Pulse dynamics of dissipative soliton resonance with large duration-tuning range in a fiber ring laser

Efficient Raman pulse fiber laser pumped by a dissipative soliton resonance pulse near 2 µm

A high-efficiency Raman conversion from 1.987 µm to 2.177 µm is demonstrated experimentally in 45 m GeO₂-doped silica fiber, adopting a dissipative soliton resonance (DSR) rectangular pulse as the pump. Over the entire spectral distribution, the spectral purity of the first-order Raman pulse is up to 96.8%, suggesting a nearly complete pump depletion before the onset of cascaded Raman shifts. The corresponding pump-to-Raman conversion efficiency of 67.4% is the highest up to date in this spectral region. Meanwhile, a large Raman pulse energy of 1.03 µJ was obtained at the repetition rate near MHz level, corresponding to 0.893 W average power. In the total output, the Raman-dominated spike has a Full Width Half Maximum (FWHM) of 1.18 ns far narrower than DSR's pulse duration of 10.25 ns. The results indicate that DSR is a promising candidate for developing efficient Raman nanosecond pulse fiber laser in mid-infrared (MIR) region.

Dissipative pure-quartic soliton fiber laser

The evolution of ultrafast laser technology hinges partially on the understanding of the soliton nonlinear dynamics. Recently, the concept of pure-quartic soliton (PQS) that arises from the balance of pure negative fourth-order dispersion (FOD) and nonlinearity was proposed to generate high peak power pulse. Herein, we investigate the generation of dissipative pure-quartic soliton (DPQS) in a fiber laser, which is balanced among the positive FOD, nonlinearity, gain and loss. The DPQS features the shape-preserving propagation despite the asymmetrical temporal profile at higher pulse energy. It is found that the asymmetrical temporal profile of DPQS is resulted from the mismatching of the phase shift profiles caused by self-phase modulation and FOD. Moreover, it is demonstrated that the DPQS possesses a higher energy-scaling ability compared to conventional dissipative soliton, owing to the nonlinear relationship between the pulse energy and pulse duration. These findings demonstrated that the employment of positive FOD could be a promising way for manipulation of optical pulse as well as the improvement of laser performance.

Autosetting soliton pulsation in a fiber laser by an improved depth-first search algorithm

Soliton pulsation is one of the most fascinating phenomena in ultrafast fiber lasers, owing to its rich nonlinear dynamics and potential generation of high peak power pulse. However, it is still a challenge to efficiently search for pulsating soliton in fiber lasers because it requires a fine setting of laser cavity parameters. Here, we report the autosetting soliton pulsation in a passively mode-locked fiber laser. The parameters of electronic polarization controller are intelligently adjusted to search for pulsating soliton state by the improved depth-first search algorithm. Moreover, the intensity modulation depth of pulsating soliton could be flexibly controlled. These findings indicate that the intelligent control of a fiber laser is an effective way to explore on-demand soliton dynamics and is also beneficial to the optimization of ultrafast laser performance.

1.3 µm dissipative soliton resonance generation in Bismuth doped fiber laser

In this work, a Figure-9 (F9) bismuth-doped fiber laser (BiDFL) operating in the dissipative soliton resonance (DSR) regime is presented. The 1338 nm laser used a BiDF as the active gain medium, while a nonlinear amplifying loop mirror (NALM) in an F9 configuration was employed to obtain high energy mode-locked pulses. The wave breaking-free rectangular pulse widened significantly in the time domain with the increase of the pump power while maintaining an almost constant peak power of 0.6 W. At the maximum pump power, the mode-locked laser delivered a rectangular-shaped pulse with a duration of 48 ns, repetition rate of 362 kHz and a radio-frequency signal-to-noise ratio of more than 60 dB. The maximum output power was recorded at around 11 mW with a corresponding pulse energy of 30 nJ. This is, to the best of the author's knowledge, the highest mode-locked pulse energy obtained at 1.3 μm as well as the demonstration of an NALM BiDFL in a F9 configuration.

