Fig. 1. (a) Schematic diagram of a square core fiber waveguide. (b) Diagram of the transmission results and the beam spots.

Fig. 2. Diagram of the beam quality and beam profile at different integer multiple of the imaging length.

Fig. 3. (a) Schematic diagram of the beam combining device. (b) Schematic diagram of the all-fiber CBC system with a square fiber combiner.

Fig. 4. (a) Beam quality as a function of NA. (b) Beam efficiency as a function of NA.

Fig. 5. (a) Beam quality as a function of fiber core size and square fiber core size. (b) Beam efficiency as a function of fiber core size and square fiber core size.

Fig. 6. (a) Optimal beam quality as a function of fiber core size. (b) Beam efficiency as a function of fiber core size with W being six times the input fiber core size.

Fig. 7. (a) Beam quality as a function of NA with different fiber arrays. (b) Beam efficiency as a function of NA with different fiber arrays. (c) Diagram of typical intensity distribution of a 5×5 fiber array after combination. (d) Diagram of the intensity profiles of the combining beam spot of a 2×2 fiber array and a 5×5 fiber array along the x direction.

Fig. 8. (a) Input intensity distribution with the 2×2 fiber array. (b) Output intensity distribution after combination with the 2×2 fiber array.

Fig. 9. (a) Diagram of output intensity distribution from the 2×2 fiber array. (b) Diagram of output intensity distribution after combination with the tilled aperture in the case of the 2×2 fiber array. (c) Diagram of output intensity distribution after combination with the square fiber in the case of the 2×2 fiber array. (d) Diagram of output intensity distribution from the 3×3 fiber array. (e) Diagram of output intensity distribution after combination with the tilled aperture in the case of the 3×3 fiber array. (f) Diagram of output intensity distribution after combination with the square fiber in the case of the 3×3 fiber array.

Fig. 10. (a) Beam quality as a function of wavelength. (b) Beam efficiency as a function of wavelength.

Fig. 11. Diagram of the comparison and data fitting of the combining efficiency of different fiber arrays.

Fig. 12. Diagram of the cross section of the square fiber.

Fig. 13. Diagram of the experimental structure.

Fig. 14. (a) Diagram of the beam spot from MFA. (b) M2 measurement of the laser beam from MFA with the 4σ method.

Fig. 15. Diagram of the side view of the splice point between the output fiber and the square core fiber.

Fig. 16. (a) Diagram of the beam spot at the 5.5 cm length of the square fiber. (b) Diagram of the beam spot at the 11 cm length of the square fiber. (c) M2 measurement of the laser beam at the length of 5.5 cm of the square fiber with the 4σ method.

Fig. 17. Theoretical and experimental comparison of the self-imaging effect in the square fiber.