Massive-scale spatial multiplexing of multimode VCSELs with a 3D-printed photonic lantern.

Incoherent beam combining is widely used in high-power laser systems due to its simplicity, stability, and scalability, as it avoids frequency, phase, and polarization locking. However, efficiently coupling light from large multimode VCSEL arrays into multimode fibers with matched modal capacity, while preserving brightness, remains challenging. This work presents a 3D-printed microscale photonic lantern (PL) for efficient incoherent combining of multimode sources, enabling direct multiplexing of many few-mode VCSELs into MMFs with matched modal capacity. Unlike conventional PLs designed for single-mode inputs, the proposed PL supports few-mode sources. We demonstrate PLs multiplexing 7, 19, and 37 six-mode VCSELs, fabricated directly on the laser apertures, achieving coupling losses as low as -0.6 dB(19-MM PL) and -0.8 dB (37-MM PL) into a 50 μm, NA = 0.22 step-index MMF. Comprehensive experiments demonstrate efficient power delivery, preserved brightness, and relaxed alignment, highlighting 3D-printed PLs as compact and scalable solutions for high-power laser systems and optical communications.