Fiber Laser Research Articles

Realizing a kilowatt-level fiber amplifier with a 42 μm core diameter fiber for improved multi-mode performance towards single mode operation output through adaptive spatial mode control utilizing a 3×1 photonic lantern

The photonic lantern, a coherent beam combiner capable of controlling the phase, amplitude, and polarization of input light, has been utilized to enhance the brightness of fiber lasers by managing the output beam’s mode. In this work, a 3×1 photonic lantern-based adaptive spatial mode control system is employed to realize kilowatt-level operation in a 42 μm core fiber laser amplifier. Both simulation and experimental outcomes affirm the ability of this approach to manage modes within large-mode-area fiber laser systems through the use of 3 input arms. The experiment not only streamlines the overall system design but also has the potential to reduce production costs and complexities. Additionally, the spectrum width has been optimized to 10 GHz, striking a balance between the SBS threshold and the coherence of the photonic lantern’s input arms. By implementing this system, we have successfully achieved a stable, improved multi-mode performance towards single mode operation output of 1.08 kW, with a beam quality factor M2 of 2.20. This research furthers our understanding of how photonic lanterns can stabilize and enhance beam quality in high-power fiber lasers, paving the way for potential improvements in their performance and applications.

Zn-MOF as a saturable absorber for thulium/holmium-doped fiber laser

Metal–organic framework (MOF) is a class of material that is highly porous and modular. Due to their unique properties, MOFs have found applications in gas storage, gas separation, sensing, and supercapacitors. [Zn2(H2L)2(1,2-Bis(4-pyridyl)ethene)4]n, zinc (Zn)-based MOF was used in this work to achieve mode-locked operation in a thulium/holmium-doped fiber laser due to its excellent optical absorption at a wavelength of 1925 nm. The saturable absorber (SA) was fabricated by drop-casting a mixture of Zn-MOF and isopropanol on an arc-shaped fiber. The center wavelength of the mode-locked laser is 1906.75 nm, with a maximum average output power of 3.251 mW. The fundamental repetition rate and the pulse width were 12.89 MHz and 1.772 ps. At the same time, the pulse energy and peak power were 252 pJ and 142 W, respectively. To the authors’ knowledge, this is the first time an MOF has been used for mode-locked pulse generation in a thulium/holmium-doped all-fiber laser. This work extends the use of MOF material as a saturable absorber for mode-locking applications in near-infrared fiber lasers.

Compact mid-infrared dual-wavelength optical parametric oscillator pumped by Yb-doped fiber lasers based on two PPMgLN crystals

A compact mid-infrared (MIR) dual-wavelength optical parametric oscillator (OPO) pumped by Yb-doped fiber lasers (YDFLs) based on dual-crystal with an L-shaped cavity structure is demonstrated. Two periodically poled MgO-doped lithium niobite (PPMgLN) crystals with polarization periods of 30.44 μm and 28.96 μm are pumped by two YDFLs, respectively. The dual-wavelength output at 3.45 μm and 4.00 μm is obtained synchronously by adjusting the double pump power. When the total power of double-end pumping is 28.98 W with a ratio of 2:3, the pulse width is 60.80 ns under the repetition frequency of 110 kHz, the output power is 1.483 W@3.45 μm and 1.703 W@4.00 μm, respectively. The total conversion efficiency is 10.99%. By utilizing this cavity structure, the gain and wavelength tuning of the two OPOs can be controlled separately. Meanwhile, the pulse width is 46.93 ns@3.45 μm and 39.38 ns@4.00 μm, respectively. The laser beam quality closely approaches the theoretical quality of the fundamental mode beam. Additionally, by independently adjusting the temperature of the two PPMgLN crystals from 20 °C to 150 °C, tunable mid-infrared laser outputs with wavelengths of 3.448–3.272 μm and 4.006–3.864 μm are achieved. The corresponding tuning bandwidths are 176 nm and 142 nm, respectively.

