Photonic coherence effects from dual-waveguide coupled pair of co-resonant microring resonators

We theoretically describe photonic manifestations of electromagnetically induced transparency (EIT) and absorption (EIA) using co-resonant coupled microresonators (CMRs) as opposed to detuned CMRs explored previously. Here the coherent optical interactions between the two resonators are mediated via two adjacent waveguides and the photonic EIT and EIA are achieved by coupling two identical resonators to the waveguides with equal strength, although this coupling is distinct for each waveguide. Using co-resonant CMRs based on either identical or distinct intrinsic quality factor (Q) resonators, these effects may be obtained in both transmission and reflection. We elucidate origin of the sharp features in the spectra of co-resonant CMRs. Furthermore, we demonstrate tunability of these features using Q-tunable resonators, which may lead to tunable slow and fast light effects. The theoretical model described here greatly simplifies accurate numerical studies of coupled-resonator effects, as no additional calculations are required to account for the waveguide dispersion.