The photonic lantern is a new type of photonic device that combines the advantages and characteristics of single-mode fiber and multi-mode fiber. It has important applications in the fields such as astronomical photonics, optical fiber communication mode division multiplexing, and optical fiber laser mode control.

This review introduces the structure and mode evolution theory of photonic lanterns, fabrication technology, the mode adaptive control based on photonic lanterns, their application in high-power fiber laser amplifiers to suppress the transverse mode instability, and utilization in large mode area fiber to excite special structural beams (such as orbital angular momentum modes). Through theoretical simulations and experimental exploration, the original design and fabrication criteria of photonic lanterns are improved. Meanwhile, two key design criteria for mode adaptive control are added: 1) optimizing the input fiber arrangement to improve the control bandwidth; 2) selecting the appropriate input core cladding ratio to expand the optional range of the output fiber. According to the above design requirements, N×1 photonic lanterns with excellent performance are prepared (N=3,5,6,7,…), as shown in Fig. 12. The phase of the input beams is actively modulated by the stochastic parallel gradient descent (SPGD) algorithm. The output beam of the optimized 3×1 photonic lantern with 30/125 μm output fiber is stable, and the M² factor is lower than 1.18 (Fig. 15). Orbital angular momentum modes (OAM₀¹ or OAM₀² modes) and higher-order linear polarization modes (LP₁₁or LP₂₁ modes) are obtained, and the corresponding modes purities are more than 0.85, as shown in Figs. 16 and 26(a). The mode adaptive control system based on photonic lanterns achieves stable fundamental mode output with M² factor ~1.4 in large mode area fiber with a core diameter of 50 μm. By adopting photonic lanterns, the transverse mode instability is suppressed in a fiber amplifier with a core diameter of 42 μm (Figs. 22 and 23). Finally, a possible technical solution is provided for further increasing the power of near-diffraction-limit fiber lasers with large mode areas and high brightness.

The mode adaptive control system based on photonic lanterns can effectively suppress TMI in the 42 μm core fiber amplifier. The results of selective amplification of high-order mode and OAM beams achieved by this technique has a wide application prospect in the fields requiring high power special beams. Further research will be focused on the design and fabrication of the photonic lanterns with more channels and better performance, as well as increasing the modulated parameters of the adaptive control system such as polarization and intensity.