Fig. 4: The temporal fluctuation eigenchannels of a bending multimode optical fibre.
a, Schematic of the experiment. The TM of an MMF is measured in nine different configurations, from which the time-averaged TM 〈T〉t is calculated. NA, MMF’s numerical aperture; core rad., MMF’s core radius. b, Decorrelation of the fibre TM as the MMF is bent. Top: the normalized correlations (absolute value of the overlap integral) between the TM of the MMF in bend state 5 with every other bend state. Supplementary Section 7 shows correlations between all TMs. Middle row: when an output focus is created by calculating an input field based on the TM of the MMF in state 5, we see this focus completely disintegrate as the fibre is bent into other states. Bottom row: a fixed random input field results in different output speckle fields for each bend state, yielding a fluctuation level of Fl = 0.8. c, The magnitudes of the eigenvalues of \({\langle {\bf{T}}\rangle }_{t}^{\dagger }{\langle {\bf{T}}\rangle }_{t}\), arranged in ascending order and normalized to a maximum value of 1. d, Experimentally measured temporal fluctuation levels when the bending MMF is illuminated with 754 eigenvectors of \({\langle {\bf{T}}\rangle }_{t}^{\dagger }{\langle {\bf{T}}\rangle }_{t}\). The top ~150 channels (region highlighted in pink) exhibit fluctuations lower than that of a random input field (Fl = 0.8, marked with hatched red line). e, The transmitted intensity patterns of selected temporal fluctuation eigenchannels as the MMF is moved through all nine bend configurations. Output optical fields (with fibre in bend state 5) are shown to the right.
