Simplified decoy-state quantum key distribution based on planar lightwave circuit integration module

Abstract

The BB84 protocol with decoy states for quantum key distribution (QKD) has generated significant interest due to its theoretical unconditional security. Presently, the most of QKD systems demonstrated rely on bulk optics. Nevertheless, in upcoming large-scale commercial availability, it is imperative to have highly integrated, consistently performing, and cost-effective systems. Photonic integrated circuits (PICs) based on silica planar lightwave circuits (PLCs) play a crucial role in QKD due to its mature manufacturing process, excellent stability, low loss, and high integration level. We develop a simplified BB84 time-bin QKD experiment system that can significantly improve the key rate because it does not require time basis decoding. And two silica PLC asymmetric Mach-Zehnder interferometer (AMZI) module are used with a high-precision temperature control system (±0.01 °C). Three quantum states |ψ0⟩, |ψ1⟩ and |ψ+⟩ are encoded and decoded with the module. The system achieves an estimated key rate about 3.4 Mbps using an analytical model with one decoy state at a clock repetition rate of 1.25 GHz. Finally, we experimentally obtain a key rate of 531 kbps over a 20 km single-mode fiber (SMF) at a clock repetition rate of 156.25 MHz.