In this paper the optical properties of the TiO2/Ag/TiO2 multilayer are studied. The optical properties of the bare glass substrate, of various thicknesses of TiO2 and silver layers and of TiO2/Ag samples are also studied to obtain a better understanding. The optical transmission spectra in the IR, visible and UV ranges are measured for all samples. The authors attempt to clarify in particular the contribution of the silver layer, and a model based on the diffraction phenomena is elaborated. This model can be used to explain the variation with wavelength of the optical transmission in the visible and IR ranges.