Fe3O4 nanoparticle-enabled mode-locking in an erbium-doped fiber laser

In this paper, we have proposed and demonstrated the generation of passively mode-locked pulses and dissipative soliton resonance in an erbium-doped fiber laser based on Fe3O4 nanoparticles as saturable absorbers. We obtained self-starting mode-locked pulses with fundamental repetition frequency of 7.69 MHz and center wavelength of 1561 nm. The output of a pulsed laser has spectral width of 0.69 nm and pulse duration of 14 ns with rectangular pulse profile at the pump power of 190 mW. As far as we know, this is the firsttimethatFe3O4 nanoparticles have been developed as low-dimensional materials for passive mode-locking with rectangular pulse. Our experiments have confirmed that Fe3O4 has a wide prospect as a nonlinear photonics device for ultrafast fiber laser applications.

Peak-power-clamping in an all-polarization-maintaining Q-switched mode-locking fiber laser

We report the peak-power-clamping (PPC) effect in a polarization-maintaining (PM) Q-switched mode locking fiber laser. The laser cavity with a compact and stable all-PM fiber configuration can clearly demonstrate three different output states including normal Q-switching, PPC Q-switching, and PPC Q-switched mode-locking (QML) with the increasing pump power. To the best of our knowledge, it is the first time that PPC effect is successfully obtained and analyzed from the Q-switching to QML. This research extends the theory of PPC in pulsed lasers and reveals the potential to achieve ultra-high pulse energy.

Dynamical diversity of pulsating solitons in a fiber laser

Pulsating behavior is a universal phenomenon in versatile fields. In nonlinear dissipative systems, the solitons also pulsate under proper conditions and show many interesting dynamics. However, the pulsation dynamics are generally concerned with single-soliton cases. Herein, by utilizing real-time spectroscopy technique, namely, dispersive Fourier-transform (DFT), we reveal the distinct dynamical diversity of pulsating solitons in a fiber laser. In particular, the weak to strong explosive behaviors of pulsating solitons, as well as the rogue wave generation during explosions are observed. Moreover, the concept of soliton pulsation is extended to the multi-soliton case. It is found that the simultaneous pulsations of energy, separation and relative phase difference could be observed for solitons inside the molecule, while the pulsations of each individual in a multi-soliton bunch could be regular or irregular. These findings will shed new insights into the complex nonlinear behavior of solitons in ultrafast fiber lasers as well as dissipative optical systems.

Multiple stable states of dissipative soliton resonance in a passively mode-locked Yb-doped fiber laser

Dissipative soliton resonance (DSR) with multiple stable states has been experimentally demonstrated in a passively mode-locked Yb-doped fiber laser. The generation of the DSR square pulse has been achieved with the nonlinear optical loop mirror technique. The duration of the square pulse varies from 16 to 123 ns, while the amplitude of the pulse remains constant. Experimentally, by fixing the pump power and changing the orientations of the polarization controllers, we have observed three different square pulses that all operate in the DSR regime. At the same time, we have obtained a wavelength-tunable square pulse, which demonstrates that the DSR and operation wavelength are independent of each other. We also analyzed the ideal state in the DSR regime.

Long cavity ring fiber mode-locked laser with decreased net value of nonlinear polarization rotation

We investigate a new configuration of a mode-locked fiber laser by using a nonlinear polarization rotation-based design to generate soliton pulses with low repetition rate. Unlike with previously reported configurations, we introduce a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 437 m including a 400-m long twisted SMF-28 fiber. The fiber was twisted to cancel the linear birefringence and to ensure that the polarization ellipticity is not altered as the pulse travels along the fiber. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. Depending on the polarization state we observed three different emission regimes, the single soliton regime (SR), conventional noise-like pulses (NLP) and noise-like square-waveform pulse (NLSWP). In the SR, a 467.2 kHz train of solitons was obtained with pulse duration of 2.9 ps at 1558.7 nm.

