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We propose and demonstrate a novel structure of dislocated double-layer metal grating(DDMG)[1-3] as a unidirectional coupler which is capable of launching surface plasmon polaritons(SPPs)in a desired direction under normal illumination.This structure consists of a slanted dielectric grating sandwiched between two gold gratings.The upper gold grating has a nonzero lateral relative displacement with respect to the lower one.We developed a simple and cost-effective technique to fabricate the structure via tilted two-beam interference lithography and subsequent shadow deposition of gold.