All-Fiber Broadband Wavelength-Division Multiplexing using Heterogeneous Photonic Lanterns

This work presents an all-fiber broadband wavelength-division multiplexing architecture using 1x7 heterogeneous photonic lanterns (PLs), specifically PL-(6+1) and PL-(4+3). By combining mismatched single-mode cores, namely SM450 and SMF28, without rigid geometric constraints, these devices break system degeneracy and enable passive, wavelength-selective spatial routing. Experimental characterization reveals distinct dual-regime performance across a wide spectral range. In the visible band (350-740 nm), the devices function as multi-channel broadband collectors, effectively guiding light across all channels without spatial separation. Conversely, in the H-band (1520-1610 nm), core asymmetries lift mode degeneracy and maximize propagation constant (beta) matching conditions, thereby enabling passive spectral sorting. These results confirm that unconstrained, free-packaged heterogeneous fiber bundles can meet adiabatic transition criteria, showcasing their potential for next-generation astronomical facilities that require simultaneous multi-wavelength capabilities to feed separate, band-optimized spectrographs.