Impact of third-order dispersion on the dynamics of dissipative solitons in an ultrafast fiber laser.

Dissipative solitons (DSs), due to the complex interplay among dispersion, nonlinear, gain and loss, illustrate abundant nonlinear dynamics behaviors. Especially, dispersion plays an important role in the research of DS dynamics in ultrafast fiber lasers. Previous studies have mainly focused on the effect of even-order dispersion, i.e., group velocity dispersion (GVD) and fourth-order dispersion. In fact, odd-order dispersions, such as third-order dispersion (TOD), also significantly influences the dynamics of DSs. However, due to the lack of dispersion engineering tools, few experimental researches in this domain have been reported. In this work, by employing a pulse shaper in ultrafast fiber laser, an in-depth exploration of the DS dynamics influenced by TOD was conducted. With the increase of TOD value, the stable single DS undergoes a splitting into two solitons and then enters explosion state, and ultimately evolves into a chaotic state. The laser operation state is correlated to dispersion profile, which could be controlled by TOD. Here, the positive dispersion at long-wavelength side will be gradually shifted to negative dispersion by increasing the TOD, where soliton effect will drive the transitions. These findings offer valuable insights into the nonlinear dynamics of ultrafast lasers and may also foster applications involving higher-order dispersion.

Spatiotemporal dual-periodic soliton pulsation in a multimode fiber laser.

Spatiotemporal mode-locked (STML) fiber lasers have become a new platform for investigating nonlinear phenomena. In this work, spatiotemporal dual-periodic soliton pulsation (SDSP) is firstly observed in an STML fiber laser. It is found that in the SDSP, the long-period pulsations (LPPs) of different transverse modes are synchronous, while the short-period pulsations (SPPs) exhibit asynchronous modulations. The numerical simulation confirms the experimental results and further reveals that the proportion of transverse mode components can manipulate the periods of the LPP and SPP but does not affect the synchronous and asynchronous pulsations of different transverse modes. The obtained results bring the study of spatiotemporal dissipative soliton pulsation into the multi-period modulation stage, which helps to understand the complex spatiotemporal dynamics in STML fiber lasers and discover new dynamics in high-dimensional nonlinear systems.

Periodically tunable multimode soliton pulsation in a spatiotemporal mode-locked fiber laser.

Multimode fiber lasers have become a new platform for investigating nonlinear phenomena since the report on spatiotemporal mode-locking. In this work, the multimode soliton pulsation with a tunable period is achieved in a spatiotemporal mode-locked fiber laser. It demonstrates that the pulsation period drops while increasing the pump power. Moreover, it is found that different transverse modes have the same pulsation period, asynchronous pulsation evolution and different dynamical characteristics through the spatial sampling technique and the dispersive Fourier transform technique. To further verify the experimental results, we numerically investigate the influences of the gain and the loss on the pulsation properties. It is found that within a certain parameter range, the pulsation period drops and rises linearly with the increase of the gain and the loss, respectively. The obtained results contribute to understanding the formation and regulating of soliton pulsations in fiber lasers.

Sub-50†fs, 0.5†W average power Nd-doped fiber amplifier at 920†nm.

We develop an all polarization-maintaining (PM) 920 nm Nd-doped fiber amplifier delivering a train of pulses with ∼0.53 W average power and sub-50 fs duration. The sub-50 fs pulse benefits from the pre-chirping management method that allows for over 60 nm broadening spectrum without pulse breaking in the amplification stage. By virtue of the short pulse duration, the pulse peak power can reach to ∼0.31 MW in spite of the moderate average power. These results represent a key step in developing high-peak-power pulse Nd-doped fiber laser systems at 920 nm, which will find important applications in fields such as biomedical imaging, ultrafast optical spectroscopy, and excitation of quantum-dot single photon sources.

Auto-setting multi-soliton temporal spacing in a fiber laser by a hybrid GA-PSO algorithm.

