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Extraction of more than 10kW from a single ytterbium-doped MM-fiber
... 1,2 From the structure of high-power fiber laser, there are mainly two categories: fiber amplifiers [3][4][5] and fiber oscillators. [6][7][8] Owing to the advantages of strong anti-reflection ability and easy control logic, fiber oscillators are more popular than fiber amplifiers in industrial applications. 9 With the improvement of fiber components and pump sources, the output power of fiber oscillators has been greatly boosted since the last decade. ...
... 9 With the improvement of fiber components and pump sources, the output power of fiber oscillators has been greatly boosted since the last decade. [6][7][8][9][10] Up until now, the highest output powers of an all-fiber oscillator and a spatial structure fiber oscillator are 8 kW 8 and 17.5 kW, 7 respectively. In order to achieve high power fiber oscillators, it is urgent to fabricate fiber components in large-core fibers, such as fiber Bragg gratings (FBGs). ...
In this paper, a fs-laser phase mask inscription system based on a galvanometer scanning strategy is designed and set up for the fabrication of large-core fiber Bragg gratings (FBGs). Based on this setup, a homogeneous cross-sectional refractive index modulation can be achieved in the core of large-mode-area fiber and a pair of FBGs are fabricated in fibers with core diameter of 30 μm. To investigate the performance of the fabricated FBGs, a high power all-fiber oscillator is built using a pure backward pumping structure. The FBGs work well and the maximum output power of 7920 W is achieved with an optical-optical conversion efficiency of 77.3%. To the best of our knowledge, this is the highest power of all-fiber oscillators based on fs-written FBGs. This work provides a flexible, stable and economic scanning strategy for large-core FBG inscription and exhibit excellent performance for high power fiber lasers.
... Compared with the MOPA structure, the fiber oscillator consisting of a resonant cavity enjoys the advantages of compact structure, fewer components and superior reliability. With the improvements of LMA fiber Bragg grating (FBG) manufacturing technique, the output power of fiber oscillators has scaled remarkably over the past few years [8]- [15]. In 2012, Xiao et al reported a monolithic fiber laser oscillator with an output power of 1 kW, which was based on ytterbium-doped fiber (YDF) with core/inner cladding diameters of 20/400 μm and pumped by 915 nm LDs [8]. ...
... Then, Fujikura Inc. has successively realized 3 kW and 5 kW near diffraction limited monolithic fiber laser oscillators based on the specially designed YDF [13], [14]. Recently, the output power of the fiber oscillator was up to more than 10 kW with multimode operation based on a ytterbium-doped extra-large mode area fiber in a bulk-optic resonator setup [15]. ...
In this paper, we construct a high power monolithic fiber laser oscillator based on a commercial ytterbium-doped fiber with core/inner cladding diameter of 25/400 μm. The output performances of the fiber oscillator are experimentally investigated in the conditions of either with or without an external feedback. In the presence of external feedback, a very strong stimulated Raman scattering (SRS) (~9 dB below the signal light) emerges at the output power of ~3.56 kW, where the onset of the transverse mode instability (TMI) limits further power scaling. By large angle cleaving the signal arm of the forward combiner to avoid external feedback, the maximum output power of 5.07 kW is achieved with no sign of TMI. The Raman stokes light is ~35 dB below the signal light and the M2 factor is measured to be ~1.6. To directly characterize its power stability and engineering capability, the fiber oscillator is tested for continuous 5-hour operation at ~5.07 kW with power fluctuation less than 0.42%. During the test process, the output power, spectrum, beam quality and temporal signal perform excellent stability. The experimental results reveal that thresholds of SRS and TMI strongly depend on the external feedback in high power fiber oscillators.
... As early as 2009, they launched a nearly-single-mode 10 kW fiber laser [4]. With years of development, multiple research institutions have accumulated rich experience and achieved fruitful results in the field of fiber lasers [5][6][7][8][9][10][11][12]. Before the discovery of transverse mode instability (TMI), nonlinear effects represented by stimulated Raman scattering (SRS) were the main limiting factors for the increase in the output power of high-power fiber lasers [13]. ...
