Effect of both mode couplings (spatial mode coupling (SMC) and frequency mode coupling (FMC)): minimal value of the effective refractive index n_eff as a function of the distance p₂ between two resonators for several values of the side length a_e of the electric resonator. The side length of the magnetic resonator is a_m = 60 μm. The two arrows denote increasing mode coupling. The minimum of the real part of the effective index is n_effmin = −2.8.