Monolithic Multi-Channel SiGe Quantum Key Distribution Transmitter Chip

Quantum key distribution (QKD) allows the secure transmission of encryption keys in the dawning age of quantum computers. However, despite photonic integration efforts, the size and complexity of current QKD systems remains a roadblock for practical deployment in cost-sensitive applications. Here we show a monolithic integrated QKD transmitter that exclusively builds on silicon photonics. We introduce a germanium-on-silicon light emitter acting as source for a co-integrated quantum state encoder, to generate a secure key over a 45.9 km field-installed fiber link. On top of this, we demonstrate the broadband operation of our QKD transmitter by generating keys over 32 wavelength channels, making it an integrated colorless QKD transmitter with full C-band coverage. Employing monolithic silicon technology paves the way towards fully integrated optoelectronic QKD transmitters, enabling a drastic reduction of size and cost while benefiting from the maturity and mass production capabilities of complementary metal–oxide–semiconductor (CMOS) technology. Moreover, omitting the need for rare and costly III-V semiconductor materials to generate light can drastically reduce the overburdening assembly and packaging requirements inherent to optoelectronics, potentially enabling QKD to finally enter new application domains closer to the consumer market.