High-performance racetrack resonator in silicon nitride - thin film lithium niobate hybrid platform

In this paper, we propose an electro-optic modulator design in a hybrid Si₃N₄-X-cut LiNbO₃. The modulator is based on a modified racetrack resonator and performs at both DC and heightened frequencies. Here the driving electrodes are defined along the straight section of the racetrack. This is done to maximize modulation and minimize modulation-cancelation that occurs in a conventional X-cut LiNbO₃-based resonator due to the directional change of the electric field in the micro-ring. The single bus racetrack resonator is formed in a hybrid Si₃N₄-LiNbO₃ platform, to guide the optical mode. The fabricated device is characterized and has a measured tunability and intrinsic quality factor (Q) of 2.9 pm/V and 1.3 × 10⁵, respectively. In addition, the proposed racetrack device exhibits enhanced electro-optic conversion efficiency at modulation frequencies that match with the racetrack's optical free spectral range (FSR). For example, at the modulation frequency of 25 GHz, which corresponds to the fabricated device's optical FSR frequency, a ∼10 dB increase in electro-optic conversion efficiency is demonstrated. With the enhancement, our measured device demonstrates a conversion efficiency comparable to non-resonant thin-film LiNbO₃ devices that possess RF electrodes that are 10 times longer in length.