The invention relates to a polarization-insensitive optical filter centered on a wavelength measured in vacuum, comprising: first and second waveguides each having a propagation mode; a first grating formed in or on the surface of the first waveguide, the first grating being periodical at least along a first axis Ox defining a first orthonormal base Oxyz; a second grating formed in or on the surface of the second waveguide, the second grating being periodical at least along a second axis Ox′ defining a second orthonormal base Ox′y′z; wherein the first and second grating are provided one above another and are such that the first axis Ox and the second axis Ox′ define an angle ξ different from ±π/2 radians so that, when the first grating is illuminated by a light beam, the propagation modes are excited and have orthogonal fields for an angle of incidence of the light beam.