Output Power Of Fiber Laser Research Articles

Experimental Modeling, Statistical Analysis, and Optimization of the Laser-Cutting Process of Hardox 400 Steel.

Fiber laser cutting machines are widely used in industry for cutting various sheet metals. Hardox steel is widely used in the construction of machinery and equipment that are subjected to wear and impact due to its anti-wear properties and good impact resistance. In this experimental study, the effect of input parameters including laser output power (LOP), laser-cutting speed (LCS), and focal point position (FPP) of fiber laser on the surface roughness and kerf width of Hardox 400 steel sheets are studied. In addition, the optimization of input parameters to achieve the desired surface roughness and kerf width are investigated and analyzed using the response surface methodology (RSM). The experiments are performed using a 4 kW fiber laser-cutting machine and the output results including surface roughness and kerf width are measured using roughness meters and optical microscope. The results of the analysis of variance (ANOVA) for surface roughness and kerf width show that the FPP and LCS are the most significant process parameters affecting the surface roughness and kerf width. With a positive focal point, the surface roughness decreases while the kerf width increases. With increasing the laser-cutting speed, both the surface roughness and kerf width decrease.

Investigation of a twisting-fused side-pump coupler based on tellurite fiber

Fiber side-pump couplers can enhance the output power of fiber laser due to their dependable and efficient operation and impressive power handling capability. We developed a tellurite fiber side-pump coupler by twisting and fusing a tapered pump fiber onto a target fiber. The effect of twisting parameters on coupling efficiency was comprehensively investigated through theoretical simulations and experiments. Experimental results exhibited an impressive coupling efficiency of 76.5% and a root mean square stability of 0.086% and 0.091% before and after one month, respectively, driven by an incident pump power of up to 4.2 W.

Fabrication of double-cladding fluoroindate glass fibers and watt-level 2.7 μm laser application

We report a double-cladding fluoroindate fiber with three layers of step refractive index glass. The gain double-cladding fluoroindate fiber is fabricated by the traditional rob-in-tube method. It possesses a tunable refractive index from 1.46 to 1.51 via modification of glass components. The good thermal–mechanical performance of fluoroindate glass protects fiber against thermal damage. The luminescence characteristics and radiation parameters are studied, and the results indicate enhanced emission with the higher Er3+ doping concentration. The maximum output power and the slope efficiency of heavily erbium-doped fiber laser are about 1.2 W and 16.3 %, respectively. The numerical modeling of a heavily-erbium-doped fluoroindate fiber laser is also carried out and compared with our experimental results. The low phonon energy and high laser damage threshold of fluoroindate glass allow for higher output power and efficiency of fiber lasers. In brief, this is the first study on watt-level 2.7 μm fiber laser in all-solid double-cladding fluoroindate fibers to our knowledge.

Ultrafast Fiber Laser Based on Tungsten Sulphoselenide Materials

Tungsten sulphoselenide (WSSe) alloys, belonging to the transition metal dichalcogenide family, have attracted significant interest in the area of optoelectronics because of their unique optical and electronic properties. However, there has been a dearth of sufficient research on the saturable absorption features and ultrafast lasers applications. Herein, we fabricated a WSSe-microfiber saturable absorber (SA) based on WSSe nanosheets prepared by liquid exfoliation technique. The SA provided a saturation intensity of a modulation depth of 27.95% and a nonsaturable loss of 21.34%. To investigate the potential applications of WSSe in ultrafast photonics, the prepared WSSe-microfiber was incorporated into an Er-doped fiber laser ring cavity. The results demonstrated that the WSSe-based SA successfully generated mode-locking laser pulses with a remarkably short pulse width of 231 fs. Furthermore, the output power of this ultrafast fiber laser reached an impressive value of 15.68 mW. These findings provide valuable views into the unique features of WSSe alloys in the areas of ultrafast optics and develop recipes for SA in ultrafast fiber lasers.

