A zero order diffractive filter for polarised or unpolarised polychromatic light, comprises a grating line (10) microstructure (1) formed by a surrounding medium (12) with low index of refraction nlow and a waveguiding layer (11) with high index of refraction nhigh, the grating lines (10) having a period length Λ that is smaller than the wavelength of light for which the filter is designed. A plurality of single nanostructures (2) with dimensions in the nanometre range is superposed on a first interface (13) between the surrounding medium (12) and the waveguiding layer (11).