Abstract: A new structure of dual side metal grating used to improve coupling efficiency was demonstrated. By using the three dimensional finite difference time domain algorithm, the proposed dual side metal grating for GaAs/AlGaAs Quantum Well Infrared Photodetector was studied. The optimization parameters at wavelength 4.8 m were confirmed by the electric field distribution and relative coupling efficiency at different periods, duty circles and metal thicknesses. The relative coupling efficiency of the proposed dual side metal grating was over three times of the counterparts of single side metal grating at front or back. The bimodal curve of the relative coupling efficiency for the dual side metal grating inspires possibility for potential application for two color Quantum Well Infrared Photodetector. The dual side metal grating can also be used to couple perpendicular incident light into one color, two color and multi color Quantum Well Infrared Photodetectors and offers a high coupling efficiency.