Optical waveguide circuit

1. An optical waveguide circuit comprising:

a ring waveguide;

an input connection waveguide;

an output connection waveguide; and

an optical multiplexing/demultiplexing part that optically connects the ring waveguide with the input connection waveguide, and that optically connects the ring waveguide with the output connection waveguide, wherein

at least one of the input connection waveguide and the output connection waveguide includes a plurality of curved waveguides,

a sum total of products of curvature signs and bending angles of the curved waveguides and a sum total of a curvature sign and a bending angle of the ring waveguide have a same absolute value with signs opposite to each other, and

rotation of a polarization plane of light generated in the ring waveguide and rotation of a polarization plane of light generated in the curved waveguides cancel each other out.

2. The optical waveguide circuit according to claim 1 , wherein curvature radii of the curved waveguides and a curvature radius of the ring waveguide are different from each other.

3. The optical waveguide circuit according to claim 1 , wherein an absolute value of the sum total of the products of the curvature signs and the bending angles of the curved waveguides is 360 degrees.

4. The optical waveguide circuit according to claim 1 , wherein each of the curved waveguides has a curvature radius with which light loss through the waveguides is 1.0 dB/cm or less.

5. The optical waveguide circuit according to claim 1 , wherein

the optical multiplexing/demultiplexing part includes two optical multiplexers/demultiplexers, and

one end of the input connection waveguide and one end of the output connection waveguide are extended toward a same side face.

6. The optical waveguide circuit according to claim 1 , comprising a plurality of the ring waveguides, wherein

the input connection waveguide includes at least one branch part and a plurality of branched paths that are branched from the at least one branch part and optically connected to each of the ring waveguides,

the branched paths include two or more of the curved waveguides, and

sum totals of products of curvature signs and bending angles of the curved waveguides in each of the branched paths are equivalent with each other.

7. The optical waveguide circuit according to claim 1 , comprising a plurality of the ring waveguides, wherein

the input connection waveguide includes at least one branch part and a plurality of branched paths that are branched from the at least one branch part and optically connected to each of the ring waveguides,

the branched paths include two or more of the curved waveguides, and

the ring waveguides include ring waveguides having light circulating directions different from each other.

8. The optical waveguide circuit according to claim 7 , wherein sum totals of products of curvature signs and bending angles of the curved waveguides in each of the branched paths are different from each other.

9. The optical waveguide circuit according to claim 1 , comprising a plurality of the ring waveguides, wherein

the ring waveguides include ring waveguides having waveguide lengths different from each other.

10. The optical waveguide circuit according to claim 1 , wherein

when TE-polarized or TM-polarized light of single polarization is input from the input connection waveguide, a polarization mode coupling amount of light output from the output connection waveguide is −25 dB or less.

11. The optical waveguide circuit according to claim 1 , wherein

the input connection waveguide, the ring waveguide, the output connection waveguide, and the optical multiplexing/demultiplexing part are formed with a core, and the core is a buried waveguide buried in a cladding.

12. The optical waveguide circuit according to claim 11 , wherein a relative refractive-index difference of the core with respect to the cladding is 4.5% or more.

13. The optical waveguide circuit according to claim 11 , wherein the core contains ZrO 2 .