High-accuracy and stable measurement of optical time delay based on an optical Hilbert transformer

High-accuracy optical time delay measurement is essential to optical beamforming networks, multi-antenna GNSS-overfiber systems, and clock synchronization networks. To meet the demand of high-performance measurement, a time delay measurement system via microwave phase shift analysis is proposed, in which a modulator bias controller (MBC) is employed to stabilize the bias point of Mach-Zehnder modulator. However, because the MBC is easy to lose lock in long-term use, the stability of the measurement system is limited. To overcome the above problem, we propose an enhanced measurement system, in which the intensity modulation is achieved using a phase modulator and an optical Hilbert transformer. To verify the performance of the proposed system, a proof-of-concept experiment is carried out. The measurement results show that an accuracy of ±0.05 ps is obtained.