Resolution analysis of coincidence imaging based on OAM beams with equal divergence angle

The multi-mode orbital angular momentum (OAM) beams can be effectively applied in target detection when the divergence angles are equal. The resolution threshold of the coincidence imaging system with multi-mode OAM is analyzed assisted by the subspace projection method. First, the relationship between the imaging resolution and the correlation function (CF) of the measurement mode is obtained based on the first-order correlation algorithm for the multi-mode OAM-based coincidence imaging (MM-OAMCI). Then, the feature vector of each imaging unit is extracted to distinguish the imaging point in the discretized imaging plane. Finally, the resolution threshold is given based on three factors, i.e., the feature vector, the noise, and the reconstruction algorithm. Specifically, the resolution of the MM-OAMCI system is determined by the deployment of the transmitting array, the reconstruction algorithm and the noise caused by the system design, the imaging modeling, and the environment noise. The super-resolution capability of the multi-mode OAM coincidence imaging system is validated by the simulations and experiments. The imaging results show that the resolutions in elevation and azimuth of the reconstructed image can be improved largely compared with the traditional microwave coincidence imaging (TMCI) methods, which is consistent with the theoretical analysis results.