3D-printed mode-selective micro-scale photonic lantern spatial (de)multiplexer

We present the design, fabrication, and characterization of a dual polarization, mode-selective photonic lantern (PL) spatial multiplexer supporting three fiber modes (LP₀₁, LP^a₁₁, LP^b₁₁), measuring only 300 μm in length, for converting between three single-mode input sources and a single three-mode optical fiber. The PL is fabricated directly on the three sources, in this case three cores of a multi-core fiber, using a commercial two-photon polymerization-based 3D nanoprinter. Despite the diminutive size and high index contrast of the polymer core/air cladding waveguides, we observed low insertion loss multiplexing (less than −1.7 dB), low polarization dependent loss (less than −0.25 dB), mode dependent loss of −1.7 dB, low wavelength dependence, and mode group crosstalk of less than −16 dB. We demonstrate mode group multiplexed transmission using our mode-selective multiplexer/ demultiplexer pair and a short three-mode fiber link in an on-off keying intensity modulation/direct detection (IM/DD) experiment, recovering two 12.5 Gb/s signals without MIMO processing.