Traditional ytterbium-doped high-power fiber lasers generally use a unidirectional output structure. To reduce the cost and improve the efficiency of the fiber laser, we propose a bidirectional output fiber laser (BOFL). The BOFL has many advantages over that of the traditional unidirectional output fiber laser (UOFL) and has a wide application in the industrial field. In theory, the model of the BOFL is established, and a comparison of the nonlinear effect in the traditional UOFL and the BOFL is studied. Experimentally, high-power continuous wave (CW) and quasi-continuous wave (QCW) BOFLs are demonstrated. In the continuous laser, we first combine the BOFL with the oscillating amplifying integrated structure, and a near-single-mode bidirectional 2 × 4 kW output with a total power of above 8 kW is demonstrated. Then, with the simple BOFL, a CW bidirectional 2 × 5 kW output with a total power of above 10 kW is demonstrated. By means of pump source modulation, a QCW BOFL is developed, and the output of a near-single mode QCW laser with a peak output of 2 × 4.5 kW with a total peak power of more than 9 kW is realized. Both CW and QCW output BOFL are the highest powers reported at present.
... (a) Structure schematic; (b) output laser beam profile 图 4 相干公司 3 kW 级空间结构光纤激光振荡器 ［42］ 。 (a)结构示意图； (b)实验结果 Fig. 4 3 kW fiber laser oscillator developed by Coherent Inc. [42] . (a) Structure schematic; (b) experimental results [52] . Fig. 6 2 kW allfiber laser oscillator developed by Rofin [40] . ...
... High-power fiber laser is one of the research focuses in the area of laser technology due to the advantages of simple structure, good beam quality and high efficiency [1,2]. In particular, the linearly polarized fiber laser is part of the study because it's widely used in coherent beam combination [3], nonlinear frequency conversion [4] and coherent detection [5], which demand high polarization extinction ratio (PER) output. ...
In this article, a thorough model of linearly polarized fiber laser considering polarization coupling, mode coupling, SBS, and SRS effects is established. The output results of direct pumping and tandem pumping linearly polarized fiber laser under different SBS and SRS intensity settings are simulated. The results show that direct pumping is a better pumping scheme at present, and if the doping concentration of gain fiber can be further increased and the mode field quality of corresponding passive fiber can be optimized, the disadvantages of tandem pumping can be suppressed. To explore the potential of tandem pumping, a backward tandem pumped linearly polarized fiber amplifier is built and 875 W over 13 dB linearly polarized laser output is obtained.
... This severely limits the extractable gain for low-average-power seed pulses [17,18]. For these reasons, doped multimode fibers are almost exclusively limited to amplification of nanosecond-scale pulses with highly multimode beams, at average power levels of at least 10 W [19][20][21][22][23][24]. ...
The peak power performance of ultrafast fiber lasers scales with fiber mode area, but large fibers host multiple modes that are difficult to control. We demonstrate a technique for single-mode operation of highly multimode fiber based on regenerative amplification. This results in a short-pulse fiber source with, to our knowledge, an unprecedented combination of features: high gain (>55dB) with negligible amplified spontaneous emission, high pulse energy (>50µJ), good beam quality ( M ² ≤1.3), and transform-limited (300 fs) pulses from a single amplification stage. We discuss peak intensity scaling to much higher levels and other opportunities for short-pulse generation in regenerative fiber amplifiers.
... High-power ytterbium-doped fiber laser is an ideal light source for industrial processing, such as laser cutting and laser welding. In the past 20 years, the output power of fiber laser has achieved a leap from hundreds of watts to 10 kW level [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. According to the current public reports, the technology of fiber lasers with output power exceeding 10 kW has gradually matured, and the difficulty lies in achieving high power and high beam quality (that is, high brightness) simultaneously. ...
Up to now, transverse mode instability (TMI) and stimulated Raman scattering (SRS) have become the main factors limiting the power scaling of conventional ytterbium-doped fiber laser. Many technologies are proposed to suppress the SRS or TMI individually, but most of them are contradictions in practical application. In this article, we focus on the technologies that can balance the suppression of both SRS and TMI, including fiber coiling optimization, pump wavelength optimization, pump configuration optimization, and novel vary core diameter active fiber. Firstly, we validate the effectiveness of these technologies in both theoretical and relatively low-power experiments, and introduce the abnormal TMI threshold increasing in a few-mode fiber amplifier with fiber coiling. Then, we scale up the power through various types of fiber lasers, including wide linewidth and narrow linewidth fiber lasers, as well as quasi-continuous wave (QCW) fiber lasers. As a result, we achieve 5~8 kW fiber laser oscillators, 10~20 kW wide linewidth fiber laser amplifiers, 4 kW narrow linewidth fiber amplifiers, and 10 kW peak power QCW fiber oscillators. The demonstration of these new technical schemes is of great significance for the development of high-power fiber lasers.
