Yb-doped Fiber Research Articles

Dynamic analysis and manipulation of self-starting single-pulse mode-locking in a Yb-doped fiber laser with Figure-9 all-normal-dispersion

The self-starting single-pulse mode-locked mechanisms in an all-normal-dispersion (ANDi) Figure-9 fiber laser are portrayed via an integrated simulation approach, which combines rate equations with the General Nonlinear Schrödinger Equation (GNLSE). The simulation results indicate that the mode-locking performances and pulse characteristics are significantly influenced by the splitting ratio, linear phase shift, gain, and asymmetric placement of gain fiber positions within the loop directly, providing effective quantified guidance for self-starting high-quality pulse generation. An experimental oscillation based on a nonlinear amplifying loop mirror (NALM) was established, operating under different widths of bandpass filters. Combining simulation for parameter optimization, the introduced linear phase shift and the coupling ratio were adjusted by changing the rotation angle of the combination wave plate to determine the optimal mode-locked operating point. A spectral bandwidth of 10.4 nm and a pulse duration of 17.5 ps, delivering 0.67 nJ of pulse energy, have been achieved in a modified mode-locked Yb-doped fiber laser.

Optical cooling of a Yb-doped alumino-phosphosilicate fiber in air by -250 mK.

Recent progress in the fabrication of Yb-doped silicate fibers with low concentration quenching and low background absorption loss has led to the demonstration of anti-Stokes-fluorescence cooling in several aluminosilicate compositions. This breakthrough is critical to combat deleterious thermal effects due to the quantum defect in fiber lasers and amplifiers. Since cooling efficiencies remain low (1-2.7%), it is paramount to engineer compositions that improve this metric. We report a silica fiber with a core glass heavily doped with aluminum and phosphorus that sets, to our knowledge, a few new records. This few-mode fiber (16-µm core) was cooled in air by -0.25 K from room temperature with ∼0.5 W of 1040-nm power. The measured cooling efficiency is 3.3% at low pump power and 2.8% at the power that produced maximum cooling. The critical quenching concentration inferred from the measured dependence of cooling on pump power and careful calibration of the pump absorption and saturation is 79 wt.%. The inferred background absorption loss is 15 dB/km. Together with the fiber's average Yb concentration of 4.2 wt.%, these metrics rank among the best reported in a silica glass.

Impact of Yb2+ on the anti-Stokes fluorescence cooling performance of Yb-doped silica fibers

To unlock the full potential of laser-cooled silica optical fibers, a better understanding of the internal mechanisms of heat generation is required. This work explores ytterbium-doped aluminosilicate fibers produced via industry-standard modified chemical vapor deposition (MCVD) techniques with varied levels of divalent ytterbium to determine their effect on anti-Stokes fluorescence thermal performance. The inclusion of Yb2+ is shown to have a significant negative impact on cooling potential. Yb2+ ions are shown to correlate with heat generation by two distinct mechanisms, absorption and quenching of active Yb3+ ions. This excess heating represents a reduction in quantum efficiency that is detrimental to Yb-doped fiber lasers and amplifiers beyond the laser-cooling application.

High efficiency laser ablation of gold thin film by 2.8 GHz intraburst repetition rate pulses

This work initially presents our progress in developing a 14 W all-polarization-maintaining (PM) Yb-doped fiber laser system. This system can generate bursts with a 2.8 GHz intra-burst repetition rate and offers flexibility in burst repetition rates, starting from 100 kHz. The laser produces pulse energies up to 210 nJ, which can be dechirped to approximately 650 fs. Subsequently, we utilized the developed laser in thin film gold processing. We sent up to 6.4 W and employed three different intraburst pulse configurations on a 100 nm-thick gold film coated on glass. We achieved a record gold removal efficiency of 125 μg/W.s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu \ ext{g}/\ ext {W.s}$$\\end{document} using ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}5 nJ pulses. Moreover, we determined an ablation pulse energy threshold of approximately 1 nJ, representing the lowest pulse energy to the best of our knowledge.