Optimization and demonstration of a bidirectional output linear-cavity fiber laser with a record high power of 2 × 4 kW

The bidirectional output fiber laser can achieve two laser outputs from a single resonant cavity, which can reduce the volume and cost of high-power fiber laser systems and has good application prospects in the industry. In this work, we demonstrated a bidirectional output fiber laser oscillator structure, and a total output power of 8 kW at the 2 ports × 4 kW level was achieved experimentally for the first time. In order to suppress stimulated Raman scattering (SRS) and transverse mode instability (TMI), the double cladding ytterbium-doped fiber with a core/cladding diameter of 30/400 µm, a pair of matched output coupler fiber Bragg gratings (OCFBG) with a 3 dB bandwidth of 2 nm, and the pump source with wavelength-stabilized 981 nm laser diodes (LDs) were employed. The effect of the coiling method and diameter of the active fiber on the optical-to-optical (O-O) efficiency and TMI threshold were studied intensively. The comparison of laser performance with a unidirectional output oscillator was further exploited, and results indicated that the bidirectional output fiber laser oscillator possessed a higher O-O efficiency and TMI threshold. By optimizing the fiber coiling diameter and coiling method, we finally achieved a total laser output power of 8169 W (3769 W at end A and 4400 W at end B), with an efficiency of 74.6% and beam quality of M2A ∼ 2.13, M2B ∼ 2.36, while the total output power achieved by unidirectional output structure was only 5805 W with signs of TMI. To the best of our knowledge, it is the highest output power of the bidirectional output fiber laser.

10-W random fiber laser based on Er/Yb co-doped fiber

In this study, we presented a 1550-nm, high-power, high-efficiency random fiber laser to improve the output power and slope efficiency of erbium-ytterbium co-doped fiber–based random fiber lasers. By optimizing the length of the erbium-ytterbium co-doped fiber and increasing the 3-dB reflection bandwidth of fiber Bragg grating, the output power and slope efficiency of the random fiber laser were improved. Furthermore, the influence of different fiber lengths on the generation threshold of the amplified spontaneous emission from the Yb3+-ions was studied. An output power of more than 10 W was achieved, with a slope efficiency of 36.7 % and a single transverse mode output. The proposed random fiber laser showed excellent stability in the millisecond scale and long timescale (10 min). The findings of this study can provide a basis for the development of high-performance light sources for a variety of applications.

Output Power Saturation Effect in Cladding-Pumped Bismuth-Doped Fiber Lasers

In this article, output power characteristics of cladding-pumped lasers based on bismuth-doped phospho- and germanosilicate core glass fibers were thoroughly studied and analyzed. The developed lasers are capable of providing the output power of several hundred milliwatts with the slope efficiency close to 1%. The output power saturation for the Bi-doped germanosilicate fiber laser and absence of the saturation regime for the Bi-doped phosphosilicate fiber one was found. This effect is explained by a relatively long relaxation time of bismuth active centers (BACs), namely a non-radiative transition from the higher-lying pump level to the upper laser (metastable) level in the corresponding energy levels diagram. The experimentally obtained data are in good agreement with the results of numerical simulation. In addition, it was investigated that the relaxation time of the BACs from the higher-lying level can have a significant impact on the laser efficiency and the achieved output power. The consequences caused by the saturation effect is possible to overcome with dual-wavelength pumping (combining cladding-pumping at 808-nm wavelength and core-pumping at a wavelength in the range of 1930 – 2040 nm), which provides both the BACs excitation and the stimulated relaxation of BACs from the excited (pump) state to the upper laser level. Using this approach the output power of the Bi-doped fiber laser was increased by almost two times.

Contribution of different factors in heat production in Yb3+-doped fiber laser: a review

The three important factors that affect the output power and temperature of fiber lasers (FLs) were investigated in a large mode area step-index FL under a high-power operation. Photodarkening (PD), quantum defect (QD), and background loss cause increases in the FLs temperature and reductions in beam quality, stability, and power. PD and background loss coefficients have different values for the signal (laser) or pump wavelength. But QD depends on the difference between the pump and the laser wavelength. By considering the PD attenuation in the rate equations, the effects of forward, backward, and bidirectional pump schemes on heat distribution agents were investigated. FL characters, including core and clad sizes, both side reflectors, and FL lengths in each heat generation agent, were studied in detail.