Chirp-adjustable square-wave pulse in a passively mode-locked fiber laser

A passively mode-locked fiber laser to generate chirp-adjustable square-wave pulses is reported. A simple chirp measurement system is designed to study the output chirp of the fiber laser. The results indicate that the chirp of the square-wave pulses in our fiber laser can be adjusted by the polarization controllers inside the cavity. Three typical chirp states, including random chirp, V-shaped chirp and linear chirp, are achieved. This kind of fiber laser cannot only help to further understand the characteristics of square-wave pulse but also serve as multifunction light source for potential applications.

Mechanism of dissipative-soliton-resonance generation in fiber laser mode-locked by real saturable absorber

Generation of dissipative soliton resonance (DSR) is numerically investigated in an all-normal-dispersion Yb-doped fiber laser mode-locked by a real saturable absorber (SA). In the simulation model, the SA includes both the saturable absorption and reverse saturable absorption (RSA) effects. It is found that the RSA effect induced by the SA material itself plays a dominant role in generating the DSR pulses. We also systematically analyze the influence of key SA parameters on the evolution of DSR pulses in the cavity. Our simulation results not only offer insight into the underlying mechanism of DSR generation in mode-locked fiber lasers by means of real SAs, but also provide a guideline for engineering SA parameters to generate optical pulses with the highest possible energy.

Buildup dynamics of dissipative soliton in an ultrafast fiber laser with net-normal dispersion

Taking advantage of technology of spatio-temporal reconstruction and dispersive Fourier transform (DFT), we experimentally observed the buildup dynamics of dissipative soliton in an ultrafast fiber laser in the net-normal dispersion regime. The soliton buildup dynamics were analyzed in both the spectral and temporal domains. We firstly revealed that the appearing of the spectral sharp peaks with oscillation structures during the mode-locking transition is caused by the formation of structural dissipative soliton. The experimental results were explained by the numerical simulations. These findings would give some new insights into the dissipative soliton buildup dynamics in ultrafast fiber lasers.

Dissipative soliton resonance mode-locked all-polarization-maintaining double clad Er:Yb fiber laser

Our first demonstration of an all-PM fiber double clad erbium-ytterbium figure-8 laser mode-locked in a dissipative soliton resonance regime is presented. The laser generated µJ-level rectangular-shaped pulses with a maximum average output power of 1 W at 994 kHz repetition rate. The proposed configuration was characterized for two values resonator lengths - 44 and 205 m (total net-dispersion -0.9274 ps² and -4.3084 ps², respectively) to verify the possibility of non-complex tailoring of pulse parameters. The long-term stability of the all-PM configuration and self-starting of the mode-locking was experimentally confirmed by exposing the laser to forces of -5G to 7G magnitude on a vibration generator.

Dissipative soliton resonance in Bismuth-doped fiber laser

We experimentally demonstrate the generation of dissipative soliton resonance (DSR) in a passively mode-locked Bi-doped fiber ring laser based on nonlinear polarization rotation (NPR) technique. The DSR with the central wavelength of 1169.5 nm has a repetition rate of 343.7 kHz. By purely increasing the pump power, the DSR evolves from Gaussian shape to rectangular shape with the duration extending from 2.1 ns to 13.1 ns, while keeping the pulse amplitude and the 3-dB spectrum bandwidth almost constant. The single-pulse energy reaches 24.82 nJ. Furthermore, we construct a lumped model to reproduce the mode-locking process and the traits of the DSR pulse. The obtained results indicate that it could achieve higher pulse energy in mode-locked Bi-doped fiber laser by generating DSR.

Pulse-spacing manipulation in a passively mode-locked multipulse fiber laser

Passively mode-locked fiber lasers have been intensively applied in various research fields. However, the passive mode-locking typically operates in free-running regime, which easily produces messy multiple pulses due to the fruitful nonlinear effects involved in optical fibers. Actively controlling those disordered pulses in a passively mode-locked laser is of great interest but rarely studied. In this work, we experimentally investigate a flexible pulse-spacing manipulation in the passively mode-locked multipulse fiber laser by both intracavity and extracavity methods. A tuning range of pulse spacing up to 1.5 ns is achieved. More importantly, continuous pulse-spacing modulation is successfully demonstrated through external optical injection. It is anticipated that the results can contribute to the understanding of laser nonlinear dynamics and pursuing the optimal performance of passively mode-locked fiber lasers for practical applications.

