In this paper, a preliminary demonstration of all-fiber coherent beam combining (CBC) with active polarization-and- phase control is proposed. The CBC system was composed of two laser channels combined with a fiber coupler. One channel utilized non-polarization-maintained (non-PM) fiber, and the state of polarization of laser was controlled by using a dynamic polarization controller (DPC). The other channel adopted polarization-maintained (PM) fiber, and the phase of laser was controlled by using a phase modulator. In the central controller, hill-climbing algorithm and stochastic parallel gradient descent (SPGD) algorithm were applied for phase-locking and polarization-locking respectively. With this system, 82.3% of combining efficiency was demonstrated, the extinction ratio of the combined laser was 97.3% and the phase-locking efficiency reached 96.05%.
This paper comprehensively considers the suppression effect of fiber parameter control on Stimulated Brillouin Scattering (SBS), and studies the influence of different phase modulation modes, different linewidths, different fiber Yb ion densities, and different fiber lengths on the SBS threshold of the whole system, The best system setting scheme for improving SBS threshold is also given.
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.
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.
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