The optical device comprises a group of Fabry-Perot resonators, formed by a stack of a first and second partial reflection layer and an intermediate layer between the first and second partial reflection layer. The intermediate layer comprises a dielectric material and a group of arrays of posts embedded in the dielectric material at different positions along the intermediate layer. Each array in the group contains posts of a different non-circular shape and/or orientation in cross-section with a plane parallel to the reflection layers. As a result, Fabry-Perot resonators are formed in areas that contain different arrays, each having first and second resonance peaks at mutually different resonance frequencies for different polarization components. Light intensity sensors may be provided located below the different areas. From the intensities measured by the sensors, the intensities of different polarization components of the light can be computed over a range of wavelengths.