High‐Efficiency and High‐Speed Electro‐Optic Modulator Based on Heterogeneous Integration of Calcium Titanate and Thin‐Film Lithium Niobate

ABSTRACT Electro‐optic (EO) modulators are indispensable components in modern optical communication systems. However, the performance of thin‐film lithium niobate (TFLN) modulators has long been limited by the inherent trade‐off between modulation efficiency and bandwidth. In this work, we propose a heterogeneous TFLN modulator using a high‐permittivity (high‐κ) calcium titanate (CaTiO 3 ) cladding that helps mitigate this trade‐off. The high‐κ dielectric CaTiO 3 concentrates the modulation electric field within the optical mode region, thereby improving the EO interaction. Therefore, the fabricated device achieves a high modulation efficiency of 1.3 V·cm, while the EO bandwidth exceeds 110 GHz, providing an effective approach to mitigating the trade‐off between modulation efficiency and bandwidth. Meanwhile, owing to the suppression of sidewall scattering by the dense CaTiO 3 cladding and the repair of lattice damage via high‐temperature annealing, the device exhibits a low on‐chip insertion loss of 0.86 dB after excluding grating‐coupler losses. By combining this heterogeneous integration process with typical microfabrication flows, this work provides a practical route to scalable, high‐density, and low‐power photonic integrated circuits that can be manufactured on a large scale.