Complete crossing of Fano resonances in an optical microcavity via nonlinear tuning

We report on the modeling, simulation, and experimental demonstration of complete mode crossings of Fanoresonances within chip-integrated microresonators. The continuous reshaping of resonant line shapes is achievedvia nonlinear thermo-optical tuning when the cavity-coupled optical pump is partially absorbed by the material.The locally generated heat then produces a thermal field, which influences the spatially overlapping opticalmodes, allowing us to alter the relative spectral separation of resonances. Furthermore, we exploit such tunabilityto continuously probe the coupling between different families of quasi-degenerate modes that exhibit asymmetricFano interactions. As a particular case, we demonstrate a complete disappearance of one of the modal features inthe transmission spectrum as predicted by Fano [Phys. Rev. 124, 1866 (1961)]. The phenomenon is modeled as athird-order nonlinearity with a spatial distribution that depends on the stored optical field and thermal diffusion within the resonator. The performed nonlinear numerical simulations are in excellent agreement with the experimental results, which confirm the validity of the developed theory. © 2017 Chinese Laser Press