1. Introduction . In recent years, virtual reality (VR) devices have gained widespread attention as emerging technology products, triggering an unstoppable boom in the display market [ 1 , 2 ]. In comparison to the VR systems that rely on the geometric waveguide, VR apparatuses employing the diffractive waveguide gratings offer notable advantages, such as lighter structures, simplified processing technology, and reduced costs [ 3 , 4 ]. Diffractive grating is a pivotal component tha...