... High-power ytterbium-doped fiber lasers are widely used in industrial processing and other fields [1,2]. With the rapid development of double-cladding fiber, laser diode (LD) pumps, and fiber devices, the output power of fiber laser has been continuously improved, and fiber laser technology with an output power of several kilowatts or even 10 kilowatts has been relatively mature [3][4][5][6][7]. The special structure of fiber makes it easy to produce strong nonlinear effects under high-power conditions. ...
Thanks to the advantage of balancing nonlinear effects and transverse mode instability, vary core diameter active fiber (VCAF) has been widely used in high power ytterbium-doped fiber lasers in recent years. Up to now, VCAF has developed from the basic form of the original tapered fiber to the spindle-shaped and saddle-shaped fiber with different characteristics and has been applied in conventional fiber lasers, oscillating–amplifying integrated fiber lasers, and quasi-continuous wave fiber lasers and successfully improved the performance of these lasers. In the present study, a 6110 W fiber laser amplifier is realized based on a tapered fiber. The maximum output power of a fiber laser amplifier based on spindle-shaped fibers is 6020 W with a beam quality of M2~1.86. In this paper, we first introduce the basic concept of VCAF and summarize its main fabrication methods and advantages in high-power fiber laser applications. Then, we will present the recent research results of high-power fiber laser employing VCAF in our group and clarify the outstanding advantages of VCAF compared with the constant core diameter active fiber (CCAF).
... For many industrial applications such as macro-material processing and so on, there is a continuous strong demand on the power scaling of fiber lasers [5], [6]. Output powers in the multi-kilowatt even tens of kilowatt range have already been reported, using either free-space coupled bulk components [7], [8], or all fiber components such as tapered fused bundle [9], [10] for coupling in and out of the fiber. Comparatively, high power lasers in all fiber format are preferred in commercial deployment for compact and robust configuration, the power of which, as a matter of fact, is greatly relying on the rapid development of constituent all-fiber components. ...
High power cladding mode stripper device has been developed in robust configurations, which demonstrated high attenuation and low temperature rise, allowing to remove 2.16 kW of power with efficiency being 21.7 dB. The maximum temperature in packaging did not exceed 55 °C at a room temperature of 20 °C. The signal insertion loss was measured to be below 0.05 dB, indicating the ability to strip the cladding light efficiently but keep the core light almost intact. A 40-min stress test has been carried out, which confirmed the working stability and reliability of the proposed cladding mode stripper. Moreover, the device presented is in a compact and closed pack, more than 2 kW of power could be completely dissipated inside a housing with merely 200 mm of length, which could not only be benefit for suppressing nonlinear effects during power delivering but also be easily integrated into high power monolithic fiber laser systems.
... Because the heat load mainly concentrate on the gain fiber and the Splice II, here we only compare the temperature of gain fiber and Splice II between these two systems respectively pumped by 976 nm LD sources and 915 nm LD sources. The data we measured has been processed to the real temperature of fiber core according to Eq. (2). ...
In this manuscript, we studied the thermal properties of hundred-watt fiber laser oscillator by real-time in-situ distributed temperature measurement. Optical frequency domain reflectometry (OFDR) was introduced to measure the temperature distribution of gain fiber core. The fiber laser oscillator operated at 1080 nm and the wavelength of detecting signal from OFDR was ~1550 nm. The maximum output power of this fiber oscillator was 100 W. The fiber core temperature distributions in experiment agree well with our theoretical simulation. The temperature measurement of gain fiber core in oscillator has always been a problem because the backward laser from the oscillator may reduce the signal-to-noise ratio in OFDR. To the best of our knowledge, this is the first temperature distribution measurement of fiber core in hundred-watt oscillator. By the experimental measurement and theoretical model, we also analyzed the thermal properties of laser oscillator respectively pumped by 915 nm and 976 nm LD sources. We found fiber laser oscillator pumped by 976 nm LD sources experienced not only higher maximum thermal load but also higher average thermal load than that pumped by 915 nm LD sources at the same level output power. We also analyzed the fiber core temperature of other components in system, such as combiners and fiber Bragg gratings (FBG). These results are meaningful for us to improve the thermal design and management in fiber lasers.
