Fig. 1. Structure diagram of photonic lantern^[8]. (a) Structure diagram of a photonic lantern pair composed of MMF-SMFs-MMF. MMF and SMFs are connected through tapered transition segment, and MMF filtering is realized through FBGs on SMFs; (b) schematic diagram of mode evolution in photonic lanterns

Fig. 2. Structure diagram of photonic lantern used in mode control system^[29]

Fig. 3. Correspondence between input and output modes in photonic lantern. (a) From SMFs to MMF; (b) from MMF to SMFs

Fig. 4. Comparison of mode evolution in 3×1 photonic lantern with SMFs in different arrangements^[11]. (a) Equilateral triangle arrangement; (b) linear arrangement

Fig. 5. Several typical photonic lanterns. (a) SMF bundle arrangement; (b) corresponding spatial modes

Fig. 6. Mode evolution in 3×1 photonic lantern^[24]. (a) Schematic diagram of structure; (b) three mode evolution processes; (c) input-output correspondence

Fig. 7. Structure diagram of 5×1 photonic lantern

Fig. 8. Mode evolution in 5×1 photonic lantern^[32]. (a) Evolution processes of fundamental mode and OAM₀⁺¹ mode; (b) evolution matrix of 5×1 photonic lantern

Fig. 9. Early photonic lantern fabrication schemes^[1,31,34-35]. (a) Photonic crystal fiber (PCF) drawn from filled ferrule; (b) multicore PCF collapse method; (c) multicore fiber tapering method; (d) ultrafast laser etching

Fig. 10. Photonic lantern fabricated by SMF-bundle-tube tapering method^[36]. (a) Structure diagram; (b) optical micrographs of different sections

Fig. 11. M² factor of photonic lantern output beam varies with input fiber core cladding ratio^[32]. (a) 5×1 photonic lantern; (b) 3×1 photonic lantern

Fig. 12. Optical micrographs^[32]. (a) End face at end of taper of 3×1 photonic lantern; (b) end face at end of taper of 5×1 photonic lantern; (c) splicing point of MMF and SMF bundle-end of taper of glass tube

Fig. 13. Mode adaptive control based on photonic lantern^[25]. (a) Schematic diagram of mode control system; (b) mode control effect

Fig. 14. Influence of addition of photonic lantern-based mode adaptive control system in fiber amplifier on variation of output power with pump power^[25]

Fig. 15. Spot shapes of output beam and change of M² factor in open and closed loop of control system^[38]

Fig. 16. Achieving stable LP₁₁ mode output and corresponding mode decomposition in photonic lantern-based mode adaptive control system^[38]

Fig. 17. Structure diagram of 3×1 photonic lantern after optimization design^[37]

Fig. 18. Control effect of fundamental mode in optimized 3×1 photonic lantern-based mode adaptive control system^[37]

Fig. 19. Control effects of fundamental modes at three different output positions^[37]

Fig. 20. Schematic diagram of mode adaptive control and fiber laser amplifier TMI suppression system based on 5×1 photonic lantern^[39]

Fig. 21. Temporal and frequency variations when output beam amplifies with power in a conventional seed Ytterbium-doped fiber amplifier^[39]. (a) Temporal variation; (b) frequency variation

Fig. 22. Temporal and frequency variations in photonic lantern mode cotrol system-seeded Ytterbium-doped fiber amplifier^[39].(a) Temporal variation; (b) frequency variation

Fig. 23. M² factors of conventional seed amplifier and photonic lantern mode cotrol system-seeded amplifier when output is above TMI threshold^[39]. (a) Conventional seed amplifier; (b) photonic lantern mode cotrol system-seeded amplifier

Fig. 24. Achieving stable higher-order mode output above TMI threshold using photonic lantern mode cotrol system-seeded amplifier^[39]. (a) LP_11o mode; (b) LP_21o mode; (c) LP₀₂ mode

Fig. 25. Ideal input condition and output effect of OAM modes using 5×1 photonic lantern^[41]. (a) Input condition; (b) output effect

Fig. 26. Generation of stable OAM₀¹ mode based on 3×1 mode selective photonic lantern^[42]. (a) 30 µm low power output; (b) 42 µm high power output

Fig. 27. Suppressing wavefront distortion caused by atmospheric turbulence in external optical path using photonic lantern mode adaptive control system under different transmission distances^[39]. (a) Transmission distance is 0.1 km; (b) transmission distance is 1 km; (c) transmission distance is 10 km