Multi-soliton operation in fiber lasers is a promising platform for the investigation of soliton interaction dynamics and high repetition-rate pulse. However, owing to the complex interaction process, precisely manipulating the temporal spacing of multiple solitons in a fiber laser is still challenging. Herein, we propose an automatic way to control the temporal spacing of multi-soliton operation in an ultrafast fiber laser by a hybrid genetic algorithm-particle swarm optimization (GA-PSO) algorithm. Relying on the intelligent adjustment of the electronic polarization controller (EPC), the on-demand temporal spacing of the double solitons can be effectively achieved. In particular, the harmonic mode locking with equal temporal spacing of double solitons is also obtained. Our approach provides a promising way to explore nonlinear soliton dynamics in optical systems and optimize the performance of ultrafast fiber lasers.

Anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser.

Due to its unique geometric structure, the bidirectional ultrafast fiber laser is an excellent light source for dual-comb applications. However, sharing the same gain between the counter-propagating solitons also gives rise to complex dynamics. Herein, we report the anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser. The in-phase and anti-phase soliton pulsation can be manipulated by adjusting the intracavity birefringence. The periodic modulation of polarization-dependent gain (PDG) caused by polarization hole burning (PHB) in the gain fiber can be responsible for anti-phase pulsation of bidirectional dissipative solitons. These findings offer new, to the best of our knowledge, insights into the complex dynamics of solitons in dissipative optical systems and performance improvement of bidirectional ultrafast fiber lasers.

Revealing the pulse dynamics in a Mamyshev oscillator: from seed signal to oscillator pulse.

The Mamyshev oscillator (MO) is a promising platform to generate high-peak-power pulse with environmentally stable operation. However, rare efforts have been dedicated to unveil the dynamics from seed signal to oscillator pulse, particularly for the multi-pulse operation. Herein, we investigate the buildup dynamics of the oscillator pulse from the seed signal in a fiber MO. It is revealed that the gain competition among the successively injected seed pulses leads to higher pump power that is required to ignite the MO, hence resulting in the higher optical gain that supports buildup of multiple oscillator pulses. The multiple oscillator pulses are identified to be evolved from the multiple seed pulses. Moreover, the dispersive Fourier transform (DFT) technique is used to reveals the real-time spectral dynamics during the starting process. As a proof-of-concept demonstration, a highly intensity-modulated pulse bunch was employed as the seed signal to reduce the gain competition effect and avoid the multi-pulse starting operation. The experimental results are verified by numerical simulations. These findings would give new insights into the pulse dynamics in MO, which will be meaningful to the communities interested in ultrafast laser technologies and nonlinear optics.

Association between alkaline phosphatase/albumin ratio and the prognosis in patients with chronic kidney disease stages 1-4: results from a C-STRIDE prospective cohort study.

Background: The alkaline phosphatase-to-albumin ratio (APAR) has been demonstrated to be a promising non-invasive biomarker for predicting prognosis in certain diseases. However, the relationship between APAR and prognosis in non-dialysis chronic kidney disease (CKD) patients remains unclear. This study aims to identify the association between APAR and prognosis among CKD stages 1-4 in China. Methods: Patients with CKD stages 1-4 were consecutively recruited from 39 clinical centers in China from 2011 to 2016. New occurrences of end-stage kidney disease (ESKD), major adverse cardiovascular and cerebrovascular events, and all-cause deaths were the outcome events of this study. Subdistribution hazard competing risk and Cox proportional hazards regression models were adopted. Results: A total of 2,180 participants with baseline APAR values were included in the analysis. In the primary adjusted analyses, higher APAR level [per 1-standard deviation (SD) increase in natural logarithm transformed (ln-transformed) APAR] was associated with 33.5% higher risk for all-cause deaths [adjusted hazard ratio (HR) 1.335, 95% confidence interval (CI) 1.068-1.670]. In addition, there was evidence for effect modification of the association between APAR and ESKD by baseline estimated glomerular filtration rate (eGFR) (P interaction < 0.001). A higher APAR level (per 1-SD increase in ln-transformed APAR) was associated with a greater risk of ESKD among participants with eGFR ≥ 60 ml/min/1.73 m2 (adjusted SHR 1.880, 95% CI 1.260-2.810) but not in eGFR < 60 ml/min/1.73 m2. Conclusion: Higher APAR levels in patients with CKD stages 1-4 seemed to be associated with an increased risk of all-cause death. Thus, APAR appears to be used in risk assessment for all-cause death among patients with CKD stages 1-4.

