We report a lossless all-fiber 7x1 signal combiner, which can be used to combine more than 10 kW laser power. The measured power transmission efficiency is larger than 98.1% and power handle capability is more than 2 kilowatt (kW) for each port. When the combiner is put on a 20°C water cool plate, the average temperature rise is less than 3°C/kW. Due to the nearly lossless efficiency and good thermal performance, we can conclude that this combiner is capable of more than 10 kW power.
In this paper, a ring-doped fiber with Yb3+ is designed and fabricated. The intensity distribution of the fiber’s transverse modes is calculated and there are only four types of modes named as HEm1, TE01, TM01, and EHm1 in this fiber. Their near-field distribution is also investigated and it changes from thin-ring shape to thick–ring shape. A smart ring-doped fiber laser based on free space coupled optical oscillator is demonstrated firstly in experiment. It delivers 1038 W laser at 1071 nm with 1.6 nm 3dB bandwidth and the slope efficiency is 66.5%. The beam profile could be adjusted intelligently from ring-shape to flattop-shape which is benefit in industrial process.
Thermal effects are critical limit relevant to the power scaling of single crystalline fiber laser. In this paper, thermal effects in thin-rod single crystalline fiber are numerically researched. The simulation results show that thermal effects can be effectively reduced by enhancing the convective coefficient and decreasing the diameter of single crystalline fiber. For the most thin-rod single crystalline fibers utilized with diameter of 1 mm and length of 40 mm, the maximum heat load is only about 107 W due to the thermal rupture effect, which limits the laser output power to ~1 kW levels. The numerical results provide references for the developments and designing of thin-rod SCF laser
The design of annular doping region located in the cladding can reduce signal overlap with the doped region in order to reduce saturation and minimize gain compression, which has important applications in EDFAs. Here, we present the design and power scaling characterization of a cladding-pumped amplifier with ytterbium dopant located in an annular region near the ultra low NA core in the cladding, which is found to be a promising way to achieve multi-kilowatt single mode fiber lasers. The ultra low NA ensures that the fiber amplifiers operate in single mode state, which results to that the fiber amplifiers are free of the limitation of the transverse mode instability, and that the mode field of the signal laser extends into the cladding to extract gain amplification. The annular ytterbium-doped region located in the cladding can overcome the contradiction between high doping concentration and ultra-low NA design, which can simultaneously obtain high pump absorption with ultra low NA. The size of annular ytterbium-doped region under different core NA has been studied for various core sizes, which shows that the optimal size of annular ytterbium-doped region is related to the core NA and the core size. Detail analysis of high power amplification of cladding-ring-up-doped ultra low NA single mode fiber amplifier has been presented, which includes various nonlinear effects and thermal effects. It shows that, due to the specific design, the single mode characterization of the fiber is less influenced by the detrimental thermo-optic effect, which means that the cladding-annular-doped ultra-low NA fiber has high mode instability threshold than the ultra-low NA fiber with the core being fully uniformly doped. The cladding-pumped fiber amplifiers based on cladding-annular-doped ultra low NA fiber has the capability to achieve >10kW single mode fiber lasers.