Microstructure evolution and grain growth characteristics of IN625 in laser surface melting: Effects of laser power and scanning speed

This study investigated the effects of laser power and scanning speed on the microstructure evolution and grain growth characteristics of IN625 in laser surface melting. Laser powers of 400 W, 600 W and 800 W at scanning speeds from 200 mm/min to 800 mm/min were employed to melt the surface of as-cast IN625 using a continuous Yb-doped fibre laser. The microstructure from the surface to the melt pool boundary was characterised by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). It was shown that a cellular structure was developed at low energy densities (≤ 240 J/mm2), since low energy densities resulted in more rapid solidification. A coarse grain region was found near the surface after melting and a columnar grain growth region was formed close to the melt pool boundary at increasing laser power. Large angle grain boundaries were eliminated and medium angle grain boundaries exhibited an area fraction of 90 % after laser surface melting. This was due to the fact that the twinned grains were fully melted in the melt pool and no twins were formed after solidification. An analytical approach was proposed to the estimate the melt pool depth and good agreement between experimental and calculated melt pool depth was obtained at laser power of 400 W and 600 W.

Modeling and experimental characterization of two-wave mixing in Yb-doped fiber amplifiers.

Two-wave mixing between forward- and backward-propagating signal light has recently been observed in frequency-modulated single-frequency fiber laser systems. The phenomenon is a potential limiting factor for power scaling of such frequency-tunable lasers. In this contribution, we derive a perturbative coupled-mode theory for two signals that counter-propagate in an Yb-doped fiber with a constant frequency detuning. We apply the theory to analyze experimental results dedicated to extracting the central material parameter that relates the Yb inversion to a (real) refractive-index change. The perturbative theory is derived to all orders, and argued to be convergent. The experimental results and our analysis support previous estimates of the ratio between changes in the gain coefficient and the refractive index.

High-temperature-insensitivity high-power Yb-doped fiber laser directly in-band pumping by 1018 nm laser diodes.

In this Letter, we demonstrate a high-power ytterbium-doped fiber laser (YDFL) based on a directly in-band pumping scheme (DIPS) which employs 1018 nm laser diodes (LDs) as pump sources. The wavelength of the LDs is designed theoretically, considering the distribution of Yb3+ absorption cross section (σa) as well as quantum defect (QD). The flat distribution of σa around 1018 nm ensures excellent temperature insensitivity and flexibility for the YDFL. Besides, lower QD and more compact structure promise higher optical-to-optical (O-O) and electrical-to-optical (E-O) efficiencies. Based on the experimental setup, as the cooling temperature of the 1018 nm LDs ranges from 6 to 23°C, an output power of 2 kW level is achieved that varies by only 2.01% without adjusting the operating current of the LDs subjectively. The output power is then scaled up to 5 kW level. Furthermore, there is a great potential to achieve higher output power and E-O efficiency in YDFLs based on the DIPS.

Coherent beam combining of optical vortices.

We experimentally demonstrate the power scaling of optical vortices using the coherent beam combining technique, encompassing topological charges ranging from ℓ = 1 to ℓ = 5 realized on the basis of a Yb-doped fiber short-pulsed laser system. The combining efficiency varies from 83.2 to 96.9% depending on the topological charge and beam pattern quality generated by the spatial light modulators. This work is a proof of concept for using a coherent beam combining technique to surpass the physical power/energy limitation of any single source of optical vortices, regardless of the generation methods employed. These results open a pathway to power scaling of optical vortices with diverse applications in science and industry by utilizing advances in light-matter interactions.

Generation of Bright–Dark Pulse Pairs in the Er-Doped Mode-Locked Fiber Laser Based on Doped Fiber Saturable Absorber

This study reports new types of passive mode-locked Er-doped fiber laser (EDFL) based on a segment of doped fiber saturable absorber (DFSA) with Tm/Ho-doped fiber (THDF), Yb-doped fiber (YDF), and Er-doped fiber (EDF). By employing THDF-SA, a bright pulse sequence with a fundamental repetition rate of 17.86 MHz was obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, and second-harmonic pulses, were obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in both polarization directions was verified. Furthermore, using EDF-SA and YDF-SA, dark pulses and dark–bright pulses were obtained. A comparison of the three experiments revealed that THDF-SA effectively reduces the mode-locked threshold and improves the average output power. Compared with bright pulses, dark pulses offer several advantages such as resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL can find broad application in long-distance transmission, precision measurement, and other fields.

