Asymmetric Vortex Beam Generation from Dielectric Janus Metasurfaces

Chang-Yi Lin^1*, Jhih-Hao Huang¹, Lu-Yun Wang¹, Po-Cheng Yang¹, Yao-Wei Huang¹

¹Department of Photonis, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

* Presenter:Chang-Yi Lin, email:elliot.ee11@nycu.edu.tw

Janus metasurfaces provide degree of freedom by imparting the light with the different incident direction. Directional Janus metasurfaces operating at microwave and near infrared region have been demonstrated several years ago. However, these devices typically relied on multi-layer structures made from metal materials. This results in multi-layer fabrication processes and Joule loss, primarily due to the inherent characteristics of metal materials, especially operating within the visible spectrum. In our study, we numerically clarify an innovative Jones matrix for single-layer TiO₂ based Janus metasurfaces capable of generating various states of spin and orbital angular momentum (OAM) at wavelength of 532 nm. Our Janus metasurfaces allow us to effectively create two asymmetric OAM states of vortex beams, depending on what the direction of incidence is. In addition, we experimentally demonstrate that our Janus metasurfaces operate under the light with the arbitrary polarization illumination. By taking advantage of the propagation and geometric phase control, different desired states of OAM for two opposite directions are achieved. Furthermore, our direction-switchable Janus metasurfaces open up new possibilities in the field of polarization optics. This advancement facilitates compact and versatile phase manipulation, including lens, holograms, and optical combiner, broadening its applicability across diverse domains.

Keywords: dielectric metasurfaces, phase control, visible wavelength, asymmetric transmission, orbital angular momentum