A Fast Solution of the Dynamic Rate Equation for a High-Power Fiber Laser

A Fast Solution of the Dynamic Rate Equation for a High-Power Fiber Laser

Use of an endoscopic virtual ruler based on the fiber laser principle and artificial intelligence technology

Use of an endoscopic virtual ruler based on the fiber laser principle and artificial intelligence technology

Analyzing the effect of different shielding atmospheres on fiber laser welding parameters for modified 9Cr-1Mo steel

The present research aims to investigate the influence of and the relationship between welding speed ( v), focal position ( FP), and laser power ( LP) as input parameters for fiber laser to weld P91 under pure argon and CO2 shielding atmospheres using response surface methodology and using the desirability approach; optimization of input parameters has been performed to maximize the depth of penetration ( DP) while minimizing the top bead width ( TW) and heat-affected zone width ( HW). The results indicate that laser power ( LP) has the most significant impact on depth of penetration ( DP), whereas welding speed ( v) affects top bead width ( TW) and heat-affected zone width ( HW). The optimal combination of parameters under argon shielding results in a significantly low heat input of 48 J/mm (0.048 kJ/mm) and 50 J/mm (0.050 kJ/mm) pure argon and CO2 shielding atmospheres, respectively. Despite the difference in heat input being only 4.08%, an 11.618% increase in DP is observed under the CO2 shielding atmosphere. Due to the high-speed nature of the welding process (argon: 82.65 mm/s and CO2: 79.283 mm/s) combined with the significant reduction in heat input, the heat-affected zone is limited to a mere width of 0.203 mm under an argon shielding atmosphere and 0.263 mm under the CO2 shielding atmosphere compared with that reported in the other welding processes without the dissolution of precipitates in the fusion boundary of heat-affected zone. Microstructural characterization of the fusion zone has revealed the presence of an untempered lath martensite structure with precipitate dissolution. The precipitate dissolution has resulted in grain coarsening of 47.76% in argon weld and 39.65% in CO2 weld compared with the base metal grain size of 6.07 µm.

Kilowatt-Level High-Efficiency Narrow-Linewidth All-Fiber Tm3+-Doped Laser

In this study, a kilowatt-level high-efficiency narrow-linewidth all-fiber Tm3+-doped continuous-wave laser operating at 1.95 μm is demonstrated. Benefitting from an advanced boost design of a two-stage main amplifier, it not only effectively manages heat dissipation resulting from the high pump-induced quantum defect but also realizes the controlled extraction of optical gain and improves the optical conversion efficiency. Finally, this laser system has realized an output power of 1018 W, a linewidth of 3.8 GHz, and a slope efficiency of 60.0% simultaneously. Moreover, a high optical signal-to-noise ratio of over 45 dB and excellent beam quality of M2 factors 1.19 are obtained. To the best of our knowledge, this represents the narrowest linewidth and highest slope efficiency achieved in a kilowatt-level Tm³⁺-doped fiber laser. Such a high-performance laser is ideally suited for mid-infrared generation and remote sensing applications.

Broadband THz Wave Generation and Detection in Organic Crystal PNPA at MHz Repetition Rates

AbstractOrganic nonlinear optical (NLO) crystals have emerged as efficient room‐temperature emitters of broadband THz radiation with high electric field strengths. Although initially confined to high‐pulse‐energy excitation in the millijoule range with kHz rates, recent efforts have focused on tailoring the physical properties of organic NLO materials for compatibility with popular MHz‐rate telecommunication wavelength lasers emitting nanojoule energy pulses. This is motivated by the large potential of such crystals for more portable and user‐safe spectroscopic systems, additionally complemented by their room‐temperature field‐sensitive THz detection capabilities. In this work, the MHz‐rate operation of the organic crystal PNPA ((E)‐4‐((4‐nitrobenzylidene)amino)‐N‐phenylaniline), which was recently discovered through data mining algorithms and reported to surpass the conversion efficiency of rivaling NLO crystals at 1 kHz repetition rate is demonstrated. Using a compact 200 mW Er:fiber laser producing 18 fs pulses at 50 MHz repetition rate, the THz field generation and detection capabilities of PNPA via performing gas phase spectroscopy in the 1.3–8.5 THz range are demonstrated. A dynamic range of 40 dB over 3.6 s and 70 dB over 2 h is obtained. The work extends the family of organic crystals compatible with telecommunication‐wavelength excitation using nJ pulses for spectroscopy beyond 5 THz.

The energy synergistic mechanism of coaxial heterogeneous-wavelength hybrid laser beam and its effect on welding molten pool dynamics for aluminum alloy