Broadband tunable single-frequency Yb-doped fiber laser with dual ring subcavity and Sagnac ring filter

We demonstrate a broadband tunable ultra-narrow linewidth single-frequency (SF) Yb-doped fiber laser (YDFL). A dual ring subcavity (DRS) as a filtering component to eliminate the dense longitudinal mode inherent in YDFL and theoretically analyzed its filtering characteristics. By inserting a 0.8 m unpumped polarization-maintaining Yb-doped fiber in the Sagnac ring, a dynamic narrowband grating (DNG) based on the saturable absorption (SA) effect is constructed to ensure SF laser output over the entire wavelength tuning range. We achieve a wide wavelength tunable SF laser output in the range of ∼74 nm, covering 1021.06 nm to 1094.98 nm. The laser has an optical signal-to-noise ratio (OSNR) of more than 62.5 dB, a slope efficiency of 3.57 %, and an ultra-narrow linewidth of 622 Hz over the entire tunable range. In addition, the stability of the wavelength and power fluctuations below 0.018 nm and 0.67 dB, respectively. This tunable SF fiber laser has a compact structure, lower cost, and excellent performance, and is expected to be used in the fields of coherent communications, precision metrology, and so on.

Dynamics of h-shape narrow bandwidth dissipative soliton in Yb-doped fiber laser

We demonstrate a narrow bandwidth mode-locked ytterbium-doped fiber laser based on the carboxyl-functionalized graphene oxide (GO-COOH). In the combination of GO-COOH and intracavity filtering effects, the narrow bandwidth spectrum exhibits an h-shape at 1060.76 nm central wavelength with a 3-dB bandwidth of 0.47 nm. Furthermore, the 3-dB bandwidth can be compressed to 0.049 nm by adjusting the polarization controller. The formation of h-shape dissipative soliton has been investigated by applying the dispersive Fourier transformation and numerical simulation. The h-shape narrow bandwidth dissipative soliton we demonstrated provides a new insight for investigating the evolution dynamics of solitons with special shapes.

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

5 kW power-level 1050 nm narrow-linewidth fiber amplifier enabled by biconical-tapered active fiber.

Effective wavelength extension is vital in the applications of high-power narrow-linewidth fiber lasers. In this work, we demonstrate a 5-kW power-level narrow-linewidth fiber amplifier at 1050 nm utilizing a homemade biconical-tapered Yb-doped fiber (BT-YDF). Up to ∼4.96 kW fiber laser is achieved with a 3 dB linewidth of ∼0.54 nm and a beam quality factor of Mx 2 = 1.46, My 2 = 1.6. The experimental comparisons reveal that BT-YDF has the advantages of improving a stimulated Raman scattering threshold and balancing transverse mode instability suppression in the fiber amplifier. This work could provide a good reference for extending the operating wavelength of high-power fiber amplifiers.

Peak-power and width tunable noise-like pulses from a figure-9 cavity with two separate gain segments

A novel feature of noise-like pulses (NLPs) from a dual pump module based figure-9 cavity has been presented in this manuscript. The laser is mode-locked by taking advantage of a non-linear amplifying loop mirror (NALM) and the cavity contains a LOOP and an ARM, each section comprises an Yb-doped fiber pumped by an independently controllable pump module. In stable conditions, the laser delivers nanosecond rectangular pulses at a fundamental repetition rate of 1.96 MHz. The NLPs are recognized from their double-scaled auto-correlation trace. Akin to typical NLPs, the pulse duration increases with the pump power of the pump modules placed at the LOOP, whereas, it is noticed that the pulse width tends to reduce with the power of the pump module placed outside the LOOP, which is an unconventional behavior for NLPs. Alongside the pulse duration, the peak power also behaves oppositely with the pump power of individual modules. In the best operating condition, the maximum average power is 766 mW corresponding to 136 W peak power and pulse energy of 390 nJ. This study offers a possible direction to explore the dynamics of NLPs in laser cavities with two independent pump modules.

LMA fibers with increased higher-order mode loss for high average power, pulsed, diffraction-limited lasers

We demonstrate new, large-mode area (LMA) gain fibers with ∼25 µm mode-field diameter, and increased higher-order mode loss that enable diffraction limited, pulsed fiber lasers operating at high average power with high pulse energy. We achieved 1.6 mJ, ns pulses, with 1.2 kW average power and 370 kW peak power in one of the new Yb-doped gain fibers. In a second, higher absorption fiber, we demonstrate 2 mJ pulse energy with peak power of >420 kW at an average power of 660 W. To the best of our knowledge these are the highest demonstrated energies, powers and peak powers for any nanosecond diffraction-limited, all-fiber laser. The TMI thresholds of two of these fibers were measured to be 1.8 kW and 1 kW respectively.

