Heterogeneously Integrated Thin-film Lithium Niobate Electro-optic Modulator Based on Slot Structure

Electro-optic modulator (EOM) takes a vital role in connecting the electric and optical fields. Here, we present a heterogeneously integrated EOM based on the lithium niobate-on-insulator (LNOI) platform. The key modulation waveguide structure is a field-enhanced slot waveguide formed by embedding silicon nanowires in a thin-film lithium niobate (LN), which is different from the previously reported LN ridge or etchless LN waveguides. Based on such slot structure, optical mode field area is reduced and enhanced electric field in the slot region can interact well with LN material with high Electro-optic (EO) coefficient. Therefore, the improvements in both aspects have positive effects on enhancing the modulation performance. From results, the corresponding EOM by adding such modulation waveguide structure achieves better performance, where the key half-wave-voltage-length product (V_πL) and 3 dB EO bandwidth are 1.78 V ∙ cm and 40 GHz under the electrode gap width of only 6 μm, respectively. Moreover, Lower V_πL can also be achieved. With these characteristics, such field-enhanced waveguide structure could further promote the development of LNOI-based EOM.