Engineering a sandwiched Si/I/LNOI structure for 180-GHz-bandwidth electro-optic modulator with fabrication...

Electro-optical modulators are essential for scalable photonic integrated circuits and are promising for many applications. The convergence of silicon (Si) and lithium niobate (LN) allows for a compact device footprint and large-scale integration of modulators. We propose a sandwiched Si/I/LNOI modulator for broad modulation with CMOS-compatible fabrication tolerances. There is a thin film SiO₂ spacer sandwiched between Si and LN, which is engineered to tailor optical and electrical properties and enhance index matching. Moreover, the SiO₂ spacer is also exploited to inhibit the radiation loss induced by mode coupling. The modulator shows a bandwidth of ∼180 GHz with a halfwave voltage of 3 V. Such a device is considerably robust to the fabrication deviations, making it promising for massive and stable manufacturing.