Silicon (Si) photonics is forming a fabless ecosystem, which is enabling low-cost and densely integrated components for optical communications and quantum information. We present a Si optical transmitter for polarization-encoded quantum key distribution (QKD). The chip was fabricated in a standard Si photonic foundry process and integrated together a pulse generator, intensity modulator, variable optical attenuator, and polarization modulator in a 1.3 mm×3 mm1.3 mm×3 mm die area. The devices in the photonic circuit meet the requirements for QKD. The transmitter was used in a proof-of-concept demonstration of the BB84 QKD protocol over a 5 km long fiber link. This work shows the potential of using foundry Si photonics for low-cost, wafer-scale fabricated components for quantum information.
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