Impact of thermal lensing on the TMI threshold powers in rod-type Yb-doped fiber amplifiers

The impact of thermal lensing (TL) on the transverse mode instability (TMI) threshold power in rod-type fiber amplifiers is investigated. Simulations are conducted with a 3D coupled mode analysis on a set of five scaled large pitch fiber (LPF) amplifiers. The LPF fibers are represented by surrogate step-index fibers (SIFs) with scaled cladding diameters, core diameters, and numerical apertures for a fixed normalized frequency V equal to 3.0 and scaled modal field overlap integrals with the core and cladding. It is found that thermal lensing decreases the TMI threshold powers due to increases in the TMI nonlinear gain. This gain increase is attributed to an increase in the nonlinear gain overlap integrals that occurs with the reduction in the fundamental mode effective area. Estimates for the TMI threshold power are in good agreement with measurements; however, the simulations overestimate the mode shrinkage factor. This discrepancy is tentatively attributed to the representation of the LPF by an effective SIF. These results may offer opportunities for fiber designs that increase the TMI threshold powers.

Review of High-Power Continuous Wave Yb-Doped Fiber Lasers near 980 nm

In this paper, the development of a high-power continuous wave (CW) fiber laser near 980 nm is reviewed. This review is focused primary on the power evolution resulting from the designation of Yb-doped fibers, which is important in the suppression of the amplified spontaneous emission (ASE) around 1030 nm. Current studies on the in-band ASE as the power limitation of the Yb-doped fiber lasers near 980 nm are also summarized in this review.

Design optimization of Yb-doped fiber lasers for operation in radiation environments

AbstractRadiation hardening should be considered for various active fiber systems operated in adverse environments to reduce their sensitivity to complex ionizing radiations. And, architecture optimization through numerical simulation provides an efficient choice. Here, introducing radiation effects into the conventional fiber laser model, a radiation model concerning the design optimization of low- and moderate-power Yb-doped fiber lasers is developed. And, experiments at different radiation levels up to 750 Gy are carried out for validation, demonstrating the ability of this model to correctly simulate the performance of the Yb-doped fiber laser in harsh environments. Then, with this model, impacts of active fiber length, pump scheme, and pump allocation on the output characteristics of Yb-doped fiber lasers are analyzed numerically. And, optimization of Yb-doped fiber lasers are conducted through architecture design. Simulations show that a proper design with relatively short active fiber and dynamic pump allocation can remarkably improve the radiation tolerance of Yb-doped fiber lasers.

Yb-doped mode-locked fiber laser with a hybrid structure of NPR and a Lyot filter as the saturable absorber.

Passively mode-locked fiber lasers based on a nonlinear polarization rotation (NPR) have attracted much attention due to their ability to generate short pulses with wide spectra and high peak power. However, environmental perturbations can easily cause the lasers to lose the mode-locked state and make it a challenge for practical application. The aim of this research is to improve the laser stability by inserting a Lyot filter into the mode-locked laser cavity. The experimental results indicate that the mode-locked state can be maintained when the radius of the fiber loop is changed from 7.5 to 1.5 cm, while the signal-to-noise ratio of the fundamental frequency remains almost the same. The tunability of the output power can be achieved by adding a half-wave plate (HWP) in the laser cavity without changing the pump power, while the mode-locked state remains stable. By adjusting the angle of the HWP2, the output power can be adjusted from 3.36 to 66.5 mW at repetition rate of 29.7 MHz.

Ultrafast nonlinear optical response of layered violet phosphorus for femtosecond noise-like pulse generation

As a new member of two-dimensional (2D) phosphorene, 2D layered violet phosphorus (VP) has unique optoelectronic properties and good environmental stability, showing its huge advantages in optoelectronic applications. In this paper, the ultrafast nonlinear optical (NLO) properties of layered VP nanosheets at 1 µm band were explored, which exhibit an obvious saturable absorption response with a modulation depth of ∼1.97%. Meanwhile, the fast and slow carrier lifetimes of VP nanosheets at 1µm band were also determined as 295.9 fs and 2.36 ps, respectively, which are much shorter than that of most reported 2D materials. The excellent saturable absorption response combined with ultrashort carrier lifetimes indicate the prospect of layered VP nanosheets as a fast saturable absorber (SA) for ultrafast laser modulation. Then we demonstrated a Yb-doped fiber laser based on the VP-deposited taper-shaped fiber (TSF) SA, which delivers stable Q-switched mode-locked (QSML) pulses, dual-wavelength mode-locked pulses and 404-fs noise-like pulses. This work fully demonstrates the great potential of 2D VP materials for 1 µm ultrashort laser pulse generation.