Dissipative soliton resonance in a figure-eight multimode fiber laser.

We report, for the first time to the best of our knowledge, a spatiotemporal mode-locked (STML) multimode fiber laser based on nonlinear amplifying loop mirror (NALM), generating dissipative soliton resonance (DSR) pulses. Due to the complex filtering characteristics caused by the inherent multimode interference filtering structure and NALM in the cavity, the STML DSR pulse has wavelength tunable function. What's more, kinds of DSR pulses are also achieved, including multiple DSR pulses, and the period doubling bifurcations of single DSR pulse and multiple DSR pulses. These results contribute to further understand the nonlinear properties of STML lasers and may shed some light on improving the performance of the multimode fiber lasers.

Periodic transition between two evolving soliton pulsation states in an Yb-doped fiber laser.

Due to the fascinating features, pulsating solitons attract much attention in the field of nonlinear soliton dynamics and ultrafast lasers. So far, most of the investigations on pulsating soliton are conducted in Er-doped fiber lasers. In this work, we reported the periodic transition between two evolving pulsating soliton states in an Yb-doped fiber laser. By using the real-time measurement techniques, the spectral and temporal characteristics of this transition state were investigated. Two evolving soliton pulsation states have similar evolution process, i.e., from pulsating towards quasi-stable mode-locked states. However, the details of the two processes are different, such as the pulse energy levels, pulsating modulation depths, duration of quasi-stable mode-locked states. The transition between two evolving soliton pulsation states could be attributed to the interaction of the polarizer and the varying polarization states of the pulse inside the laser cavity. The experimental results will contribute to the further understanding of soliton pulsating dynamics in dissipative optical systems.

Assisting the mode-locking of a figure-9 fiber laser by thermal nonlinearity of graphene-decorated microfiber.

The self-starting performance of a figure-9 fiber laser is critically dependent on the phase shift difference between the counter-propagating beams. Herein, we propose an effective approach to dynamically control the phase shift difference in a figure-9 fiber laser by utilizing the thermal nonlinearity of graphene-decorated microfiber device. With the adjustment of the control laser power injected into the graphene-decorated microfiber, the self-starting mode-locked threshold of the figure-9 fiber laser can be attained in a flexible pump power range, i.e., from 300 mW to 390 mW. These findings demonstrated that the graphene-decorated microfiber could act as a dynamical control device of phase shift difference for improving the performance of figure-9 fiber lasers, and might also open up new possibilities for applications of microfiber photonic devices in the field of ultrafast optics.

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.

Dissipative rogue waves generated by multi-soliton explosions in an ultrafast fiber laser.

Derived from oceanography, nowadays the investigation of rogue waves (RWs) has been widely spread in various fields, particularly in nonlinear optics. Passively mode-locked fiber laser has been regarded as one of the excellent platforms to investigate the dissipative RWs (DRWs). Here, we report the observation of DRW generation induced by single and multi-soliton explosions in a passively mode-locked fiber laser. It was demonstrated that through the gain-mediated soliton interactions, one soliton could erupt because of the explosion of another soliton in the laser cavity. Meanwhile, the high-amplitude waves, which fulfill the DRWs criteria, could be detected in the multi-soliton explosion states. The DRWs were identified by characterizing the peak intensity statistics of the time-stretched soliton profiles. Particularly, it was found that the ratio between the highest recorded amplitudes and significant wave heights (SWHs) of DRWs induced by multi-soliton explosions is higher than that by single-soliton explosion case. Our findings will further contribute to the understanding of the physical mechanisms of DRWs in the soliton explosion regime.

1.7 µm figure-9 Tm-doped ultrafast fiber laser.

