In a recent experimental study, we investigated a homemade distributed side-coupled cladding-pumped (DSCCP) fiber using a master oscillator power amplifier (MOPA) configuration and tandem-pumping technique. During the experiment, we observed an abnormal behavior of the residual pump power from the counter port of the pump core. This abnormal behavior exhibited a threshold-like characteristic, with both the residual power and corresponding power ratio to injected pump starting to increase exponentially above a specific value. Specifically, when the pump power injected into the system ranged from 7.2 kW to 11.77 kW, the corresponding residual power ratio increased from 4.05% to 11.01%. Simultaneously, the signal optical-to-optical conversion efficiency decreased from 84.11% to 75.33%. This sudden appearance of the phenomenon significantly limits the ability to further scale the power of the system. However, the underlying mechanism causing this abnormal behavior remains unclear and requires further investigation.
With a homemade (1+1) side-pumped fiber and 1018 nm tandem-pumping strategy, we report an experimental demonstration of 17.4 kW power output, which is apparently a remarkable achievement. The (1+1) side-pumped fiber consists of an active core, highly doped with Ytterbium up to 2000 ppm, and a pump core to transport intensive pumping power through a homemade 5×1 combiner. Stimulated Raman scattering suppression ratio at maximum power is improved to 37.8 dB due to an array of connected tilted fiber Bragg gratings performance. So, the experimental result clarifies the feasibility of combining side- and tandem- pumping in ultra high power scale of tens of kilowatts.
A ytterbium-doped large-mode-area step-index fiber perform was fabricated by chelate precursor doping technique. For
the purpose of raising the threshold of nonlinear effects and transverse mode instability simultaneously, a long tapered
fiber was drew by changing the perform drawing speed. The core/cladding diameter of this tapered fiber was varied from
10/155 to 26/400 μm in 18m-long with the tapering ratio of 2.6. Using this fiber as a gain medium for a fiber laser in
amplifier, the beam quality factor M2 was ~1.2 when the output power obtained over 1.2kW with slope efficiency of
74.5%. The laser output spectrum was centered at 1063.8nm with narrow 3dB bandwidth of 0.26nm. The stimulated
Raman scattering suppression ratio was about ~34.7dB.
To ensure sufficient absorption of tandem-pumping energy, a large-scale aluminophosphosilicate fiber with 55 μm core and 400 μm inner-clad in diameter, i.e., a 55/400 Yb-APS fiber, was experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Based on an all-fiberized master oscillator power-amplifier laser setup tandem-pumped by 1018 nm fibber laser, a 150 W 1080 nm seed was amplified to 11.18 kW successfully, along with an optical-to-optical efficiency of 79.7%.
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