Mode-locked Soliton Research Articles

Multiple soliton mode-locking operations of a Holmium-doped fiber laser based on nonlinear polarization rotation

Multiple soliton mode-locking operations are realized in a Holmium-doped (Ho-doped) fiber laser based on nonlinear polarization rotation (NPR) technique. The fundamental mode-locking (FML) operation with a repetition rate of 19.91 MHz and a pulse duration of 974 fs is realized at 2056.1 nm. Bunched solitons operation with up to 7 soliton pulses is firstly implemented in the Ho-doped fiber laser by increasing the pump power. The Ho-doped fiber laser can also evolve into the harmonic mode-locking (HML) operation at ∼ 2056 nm by finely adjusting the intra-cavity parameters. The pulse duration is 965 fs at the highest repetition rate of 139.19 MHz, which is believed to be the first report on the femtosecond HML operation in the Ho-doped fiber lasers.

Theoretical and experimental investigations of dispersion-managed, polarization-maintaining 1-GHz mode-locked fiber lasers.

High-repetition-rate (up to GHz) femtosecond mode-locked lasers have attracted significant attention in many applications, such as broadband spectroscopy, high-speed optical sampling, and so on. In this paper, the characteristics of dispersion-managed, polarization-maintaining (PM) 1-GHz mode-locked fiber lasers were investigated both experimentally and numerically. Three compact and robust 1-GHz fiber lasers operating at anomalous, normal, and near-zero dispersion regimes were demonstrated, respectively. The net dispersion of the linear cavity is adjusted by changing types of PM erbium-doped fibers (EDFs) and semiconductor saturable absorber mirrors (SESAMs) in the cavity. Moreover, the long-term stability of the three mode-locked fiber lasers is proved without external control. In order to better understand the mode-locking dynamics of lasers, a numerical model was constructed for analysis of the 1-GHz fiber laser. Pulse evolution simulations have been carried out for soliton, dissipative-soliton, and stretched-pulse mode-locking regimes under different net dispersion conditions. Experimental results are basically in agreement with the numerical simulations.

Spatiotemporally mode-locked soliton fiber laser at 2.8 μm

Abstract Spatiotemporal mode-locking creates great opportunity for pulse energy scaling and nonlinear optics research in fiber. Until now, spatiotemporal mode-locking has only been realized in normal-dispersion dissipative soliton and similariton fiber lasers. In this paper, we demonstrated the first experimental realization of a spatiotemporally mode-locked soliton laser in mid-infrared fluoride fiber with anomalous dispersion. The mode-locked fluoride fiber oscillator directly generated a record pulse energy of 16.1 nJ and peak power of 74.6 kW at 2.8 μm wavelength. This work extends the spatiotemporal mode-locking to soliton fiber lasers and should have a wide interest for the laser community.

Passively mode-locked thulium-doped fiber laser based on a SWCNTs@AFI saturable absorber

An all-fiberized, mode-locked thulium-doped laser was demonstrated using single-walled carbon nanotubes (SWCNTs) as the saturable absorber (SA). These SWCNTs were prepared by pyrolyzing tripropylamine confined in the one-dimensional nanochannels of zeolite ZnAPO-5 (AFI) single crystal and then the [email protected] SA was transferred onto the end face of fiber connector. By inserting the SA into the fiber laser cavity, stable mode-locked solitons with 810 fs pulse width, 14.12 MHz repetition rate centered at 1913.6 nm was generated, the laser output showed the long-term stability and high signal-to-noise ratio. The experimental results confirmed that the [email protected] could be an effective candidate as saturable absorption material for passively generating ultrafast pulses in 2 μm laser systems. This is, to the best of our knowledge, the first demonstration of [email protected] SA in fiber lasers at 2 μm.

Investigation of stable pulse mode-locking regimes in a NALM figure-9 Er-doped fiber laser.

We demonstrate three typical mode-locking processes of a nonlinear amplifying loop mirror (NALM) fiber laser via a general nonlinear Schrödinger equation-based (GNLSE) simulation model. First, the pulse evolutions in the NALM cavity were separately simulated under asymmetric and weakly asymmetric conditions. We found that the splitting ratio and positions of the gain fiber can result in a suitable phase bias between clockwise and counter-clockwise beams, enabling the realization of a self-starting low-threshold operating condition. To assess the roles of the splitting ratio and gain in the mode-locking process, we simulated three pulse formation processes: in the soliton, stretched-pulse, and dissipative soliton mode-locking regimes. The simulation results show that the splitting ratio, gain, and dispersion directly influence the mode-locking condition and pulse characteristics, thereby providing effective quantified guidance for high-quality pulse generation. Finally, an experimental NALM oscillation operating under stretched pulse conditions was established to investigate the impact of the splitting ratio and pump power on the pulse characteristics. The experimental results prove that the splitting ratio, gain, and dispersion can be used to manipulate the mode-locking threshold, self-starting threshold, nonlinear effects, and pulse characteristics.

