Experimental Demonstration of an Efficient Mach-Zehnder Modulator Bias Control for Quantum Key Distribution Systems

A Mach-Zehnder modulator (MZM) is necessary for implementing a decoy-state protocol in a practical quantum key distribution (QKD) system. However, an MZM bias control method optimized for QKD systems has been missing to date. In this study, we propose an MZM bias control method using N (>= 2) diagnostic pulses. The proposed method can be efficiently applied to a QKD system without any additional hardware such as light sources or detectors. Furthermore, it does not reduce the key rate significantly because it uses time slots allocated to existing decoy pulses. We conducted an experimental demonstration of the proposed method in a field-deployed 1 x 3 QKD network and a laboratory test. It is shown that our method can maintain the MZM extinction ratio stably over 20 dB (bit error rate <= 1%), even in an actual network environment for a significant period. Consequently, we achieved successful QKD performances.

Automated summary

In this study, a bias control method for Mach-Zehnder modulator (MZM) using diagnostic pulses is proposed for efficient application in a quantum key distribution (QKD) system without additional hardware. The method maintains the MZM extinction ratio stably, even in an actual network environment, and achieves successful QKD performances.