Multipulse dynamics under dissipative soliton resonance conditions

The stable multipulse emission from an erbium-doped mode-locked fiber laser in dissipative soliton resonance (DSR) regime is numerically and experimentally investigated. It shows that in the multipulse operation of DSR, all pulses have identical characteristics. The number of these pulses is determined by the initial conditions, and keeps constant with the growth of pump power. Experimental results match well with the theoretical simulations. In the experiment, we obtain as high as 86 dual-wavelength DSR pulses, which have the same characteristics and are equally spaced in the cavity. Since the pulses behave similarly to harmonic mode-locking (HML), we call this phenomenon HML under DSR. By properly adjusting the polarization controllers, other numbers of multipulse emission in DSR region can be observed, which confirms that the number of DSR pulses depends on the initial conditions.

1.2-W average-power, 700-W peak-power, 100-ps dissipative soliton resonance in a compact Er:Yb co-doped double-clad fiber laser

Mode-locked pulses in the dissipative soliton resonance (DSR) regime enable extremely high pulse energy, but typically have the limited peak power of <100  W and a nanosecond-long pulse duration. In this Letter, we demonstrate high-peak-power, ultrashort DSR pulses in a compact Er:Yb co-doped double-clad fiber laser. The linear cavity is simply formed by two fiber loop mirrors (FLMs) using a 50/50 optical coupler (OC) and a 5/95 OC. The 5/95 FLM with a short loop length of 3 m is not only used as the output mirror, but also acts as a nonlinear optical loop mirror for initiating high-peak-power DSR. In particular, the mode-locked laser can deliver ∼100  ps DSR pulses with a maximum average power of 1.2 W and a peak power as high as ∼700  W. This is, to the best of our knowledge, the highest peak power of DSR pulses obtained in mode-locked fiber lasers.

Dynamic trapping of a polarization rotation vector soliton in a fiber laser

Ultrafast fiber laser, as a dissipative nonlinear optical system, plays an important role in investigating various nonlinear phenomena and soliton dynamics. Vector features of solitons, including polarization locked and polarization rotation vector solitons (PRVSs), are interesting nonlinear dynamics in ultrafast fiber lasers. Herein, we experimentally reveal the trapping characteristics of PRVSs for the first time, to the best of our best knowledge. We show that, for the conventional soliton trapping in the ultrafast fiber laser, the soliton central wavelengths of the two polarization components are constant at the laser output port. However, it is found that the dynamic trapping can be observed for the PRVS. That is, the peak frequencies along the two orthogonal polarization directions are dynamically alternating, depending on the relative intensities of the two polarization components. The obtained results would further unveil the physical mechanism of PRVSs.

Instantaneous frequency measurement of dissipative soliton resonant light pulses

We measured the instantaneous frequency profile of two different dissipative soliton resonant (DSR) light pulses, the usual flat-top and less-common trapezoid-shaped light pulses. The DSR light pulses were provided by an ytterbium-doped polarization-maintaining fiber ring passively mode-locked laser using the adequately selected amount of net-normal dispersion. We confirmed that the DSR light pulses have a (moderately) low linear chirp across the pulse, except at the edges, where the chirp changes exponentially. This unique instantaneous frequency behavior can be succinctly resumed by the following parameters: linear chirp slope and leading and trailing chirp lifetimes. As the pump power increases, the linear chirp slope decreases, whereas the leading and trailing chirp lifetimes do not show an appreciable change. The results are compared with previous theoretical works.