The coaxial heterogeneous-wavelength hybrid laser beam (HW-HLB) heat source featuring a “Gauss + Flat top” energy distribution, which integrates the 1080 nm and 915 nm laser beam, was employed in this paper to achieve excellent stability in the welding of aluminum alloy. The interaction mechanism between aluminum alloy and laser beams with different wavelengths was taken as a point cut to explore the synergistic enhancement mechanism of coaxial HW-HLB . A thermal-fluid coupling model for HW-HLB welding, considering the synergistic effect of dual lasers, was established according to the welding experiment results. The influence of fiber laser power (PF) and diode laser power (PD) on the molten pool flow behavior during welding process was investigated. The dynamic of the molten pool and the maintenance mechanism of the keyhole were elucidated through in-situ monitoring experiments and thermal-flow simulations. The results indicated that, in contrast to the single fiber laser beam (FLB), the power density of HW-HLB presents a significant increase, which results in the “avalanche-like” augmentation of the plasma plume, as well as deeper depth of the keyhole. The energy synergistic enhancement effect of coaxial HW-HLB with PF=2800 W and PD=2500 W performs stronger and thorough changes in the morphology and flow behavior of the molten pool. The introduction of 915 nm laser beam improves the multi-reflection behavior in the inner keyhole. The findings of our research provide a theoretical framework for improving the stability of the laser weld molten pool and the quality of welds in aluminum alloys through the implementation of HW-HLB.

Linear-coupling-induced double-period pulsating vector solitons in lasers.

Pulsating solitons is a universal phenomenon originating from the Hopf-type bifurcation in dissipative systems such as lasers and microresonators. Here, we report the vector soliton in a fiber laser pulsating with two periods of different orders of magnitude. The short-period pulsation manifests as the period-tripling facilitated by the linear coupling between orthogonal polarization components, which breaks the self-consistent evolution of the vector soliton over a single round trip (RT). The long-period pulsation arises from the mode competition between the two polarization components mediated by various cavity effects. The interplay between linear coupling and mode competition gives rise to the robust double-period pulsating (DPP) vector soliton. Our results provide a clear physical mechanism for the broadly observed double-period breather, which has a significant value in exploring breathers with complex dynamics and multiple comb spectroscopy.

Pure-quartic soliton self-frequency shift in a mode-locked fiber laser

The pure-quartic soliton (PQS) offers the advantage of a wide spectrum and approximately Gaussian temporal profile, which has the potential to obtain high-energy ultrafast laser pulses. Thus, exploring the role of stimulated Raman scattering in the formation and propagation of PQSs in fiber lasers is crucial, especially considering the greater propensity for highpower and short PQS pulses compared to traditional solitons. Here, we present the modeling of a self-frequency shift (SFS) fiber laser based on the PQS, emphasizing the impact of fourth-order dispersion and the Raman effect. The significant red-shift in wavelength is discovered as the pump energy increases, revealing that the emergence of SFS is a universal attractor in mode-locked PQS fiber laser systems. Our simulations demonstrate that such wavelength tunability is a direct byproduct of the gain bandwidth limit and the stimulated Raman scattering for PQSs inside the fiber cavity, while the evolution dynamics in the gain and passive fiber show obvious differences. However, we find that the effect of SFS in a PQS fiber laser is compromised by a trade-off with the degradation of pulse quality, such as reshaping the oscillating tail and destroying the symmetry of the emission pulse. This Raman-induced nonlinear process under high pump energy facilitates the discovery of the comprehensive complexity of science for PQSs suffering from higher-dimensional forms of nonlinear effects in fiber lasers.

Large-energy operation of an Er-doped fiber laser with ZrGeTe4 saturable absorber

ZrGeTe4 as a layered semiconductor material with good stability and optoelectronic properties, and excellent saturable absorption characteristics, but its application in fiber lasers is still insufficient. In order to explore its application in fiber lasers, we prepared ZrGeTe4-PVA thin film by liquid phase exfoliation and performed a series of characterizations. A modulation depth of 13.15 %, a non-saturated loss of 6.4 %, and a saturation intensity of 5.5 MW/cm2 were obtained. Then used the ZrGeTe4-PVA thin film as the saturable absorber (SA) in an Er-doped fiber laser (EDFL), the large-energy operation could be realized. In the case of a cavity length of 234 m, when the pump power was increased to 1229 mW, a maximum single pulse energy of about 32.72 nJ was achieved, with a repetition frequency of 859 kHz. To the best of our knowledge, this is the highest single-pulse energy achieved in an EDFL based on ZrGeTe4-SA. This experiment shows that the ZrGeTe4 is a promising two-dimensional (2D) material with good nonlinear absorption properties, proving that it is a promising pulse modulation of SA and laying a foundation for its subsequent study in fiber lasers.

