Abstract: By a method for controlling the state of polarization (SOP) of an optical signal transmitted through an optical waveguide, the waveguide is buried in a planar structure and a plurality of stress-applying films, having variable stress, are placed on the top of the structure. Preferably the stress-applying films comprise materials that have thermal expansion coefficients different from that of the planar structure or comprise materials with piezoelectric properties. In this way it is possible to produce a cascaded series of optical elements with variable linear birefringence in a planar optical waveguide. Moreover according to the invention it is possible, by the method according to the invention, to manufacture optical components having an active polarisation controller.