Fig. 4

Mode transmission experiment. a Transmission matrix over 10 m of thin ring air core fiber including all states of interest. Degenerate states have been collapsed for the sake of simplicity to reduce the matrix from 24 × 24 (shown in Supplementary Fig. 1) to 12 × 12. Parasitic mode suppression is indicated by a strong diagonal trace from lower left to upper right. Undesired modes can be broken into three categories: those which are in-fiber nearest neighbors, which populate the cross-diagonal (black line), SOI-pairs, indicated by a lower cross-diagonal (teal line), and adjacent mode orders (\(\left| {\Delta L} \right| = 1\)), likely to be excited by system misalignments. b Selection of data from mode groups on interest in (a). For all modes, the strongest parasitic mode is suppressed by at least 14.2 dB, while the sum of alignment-induced crosstalk (black squares) is typically better than 14 dB. SOI pairs are typically suppressed by more than 20 dB