression of nanojoule-level 800 nm pulses can be achieved by employing short (typically 5-mm-long) commercially available photonic crystal fibers and pulse durations of around 100 fs, regardless of initial linear chirp, and without the need of additional dispersion compensation techniques. We envisage applications in a new generation of compact and efficient sub-two cycle laser pulse sources.
Evolution of dissipative-soliton-resonance (DSR) pulses in an all-normal-dispersion fiber laser with pump power under various operation conditions are experimentally studied. The fiber laser is mode-locked by using a nonlinear fiber loop mirror. Apart from the typical pulse broadening due to the peak power clamping effect, pulse breaking was observed. In addition, pulse narrowing with pump power increasing was observed. All the incompatible evolution of DSR pulses could be attributed to the multiple parameters change due to pump power increasing under specific operation conditions.
We show theoretically that the photoionization process in a hollow-core photonic crystal fiber filled with a Raman-inactive noble gas leads to a constant acceleration of solitons in the time domain with a continuous shift to higher frequencies, limited only by ionization loss. This phenomenon is opposite to the well-known Raman self-frequency red-shift of solitons in solid-core glass fibers. We also predict the existence of unconventional long-range non-local soliton interactions leading to spectral and temporal soliton clustering. Furthermore, if the core is filled with a Raman-active molecul…
We report an experimental observation of the collision between a linear wave propagating in the anomalous dispersion region of an optical fiber and a dark soliton located in the normal dispersion region. This interaction results in the emission of a new frequency component whose wavelength can be predicted using phase-matching arguments. The measured efficiency of this process shows a strong dependency with the soliton grayness and the linear wave wavelength, and is in a good agreement with theory and numerical simulations.
Atomic layer graphene possesses wavelength-insensitive ultrafast saturable absorption, which can be exploited as a full-band mode locker. Taking advantage of the wide band saturable absorption of the graphene, we demonstrate experimentally that wide range (1570 nm - 1600nm) continuous wavelength tunable dissipative solitons could be formed in an erbium doped fiber laser mode locked with few layer graphene.
We present a passively mode-locked, tunable soliton Ho:fiber ring oscillator, optimized for seeding of Ho:YLF amplifiers. The oscillator is independently tunable in central wavelength and spectral width from 2040 nm to 2070 nm and from 5 nm to 10 nm, respectively. At all settings the pulse energy within the soliton is around 800 pJ. The soliton oscillator was optimized to fully meets the spectral requirements for seeding Ho:YLF amplifiers. Its Kelly sidebands are located outside the amplifier gain spectrum, resulting in a train of about 1 ps long pedestal-free pulses with relative intensity no…
