A single dimension self-aligned retroreflecting optical system for wavelength filtering, comprising at least one wave-guide with one internal face in a focal plane of collimation optics generating a main collimated beam. A diffraction grating has parallel lines, the lines disperse, in collimated beams, the different wavelengths of the main beam in directions parallel to a dispersing plane, the dispersing plane being perpendicular to the lines of the grating. A reflector system generates self-alignment in a longitudinal plane perpendicular to the dispersing plane. The reflector system comprises a spherical lens and a single dimension self-aligned reflector arrangement, the dimension being parallel to the dispersing plane of the grating.