Symmetry breaking for transmission in a photonic waveguide coupled with two off-channel nonlinear defects

We consider light transmission in a two-dimensional (2D) photonic crystal waveguide coupled with two identical nonlinear defects positioned symmetrically aside the waveguide. With the coupled mode theory, we show three scenarios for the transmission. The first one inherits the linear case and preserves the symmetry. In the second scenario, the symmetry is broken because of different light intensities at the defects. In the third scenario, the intensities at the defects are equal but phases of complex amplitudes are different. That results in a vortical power flow between the defects similar to the dc Josephson effect if the input power over the waveguide is applied and the defects are coupled. All of these phenomena agree well with computations based on an expansion of the electromagnetic field into optimally adapted photonic Wannier functions in a 2D photonic crystal.