unidirectional optical transmission of a dual metallic grating with grooves

In this paper, a dual grating structure for unidirectional transmission is presented. the forward and backward transmission performances have been investigated by finite element method. to enhance the forward transmission and to suppress the backward transmission simultaneously, we suggested to cut grooves on the surfaces of one of the gratings, and the effects of the grooves on the optical transmission have been studied. the numerical simulation results reveal that the transmission contrast ratio and the optical unidirectional transmission of the structure can be improved markedly by properly arranging the size and the position of the grooves. the forward transmission can be more than 90%, while the backward transmission transmittance is less than 5%.