Integrated photonics is a key technology platform for optical communication, sensing, and data processing. Driven by the success of the CMOS industry and the resulting maturity of silicon-based fabrication methods, silicon photonics has evolved as an important candidate to realize integrated photonic circuits (PICs) in a cost-efficient and scalable way. Electrical control of the optical properties is critical in PICs: Fast electro-optical modulators are essential to reach high data rates, low-loss switches are needed to dynamically reconfigure networks, and low-power tuning elements are important to compensate temperature fluctuations. Traditionally, such components are implemented in silicon photonics by exploiting the plasma-dispersion effect  or Joule heating , which are, however, intrinsically linked with optical absorption or high power consumption. These challenges could be solved by using the Pockels effect as an electro-optic switching mechanism. However, because silicon lacks a Pockels effect, other materials with a non-vanishing Pockels effect need to be integrated on the technology platform.