Fig. 1. (a) Schematic of an original MM-SM-MM lantern pair (the gratings are incidental)[3];(b) photograph of a simple paper lantern[6]

Fig. 2. Schematics of (a) a one-dimensional quantum well and (b) a one-dimensional waveguide illustrating the close analogy between the propagating modes in an optical fibre (β1, β2, β3) and the energy levels of a quantum well (E1, E2, E3); (c) Kn wavevector made up of a transverse component KT and a mode propagation constant β is defined in terms of the effective refractive index seen by the mode; (d) a photonic lantern taper starting at the input bundle ofM single-mode fibers (top)[4-5]

Fig. 3. In an back-to-back lantern pair, each section supports more modes than the previous one[6]

Fig. 4. Evolution of modes throughout the tapered transition of the photonic lantern. The 14 core modes are degenerate at large diameters but become non-degenerate at smaller diameters and fill the range of effective refractive index neff available in the multimode core at the end of the transition. The red horizontal dashed lines indicate the core and cladding indices of the final multimode core (nco =1.4440, ncl=1.4431) [5]

Fig. 5. (a) Spatial modes of the 15 lowest order modes in the step index fiber core; (b) coupled waveguide arrays whose super-modes closely match the fiber modes; (c) 15 lowest order modes of nearly optimal 15 core arrangement; (d) 15 lowest order modes of an incorrect 15 core arrangement[9]

Fig. 6. (a) Cross section of the 61-port photonic lantern fabricated by 61 tapered single-mode fibers and capillary tube[10]; (b) optical micrograph of the multi-core fiber fabricated photonic lantern[11]; (c) inscription of an integrated-optic waveguide using a focused femtosecond laser beam[6]

Fig. 7. (a) Schematic of the first photonic lantern, which has a ferrule to realize the transition from a multi-mode fiber to single-mode fibers; (b) optical micrograph of the silica cane with 19 holes (cladding is about 260 nm thick); (c) scanning electron micrograph of the multimode PCF drawn from the filled ferrule[3]

Fig. 8. Photonic lantern fabricated by the application of low index capillary tube technique[7]

Fig. 9. 3-port mode selective photonic lantern[13]

Fig. 10. (a) Microscopic image of the cross section of the photonic lantern consisting of 7 fluorine-doped tubes in a hexagonal array with an outer diameter of 2 mm; (b) cross section image of one fluorine-doped capillary with an internal diameter of 275 μm, filled with 3 graded-index fibers of two different core sizes of 13 μm and 11 μm and designed to selectively excite LP01, LP11a and LP11b modes[23]

Fig. 11. (a) Micrograph showing details of the 73-core MCF; (b) entire photonic lantern with 511-core MCF; (c) multi-mode port of a photonic lantern made by tapering the MCF[24]

Fig. 12. (a) Sketch of a MM-SM integrated photonic lantern; (b) sketch of a back-to-back MM-SM-MM integrated photonic lantern[25]

Fig. 13. Differences between GNOSIS's single-mode fiber-based OH suppression unit and its planned multi-core fiber Bragg grating-based replacement in PRAXIS. Each individual fiber Bragg grating in GNOSIS has to be written and spliced manually, with a total of 133 ports (made up of seven 1 × 19 lanterns) each requiring multiple splices that were time-consuming and resulted in a bulky device once packaged. The multi-core fiber version requires only a single exposure for all cores and no splices[30]

Fig. 14. (a) Schematic of cross section of the 6-mode annular-core photonic lantern; (b) micrograph of cross section of the fabricated 6-mode annular-core photonic lantern; (c) experimental setup of the orbital angular momentum (OAM) erbium-doped fiber amplifier based on the annular-core photonic lantern[39]

Fig. 15. Schematic of phase-only SPGD based 1×3 photonic lantern[41]

Fig. 16. (a) Beam profile and (b) SPGD signal trace before and after application of the ASMC system[41]

Fig. 17. Schematic of photonic lantern coherent coupling system[43]

Fig. 18. Output power versus pump power for amplifiers without photonic lantern seeding and with photonic lantern mode control. The decreased slope in the conventional amplifier curve depicts a decrease in efficiency[43]