Compact all-fiber figure-9 dissipative soliton resonance mode-locked double-clad Er:Yb laser

The first demonstration of a compact all-fiber figure-9 double-clad erbium-ytterbium laser working in the dissipative soliton resonance (DSR) regime is presented. Mode-locking was achieved using a nonlinear amplifying loop (NALM) resonator configuration. The laser was assembled with an additional 475 m long spool of SMF28 fiber in the NALM loop in order to obtain large net-anomalous cavity dispersion (-10.4  ps²), and therefore ensure that DSR would be the dominant mode-locking mechanism. At maximum pump power (4.78 W) the laser generated rectangular-shaped pulses with 455 ns duration and an average power of 950 mW, which at a repetition frequency of 412 kHz corresponds to a record energy of 2.3 μJ per pulse.

Dissipative soliton resonance mode-locked double clad Er:Yb laser at different values of anomalous dispersion

Emission of an all-fiber, Dissipative Soliton Resonance (DSR) mode-locked, Double-Clad (DC), Erbium-Ytterbium (Er:Yb) laser configuration is investigated under several different values of large anomalous dispersion. The laser was mode-locked by means of Nonlinear Amplifying Loop Mirror (NALM) in a Figure-8 (F8) resonator configuration. The boundaries of anomalous dispersion in which the laser operated in purely DSR regime was experimentally verified by changing the length of passive SMF28 fiber spliced into the NALM. The influence of 6 different values of dispersion (-1.061 ps² to -10.7 ps²) on the pulse properties is presented and discussed.

100 W dissipative soliton resonances from a thulium-doped double-clad all-fiber-format MOPA system

In this paper, we first achieve nanosecond-scale dissipative soliton resonance (DSR) generation in a thulium-doped double-clad fiber (TDF) laser with all-anomalous-dispersion regime, and also first scale the average power up to 100.4 W by employing only two stage TDF amplifiers, corresponding to gains of 19.3 and 14.4 dB, respectively. It is noted that both the fiber laser oscillator and the amplification system employ double-clad fiber as the gain medium for utilizing the advantages in high-gain-availability, high-power-handling and good-mode-quality-maintaining. DSR mode-locking of the TDF oscillator is realized by using a nonlinear optical loop mirror (NOLM), which exhibits all-fiber-format, high nonlinear and passive saturable absorption properties. The TDF oscillator can deliver rectangular-shape pulses with duration ranging from ~3.74 to ~72.19 ns while maintaining a nearly equal output peak power level of ~0.56 W, namely peak power clamping (PPC) effect. Comparatively, the two stage amplifiers can scale the seeding pulses to similar average power levels, but to dramatically different peak powers ranging from ~0.94 to ~18.1 kW depending on the durations. Our TDF master-oscillator-power-amplifier (MOPA) system can provide a high power 2-μm band all-fiber-format laser source both tunable in pulse duration and peak power.

Dissipative soliton resonance in a full polarization-maintaining fiber ring laser at different values of dispersion

We investigated the dissipative solitons resonance in an ytterbium-doped fiber ring laser in which all the elements are polarization maintaining (PM). A semiconductor saturable absorber mirror was used as a mode-locker. The cavity included a normal dispersion single-mode fiber (SMF) and an anomalous dispersion photonic crystal fiber. The change of the length of the PM SMF allows the variation of the net-normal dispersion of the cavity in the range from 0.022 ps² to 0.262 ps². As the absolute value of the net-normal dispersion increases from 0.022 ps² to 0.21 ps², a square-shaped single pulse transformed to a single right-angle trapezoid-shaped pulse, and, at the dispersion of 0.262 ps², to multiple right-angle trapezoid-shaped pulses, per round-trip.

Generation of high energy square-wave pulses in all anomalous dispersion Er:Yb passive mode locked fiber ring laser

We have experimentally demonstrated square pulses emission from a co-doped Er:Yb double-clad fiber laser operating in anomalous dispersion DSR regime using the nonlinear polarization evolution technique. Stable mode-locked pulses have a repetition rate of 373 kHz with 2.27 µJ energy per pulse under a pumping power of 30 W in cavity. With the increase of pump power, both the duration and the energy of the output square pulses broaden. The experimental results demonstrate that the passively mode-locked fiber laser operating in the anomalous regime can also realize a high-energy pulse, which is different from the conventional low-energy soliton pulse.

