Fig. 5: Results of the optical characterization.
a Measured coupling efficiencies of the individual cores containing nanostructures (colored curves) compared to a blank core (black line). All curves are normalized to the coupling efficiency of a single bare core at normal incidence (Eq. (1), θ = 0°, λ0 = 1.55 μm). The corresponding total coupling efficiency over all seven structured cores ηtot is shown by the brown dashed line. The vertical gray dashed lines indicate the targeted optimization angles θ−1 overlapping with local maxima of η for each nanostructured core. The angular domain θ < 10° in which the 0th-diffraction is dominantly coupled into the cores is highlighted by the light gray background. The inset shows the angular interval from 65° to 85°, highlighting the coupling at almost grazing incidence. b Angular intervals (purple areas) in which the total coupling efficiency exceeds a predefined value [0.1% (bottom) to 1% (top)]. The black and green vertical dashed lines indicate the corresponding limits for bare single and multicore fibers. c Angular distribution of the measured total coupling efficiency (dots: experimental measurements, lines: numerical calculations) of nanostructure-enhanced MCFs (purple) in comparison to an MCF without nanostructures (dark gray). The light gray curve shows the corresponding distribution for a single blank core. d Integrated wide-angle total coupling efficiency defined in Eq. (2) of nanostructured-enhanced (purple) and bare MCF (dark gray) in comparison to a single core (light gray). The inset illustrates the definition of the large-angle interval (dots: experiments, lines: simulations).
