Distorted dislocations and OAM spectra of twisted partially coherent noncanonical vortex-pair beams in non-Kolmogorov atmospheric turbulence

Abstract The twist phase has recently exhibited better resistance in turbulence-induced degeneration of the signal mode in orbital angular momentum (OAM) spectra. However our attention is paid to exploring the combined influence of twist factor and noncanonical strength on “distorted dislocation” and OAM spectra in non-Kolmogorov atmospheric turbulence by introducing noncanonical vortex-pair to twisted partially coherent beams. It is found that twist factor or noncanonical strength can distort concentric ring dislocations in spatial correlation singularities into the so-called “distorted dislocations”. In turbulence propagation, noncanonical strengths can lead to annihilation and creation of distorted dislocations and change the number of dislocations, but twist factors cannot affect their numbers except for deepening the distortion in structures. Explicit expression of the OAM flux density per photon derived also indicates that noncanonical strength can further improve the OAM capacity even if twist factor reaches its extreme value. Compared to the twist factor, noncanonical strength plays a more significant role in signal modulation and detectivity of OAM spectra. If the combined effect of twist factor and noncanonical strength is considered, the detection performance of signal mode during long-distance turbulence propagation is distinctly better than that of only twist factor or noncanonical strength. The noncanonical strength should not be ignored due to its better performance in the OAM capacity and detection probability of the signal mode. This work may provide inspiration for OAM-based optical communication by the modulation of multi-degrees of freedom associated with noncanonical strengths and twist factors.