Versatile patterns of multiple rectangular noise-like pulses in a fiber laser

We report on the generation of versatile patterns of multiple rectangular noise-like pulses (NLPs) in a fiber laser mode-locked by nonlinear amplifying loop mirror (NALM). Benefiting from the strengthened nonlinear effect of a segment of highly nonlinear fiber (HNLF) in the loop, multiple rectangular NLPs with various patterns are formed depending on the cavity parameter settings. In particular, the multiple rectangular NLPs could possess unequal packet durations, which is different from the conventional multi-soliton patterns. The experimental results contribute to further understanding the characteristics of the rectangular NLP and the dynamics of multi-pulse patterns.

Successive soliton explosions in an ultrafast fiber laser

Soliton explosions, as one of the most fascinating nonlinear phenomena in dissipative systems, have been investigated in different branches of physics, including the ultrafast laser community. Herein, we reported on the soliton dynamics of an ultrafast fiber laser from steady state to soliton explosions, and to huge explosions by simply adjusting the pump power level. In particular, the huge soliton explosions show that the exploding behavior could operate in a sustained, but periodic, mode from one explosion to another, which we term as "successive soliton explosions." The experimental results will prove to be fruitful to the various communities interested in soliton explosions.

Fully-integrated dual-wavelength all-fiber source for mode-locked square-shaped mid-IR pulse generation via DFG in PPLN

First demonstration of a dissipative soliton resonance (DSR), double-clad (DC) active fiber, mode-locked figure-8 laser (F8L) enabling simultaneous amplification of 1064 nm seed signal is presented. Appropriate design supported peak power clamping (PPC) effect in the laser resonator and enabled easy tuning of the generated, square-shaped pulses from 20 ns to 170 ns. By incorporating a circulator-based isolating element in the directional loop of the laser, record pulse energy of 2.13 μJ was achieved, directly at the output of the resonator. The usability of the unique dual-wavelength design was experimentally put to a test in a difference frequency generation (DFG) setup using periodically poled lithium niobate (PPLN) crystal.

Dissipative soliton resonances in all-fiber Er-Yb double clad figure-8 laser

First demonstration of exploiting Dissipative Soliton Resonance (DSR) effects for generating high energy square-shaped pulses in an all-fiber mode-locked Double Clad (DC) erbium-ytterbium (Er-Yb) figure-8 laser (F8L) is presented. The laser was capable of generating 170 ns pulses with an average power of 1.7 W at 800 kHz repetition rate, which corresponds to a record pulse energy of 2.13 μJ, achieved directly from the resonator, without Q-switching, cavity dumping or additional amplifiers. Unique circulator-based out-coupling of high energy pulses in the directional loop is proposed as a method of preventing damage to the all-fiber setup. Appropriate laser design allowed utilizing Peak Power Clamping (PPC) effect for linear pulse duration tuning via changing the pump power.

Flexible generation of coherent rectangular pulse from an ultrafast fiber laser based on dispersive Fourier transformation technique

We propose a new solution to flexibly generate the coherent rectangular pulse from an ultrafast fiber laser based on the dispersive Fourier transformation (DFT) technique. The rectangular dissipative soliton (DS) spectra emitted from a net-normal dispersion mode-locked fiber laser is mapped into a time-domain coherent rectangular waveform through the DFT technique. The rectangular pulse can be broadened flexibly with the adjustments of the pump power. The coherence and shot-to-shot fluctuations of the achieved rectangular pulses are further verified by the Mach-Zehnder interference experiment and the recorded single-shot pulse train, respectively. The results demonstrate that the combination of DS mode-locked laser and DFT technique might be indeed an effective and flexible way to achieve highly coherent rectangular pulses.

