Laser diode directly backward pumped high-beam-quality 10-kW fiber laser

Abstract

Fiber lasers have been widely used in the industrial and scientific fields due to their advantages of high conversion efficiency, simple thermal management, and consistent stability. High brightness and high-power fiber lasers are affected by simulated Raman scattering and transverse mode instability, which limit the power scaling of fiber lasers. Therefore, there are only a few reports achieving a 10kW-level fiber laser system by laser diode direct pumping or tandem pumping. In this manuscript, we demonstrate an all-fiber laser amplifier based on home-made low numerical aperture fiber pumped by 976nm laser diodes. When the signal light is input to the gain fiber with a minimum bending diameter of 12cm, the beam quality factor M<sup>2</sup>~1.72. The onset of TMI is observed at 2467W output power, accompanied by beam quality degradation. In order to suppress the onset of TMI, the minimum bending diameter of the gain fiber was changed from 12cm to 20cm. And the signal light is input into the gain fiber with a bending diameter of 28cm. Benefiting from this operation, the fiber laser amplifier achieved a maximum output power of 10.53kW with an optical-to-optical efficiency of 74.04%, and there is no TMI onset observed. However, increasing bending diameter inevitably leads to the degradation of beam quality. At the maximum output power, the beam quality factor M<sup>2</sup> is 2.88. To the best of our knowledge, this is the highest optical-to-optical efficiency and the best beam quality among 10kW-level laser diodes pumping fiber lasers. Generally, it is believed that reducing bending diameter can suppress TMI by increasing high-order mode losses. However, this rule does not apply to few-mode fiber lasers. A larger bending diameter leads to more high-order modes being contained in the signal light instead of leaking into the cladding area. Thus, a higher output and poor beam quality are obtained. Also, it is believed that tightly coiled fiber can make mode coupling easier and trigger TMI, which results in a positive correlation between the TMI threshold and bending diameter. Low NA fibers are very sensitive to bending, and reducing the bend diameter to control the beam quality will result in lower efficiency and a lower TMI threshold. Therefore, although producing a 10kW-level fiber laser is simple, maintaining good beam quality during the power scaling process is still a challenge. The results of this article will be a valuable reference for high power fiber laser design.

Optimization and Demonstration of Direct LD Pumped High-Power Fiber Lasers to Balance SRS and TMI Effects

“…In recent years, with the goal of achieving a high-power fiber laser with high beam quality, we have been focusing on balancing SRS and TMI by optimizing the pump wavelengths and pump configuration. In the aspect of fiber coiling, we found the abnormal phenomenon of increasing the TMI threshold by increasing the fiber coiling diameter [10,72]. In addition, we propose varying core diameter active fiber represented by tapered fiber, spindle-shaped fiber, and saddle-shaped fiber, which can balance SRS and TMI in the fiber and break through the power limit of conventional fiber [73][74][75][76][77][78][79][80][81].…”

“…We realized a 10 kW fiber amplifier based on the self-designed and manufactured low-absorption and low-NA YDF [10]. Consistent with the scheme in the high-power fiber amplifier, the laser applies a counter-pump configuration to suppress SRS.…”

“…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.…”

Novel Bidirectional Output Ytterbium-Doped High Power Fiber Lasers: From Continuous to Quasi-Continuous

“…With the support of the above suppression measures, the output power of fiber lasers has achieved great breakthroughs. At present, fiber laser amplifiers with an output power of over 10 kW are relatively mature, and the output power of a single fiber has exceeded 20 kW [ 5 , 6 , 46 ]. The output power of the all-fiber structure fiber laser oscillator has also exceeded 8 kW [ 9 , 11 ].…”

Theoretical and experimental research on output characteristics of oscillating-amplifying integrated fiber laser

“…As early as 2009, IPG first realized the fiber laser amplifier with output power of more than 10 kW [1]. In recent years, many fiber laser amplifiers with output power of more than 10 kW have been reported based on LD pump or tandem pump schemes [2][3][4]. In 2020, the output power of the fiber laser oscillator has also exceeded 8 kW, and the beam quality BPP is ~0.50 mm-mrad [5].…”