Dispersion-Managed Tm-Ho Co-Doped Ultrashort Pulse Fiber Laser Using Single-Walled Carbon Nanotube and Spectral Filter

In this paper, we have demonstrated a dispersion-managed, high-power, Tm-Ho co-doped ultrashort pulse fiber laser using a single walled carbon nanotube (SWNT) dispersed in polyimide film. An in-line type spectral filter was developed to control the output pulse spectra. Two SWNT films with different modulation depths were examined as a mode-locker. Normal dispersion fiber was used in the fiber laser oscillator, and dependence on net cavity dispersion was investigated. Passive mode-locking was achieved in a wide dispersion range, from −0.319 to +0.101 ps2. Stable soliton mode-locking operation and dissipative soliton mode-locking operations were observed. The pumping efficiency was ~3 times higher than that in a Tm-doped fiber laser with a similar configuration. The developed fiber laser showed self-start and stable operations, and this laser is useful for practical applications.

Frequency combs with multiple offsets in THz-rate microresonators.

Octave-wide frequency combs in microresonators are essential for self-referencing. However, it is difficult for the small-size and high-repetition-rate microresonators to achieve perfect soliton modelocking over the broad frequency range due to the detrimental impact of dispersion. Here we examine the stability of the soliton states consisting of one hundred modes in silicon-nitride microresonators with the one-THz free spectral range. We report the coexistence of fast and slow solitons in a narrow detuning range, which is surrounded on either side by the breather states. We decompose the breather combs into a sequence of sub-combs with different carrier-envelope offset frequencies. The large detuning breathers have a high frequency of oscillations associated with the perturbation extending across the whole microresonator. The small detuning breathers create oscillations localised on the soliton core and can undergo the period-doubling bifurcation, which triggers a sequence of intense sub-combs.

Tunable spatiotemporal mode-locked conventional soliton and soliton molecule in a partial multimode linear-cavity Er-doped fiber laser

In this letter, we have demonstrated the realization of wavelength-tunable spatiotemporal mode locking (STML) in a partial multimode fiber (MMF) laser with a linear cavity. The saturable absorption effect is attributed to both the nonlinear multimode interference (NL-MMI) and the nonlinear optical loop mirror (NOLM). The laser can deliver both the conventional solitons (CSs) and loosely bound solitons (BSs) with a tuning range from ∼1573 nm to ∼1601 nm. The evolutions of these two different STML solitons as the pump power are also given and it is found that the interaction between solitons would have notable affection on the beam distribution of the MM solitons. Furthermore, a spatial instability for the STML CSs is observed within a certain pump power range. These results contribute to our understanding of the nonlinear spatiotemporal dynamics in the MMF laser system.

Q-switched and mode-locked fiber laser based on organic metal 8-hydroxyquinoline chelate as saturable absorber at 1.5 µm

This paper reports the demonstration of bis(8-hydroxyquinoline) calcium (CaQ2) as a passive saturable absorber (SA) in an erbium-doped fiber laser cavity. The SA has a saturation intensity of 511 MW/cm2 and a modulation depth of 14%. As the SA was incorporated into the cavity, a Q-switching was produced with a repetition rate and pulse duration ranging between 45.5 and 88.2 kHz and 8.76 to 2.9 µs, respectively. Then by increasing the cavity length, a soliton mode-locking operation was developed with a repetition rate and pulse duration of 1.82 MHz and 1.6 ps, respectively. Both lasers had a signal-to-noise ratio (SNR) higher than 63 dB and a central wavelength of 1561 nm. Our results suggest that CaQ2 has the potentials to act as a stable and good-performance SA. We believe that this work is the first to report CaQ2 as a functioning and promising SA.

A 1030 nm all-PM SESAM mode-locked dissipative soliton fiber oscillator and its amplification with Yb-doped fiber and a Yb:YAG thin rod

In this research, an all- polarization-maintained semiconductor saturable absorber mirror (SESAM) mode-locked fiber oscillator and its amplification by Yb-doped fiber and a Yb:YAG thin rod are presented. From a ring-type cavity configuration created with commercially accessible components, including SESAM, the dissipative soliton fiber oscillator exhibits stable mode-locking near 1030 nm. Subsequent three-stage fiber amplifiers pumped by single-mode fiber-coupled laser diodes and a single-stage Yb:YAG thin-rod amplifier boost the output power to 11.3 W at a repetition rate of 495 kHz. After pulse compression, a pulse duration of 758 fs is achieved with output power and pulse energy levels of 9 W and 18.2 μJ, respectively.

