The orbital angular momentum (OAM) has been recognized as a fundamental property of electromagnetic (EM) waves, attracting many research interests in optical fields. It is not until 1992 that Allen et al. experimentally demonstrated Laguerre-Gaussian (LG) beams carry well-defined OAM modes. OAM mode can not only be used as information carrier but also communication channels to boost the capacity and spectrum efficiency of the communication systems. Although OAM has seen remarkable progress in the optical domain, it is of great interest to employ such advanced multiplexing approach at terahertz (THz) domain. However, given the different frequency range from optical domain, THz OAM-based communication systems would require different technologies. Efficiently and unambiguously discriminating the OAM modes is one key part among all these required technologies.

Prof. Jinsong Liu’s group from Wuhan National Lab for Optoelectronics (WNLO) proposed a general method to accomplish the geometrical transformation. The transformation elements are fabricated with a 3D printer, transforming the OAM of the input beam to the linear momentum of the output beam. They experimentally demonstrated the measurement of seven individual OAM modes and two multiplexed OAM modes, which is in good agreement with simulations.

This research is supported by the Wuhan applied basic research project (No. 20140101010009), the National Natural Science Foundation of China (Nos. 11574105,61475054, 61405063), the Fundamental Research Funds for the Central Universities (Nos. 2014ZZGH021, 2014QN023), Technology Innovation Foundation From Innovation Institute of Huazhong University of Science and Technology (Nos. CXY13Q015, CX14-070).

Fig. The normalized intensity profiles of (a) multiple OAM modes and (b) the discriminated spots. Both the experimental results and simulated results are depicted.