Orbit angular momentum encoding at 0.3 THz via 3D printed spiral phase plates

Terahertz wave carrying OAM would boost the capacity of free-space communication with a high carrier frequency and additional degrees of freedom. In this work, we present a experimental demonstration of THz orbital angular momentum (OAM) encoding via 3D printed spiral phase plates(SPPs). By using four “coding” spps with toplogical values -2, - 1,+1,+2, we can encode OAM information onto THz waves and generate temporal varying OAM states with controlled sequences (i.e., 2-bit coding). By using interference between OAM beam and a reference gaussian beam, the OAM information can be detected from the interference fork pattern.