Temporal cavity solitons in a ring resonator filled with a three-level medium displaying electromagnetically induced transparency require less input power, have better shapes and produce optimal frequency combs than their two-level media counterparts.
Temporal cavity solitons in ring microresonators provide broad and controllable generation of frequency combs with applications in frequency standards and precise atomic clocks. Three-level media in the $\mathrm{\ensuremath{\Lambda}}$ configuration inside microresonators displaying electromagnetically induced transparency can be used for the generation of temporal cavity solitons and frequency combs in the presence of anomalous dispersion and two external driving fields close to resonance. Here domain walls separating regions of two dark states due to quantum interference correspond to realizations of stimulated Raman adiabatic passage without input pulses. With no need of modulational instabilities, bright temporal cavity solitons and frequency combs are formed when these domain walls lock with each other. Wide stability ranges, close to resonance operation, and the optimal shape of the cavity solitons due to three-level quantum interference can make them preferable to those in two-level media.
Cavity solitons in ring resonators have revolutionized frequency comb generation and its applications. Coexistence of bright and dark cavity solitons in these devices is, in general, associated with vectorial configurations with more than one optical field resonated in the cavity. We demonstrate the coexistence of stable bright, stable dark, and stable hybrid bright-dark cavity solitons in a single resonated field device formed by a three-level medium in a micro-resonator with normal dispersion. Each of these solitons displays unusually wide regions of stability and a multitude of secondary localized structures, including families of soliton crystals leading to an unprecedented variety of possible frequency combs in a single photonic device. Of the many possible soliton crystals, the most striking is a periodic sequence of dark cavity solitons found at huge distances from the stability region of the single dark soliton.