Thermally-induced transverse mode instability: Hopf bifurcation in high-power fiber laser

The thermally-induced transverse mode instability (TMI) has become a major challenge for further enhancing the output power of single-mode fiber laser. Even though much work has been done over the past decades, the spontaneous generation process of output spot oscillation has not been well understood yet. Here, we establish a new theoretical model of the thermally-induced TMI in a high-power fiber oscillator and provide a new mechanism explanation from the point of view of nonlinear dynamics. Theoretical analysis shows that the spontaneous oscillation (∼kHz) of the output spot caused by the thermally-induced TMI is a limit-cycle oscillation via Hopf bifurcation, and the oscillation frequency is proportional to square root of the relaxation rate γ1 of thermally-induced refractive index grating (RIG) (νTMI∝γ1) when the thermally-induced TMI is initially triggered. Furthermore, the relationship between the threshold power, together with oscillation frequency and several parameters of fiber laser system was also discussed in detail. This work help us better understand the underlying dynamics of the thermally-induced TMI.

Theoretical analysis of a 60 W solar-pumped single crystal fiber laser.

In order to improve the output power of solar-pumped single-crystal fiber (SCF) lasers, we propose a novel solar concentrating system, to the best of our knowledge, consisting of a parabolic mirror, a 3D compound parabolic concentrator, and a hollow-core reflector. By ray tracing with TracePro, the influence of the fiber's diameter and the hollow reflector's shape on the solar absorption efficiency is theoretically investigated. A typical Nd:YAG SCF with a core diameter of 1 mm, length of 150 mm, and doping concentration of 1 at.% is selected for a simulation of laser operation. The output characteristics of the laser are analyzed by solving the rate equation and power transmission equation; the maximum output power and solar-to-laser conversion efficiency are 60.62 W and 4.64%, respectively. The thermal effects of the laser are simulated by Comsol software. When the input solar power is 1307.4 W, the temperature decreases sharply first and then saturates along the SCF fiber, with the maximum value of 69.18°C at the input fiber end. This concentrating system can effectively overcome the limitation of end-launching solar power into SCFs and has great potential in improving the output power of solar fiber lasers.

Side-pumped solar Nd-doped fiber laser based on off-axis parabolic mirror array

In order to improve the output power of solar pumped fiber lasers, a new kind of transversely pumping configuration is proposed. The primary concentrator is an off-axis parabolic mirror array made up of ten fan-annular parabolic mirrors, and the secondary concentrator is a compound reflective concentrator composed of ten 3D compound parabolic concentrators (3D-CPCs) and a ring chamber. The collected sunlight passes through the 3D-CPCs’ inlet into the compound reflective concentrator which has a high reflecting film on the inner surface. An Nd-doped fiber is pumped when sunlight passes through the fiber core many times in the chamber. 490.8 W sunlight is absorbed by the fiber core according to ray tracing simulation. Based on solving the rate equation and the power transmission equation of the uniformly pumped solar fiber laser, 12.2 W laser output is obtained and the optical-to-optical conversion efficiency reaches 2.48 %. This solar concentrating system offers a new method to improve the output power of solar pumped fiber laser.

Confined-doped active fiber enabled all-fiber high-power single-frequency laser.

In this paper, we investigate the performances of an in-house fabricated confined-doped active fiber in the applications of all-fiber high-power single-frequency amplifiers. A 210-W single-frequency single-mode fiber laser is obtained directly, which confirms the excellent performance of the confined-doped active fiber for high-power single-mode operation. To further demonstrate the power scalability of the fiber amplifier, the strategy of applying a temperature gradient along the active fiber is investigated numerically and experimentally, and an up to ∼75% enhancement of the stimulated Brillouin scattering (SBS) threshold is achieved. As a result, a 368-W single-frequency fiber laser is obtained with the beam quality factor of Mx2 = 1.19, My2 = 1.26. Overall, the technique of the confined-doped active fiber provides a promising approach to scale the output power of single-frequency single-mode fiber lasers.

3.96 kW All-Fiberized Linearly Polarized and Narrow Linewidth Fiber Laser with Near-Diffraction-Limited Beam Quality.

