Fig. 5: Results of free-space-to-fiber coupling efficiency and communication performance with/without the PCVB coupling scheme.
a–c Measured received optical power levels to evaluate the coupling efficiency improvement of three distinct CVBs when coupled to a 5 km MMF. The red dotted lines indicate the measured received optical powers using the conventional lens-based direct coupling method, while the column charts represent the counterparts via PCVB coupling across varying ring radii. d, e Communication metrics of direct CVB coupling with 282 multiplexed channels, including BER curves, constellation diagrams, and EVM values. f, g Communication metrics of PCVB coupling at a twisted angle of 20° versus received optical powers. h, i Performance comparison for elaborating PCVB coupling scheme’s effect at different rotation angles. In figures, “1550.12, x2” represents the CVB+2 channel at the wavelength of 1550.12 nm with a x-polarization input, and the others can be inferenced similarly. The color gradient in the constellation diagram reflects the density distribution of the converged signal points, with the transition from blue to yellow indicating regions of higher point concentration, which corresponds to improved signal convergence.