... High average power fiber lasers (HPFL) have experienced a rapidly progress in the power scalability thanks to the development of high brightness laser diodes, fiber component and special fiber fabrication technology [1][2][3][4][5][6]. The power extraction from a single ytterbium-doped fiber laser with the near-diffraction-limited beam quality has reached over 10 kW [5]. ...
The inter-modal four-wave mixing (IM-FWM) and transversal mode instabilities (TMI) are experimentally studied in high-power distributed side-pumped fiber amplifiers. To the best of our knowledge, we have made the first demonstration of TMI and IM-FWM which can be suppressed simultaneously by increasing the bending diameter. Besides, the experimental results show that the counter-pumping scheme is beneficial to suppress both of IM-FWM and TMI, when comparing with co-pumping scheme. Furthermore, these two effects cannot be observed when the M2 factor is lower than 1.3, which can give a condition to estimate whether these two effects should be considered or not. The pertinent study can provide some guidance for understanding TMI and IM-FWM in the high-power fiber laser and amplifier.
The effect of seed power on the inter-modal four-wave mixing (IM-FWM) effect in a distributed side-pumped fiber amplifier is investigated for the first time, to the best of our knowledge. By using a seed source smaller than 70 W, the effect of seed power on the IM-FWM is studied experimentally. Surprisingly, it is found that the IM-FWM effect becomes stronger with the weaker seed. To analyze the physics behind this result, a numerical model is introduced, and the numerical results are in good agreement with the experimental observations. It is revealed that the IM-FWM enhancement is induced by the gain competition between the signal light and the anti-Stokes light of the IM-FWM. It is also found that there is an optimized seed power for suppressing the IM-FWM effect. The experimental and numerical results which are presented in this work can provide significant guidance for understanding the IM-FWM in fiber lasers and amplifiers.
The quality of Yb-doped fused bulk silica produced by sintering of
Yb-doped fused silica granulates has improved greatly in the past five
years [1 - 4]. In particular, the refractive index and doping level
homogeneity of such materials are excellent and we achieved excellent
background fiber attenuation of the active core material down to about
20 dB/km at 1200 nm. The improvement of the Yb-doped fused bulk silica
has enabled the development of multi-kW fiber laser systems based on a
single extra large multimode laser fiber (XLMA fiber). When a single
active fiber is used in combination with the XLMA multimode fiber of
1200 μm diameter simple and robust high power fiber laser setups
without complex fiber coupling and fiber combiner systems become
possible. In this papper, we will discuss in detail the development of
the core material based on Yb-doped bulk silica and the characterization
of Yb-doped fibers with different core compositions. We will also report
on the excellent performance of a 4 kW fiber laser based on a single
XLMA-fiber and show the first experimental welding results of steel
sheets achieved with such a laser.
The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.
Absorption of an incoherent pump in a double-clad fiber amplifier is analyzed in the paraxial wave approximation. Different inner cladding shapes are considered. A small spiral distortion of an otherwise circular inner cladding shape is shown to enhance the coupling efficiency significantly relative to other geometries.
Yb:glass fiber lasers have matured to the point where the average
power scaling of such devices to the kilowatt level and beyond can be
realistically pursued. In this paper, we present a comprehensive study
of thermal, stress, and average power scaling in double-clad silica
fiber lasers. We show that careful management of thermal effects in
fiber lasers will determine the efficiency and success of scaling-up
efforts
In 2007, DILAS proposed the approach to tailor the output beam characteristics of laser diodes to match the required beam quality of a desired target fiber, thus, drastically simplifying the coupling optics to basically only fast and slow axis collimation lenses. Over the last years, we developed and improved this tailored bar (T-Bar) concept together with the tooling for fully automated mass production of fiber-coupled T-Bar modules for fiber laser pumping as well as for direct applications.
