We show different phase responses in the coupled ring-resonators that exhibit an EIT-like amplitude response, corresponding to three operating regimes. This deepens our understanding of the double-resonator devices in terms of delay and nonlinear performance.
Coupled microresonators exhibit great potential for nonlinear applications. In the present work, we explore the nonlinear performance of an embedded ring resonator analogous to an electromagnetically induced transparency (EIT) medium, also known as coupled resonator induced transparency (CRIT). Interestingly, an EIT-like amplitude response can have a remarkably different power enhancement factor that varies by more than one order of magnitude, which is attributed to the different phase regimes of the embedded micro-ring resonators. In addition to the non-monotonic phase profile reported in atomic EIT systems, the phase responses featuring 2 π and 4 π monotonic transitions are identified and analyzed. We also present an interesting phenomenon, in which the power enhancement changes greatly, even with the same transfer function (both intensity and phase responses). This reveals that wisely choosing the operating regime is critical to optimize nonlinear performance of the embedded double resonator system, without adding to design or fabrication difficulty.
Electromagnetically induced transparency (EIT) and EIT-like effects have been investigated in a wide variety of coupled resonant systems. Here, a classification of the phase characteristics of the EIT-like spectral responses is presented. Newly identified phase responses reveal unexplored operation regimes of EIT-like systems. Taking advantage of these new phase regimes, one can obtain group delay, dispersion and nonlinearity properties greatly enhanced by almost one order of magnitude, compared to the traditionally constructed EIT-like devices, all of which breaks the fundamental limitation (e.g. delay–bandwidth product) intrinsic to atomic EIT and EIT-like effects. Optical devices and electrical circuits are analyzed as examples showing the universality of our finding. We show that cavity quantum electrodynamics (QED)-based quantum phase gates can be greatly improved to achieve a phase shift of π . The new phase characteristics are also believed to be useful to build novel doubly resonant devices in quantum information based cavity QED, optomechanics and metamaterials.