The evolution of multiphoton microscopy is critically dependent on the development of ultrafast laser technologies. The ultrashort pulse laser source at 1.7 µm waveband is attractive for in-depth three-photon imaging owing to the reduced scattering and absorption effects in biological tissues. Herein, we report on a 1.7 µm passively mode-locked figure-9 Tm-doped fiber laser. The nonreciprocal phase shifter that consists of two quarter-wave plates and a Faraday rotator introduces phase bias between the counter-propagating beams in the nonlinear amplifying loop mirror. The cavity dispersion is compensated to be slightly positive, enabling the proposed 1.7 µm ultrafast fiber laser to deliver the dissipative soliton with a 3-dB bandwidth of 20 nm. Moreover, the mode-locked spectral bandwidth could be flexibly tuned with different phase biases by rotating the wave plates. The demonstration of figure-9 Tm-doped ultrafast fiber laser would pave the way to develop the robust 1.7 µm ultrashort pulse laser sources, which could find important application for three-photon deep-tissue imaging.

Narrow bandwidth spatiotemporal mode-locked Yb-doped fiber laser.

We report a narrow bandwidth spatiotemporal mode-locked (STML) ytterbium-doped fiber laser, based on a homemade carbon nanotube/polyvinyl alcohol composite film and the multimode interference filtering effect. The wavelength-tunable narrow bandwidth STML operations combined with different pulse states are achieved, including single pulse, multiple pulses, and harmonics. The 3-dB bandwidth at the single-pulse state is 103 pm, while at the harmonic state, it is as narrow as 26 pm. To give an insight into the generation of the narrow bandwidth STML pulses, numerical simulations are performed. Such a laser has a wide range of potential applications in fields of optical communication and optical measurement, as well as provides a favorable platform for studying the evolution dynamics of multimode solitons.

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.

1.7 µm Tm-fiber chirped pulse amplification system with dissipative soliton seed laser.

We report on a 1.7 µm Tm-fiber chirped pulse amplification (CPA) system by virtue of a broadband dissipative soliton seed laser. The seed oscillator delivers the dissipative soliton with 10 dB spectral bandwidth of 23 nm and an average power of 4 mW. The duration of the seed pulse is directly stretched to ∼60ps by a segment of 50 m normal dispersion fiber. Using a two-stage fiber amplifier, the average power of the pulse is amplified to 1.95 W with a slope efficiency of 40.3%. The amplified pulse is then compressed to 348 fs by a pair of fused silica transmission gratings. The compressed average power of 1.3 W and peak power of 155 kW are achieved. These experimental results would pave the way to achieve a high-power femtosecond laser source at 1.7 µm, which could find important applications in fields such as three-photon deep-tissue imaging and material processing.

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.

Mutually induced soliton polarization instability in a bidirectional ultrafast fiber laser.

The bidirectional ultrafast fiber laser is a promising light source for dual-comb applications. The counter-propagating geometry could lead to soliton interaction through gain sharing, as well as the possible outcome of polarization instability. However, the polarization dynamics hidden behind the soliton interaction process in bidirectional fiber lasers were rarely investigated. Herein, we report on the polarization instability induced by the mutual soliton interactions through fiber gain in a bidirectional mode-locked fiber laser. Depending on the adjustment of the intracavity birefringence, the polarization states of two counter-propagating solitons can exhibit similar periodical polarization switching behaviors with a polarization-rotating transition state. The successive interactions of the bidirectional solitons mediated by the polarization cross-saturation effect of gain fiber could be responsible for the soliton polarization instability. These findings, in addition to the fundamental interest of the soliton nonlinear dynamics in dissipative optical systems, also open up new possibilities for creating dynamical control of the soliton polarization state and performance improvement in bidirectional ultrafast fiber lasers.

Tunable spatiotemporal mode-locked fiber laser at 1.55 µm.

We report the spatiotemporal mode-locked multimode fiber laser operating at 1.55 µm based on semiconductor saturable absorber mirrors with the mode-locking threshold as low as 104 mW. Benefiting from the multimode interference filtering effect introduced in the laser cavity not only the central wavelength can be continuously tuned from 1557 nm to 1567 nm, but also the number of the output pulses can be adjusted from 1 to 4 by simply adjusting the polarization controllers. This work provides a new platform for exploring the dynamic characteristics of spatiotemporal mode-locked pulses at negative dispersion regime. Moreover, this kind of tunable laser has potential applications in fields of all-optical signal processing, fiber sensing and information coding.