Method Draws Near-Perfect Efficiency Out of Spin Hall Effect

POSTECH and KAIST researchers developed a method for achieving near-unity efficiency of the spin Hall effect of light (SHEL). The collaborators used an artificially designed metasurface capable of transmitting most light of one polarization — near-unity transmission — and reflecting light from the other. The method and the effect it delivered would improve microscopic optical device performance and effectiveness, including beamsplitters and optical switches.

SHEL refers to a transverse and spin-dependent shift of light to the plane of incidence where it is reflected or refracted at an optical interface; when amplified, it can shift light that is several to tens of times greater than its wavelength. Previous attempts at enhancing the SHEL have involved greater light movement with little consideration for efficiency. To the researchers’ knowledge, they said, studies on achieving a large SHEL and high efficiency simultaneously have not been reported.

“The very mechanisms that enhance the SHEL in most previous studies in fact lowered its efficiency,” said Junsuk Rho, a professor of mechanical engineering and chemical engineering at POSTECH.

In measuring the transmission of their anisotropic (able to take on and exhibit different physical properties in different directions) metasurface in the high-frequency region — such as microwaves —and verifying the polarization state of the transmitted light, the researchers verified that the SHEL occurs in the high-frequency region. They subsequently demonstrated the SHEL reaching close to 100% efficiency.

The spin-dependent splitting was experimentally confirmed by measuring transmission coefficients and the spatial profile of Stokes parameters.

The research was published in Laser & Photonics Reviews (www.doi.org/10.1002/lpor.202000393).