The high-power narrow-linewidth fiber laser has become the most widely used high-power laser source nowadays. Further breakthroughs of the output power depend on comprehensive optimization of stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) and transverse mode instability (TMI). In this work, we aim to further surpass the power record of all-fiberized and narrow-linewidth fiber amplifiers with near-diffraction-limited (NDL) beam quality. SBS is suppressed by white-noise-signal modulation of a single-frequency seed. In particular, the refractive index of the large-mode-area active fiber in the main amplifier is controlled and fabricated, which could simultaneously increase the effective mode field area of the fundamental mode and the loss coefficient of higher-order modes for balancing SRS and TMI. Subsequent experimental measurements demonstrate a 7.03 kW narrow-linewidth fiber laser with a signal-to-noise ratio of 31.4 dB and beam quality factors of M_x² = 1.26, M_y² = 1.25. To the best of our knowledge, this is the highest reported power with NDL beam quality based on a directly laser-diode-pumped and all-fiberized format, especially with narrow-linewidth spectral emission.

We report a monolithic single-end-pumped all-fiber laser oscillator with 1.5 kW power output operating at 1070 nm. The laser scheme design and fiber parameter selection are based on our theoretical analysis through one rate equation model consisting of changing pump wavelengths. The laser oscillator is pumped by 49 fiber-pigtailed 915 nm laser diodes with power of 50 W each through two stage combiners. The measured laser power is 1520 W at the pump power of 2054 W, and the corresponding optical-to-optical efficiency is 74%, in agreement with numerical simulation. Stimulated Raman scattering is observed when the laser power reaches 1030 W and the power ratio of Raman power is 4% at maximum output power. The experimental results show that the beam qualities represented by the $M^2$ factor are less than 1.2 at all pump power levels.

Anti-resonant hollow-core fibers have emerged as an important medium for high-power laser delivery due to their low optical nonlinearity and high damage threshold. However, current delivery systems of high-power laser based on anti-resonant hollow-core fibers mainly rely on free-space optical components, which limits long-term stability. Here, we report an all-fiber delivery of 2 kW laser with 85.4% transmission efficiency over 2.45 km, using a self-fabricated hollow-core fiber with a record low transmission loss of 0.168 dB/km at 1080 nm. Notably, we observed the phenomenon of stimulated Raman scattering amplified within the silica nested tubes for the first time. By effectively suppressing the Raman noise from the laser source, we achieve an all-fiber laser delivery without stimulated Raman scattering of silica glass. This work marks a significant breakthrough in multi-kilometer and multi-kilowatt power delivery that is potentially useful for industrial manufacturing, nuclear decommissioning, laser drilling in oil and so on.

Thanks to the unique properties such as spatially coherent, broadband emission spectrum, and high temporal stability, superfluorescent fiber source (SFS) has shown tremendous potential in wide applications of sensing, imaging, spectroscopy, and material processing. The fast development of active fiber and pump diode provides unprecedented opportunity for the performance scaling of SFS. In this paper, the new horizon opened by the recently developed SFS will be reviewed. First, the output power scaling of SFS with different architectures will be summarized, and a kilowatt-level high power SFS based on a tandem pumping technique will be demonstrated for the first time. Second, spectrum manipulation of SFS, including coverage extending and spectrum shaping, will be introduced in detail. What is more, the spectrum evolution of narrowband SFS in power scaling will be numerically modeled and evaluated. Third, several novel applications of SFS, including midinfrared laser generation, nonlinear effect suppression, sensing, and imaging, will be given, indicating the versatile performance of SFS compared with traditional fiber laser oscillators. Based on the new developed SFS, we will present the first hundred-watt level linearly polarized random fiber laser. In the last section, future endeavors on SFS will be presented.

An all-fiberized broadband superfluorescent source based on a distributed side-coupled cladding-pumped Yb-doped fiber is demonstrated. A recorded 102 W combined output power is obtained with the angle-cleaved output ends. The bandwidth is larger than 10 nm. The power scalability of the superfluorescent source is analyzed numerically. It is found that, besides the optical feedback, the active fiber length is another key. The result shows that, by optimizing the active fiber length, it is promising to realize a 600 W superfluorescent source with this scheme.

A high-power all-fiber broadband superfluorescent source is fabricated by using a distributed side-coupled cladding-pumped Yb-doped fiber. It is found experimentally that besides the optical feedback, the active fiber parameters have a significant effect on the power scaling. By optimizing the fiber length, a record amplified spontaneous emission output of 186.3 W is achieved, and the slope efficiency with respect to launched pump power is 78%. The bandwidths are larger than 20 nm. Furthermore, the power scalability of the superfluorescent source is analyzed numerically. The parasitic laser oscillation can be suppressed further with a large core to cladding ratio.