Ring resonator comprising optical filtering device

1. An optical filtering device ( 1 ) comprising:

a ring resonator ( 2 ); and

a multimode interference coupler ( 3 ) comprising two inputs ( 4 , 7 ), two outputs ( 5 , 8 ) and a multimode waveguide ( 9 ) connecting the two inputs to the two outputs, the coupler having a first input ( 4 ) serving as an input for the filtering device and able to receive an input optical signal ( 10 ), and a first output ( 5 ) corresponding to the output of the filtering device and able to produce an output optical signal ( 12 ), the waveguide comprising a coupling zone ( 11 ) arranged between the inputs and outputs and able to form four images of the input signal, the ring resonator ( 2 ) being arranged so as to connect a second output ( 8 ) of the coupler to a second input ( 7 ) of the coupler,

wherein the filtering device comprises

a tuning element ( 6 ) able to modify locally the refractive index in the coupling zone ( 11 ) of said multimode waveguide ( 9 ) in order to vary a coupling coefficient between the coupler ( 3 ) and the ring resonator ( 2 ).

2. The device as claimed in claim 1 , wherein the tuning element ( 6 ) is able to modify the refractive index in a central part ( 14 ) of the coupling zone ( 11 ), covering two central images in the waveguide ( 9 ).

3. The device as claimed in claim 1 , wherein the tuning element ( 6 ) is able to modify the refractive index in a peripheral part ( 15 ) of the coupling zone ( 11 ) covering two peripheral images in the waveguide ( 9 ), the peripheral part ( 15 ) being centered in the longitudinal direction of the waveguide ( 9 ).

4. The device as claimed in claim 1 , wherein the tuning element ( 6 ) is able to modify the temperature of the coupling zone ( 11 ) in order to modify the refractive index.

5. The device as claimed in claim 1 , wherein the tuning element ( 6 ) is able to inject electrical charge into the coupling zone ( 11 ) decreasing the refractive index.

6. The device as claimed in claim 1 , wherein the tuning element ( 6 ) comprises a metal electrode arranged on a part centered in the longitudinal direction of the waveguide.

7. The device as claimed in claim 1 , wherein the tuning element ( 6 ) comprises a resistive heater arranged on the coupling zone ( 11 ).

8. The device as claimed in claim 1 , wherein the tuning element ( 6 ) comprises a heating film deposited on the coupling zone ( 11 ).

9. The device as claimed in claim 1 , wherein the coupler ( 3 ) has an optical length corresponding to a coupling coefficient by default equal to 50%, such that half the input optical signal ( 10 ) is transmitted to the first output ( 5 ) and half is transmitted to the second output ( 8 ).

10. The device as claimed in claim 1 furthermore comprising a module for adjusting the wavelengths filtered by the ring resonator, the adjusting module being able to modify a physical property of the ring resonator ( 2 ) in order to tune the wavelengths filtered by the ring resonator.

11. The device as claimed in claim 10 , wherein the adjusting module is able to modify the temperature of the ring resonator ( 2 ).

12. The device as claimed in claim 1 , in which the ring resonator ( 2 ), the coupler ( 3 ), and the tuning element ( 6 ) are monolithically integrated into an integrated optical component.

13. The device as claimed in claim 1 , in which the component comprises a silicon substrate.

14. The device as claimed in claim 1 , in which the component comprises an indium phosphide substrate.

15. The device as claimed in claim 1 , in which the ring resonator ( 2 ) is able to filter the input signal ( 10 ) in order to remove from its output a component of the input signal corresponding to a wavelength λ and harmonics of λ.