Silicon photonic integrated QKD transceiver utilizing an external cavity laser as the light source

Integrated silicon photonics offers a promising route toward compact and CMOS-compatible quantum key distribution (QKD) systems. However, on-chip laser integration remains a key barrier to full system miniaturization. Here, we demonstrate a fully integrated photonic device that combines an external-cavity laser (ECL) with a QKD transceiver, enabled by hybrid III-V/silicon photonic integration. The integrated transmitter and the phase-decoding receiver are combined to form a phase-encoded QKD system that demonstrates quantum bit error rates (QBER) of 1.4% (Z-basis) and 6.4% (X-basis), and a secure key rate of 28.16 kbps over a fiber channel with 8.3 dB loss at 625 MHz. The integrated system achieves a wavelength tunability of 87.61 nm, addressing the challenge of light source integration in silicon-based QKD networks. The demonstrated integration platform represents a crucial step toward the practical integration of QKD into existing optical transport networks (OTNs) and future quantum communication networks.