Fig. 1. Calculated coupling efficiency between the PLMA-GDF-25/250-M and AR-HCF with varying core diameter ranging from 20 to 40 μm. The mode-field profile is simulated via finite element method.

Fig. 2. (a) SEM image of the in-house fabricated AR-HCF. (b) Microscope image of PLMA-GDF-25/250-M. Their near-field patterns are shown in (c) for AR-HCF and (d) for PLMA-GDF-25/250-M. (e) Measured transmission loss spectrum of the AR-HCF.

Fig. 3. (a) Schematic setup for power delivery. The single-frequency laser is composed of the seed, amplifier 1 and amplifier 2. The output of the laser is butt-coupled to the AR-HCF via ceramic ferrules on a five-axis adjustment stage. Two power meters monitor the backward and transmitted power intensity. (b) Packaging of the coupled AR-HCF and PLMA-GDF-25/250-M onto a high-hardness thermally conductive base with UV-curable glue. (c) Packaged PLMA-GDF-25/250-M and AR-HCF coupler. (d) Thermal imaging of the coupling area under maximum input laser power of 108 W.

Fig. 4. (a) Output power and throughput efficiency as functions of input pump power. (b) Beam quality and near-field pattern at maximum laser power output.

Fig. 5. (a) Comparison of high-power single-frequency laser transmission through four different lengths of PLMA-GDF-25/250-M and AR-HCF: (I) 1 m panda fiber; (II) 43 m panda fiber; (III) 1 m panda fiber and 1 m HC-ARF; (IV) 1 m panda fiber and 100 m HC-ARF. (b) Back-reflected light intensity curves from the four configurations. Note here that the I, III and IV curves strongly overlap.