Multi-soliton pulse generation in a fiber laser by using a long-period fiber grating

In this paper, multi-soliton pulse generation is realized by incorporating a long period fiber grating into an Er-doped mode-locked fiber ring laser cavity. By using nonlinear polarization rotation mode-locking technique and a long period fiber grating that plays the role of spectral filter in the laser cavity, discretely tunable multi-soliton pulses can be produced at low lasing threshold of 80 mW. The number of solitons can be controlled by simply adjusting the polarization controller in the laser cavity. It is found that Kelly sideband of the traditional mode-locked solitons become weak as a result of introducing the long period fiber grating in the laser cavity, due to the fact that the nonlinearity and dispersion in the cavity are balanced, and hence stabilizing the soliton pulses. The use of long-period fiber grating has the advantages of effectively reducing the pumping threshold for the multi-soliton pulse generation, and supporting stable laser operation.

Bismuthene quantum dots integrated D-shaped fiber as saturable absorber for multi-type soliton fiber lasers

In the present work, the uniformly sized bismuthene quantum dots (BiQDs) with an average diameter of 26 nm were fabricated via the solvothermal approach. By transferring the BiQDs onto the plane of micro-machined D-shaped fiber (DSF), a new type of saturable absorber (SA) was successfully prepared. Based on the evanescent field effect of D-shaped fiber, the prepared SA exhibits excellent saturable absorption properties with the maximum modulation depth of 5.1% at around 1.5 μm. To further investigate its potential applications in ultrafast photonics, we demonstrated passive mode-locking operation in the erbium-doped fiber laser (EDFL) with BiQDs/DSF-SA. The conventional soliton pulses with duration of 835 fs at the repetition rate of 9.23 MHz and dissipative soliton pulses with duration of 575 fs at the repetition rate of 7.83 MHz were generated successfully. In addition, stable bound state of solitons with the pulse duration of 1.04 ps and sub-pulse time interval of 15.9 ps were also obtained based on the conventional soliton state by adjusting the pump power and polarization state. Our work reveals the great potential and capacity of BiQDs/DSF-SA in soliton mode-locking operations and promotes the explorative investigation of bismuth-based optoelectronic devices.

Fission free high-energy mode-locked soliton generation in an all-polarization-maintaining fiber laser

Fission free high-energy mode-locked soliton generation in an all-polarization-maintaining fiber laser

Dual-wavelength harmonic mode-locked dissipative soliton resonance of Yb fiber laser

Dissipative soliton resonance (DSR) mode-locked fiber lasers have stimulated great interest recent years due to their unique pulse-breaking-free advantage for scaling soliton pulse energy. However, the mechanism accounting for pulse breaking to generate multipulses in DSR fiber lasers has not reached a consensus. Here, we show that harmonic mode-locked DSR 1-μm Yb-doped fiber laser in the dual-wavelength regime can be realized with a semiconductor saturable absorber mirror (SESAM). In the fundamental frequency (3.5 MHz) mode-locked state, the pulse width continuously broadens from 2 to 8.9 ns as the output power increases from 1.26 to 5.1 mW (pulse energy being from 0.36 to 1.46 nJ), while the pulse peak power is clamped at 0.17 W, highlighting the typical characteristics of DSR mode-locking operation. Through simply adjusting the SESAM’s feedback conditions, the DSR fiber laser can transits from the fundamental-frequency mode locking to harmonic mode-locked states. Harmonic states from the 2nd to 9th order have been observed, with pulse repetition rate enhanced from 7 to 31.5 MHz. Under fixed pump power, increasing harmonic orders leads to reduction of the pulse width and pulse energy but does not change the unique quantization feature of the peak power. The status of the SESAM also guarantees the generation of dual wavelengths centered at 1072.5 and 1079.5 nm with spectral widths of 2.7 and 1.9 nm, respectively. This dual-wavelength harmonic mode-locked DSR Yb fiber laser can find applications in various areas.

Mechanisms of dual-wavelength dissipative soliton mode-locking in net-normal dispersion fiber lasers

Dual-wavelength mode-locked fiber lasers have attracted great attention due to their enormous potential in facilitating dual-comb spectroscopy. However, mechanism for dual-wavelength dissipative soliton mode-locking and the intracavity dynamics are still elusive. In this paper, we construct a simple and universal model to numerically investigate the intracavity buildup dynamics of dual-wavelength mode-locking in an all-normal dispersion fiber laser. By resolving the pulses evolution and their interactions, we find that the chromatic dispersion induced pulse collision plays an important role in dual-wavelength pulses formation and propagation. At the chaotic stage, the collision-induced energy upheaval results in drastic nonlinear coupling effects, which contribute to the dual-wavelength mode-locking and formation of dual-wavelength soliton molecules. While at the stable dual-wavelength mode-locking stage, the two asynchronous pulses periodically collide, accompanying extremely intense wave generation and spectral explosion. Moreover, cavity energy and gain competition are modeled and optimized to realize the self-started pulse-splitting-free dual-wavelength mode-locking.

