Bound states in photonic Fabry-Perot resonator with nonlinear off-channel defects

We consider a Fabry-Perot resonator (FPR) comprised of two off-channel nonlinear defects coupled to the photonic waveguide. For the linear case FPR can support bound states in the form of standing waves between the defects if a distance between them is quantized. For the nonlinear case the bound states appear for arbitrary distance between the defects if electromagnetic intensity is quantized. For transmission through the FPR we reveal additional resonances which are the result of coupling of incident wave with the bound states because of nonlinearity of the defects. The resonances are spaced at the eigenfrequencies of bound states with a width proportional to the input amplitude. The theory of the FPR based on the simple Wang and Fan model [Phys. Rev. E 68, 066616 (2003)] is complemented by the tight-binding one. The results for the transmission and bound states in these models agree with computations in real two-dimensional photonic crystal waveguide coupled with two off-channel defects fabricated from a Kerr-type material.