Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers.

Amplifying short pulses directly within a single fiber laser system has proven to be a challenging task, primarily due to thermally induced transverse mode instabilities and detrimental nonlinear effects. Another demanding aspect is preserving the linear polarization state at high power levels, which is even more pronounced for ultra-large-mode area fibers. This study demonstrates significant advancement in the direct amplification of narrow linewidth short pulses from tens of mW to several hundreds of Watts in a single-stage amplification, maintaining a high degree of linear polarization at the maximum output power. Through a comprehensive experimental investigation, two distinct types of Ytterbium-doped tapered double-clad fibers (T-DCFs), namely, PANDA (PT-DCF), with high built-in birefringence, and spun (sT-DCF), with ultra-low built-in birefringence, are examined. The unique geometrical architecture of the amplifiers is exploited for the realization of a compact and highly efficient picosecond fiber-based laser system, achieving more than 75% slope efficiency. In a single amplification stage, 50 ps pulses at a repetition rate of 20 MHz and an average power of 65 mW are amplified up to 457 W and 573 W of average power using PT-DCF and sT-DCF amplifiers, respectively. Both amplifiers exhibit near diffraction limited beam quality, M² < 1.4 at the highest power level. At the maximum power levels, the system maintains a high degree of linear polarisation, achieving ∼ 90% and ∼ 94% for the sT-DCF and PT-DCF, respectively. These ultra-large mode area fiber amplifiers are verified as versatile solutions for direct amplification of short pulses up to half-kW level with excellent spectral, spatial, and polarization characteristics.

We experimentally demonstrate the power scaling of optical vortices using the coherent beam combining technique, encompassing topological charges ranging from ℓ = 1 to ℓ = 5 realized on the basis of a Yb-doped fiber short-pulsed laser system. The combining efficiency varies from 83.2 to 96.9% depending on the topological charge and beam pattern quality generated by the spatial light modulators. This work is a proof of concept for using a coherent beam combining technique to surpass the physical power/energy limitation of any single source of optical vortices, regardless of the generation methods employed. These results open a pathway to power scaling of optical vortices with diverse applications in science and industry by utilizing advances in light–matter interactions.

This study presents a compact, high-power monolithic all-glass spun tapered double-clad fiber amplifier for single-stage amplification of narrow linewidth picosecond pulsed signals from a few tens of mW to several hundred watts of average power and MW level of peak power, covering a wide range of repetition rates. The absence of free-space elements in the amplifier module enhances its overall reliability by omitting the dependency on the pump alignment and internal back reflections. The versatile all-glass amplifier module delivers 50 ps pulses with over 2 MW peak power at 1 MHz, 50 ps pulses with over 625 W average power at 20 MHz, and 20 ps pulses with over 645 W average power at 1 GHz, all exhibiting excellent spectral, spatial, and polarization characteristics. This monolithic all-glass ultra-large mode area fiber amplifier is verified as a robust solution for direct amplification of short pulses attaining high peak/average power laser systems with excellent spectral, spatial, and polarization characteristics.

Fiber laser technology has been demonstrated as a versatile and reliable approach for laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges are discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers.