New material generates spin and orbital angular momenta from a linearly polarized incident beam

Spin and orbital angular momenta in waves have important applications ranging from communication to microscopy, and there has been extensive research on generating microwave beams with these characteristics. In a new paper, Shi et al. report and demonstrate an artificial material that converts a linearly polarized incoming microwave beam to an outgoing vortex wave with both spin and orbital angular momenta.

Nine alternating metallic and dielectric layers make up a unit cell of the material with a conducting metallic stripline embedded into the center dielectric layer. The stripline acts as a waveguide, and by adjusting its length, the researchers can tune the amplitude and phase delay of the transmitted wave. Proper tuning enhances polarization purity and generates a circularly polarized outgoing wave with orbital angular momentum.

The scientists used an x-polarized beam incident on a 16-by-16 array of cells to measure the amplitude and test the efficiency of the transmitted wave. The results agreed with predictions except for slight imperfections caused by manufacturing inaccuracies.

A microwave beam with orbital angular momentum has important potential for high-resolution imaging applications. “Some objects cannot be detected or imaged, because they have weak scattering when illuminated by a linearly polarized wave,” said author Hongyu Shi. “Using a wave with both spin and orbital momenta may avoid this problem.”

Source: “Generation of a microwave beam with both orbital and spin angular momenta using a transparent metasurface,” by Hongyu Shi, Luyi Wang, Xiaoming Chen, Anxue Zhang, and Zhuo Xu, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5109291 .