Complete transparency with three active-passive-coupled optical resonators

The phenomena of induced transparency, with the typical examples of electromagnetically induced transparency (EIT) in atomic media and coupled optical resonators, have attracted tremendous interest since their discoveries. Due to the limitations of the involved elements, however, near-100% transmissions were reported under highly demanding experimental conditions for atomic and other media. Based on a structure of three linearly coupled optical resonators, an active one carrying a possibly arbitrary optical gain and two passive ones simply with dissipation, we demonstrate that a transmitted light field can become completely transparent through the structure, which displays all properties similar to those of EIT. A destructive interference mechanism is discovered to totally eliminate the intracavity field in the resonator directly coupled to the transmitted field of any feasible power, when the coupling strength of two other resonators is tuned to a point inside the designed range. This mechanism works for all possible coupling strengths of the dark resonator with its neighboring resonator and the input field, as well as for any available quality factor from its fabrication. The transparency window size and the output field intensity at the transparency window center can be freely engineered by adjusting two inter-cavity couplings, without modifying the built-in optical gain which can be just slightly stronger than the dissipation of the active resonator.