Unidirectional transmission in non-symmetric gratings made of isotropic material.

We achieve a broadband unidirectional transmission or One-way diffraction grating by cascading two parallel gratings made of isotropic material with different periods. In order to significantly reduce the reciprocal transmission of the zero order, one of them is chosen to be a subwavelength grating and designed as a wideband reflector for the incident-wave. It is demonstrated that more than 65 percent of the incident-wave energy can be transmitted unidirectionally with less than 0.22 percent transmission in the opposite direction at normal incidence for TE polarization. And, the relative bandwidth of the unidirectional transmission is greater than 10 percent.