Near-single-mode 3  kW monolithic fiber oscillator based on a longitudinally spindle-shaped Yb-doped fiber

Abstract

In order to balance the mitigation of transverse mode instability and stimulated Raman scattering effect in the high power fiber lasers, a specially designed Yb-doped fiber, named spindle-shaped Yb-doped fiber, was fabricated with a core/cladding diameter of 20/400 µm at both ends and 30/600 µm in the middle. Based on this fiber, an all-fiber laser oscillator was built and over 3 kW near-single-mode ( M 2 factor ∼ 1.3 ) laser was achieved with an optical-to-optical conversion efficiency of 78.4%. While operating at the maximum power, the transverse mode instability is well mitigated and the stimulated Raman scattering effect is well suppressed ( > 34 d B lower than signal laser). Further power scaling is promising by optimizing the structure of the Yb-doped fiber.

Theoretical and Experimental Study of High-Peak-Power High-Brightness Quasi-CW Fiber Laser

“…Two years later, in 2020, Zeng, etc. in [9] achieved the same power with a much longer (31m) spindle-shaped gain fiber, whose both ends' core/cladding diameters were 20/400 μm. The M 2 factor of the output laser in that experiment was also ∼1.3, but the SRS intensity was much lower, about 31 dB lower than that of the signal, experimentally demonstrating the superiority of the spindle-shaped gain fibers in those scopes where needed to suppress SRS while maintaining a good beam quality.…”

“…In order to control the beam quality and increase the relative brightness, we focus on a new type of spindle-shaped gain fiber, as shown in Fig. 1, whose core and cladding diameters vary with longitude as the same ratio, which has been theoretically and experimentally verified to have many advantages, such as excellent capacity of suppressing nonlinear effects, and maintaining good beam quality [9]- [11]. Specifically, Yang, etc.…”

High‐Power Laser Systems

“…[ 421 ] Moreover, 1.8 and 3 kW TMI‐free output have been achieved using the improved bidirectional pumping under an all‐fiber spindle‐shaped oscillator. [ 410,422 ] Finally, the power was scaled to 5 kW ( M 2 ≈ 1.9) by slightly increasing the fiber size and adopting a MOPA configuration. This is the highest CW power record by TDCF, the relatively low optical‐to‐optical conversion efficiency of 66.6% is expected to be further improved by optimizing the longitudinal fiber profile.…”

“…Tapered fiber opens a new way for high‐power fiber amplifiers. At present, it has been adopted in kW‐level all‐fiber resonators, [ 410 ] MOPA amplifiers, [ 411 ] MW‐level CPA‐free amplification, [ 409,412 ] and high‐power single‐frequency (SF) laser output. [ 413,414 ]…”

Comparison and Optimization on Transverse Mode Instability of Fiber Laser Amplifier Pumped by Wavelength-Stabilized and Non-Wavelength-Stabilized 976 nm Laser Diode

“…With the development of large mode area fiber and cladding pump technology, the nonlinear effects such as stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) are suppressed excellently in recent years [4][5][6]. However, the emergence of the transverse mode instability (TMI) effect limited the further improvement of the output power and deteriorated the beam quality, and limited the application of fiber laser in the above-mentioned fields at the same time [7][8][9][10].…”