Analytical identification of soliton dynamics in normal-dispersion passively mode-locked fiber lasers: from dissipative soliton to dissipative soliton resonance

A combined analytical approach to classify soliton dynamics from dissipative soliton to dissipative soliton resonance (DSR) is developed based on the established laser models. The approach, derived from two compatible analytical solutions to the complex cubic-quintic Ginzburg-Landau equation (CQGLE), characterizes the pulse evolution process from both algebraic and physical points of view. The proposed theory is proved to be valid in real world laser oscillators according to numerical simulations, and potentially offers guideline on the design of DSR cavity configurations.

Different polarization dynamic states in a vector Yb-doped fiber laser

Different polarization dynamic states in an unidirectional, vector, Yb-doped fiber ring laser have been observed. A rich variety of dynamic states, including group velocity locked polarization domains and their splitting into regularly distributed multiple domains, polarization locked square pulses and their harmonic mode locking counterparts, and dissipative soliton resonances have all been observed with different operating parameters. We have also shown experimentally details of the conditions under which polarization-domain-wall dark pulses and bright square pulses form.

Noise-like pulse trapping in a figure-eight fiber laser

We report on the trapping of noise-like pulse in a figure-eight fiber laser mode locked by nonlinear amplifier loop mirror (NALM). After achievement of noise-like vector pulse, it was found that the wavelength shift of the two resolved polarization components responsible for the pulse trapping was very sensitive to the cavity birefringence. By properly rotating the polarization controllers (PCs), the wavelength shift could be up to 4.8 nm, which is much larger than that of conventional soliton trapping. The observed results would shed some light on the fundamental physics of noise-like pulse as well as its vector features in fiber lasers.

Generation and evolution of mode-locked noise-like square-wave pulses in a large-anomalous-dispersion Er-doped ring fiber laser

In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, we experimentally demonstrate the formation of noise-like square-wave pulse, which shows quite different features from conventional dissipative soliton resonance (DSR). The corresponding temporal and spectral characteristics of a variety of operation states, including Q-switched mode-locking, continuous-wave mode-locking and Raman-induced noise-like pulse near the lasing threshold, are also investigated. Stable noise-like square-wave mode-locked pulses can be obtained at a fundamental repetition frequency of 195 kHz, with pulse packet duration tunable from 15 ns to 306 ns and per-pulse energy up to 200 nJ. By reducing the linear cavity loss, stable higher-order harmonic mode-locking had also been observed, with pulse duration ranging from 37 ns at the 21st order harmonic wave to 320 ns at the fundamental order. After propagating along a piece of long telecom fiber, the generated square-wave pulses do not show any obvious change, indicating that the generated noise-like square-wave pulse can be considered as high-energy pulse packet for some promising applications. These experimental results should shed some light on the further understanding of the mechanism and characteristics of noise-like square-wave pulses.

Switchable dual-wavelength Q-switched and mode-locked fiber lasers using a large-angle tilted fiber grating

We proposed and demonstrated pulsed fiber lasers Q-switched and mode-locked by using a large-angle tilted fiber grating, for the first time to our best knowledge. Owing to the unique polarization properties of the large-angle tilted fiber grating (LA-TFG), i.e. polarization-dependent loss and polarization-mode splitting, switchable dual-wavelength Q-switched and mode-locked pulses have been achieved with short and long cavities, respectively. For the mode-locking case, the laser was under the operation of nanosecond rectangular pulses, due to the peak-power clamping effect. With the increasing pump power, the durations of both single- and dual-wavelength rectangular pulses increase. It was also found that each filtered wavelength of the dual-wavelength rectangular pulse corresponds to an individual nanosecond rectangular pulse by employing a tunable bandpass filter.

Flexible rectangular wave-breaking-free pulse generation in actively mode-locked ytterbium-doped fiber laser

We demonstrate nanosecond scale rectangular wave-breaking-free pulse generation in an actively mode locked Yb-doped fiber laser based on a combined action of active periodic cavity loss modulation and nonlinear polarization rotation effect. The pulse width of the laser can be controlled in the range of 890 ps to above 124 ns instantaneously by adjusting the electrical signal applied on the modulator. As high as 19.8 nJ wave-breaking-free pulse is achieved with maximum available pump power. The output pulse temporal dynamics exhibit various distinct characteristics under different modulation and polarization control. The laser presents unusually flexible tunabilities in pulse width, pulse energy and pulse shape.

