A 100 Gb s^-1 quantum-confined Stark effect modulator monolithically integrated with silicon nitride on Si

The exponential growth of data-intensive artificial intelligence necessitates ultra-fast and energy efficient transceivers in data centres. Quantum-confined Stark effect (QCSE) modulators offer promising solutions, combining high-speed modulation with minimal footprint and superior energy efficiency. Here, we demonstrate a monolithically integrated O-band Ge/SiGe QCSE modulator operating at 100 Gb s^-1, seamlessly integrated with silicon nitride (SiN) waveguides on both silicon and silicon-on-insulator substrates. Our modulator achieves <1 dB coupling loss,  <63 fJ bit^-1 energy consumption, and  >5 dB static extinction ratio, while maintaining performance across a 20-80 °C temperature range. Leveraging CMOS-compatible fabrication processes, we incorporate multiple quantum-well stacks grown at wafer scale on silicon, enabling large-scale production. The modulator's substrate-agnostic integration with back-end of line grown SiN layers, presents a scalable approach for cost-effective co-integration of electronic and photonic components. This work advances high-speed, energy-efficient optical modulators and paves the way for next-generation photonic integrated circuits in data centre interconnects.