Generation of broadband parabolic pulses based on a pre-chirper free, core-pumped nonlinear fiber amplifier for coherent anti-Stokes Raman imaging

We report the generation of parabolic pulses with broadband spectrum from a core-pumped Yb-doped fiber amplifier seeded by a dispersion managed fiber oscillator. The net cavity dispersion of Yb-doped oscillator was continuously changed from 0.074 to -0.170ps2, which enabled us to achieve dissipative soliton, stretched pulse and soliton mode-locking operations. Spectral evolution processes in the core-pumped nonlinear fiber amplifier seeded by various input solitons were investigated experimentally and theoretically. Our finding indicates that cavity dispersion of oscillator can be used to engineer the input pulse parameter for amplifier, thus forming a pre-chirper free fiber amplification structure. In the experiment, we obtained 410-mW parabolic pulses with spectral bandwidth up to 56 nm. In combination with a passively synchronized frequency-doubled Er-doped fiber laser, we have demonstrated coherent anti-Stokes Raman imaging. The compact dual-color fiber laser source may facilitate practical applications of nonlinear biomedical imaging beyond the laboratory environment.

Ultrashort pulse thulium-doped fiber laser with molybdenum trioxide on tapered fiber

This paper demonstrates ultrashort pulse generation using molybdenum trioxide (MoO3) saturable absorber (SA) integrated into a thulium-doped fiber laser. The average particle size of the MoO3 material was 9.54 µm. The MoO3/polydimethylsiloxane composite was prepared and spin-coated on a tapered fiber to fabricate the SA device. It had a modulation depth of 2.89% and demonstrated a high damage threshold, extending beyond 19.34 GW/cm2. From the evanescent light-matter interaction, stable self-starting mode-locked soliton pulses of 1.22 ps duration at 1941.4 nm central wavelength were obtained. The pulse repetition rate was 10.84 MHz with 3.3 nm spectral bandwidth. At 1.15 W pump power, the soliton pulse energy was 0.68 nJ corresponding to a peak power of 492 W. The work exhibited comparable pulse performances in the 2 µm wavelength range while utilizing simple SA fabrication procedures of micro-sized MoO3 materials.

Synchronized multi-wavelength soliton fiber laser via intracavity group delay modulation

Locking of longitudinal modes in laser cavities is the common path to generate ultrashort pulses. In traditional multi-wavelength mode-locked lasers, the group velocities rely on lasing wavelengths due to the chromatic dispersion, yielding multiple trains of independently evolved pulses. Here, we show that mode-locked solitons at different wavelengths can be synchronized inside the cavity by engineering the intracavity group delay with a programmable pulse shaper. Frequency-resolved measurements fully retrieve the fine temporal structure of pulses, validating the direct generation of synchronized ultrafast lasers from two to five wavelengths with sub-pulse repetition-rate up to ~1.26 THz. Simulation results well reproduce and interpret the key experimental phenomena, and indicate that the saturable absorption effect automatically synchronize multi-wavelength solitons in despite of the small residual group delay difference. These results demonstrate an effective approach to create synchronized complex-structure solitons, and offer an effective platform to study the evolution dynamics of nonlinear wavepackets.

Generation and dynamics of soliton and soliton molecules from a VSe2/GO-based fiber laser

Abstract 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 0.93 MW/cm2. The conventional soliton is obtained with pulse width of 573 fs, which is currently the narrowest pulse width based on VSe2-related material, and has a signal-to-noise ratio of 60.4 dB. In addition, the soliton molecules are realized based on the VSe2/GO for the first time and have a pulse interval of ∼2.2 ps. We study the soliton dynamics through numerical simulation and reveal that before the formation of the soliton, it undergoes multiple nonlinear stages, such as soliton mode-locking, soliton splitting, and soliton oscillation. Furthermore, the results of numerical simulation are agreed well with the experimental data. These results indicate that the VSe2/GO might be another promising saturable absorber material for ultrafast photonics, and deepen the understanding of soliton dynamics in ultrafast fiber lasers.

Experimental revealing of fiber laser soliton build-up activated by shaking-soliton triplets

Optimization of self-starting in passively mode-locked optical soliton fiber laser resonators results from a complex transient dynamic involving soliton molecules, soliton-based complexes and supramolecular structures, with particle-like properties. By means of time-stretch dispersive Fourier transform based real-time spectroscopy, we identify a new route to the passive mode-locking of fiber laser solitons. A raised relaxation oscillation stage is followed by the generation of shaking-soliton molecular triplets. The relative phase between satellite and main pulses of shaking soliton triplets evolves chaotically, while the two satellite pulses are orthogonal to each other in their state of polarization. These results provide new perspectives into the soliton formation and the internal dynamics of soliton molecules with higher degrees of freedom.