Institute of Optics and Electronics (IOE) of Chinese Academy of Sciences reported theoretical study on asymmetric photonic spin-orbit interactions (SOIs) in a metasurface in the 3rd issue 2017 of Opto-Electronic Engineering (OEE). OEE is an international academic journal and sponsored by IOE. The proposed metasurface can efficiently convert left- and right-circular polarizations into orbital angular momentum (OAM) beams with asymmetric topological charges. Recently, Harvard University used the same principle to do a similar research and experimentally proofed the concept of asymmetric SOIs. Furthermore, the researchers also analyzed the optical field distributions of hybrid OAM beams with the illumination of elliptical polarizations. The results were published in Science.  

Same as the electron, the photon also carries spin angular momentum (SAM) and OAM. OAM beams have many applications in the field of classical and quantum optics, such as optical and quantum communications, particle manipulation, super-resolution imaging. Traditional optical devices for OAM generation are bulky and heavy, and have no SOIs existence. The metasurface based on geometric phase allows symmetric SOIs, however, the symmetry limits the applications of SOIs. 

The metasurfaces, designed by the two teams, are composed of high refractive index dielectric cylinder with different geometrical features, which can simultaneously introduce spin-independent waveguide retardation phase and spin-dependent geometric phase. The superposition of the two phase-gradients does not only allow SOIs, but also break the inherent asymmetry of spin-dependent wavefront shaped by geometric phase. Due to the independent tunability of the two phase-gradients, the proposed metasurfaces have the capabilities of producing two independent wavefront for two spin components of incident light, leading to arbitrary spin-to-orbit angular momentum conversion of photon. 

Related original article: 

Opto-Electronic Engineering, 2017, 44(3): 319-325. DOI: 10.3969/j.issn.1003-501X.2017.03.006. 

Science, 2017, 358(6365): 896-901. DOI: 10.1126/science.aao5392