Multicentre study comparing outcomes of RIRS using traditional suction ureteral access sheath (SUAS) and flexible and navigable suction UAS (FANS)

Objective: We aim to compare the stone-free rate (SFR), complications, and re-treatment rates in retrograde intrarenal surgery (RIRS) using a traditional suction ureteral access sheath (SUAS) with the more advanced flexible and navigable suction UAS (FANS). Materials and methods: Retrospective analysis was performed on patients who underwent RIRS using SUAS versus FANS across five institutions internationally as part of an audit. We analysed baseline and pre-operative characteristics such as stone location and density, intra-operative characteristics such as type of ureteroscope and laser, laser, and fluoroscopy time, as well as post-operative complications and residual fragments (RFs). Results: A total of 45 patients were included in each arm, with no significant difference in baseline characteristics. The commonest sheath size in the FANS group was 10–12 Fr (64.4%), while 11–13 Fr was preferred in SUAS (73.3%). Despite similar lasers (thulium fibre laser (TFL) and high-power holmium laser with MOSES), stone dusting (48.9%) and popcorning (95.6%) were carried out in FANS with minimal need for baskets (4.4%), while popcorning (64.4%) and basket extraction (40.0%) were required in SUAS. Although FANS had significantly longer operative times (65 minutes versus 55 minutes), it also had significantly higher rates of 100% SFR (80.0% versus 13.3%), and lower rates of clinically significant residual fragment (CSRF) (8.9% versus 53.3%), clinically insignificant residual fragment (CIRF) (11.1% versus 33.3%), and reintervention for CSRF (4.4% versus 37.8%). In addition, minor complications such as intra-operative oozing from mucosa not requiring intervention (8.9% versus 31.1%) and post-operative fever (11.1% versus 40.0%) were less common in FANS. On additional multivariate analysis, FANS was the only significant factor for higher SFR. Discussion and conclusion: The results of our study demonstrate that with its flexible and navigable tip, FANS proves advantageous over SUAS in terms of improving immediate SFR with negligible complications. By navigating the sheath into targeted individual calyces, fragments and dust are more successfully aspirated. FANS can therefore help to achieve the trifecta of high single-stage SFR, minimal minor and no major complications, and negligible reintervention rates. Level of evidence: Not applicable.

Revealing fractal dynamics by dispersion tuning in a mode-locked fiber laser

Fractal dynamics was previously observed by tuning nonlinearity through pump currents in a mode-locked laser. Here we show that the fascinating fractal dynamics (the devil’s staircase) can also be accessed by tuning dispersion only. In this case, the fractal dimension is also the same as that of the devil’s staircase. Standard dispersion control via the cut-back methods is not precise enough to observe the fractal phenomena. A precise and readily dispersion tuning method through software control is thus proposed and confirmed by the numerical simulations. Third-order dispersion is later considered and does not destroy the phenomena, confirming the robustness of the devil’s staircase. Our work confirms the universality of the fractal phenomena in mode-locked lasers, and that the numerical simulations could stimulate future experimental investigations.

Controllable lasing characteristics in Brillouin random fiber lasers by tailoring gain and random feedback fibers

Brillouin random fiber lasers (BRFLs), the combination of stimulated Brillouin scattering (SBS) gain and random distributed feedback, offer narrow linewidth lasing with simplicity and flexibility. However, BRFLs may not gain broad acceptance unless the fundamental lasing mechanisms governing their operation are fully understood and the lasing properties are effectively manipulated. Here, we demonstrate the control of lasing characteristics in BRFLs by tailoring the SBS gain fiber and the scattering pattern of the random feedback fiber. Experimental results show that BRFLs with 5 cm random fiber gratings (RFGs) feedback exhibit lower intensity fluctuation, longer coherence time, and more stable frequency compared to those with 6 km Rayleigh scattering fiber (RSF) feedback thanks to more correlated phase, lower mode density, and weaker dependence on external variations of RFGs. The low-randomness RFG feedback further improves the coherence time and intensity fluctuation attributed to the small period variation of sub-gratings. Moreover, the BRFL based on the high gain fiber and the strong scattering RFG feedback with low loss achieves high lasing efficiency and low threshold. The frequency jitter, intensity noise, and coherence time are also improved by reducing the gain fiber from 20 km to 1 km due to decreased mode hopping from mode competition. These results clarify the impact of gain and random feedback fibers on BRFL performance, offering insights for optimizing complex laser design for applications requiring high frequency stability and long coherence time.

