Characterisation of an InP-based PIC Transmitter in a QKD setup

In this work, an indium phosphide (InP) based quantum key distribution (QKD) transmitter on a photonic integrated circuit (PICs) is examined. The PIC, which was designed by the authors from Eindhoven University of Technology, and characterised in the QKD system by the authors from Austrian Institute of Technology, features a ring laser structure, a single Mach-Zehnder modulator (MZM) structure with integrated radio frequency (RF) phase modulators for pulse carving, intensity modulation and phase modulation and an absorber for attenuation. The individual components were characterised. Additionally, the PIC was tested in a 4-state time-bin BB84 protocol including a bulk receiver, key performance measures like quantum bit error rate (QBER) and secret key rate (SKR) were analysed. The high performance PIC is capable of generating a SKR in the kbits/s range exhibiting high stability over a measured time frame of around an hour.