In this paper, we realize a 3.96 kW all-fiberized and polarization-maintained (PM) amplifier with narrow linewidth and near-diffraction-limited beam quality. Based on a master oscillator power amplifier (MOPA) configuration seeded with phase-modulated single-frequency laser, a 3.96 kW signal laser is achieved with a 3 dB linewidth of 0.62 nm at the pump power of 5.02 kW. At the maximum output power, the polarization extinction ratio (PER) is ~13.9 dB, and the beam quality (M2 factor) is M2x = 1.31, M2y = 1.41. As far as we know, this is the maximum output power of PM narrow linewidth fiber laser with near-diffraction-limited beam quality and all-fiber format.

6.85 kW Ytterbium-Raman Fiber Amplifier Based on Adjustable Raman Threshold Method

To achieve a high spectral purity Raman laser in a wide range of pump power, we propose the adjustable Raman threshold method and experimentally demonstrate a 6.85 kW ytterbium-Raman (Yb-Raman) fiber amplifier in this paper. The Raman threshold is adjusted to coordinate with pump power level via manipulating the Raman proportion from the master oscillator. The spectral purity of Raman laser at 1120 nm reaches 86.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> at the highest output power and keeps over 65 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> throughout. And the 3 dB bandwidth is maintained within 2.5 nm. The system shows potential in further power scaling-up because the four-wave-mixing-induced high-order Raman noise is circumvented by designing wavelengths of the seeders. This work not only reports the highest output power of the Yb-Raman fiber lasers (to the best of our knowledge), but also provides an approach to achieve an agile lasing threshold in the Yb-Raman fiber amplifiers without any structural adjustments. The Yb-Raman fiber amplifiers with high spectral purity over a broad range of power will have promising applications in communications, industry and scientific researches.

Internal phase control of coherent fiber laser array without ambiguous phase based on double wavelength detection.

High-power fiber lasers have been widely utilized in manufacturing, medical care, and many other fields. Due to mode instability, nonlinear effects, and so on, the output power of a monolithic fiber laser is limited. Coherent beam combining (CBC) of fiber lasers is a promising way to obtain higher output power. An all-fiber CBC structure with internal phase detection has a compact construction and potential for a larger fiber laser array. For the existing internal active phase control of an all-fiber structure, π phase ambiguity always occurs because of double passing the fiber path. Additional compensation is needed under this condition, and the compactness of the system will decrease. In this paper, internal phase control of an all-fiber structure based on double wavelength detection without π-ambiguity is proposed. By adding a beacon laser with a different wavelength, phase locking of a coherent fiber laser array can be achieved internally without π-ambiguity. A corresponding math model is established, and a phase matched condition is derived. The spectral width of the beacon laser is analyzed, and the result shows that it can reach tens of nanometers with a proper optical path difference. Simulations of seven, 19, and 37 beams are carried out, and the results show that the structure proposed in this paper has the ability to achieve phase control with good robustness. The control bandwidth in the simulation is better than 1 kHz. By properly designing elements, the structure is expected to achieve high-power CBC of an all-fiber structure experimentally.

Nonlinear photoresponse of high damage threshold titanium disulfide nanocrystals for Q-switched pulse generation

A passively Q-switched Er-doped fiber laser with two wavelength at 1530 nm and 1556 nm wavelength was designed based on the titanium disulfide (TiS2) saturable absorber, the ultra-fast modulator was fabricated with TiS2 by the liquid-phase exfoliation and spin-coating methods and transferred onto a fiber ferrule. In the experiment, two single-mode 980 nm pump sources were applied in order to detect the high damage threshold of TiS2. The shortest pulse duration and maximum output power of the stable self-starting Q-switched fiber laser are 1.45 µs and 3.93 mW, respectively. The adjustable range of the repetition rate is from 25.8 kHz to 126.8 kHz with about 100 kHz tuning range, and the pulse with energy up to 39.3 nJ. Our experimental results conclusively suggest that TiS2 nanocrystals were advanced nanomaterial with high damage threshold would have extensive application prospects in the field of pulse fiber lasers.