Nanostructured LNTO saturable absorber for generating multi-wavelength laser in Q-switched EDFL

In this paper, we propose a new and efficient ferroelectric nanostructure metal oxide lithium niobate [(Li1.075Nb0.625Ti0.45O3), (LNTO)] solid film as a saturable absorber (SA) for modulating passive Q-switched erbium-doped fiber laser (EDFL). The SA is fabricated as a nanocomposite solid film by the drop-casting process in which the LNTO is planted within polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] as host copolymer. The optical and physical characteristics of the solid film are experimentally established. The SA is incorporated within the cavity of EDFL to examine its capability for producing multi-wavelength laser. The experimental results proved that a multi-wavelength laser is produced, where stable four lines with central wavelengths at 1529.5, 1530.5, 1531.5, and 1532 nm are observed on the laser spectrum at 157 mW pumped power. Furthermore, at maximum available pumped power (157 mW), laser pulses are running with a rate of 178 kHz and pulse width of 2.64 μs. The output power of 3.7 mW is attained at pumped power of 157 mW. The result proved that the LNTO-SA could be a potential candidate for generating multi-wavelength passive Q-switched fiber laser pulses.

Dynamics of coupled erbium-doped fiber lasers: Modulation effects and synchronization patterns

Studying the dynamics of coupled Erbium-Doped Fiber Lasers helps in optimizing the performance of these systems in different applications. An important factor in these systems is the modulation signal which can affect the dynamics of systems, leading to complex behaviors including diverse periodic and chaotic dynamics. This paper investigates the dynamics of a ring network of Erbium-Doped Fiber Lasers and compares its behaviors in the presence and absence of the modulation. The results reveal that although complete synchronization is not reachable, certain synchronization patterns exist during the periodic oscillations. In the non-modulated network, two distinct clusters are formed which can achieve lag synchronization under specific coupling intensities. While in the coupled modulated systems, the chimera state may form. These findings represent the complex relationship among modulation, coupling intensity, and network dynamics in EDFL systems.

Nonlinear Absorption in 2D Ruddlesden-Popper Perovskites: Pathways to Ultrafast Optical Applications.

Owing to their distinctive photophysical properties resulting from their larger exciton binding energy and the influence of dielectric and quantum confinement effects, considerable research interest has been directed toward two-dimensional Ruddlesden-Popper halide perovskites (2D RP-HPs). Particularly, 2D RP-HPs exhibit exceptional multiphoton absorption (MPA) effects that reveal versatile applications. In this work, two-photon absorption (2PA) and three-photon absorption (3PA) in 2D RP-HPs, specifically (PEA)2PbBr4 and (BA)2PbBr4 platelets, have been demonstrated through their photoluminescence spectra under multiphoton excitation, revealing a power law relationship with excitation energy. On the other hand, polarization-dependent MPA measurements are also conducted to obtain their anisotropy properties. The excellent 2PA and 3PA effects of 2D RP-HPs have found applications in ultrafast optics to construct fringe-resolved autocorrelation traces, enabling the retrieval of pulse duration not only passively mode-locked Ti:sapphire at 800 nm but also Yb-doped fiber lasers at 1030 nm.

Structure and Wet-Sliding Characterization of a Laser Powder Bed Fusion Ti-6Al-4V Biomedical Alloy: Effect of Laser Surface Modification

The effect of laser modification on the structure and wet (Simulated Body Fluid)-sliding behaviour of a Laser Powder Bed Fusion alloy Ti-6Al-4V was studied. The scanning of 400 W fiber laser with a speed of 10 mms –1 led to a surface melting with an increase in hardness (780–820 HV) and 20%-decrease in wear. Under the scanning speeds of 40–60 mms –1 the surface was refined almost without melting to provide a 7–8% increase in hardness/wear resistance accompanied by a decrease in the friction coefficient

Generation of noise-like pulses in a linear-cavity Tm fiber mode-locked laser based on FMF saturable absorber

As a real saturable absorber (SA) based on the nonlinear multimode interference (NL-MMI) effect, the devices based on the few-mode fiber possess numerous exciting characteristics due to their all-fiber structure, straightforward manufacturing process. In this paper, by employing a SA with the SMF-FMF-SMF structure in a linear cavity, we demonstrate a stable mode-locked Tm-doped fiber laser. At the pump power of 1 W, a single noise-like pulse (NLP) with a pedestal pulse duration of 28 ps and coherent peak width of 0.77 ps is generated at a central wavelength of 1940 nm with a 3 dB bandwidth of 10.51 nm. The stable noise-like pulse can be sustained from the lasing pump threshold up to the maximum pump power of 2.2 W without experiencing pulse splitting. The experiment results in a peak average output power of 116 mW, along with a corresponding maximum pulse energy of 24.73 nJ at a repetition frequency of 4.69 MHz. The high stability of our fiber laser is confirmed by the signal-to-Noise Ratio (SNR) of 63 dB, and its enduring stability is additionally validated over an 8-hour period. The experimental findings suggest that the SMF-FMF-SMF structure has significant potential in the simple and robust all-fiber mode-locked lasers operating in the noise-like pulse regime.