Tunable Autler–Townes Splitting Observation in Coupled Whispering Gallery Mode Resonators

In this paper, we experimentally demonstrated an Autler-Townes splitting (ATS) effect in a cascaded optical whispering gallery mode resonator system. Although electromagnetically induced transparency (EIT) has been investigated as an interesting Fano resonance in the recent decades, the critical resonance matched condition of a high quality factor resonator and a low-quality factor resonator makes EIT difficult to realize and hardly tunable. In contrast, ATS requires relatively simple system configurations, and the effect can be preserved over a large tuning range. In our approach, a theoretical model based on coupled mode theory is developed, and the methodology of creating and controlling the ATS modes is demonstrated. In our experiment, the optical resonators have a loaded quality factor of about 3 × 10
⁵
and cascaded in a strong coupling condition. For the experimental demonstration, a thermo-optical mechanism is utilized to control the splitting modes in our system. The asymmetric shape of a splitting resonances shift has a perfect fit with the theoretical calculations and numerical modeling results. Utilizing the precise tenability of splitting modes, the ATS has an extra degree of freedom to perform resonance tuning, which has become an ideal method to overcome the current detection limit.