Near-single-mode 2-kW fiber amplifier based on M-type ytterbium-doped fiber

High power fiber laser systems have attracted extensive attention due to compactness, good beam quality, efficient heat dissipation and high conversion efficiency. They are widely used in industrial processing, military, medical treatment and other fields. Over the past two decades, owing to the development of double cladding fiber and high-brightness laser diodes, the output power of fiber lasers has been greatly improved. Unfortunately, nonlinear effects (NLEs), such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), restrict the further enhancement of the output power of fiber lasers. Apparently, increasing the core diameter is the most common way to suppress NLEs in the fiber, but this causes another limiting factor, i.e. mode instability (MI), resulting in the deterioration of the beam quality and in the limitation of the power scaling. Therefore, it is important and urgent to suppress the NLEs and MI simultaneously in fiber lasers. The M-type fiber, by designing refractive index profile, breaks through the stringent trade-off between mode area and numerical aperture (NA), so it possesses a larger mode area than the step index fiber, which helps to avoid NLEs and expand the power range. The M-type ytterbium doped double-clad fiber is fabricated by the modified chemical vapor deposition (MCVD) process with solution doping technology (SDT), the core/cladding diameter is 25/400 μm. The NA of high index ring and index dip in the core are 0.054 and 0.025, respectively. To test the performance of the M-type fiber during high-power operation, a 976 nm bidirectional pumped all-fiber amplifier is constructed. As a result, maximum output power of 2285 W is achieved with an optical-to-optical conversion efficiency of 66.5% under bidirectional pumping scheme, and the measured &lt;i&gt;M&lt;/i&gt;&lt;sup&gt; 2&lt;/sup&gt; factor is 1.42, the central wavelength and 3 dB linewidth of output laser are 1080 nm and 3.01 nm, respectively. To the best of our knowledge, this is the highest output power in a continuous-wave fiber laser employing an M-type fiber at present. However, the MI effect is observed at the output power of 2252 W. The future work will focus on optimizing the structure of the M-type fiber to achieve a stabler higher-power and higher-efficiency laser output.

Comparison of Heat Transfer Theory, CFD and Experimental Results in the Design Process of High-Power Fiber Laser Cooling Plate

For the stabilization of laser output power and wavelength of the high power fiber laser, the cooling plate must be properly taken into account. In this study, three analyzing methods which are heat transfer theory, CFD and experiment are used to analyze cooling plate performance by measuring pump Laser Diode(LD) temperature. Under limited operating conditions of a cooling plate, the internal flow of cooling plate is transitional flow so that the internal flow is assumed to be laminar and turbulence flow and conducted theoretical calculation. Through CFD, temperature of pump LD and characteristics of the internal flow were analyzed. By the experiment, temperature of pump LD was measured in real conditions and the performance of the cooling plate was verified. The results of this study indicate that three analyzing methods are practically useful to design the cooling plate for the high power fiber laser or similar things.

Research on a 4×1 fiber signal combiner with high beam quality at a power level of 12kW.

At present, increasing the output power of a single fiber laser is a problem worthy of attention, and a fiber signal combiner which can carry high power and high beam quality is a solution to this problem. In this paper, a high beam quality 4×1 fiber signal combiner was developed. Firstly, the simulation model of a 4×1 fiber signal combiner was established, and the factors affecting the beam quality and the transmission efficiency of combiner were simulated. Secondly, based on corrosion technology, a high beam quality 4×1 fiber signal combiner with an output fiber of 50/400 µm (NA=0.12) was fabricated by using the taper-fused fiber bundles technology according to simulation results. Finally, four Yb-doped fiber lasers with a central wavelength of 1080 nm were used to test the output power and beam quality of combiner. The test result showed that the total output power of the signal combiner was 12.03 kW, the overall transmission efficiency was more than 96%, and the M2 factor was measured to be 4.03.

1.3 kW Continuous Wave Output Power of Ytterbium-Doped Large-Core Fiber Laser

A very efficient key cladding-pumped trivalent ytterbium (Yb3+) doped fiber laser has been developed. The whole fiber laser system generated 1.3 kW of continuous-wave (CW) maximum output power with very high efficiency at 1.1 μm and near the diffraction beam quality (M2 = 1.27). The measure slop efficiency is 76% and shows no limit of temperature and nonlinear effects. In a preliminary proof of principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped fiber laser with a diameter core and a numerical aperture of 0.09 has been demonstrated. When pumped to the ends of both fibers, they have strong beam quality and display no signs of rolling over even at the highest output power. The large core ytterbium doped fiber laser (YDFL’s) is end pumped with diodes stack source through opposite ends of fiber. This design of fiber can delivers maximum output power which is restricted mostly by accessible pump power.