Fig. 1. Output signal fiber of the backward combiner

Fig. 2. Schematic diagram of the backward BPSC

Fig. 3. Schematic diagram of the end face of the two fibers

Fig. 4. Schematic diagram of the LP₁₁ mode coupling efficiency

Fig. 5. Concentration of energy distribution in the core (a) for the LP₀₁ mode, (b) for the LP₁₁ mode

Fig. 6. Relationship between core diameter mismatch and transmission efficiency

Fig. 7. Testing system of the backward combiner

Fig. 8. (a) 0.065NA 20/400 backward combiner, (b) 0.065NA 25/400 backward combiner

Fig. 9. Signal transmission efficiency of the 0.11NA 25/400 backward combiner

Fig. 10. Infrared thermal images of two (6+1)×1 BPSCs

Fig. 11. Beam quality testing system for backward combiners

Fig. 12. Beam quality of the oscillator in the test system

Fig. 13. (a) Beam quality of test A, (b) beam quality of test B

Fig. 14. Output power of the 3 kW MOPA

Fig. 15. Beam quality of the MOPA