We present results on the improvement of T-Bars tailored for optimized coupling into fibers with a diameter of 200 μm with NA 0.22 corresponding to a beam parameter product of 22 mm·mrad. Cost efficient coupling to this fiber requires a tailored beam parameter product smaller than 15.5 mm·mrad in slow axis direction corresponding to a slow axis beam divergence of 7° (full angle, 95% power content) for five 100 μm wide emitters. The improved T-Bars fulfil this requirement up to an output power of 52 W with a brightness of 3.1 W/mm·mrad and a power conversion efficiency achieving 69%. This progress in the T-Bar performance together with modifications in the module design led to the increase of the reliable output power from 135 W in 2009 to 360 W in 2017 for a T-Bar module with one baseplate. We will also give a review of the main development steps and further R and D improvements. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A multi-mode 9XXnm-wavelength laser diode was developed to optimize the divergence angle and reliable ex-facet power. Lasers diodes were assembled into a multi-emitter pump package that is fiber coupled via spatial and polarization multiplexing. The pump package has a 135μm diameter output fiber that leverages the same optical train and mechanical design qualified previously. Up to ~ 270W CW power at 22A is achieved at a case temperature ~ 30ºC. Power conversion efficiency is 60% (peak) that drops to 53% at 22A with little thermal roll over. Greater than 90% of the light is collected at < 0.12NA at 16A drive current that produces 3.0W/(mm-mr)² radiance from the output fiber.
High-brightness laser diode module over 300 W with 100 μm core/NA 0.22 fiber has been developed by integrating the several tens of optimally designed single emitter laser diodes in a newly designed package. We employed the Asymmetric Decoupled Confinement Heterostructure (ADCH) and the wide strip width to increase the durability for the catastrophic optical damage. High fiber-coupling efficiency was obtained with the uniquely designed micro-optical system. In addition, low thermal resistance made it possible to operate higher power. As a result, 300 W power was achieved without thermal rollover at 15.5 A with significantly high reliability. The high-brightness modules have a great advantage for high power fiber lasers such as 10 kW and beyond.
Continuous cost reduction, improved reliability and modular platform guide the design of our next generation heatsink and packaging process. Power scaling from a single device effectively lowers the cost, while electrical insulation of the heatsink, low junction temperature and hard solder enable high reliability. We report on the latest results for scaling the output power of bars for optical pumping and materials processing. The epitaxial design and geometric structures are specific for the application, while packaging with minimum thermal impedance, low stress and low smile are generic features. The isolated heatsink shows a thermal impedance of 0.2 K/W and the maximum output power is limited by the requirement of a junction temperature of less than 68oC for high reliability. Low contact impedance are addressed for drive currents of 300 A. For pumping applications, bars with a fill factor of 60% are deployed emitting more than 300 W of output power with an efficiency of about 55% and 8 bars are arranged in a compact pump module emitting 2 kW of collimated power suitable for pumping disk lasers. For direct applications we target coupling kilowatts of output powers into fibers of 100 μm diameter with 0.1 NA based on dense wavelength multiplexing. Low fill factor bars with large optical waveguide and specialized coating also emit 300 W.
Fiber laser based brightness converters enable diode laser beam sources
to access a superior beam quality of better than 10 mm × mrad in
combination with multi kW output power. A design of a fiber laser that
is based on a single active optical converter fiber that is pumped by a
direct diode is presented. Due to the high transfer efficiency of such
brightness converters an electrical/optical efficiency > 25% can be
achieved. The current status with an output power > 4 kW in
combination with a beam quality of < 5 mm × mrad will be
described. The principal design of such diode laser based fiber
brightness converters will be presented and building blocks of such
lasers will be outlined. As an application example laser welding will be
presented of both the fiber converter laser and direct diode laser using
optical light guides with identical core diameters on both lasers for
comparison. Additionally, fibers with a core diameter of 200μm will
be used on the fiber converter laser to perform remote welding. The weld
results will be compared regarding welding depth and surface quality of
the weld samples to determine the optimum power/brightness levels for
different aluminum and steel materials.
A 15 kW Fiber-coupled Diode Laser for Pumping Applications
- Mathews