An optical apparatus comprises a first arm comprising a first optical waveguide configured to propagate a first optical signal, and a first thermo-optic (TO) phase shifter arranged proximate to the first optical waveguide. The optical apparatus further comprises a second arm comprising a second optical waveguide configured to propagate a second optical signal, and a second TO phase shifter arranged proximate to the second optical waveguide. The optical apparatus further comprises a thermal bridge arranged between the first TO phase shifter and the second TO phase shifter.