Two normalized parameters (i.e.,s=&lgr;/gandh=a/g, wheregis the grating period andais the width of metal dot) are introduced to characterize the two‐dimensional (2D) double periodic reflection metal grating coupler for a multiquantum well infrared photodetector (QWIP). The ‘‘method of moments’’ is used to analyze this square metal grating structure for coupling the normal incident infrared (IR) radiation into the quantum wells. The main advantage for such a grating structure is that the coupling of the normal incident IR radiation is independent of its polarization direction. Two universal graphs relating the higher‐order diffracted power and diffracted angle to the normalized wavelength have been constructed for the design of 2D metal grating coupled QWIPs. By using a simple scaling rule, the coupling quantum efficiency versus wavelength over a broad IR spectrum can be obtained for the grating coupled QWIPs.