Suppressing White-Noise Interference for Orbital Angular Momentum Waves via the Forward–Backward Dynamic Mode Decomposition

When the orbital angular momentum (OAM)-carrying beam propagates in a highly boisterous environment, it causes the degradation of the OAM modes’ purity, which brings the crosstalk in the demultiplexing process. To address this issue, we extend the dynamic mode decomposition (DMD) method to suppress white-noise interferences of OAM by using the forward–backward DMD (FBDMD) approach. The FBDMD-based scheme retrieves the noise-free DMD mapping matrix corresponding to the actual OAM’s topological charges by combining the forward and backward DMD mapping matrix in the noisy environment and consequently reduces the crosstalk, particularly for sorting the superposed OAM modes. Numerical examples are provided to demonstrate the effectiveness and advantages of the proposed approach. It is found that the white-noise interference can be significantly suppressed in sorting the OAM modes process compared with previous works. Also, FBDMD is feasible for the whole aperture receiving and partial aperture receiving (PAR). This work offers a practical tool for OAM coaxial demultiplexing in a noisy environment.