In this thesis the interaction of light with plasmonic nanostructures using Rigorous Coupled-Wave Analysis (RCWA) method is investigated and is modeled using these method, plasmonic and photonic modes. The structures under study, periodic array of plasmonic nanorods made of silver, silicon and gold placed on the substrate of the same material. We will show that a significant number of optical modes can be stimulated using these structures. Parameters such as height of nanorods, period and angle of illumination of the incident to the structure, affect location of formation optical modes, the case also has been investigated in this thesis. by drawing reflection and absorption graphs and also drawing of the magnetic field intensity distribution, the influence of these parameters is indicated. This types of structures have lots of usages because of excitation optical modes including use in solar cells to increase the absorption of light in the cells and also light absorption in the graphen. And finally the way to increase light absorption by using RCWA method has been investigated