Rotational photonic spin Hall effect on twisted bilayer metasurfaces

Optical differential operations possess the remarkable advantages of high efficiency and real-time imaging, which can improve the ability of image processing to enhance image edge detection. The photonic spin Hall effect has been demonstrated to realize optical differential operations. However, the direction of optical differential operation generated by the conventional photonic spin Hall effect is single and fixed. Here, we propose a scheme for the rotational photonic spin Hall effect on twisted bilayer metasurfaces to obtain the optical differential operations in any desirable directions and phase reconstruction. The rotation angle of the rotational photonic spin Hall effect is defined as the tangent of the in-plane spin-dependent shift to the transverse spin-dependent shift. The twist angle of the bilayer metasurfaces influence the Fresnel reflection coefficients which affect the transverse spin-dependent shift and the in-plane spin-dependent shift. Therefore, the direction of rotational photonic spin Hall effect can be controlled by the twist angle of the bilayer metasurfaces. Moreover, we show applications of the rotational photonic spin Hall effect including image edge detection and phase reconstruction. These findings open up new horizons for future applications of the rotational photonic spin Hall effect in optics.