Fig. 1. Schematic setup of active phase control coherent beam combining^[7]

Fig. 2. Structural diagram and typical results of a 6 kW narrow line-width fiber laser^[27]. (a) Structural diagram; (b) output power and backward power as a function of pump power; (c) output spectrum at maximum output power; (d) temporal trace at maximum output power

Fig. 3. AFOC based on flexible hinge^[40]. (a) Schematic diagram; (b) structural diagram; (c) deviation angle as a function of applied driving voltage; (d) frequency behavior as a function of driving frequency with phase and gain curves

Fig. 4. Fiber endcap positioner based on piezoelectric bimorph actuators^[41]. (a) Structure of the positioner; (b) temperature distribution at the output power of 2.12 kW; (c) displacement distance at the X direction; (d) displacement distance at the Y direction

Fig. 5. Schematic setup of coherent beam combining phase control system based on multi-dithering

Fig. 6. Schematic setup of coherent beam combining phase control system based on heterodyne interferometer

Fig. 7. Principle of phase control based on DL algorithm

Fig. 8. Optical path and phase simultaneous control based on spectral filtering^[87]. (a) Experimental setup; (b) interference light intensity variation curve

Fig. 9. High power laser collimator based on defocus compensation^[95]. (a) Principle schematic; (b) experimental results

Fig. 10. Schematic of the beam combiner based on prism^[104]. (a) 3 channels; (b) 7 channels

Fig. 11. Schematic of the beam combiner based on rod lens^[105]. (a) A single rod lens collimator; (b) combiner

Fig. 12. Schematic of polarization beam combination of two beams. (a) Non-coherent beam combination; (b) coherent beam combination

Fig. 13. Coherent polarization beam combination of four fiber lasers with output power of 5.02 kW^[111]. (a) Experimental setup; (b) variations in output power and combining efficiency with total injected power

Fig. 14. Far-field long exposure patterns of coherent beam combing with 20 kW level fiber laser^[11]. (a) Open loop; (b) close loop

Fig. 15. Structure and experimental results of coherent beam combining of a hundred level fiber lasers^[58]. (a) Experimental setup; (b) simulated near-field pattern; (c) measured long-exposure far-field pattern in open loop; (d) measured long-exposure far-field pattern in closed loop; (e) simulated far-field pattern

Fig. 16. Experimental structure and typical results of coherent beam combining of thousand level laser beams^[68]. (a) Experimental structure diagram; (b) laser array intensity map in the near field; (c) long-exposure far-field pattern in open loop; (d) long-exposure far-field pattern in closed loop

Fig. 17. Experimental results of coherent beam combining of ultrafast lasers based on fiber stretcher phase locking^[130]. (a) Normalized temporal intensity fluctuation in the open and closed loop; (b) spectra of lasers before and after combination; (c) autocorrelation curves of the compressed pulse of single channel and combined beam

Fig. 18. Experimental setup for target in the loop coherent beam combining

Fig. 19. Experimental results for target in the loop coherent beam combining. (a) Normalized evaluation function; (b) probability density distribution of normalized evaluation function; (c)-(h) long exposure far-field intensity patterns

Fig. 20. Schematic drawing of the internal sensing phase-locking technique

Fig. 21. Schematic drawing of cascaded internal sensing phase-locking technique^[150]

Fig. 22. Experimental results of coherent beam combining based on the cascaded internal sensing phase-locking. (a) In the open loop; (b) controllers were turned on without external phase differences compensation; (c) after external phase differences compensation

Fig. 23. Schematic of all-fiber active internal phase control coherent beam combining system

Fig. 24. Long-exposure far-field patterns of coherent beam combining of three fiber lasers based on all-fiber internal phase locking^[153]. (a) Open loop; (b) closed loop; (c) simulation result; (d) interference fringe of beams 1 & 3; (e) interference fringe of beams 1 & 2; (f) interference fringe of beams 2 & 3

Fig. 25. Schematic drawing of generating the vortex beams array by modulating fill factor of laser array^[158]

Fig. 26. Theoretical and experimental results of vortex beams array^[158]. (a) Phase distributions when TC value was +1; (b) corresponding simulated intensity distribution when TC value was +1; (c) experimental intensity distribution when TC value was +1; (d) phase distributions when TC value was -1; (e) corresponding simulated intensity distribution when TC value was -1; (f) experimental intensity distribution when TC value was -1

Fig. 27. Experimental results of 1.5 kW vortex beams. (a) Far-field pattern in the open loop; (b) far-field pattern in the closed loop; (c) intensity distribution of vortex beam with a topological charge (TC) value of -1; (d) intensity distribution of vortex beam with a TC value of -2; (e) intensity distribution of vortex beam with a TC value of -3; (f) intensity distribution of vortex beams array with a TC value of -1

Fig. 28. Schematic diagram for tight focusing of combined cylindrical vector beams^[162]

Fig. 29. Intensity distributions and illustrations of the polarization direction of combined cylindrical vector beams at the focal plane for different values of initial polarized orientation^[162]. (a1) (a2) φ0=0; (b1) (b2) φ0=π/4; (c1) (c2) φ0=π/2

Fig. 30. Comparison of numerical simulation and experimental results of intensity distributions of combined cylindrical vector beams at the focal plane for different values of initial polarized orientation^[163]. (a1) (b1) φ0=0; (a2) (b2) φ0=π/2