An optical interference filter device, especially for an optical wavelength locking device, the optical interference filter device defining a first periodic filter frequency response between a first filter output port and a filter input port and a second periodic filter frequency response having the same free spectral range (FSR M ) as the first periodic frequency response between a second filter output port and the filter input port , wherein the first and second periodic filter frequency responses are shifted versus each other by a predetermined optical frequency distance (fsr 12 ), wherein the optical interference filter device comprises a first structure and an optical combining and phase shifting structure , wherein the optical combining and phase shifting structure has a first and second input port and a first and second output port, the first input port being connected to a first output port of the first structure and the second input port being connected to a second output port of the first structure, the first and second output ports of the optical combining and phase shifting structure defining the first and second filter output ports , respectively, and wherein the optical combining and phase shifting structure comprises a first crossover path between the first input port and the second output port, a second crossover path between the second input port and the first output port, a first pass-through path between the first input port and the first output port and a second pass-through path between the second input port and the second output port, wherein in both pass-through paths and/or both crossover paths optical phase shifting means (198, 200; 198', 200') are provided which are configured to effect a phase shift difference of plus or minus 90 degrees between the optical signals that are guided in the first pass-through path and the second crossover path and a phase shift difference of minus or plus 90 degrees between the optical signals that are guided in the second pass-through path and the first crossover path , the optical interference filter device being characterised in that the first structure is an optical ring resonator structure comprising two optically coupled ring-shaped optical waveguides , each of which is further coupled to a dedicated optical port waveguide , wherein one of the optical port waveguides defines the filter input port at a first end thereof and the first resonator output port coupled to the input port of the optical combining and phase shifting structure at the second end thereof and wherein the other of the optical port waveguides has an open first end and defines the second resonator output port coupled to the second input port of the optical combining and phase shifting structure at a second end thereof, wherein the optical ring resonator structure is designed in such a way that it defines a periodic frequency response between the first resonator output port and the filter input port and a complementary periodic frequency response between the second resonator output port and the filter input port , the periodic frequency response comprising two superimposed partial periodic frequency responses which are shifted versus each other by a predetermined optical frequency distance equal to the frequency shift between the first and the second periodic filter frequency responses and which have a free spectral range equal to the free spectral range of the first and second periodic filter frequency responses. <EOS>