Evaluation of the Purity of OAM Modes Using the Reverberation Chamber Technique

Orbital angular momentum (OAM) waves have been applied to various applications thanks to the orthogonality between different OAM modes. OAM waves can be generated using various techniques. However, the generated OAM waves in practice are not pure, which influences the OAM orthogonality. Thus it is important to evaluate the purity of the OAM modes. The common method for purity assessment is less convenient in practical measurements. In this paper, a novel method based on reverberation chamber (RC) is proposed to evaluate the purity of the OAM mode. Extensive RC measurements show that the correlation coefficient between OAM modes can be used to evaluate the purity of the OAM mode. Moreover, in contrast to the conventional measurement in the anechoic chamber, the proposed method can conveniently evaluate the purity over the entire measurement bandwidth for one measurement set, which is helpful in determining the working bandwidth of the OAM generator.