Flexible operability and amplification of gray pulses

We have investigated experimentally the flexible production and amplification of gray pulses for the first time to our knowledge. Switchable wavelengths, tunable pulse-widths, and adjustable contrasts have all been obtained in a fiber laser. Amplification of gray pulses was also experimentally investigated in detail. The contrast of the pulses could also be increased in an amplifier. The robust stability that results from the interactions between adjacent harmonic mode locking counterparts of gray pulses was found to last for up to ten hours. To the best of our knowledge, the gray pulses trains we have generated are the most stable achieved to date in an all-fiber laser system. This finding can be used as a guide for the establishment of robust gray pulses as laser sources.

Vector nature of multi-soliton patterns in a passively mode-locked figure-eight fiber laser

The vector nature of multi-soliton dynamic patterns was investigated in a passively mode-locked figure-eight fiber laser based on the nonlinear amplifying loop mirror (NALM). By properly adjusting the cavity parameters such as the pump power level and intra-cavity polarization controllers (PCs), in addition to the fundamental vector soliton, various vector multi-soliton regimes were observed, such as the random static distribution of vector multiple solitons, vector soliton cluster, vector soliton flow, and the state of vector multiple solitons occupying the whole cavity. Both the polarization-locked vector solitons (PLVSs) and the polarization-rotating vector solitons (PRVSs) were observed for fundamental soliton and each type of multi-soliton patterns. The obtained results further reveal the fundamental physics of multi-soliton patterns and demonstrate that the figure-eight fiber lasers are indeed a good platform for investigating the vector nature of different soliton types.

Dual-wavelength rectangular pulse Yb-doped fiber laser using a microfiber-based graphene saturable absorber

We reported on the generation of dual-wavelength rectangular pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength rectangular pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the rectangular pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength rectangular pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.

Wave-breaking-free pulse in an all-fiber normal-dispersion Yb-doped fiber laser under dissipative soliton resonance condition

We reported on the dissipative soliton resonance (DSR) phenomenon in a mode-locked Yb-doped fiber laser by using the nonlinear polarization rotation technique. It was found that the multi-pulse oscillation under high pump power could be circumvented by properly adjusting the polarization controllers, namely, the wave-breaking-free rectangular pulse in DSR region was achieved. As the DSR signature, the pulse duration varied from 8.8 ps to 22.92 ns with the increasing pump power. Correspondingly, the maximum pulse energy was 3.24 nJ. The results demonstrated that the DSR phenomenon could exist in Yb-doped fiber lasers, which could be used to achieve wave-breaking-free, ultrahigh-energy pulse.

Vector dissipative soliton resonance in a fiber laser

We report on the vector nature of rectangular pulse operating in dissipative soliton resonance (DSR) region in a passively mode-locked fiber laser. Apart from the typical signatures of DSR, the rectangular pulse trapping of two polarization components centered at different wavelengths was observed and they propagated as a group-velocity locked vector soliton. Moreover, the polarization resolved soliton spectra show different spectral distributions. The observed results will enhance the understanding of fundamental physics of DSR phenomenon.

Dissipative soliton resonance in a passively mode-locked figure-eight fiber laser

The generation of mode-locked rectangular pulses operating in dissipative soliton resonance (DSR) region is demonstrated in an erbium-doped figure-eight fiber laser with net anomalous dispersion. The duration of the wave-breaking-free rectangular pulse broadens with the increase of pump power. At a maximum pump power of 341 mW, the pulse energy can be up to 3.25 nJ with a repetition rate of 3.54 MHz. Particularly, the spectrum of rectangular pulse operating in DSR exhibits conventional soliton sidebands. The observed results show that the formation of pulse operating in DSR region is independent of mode-locking techniques, which may be helpful for further understanding the DSR phenomenon.