High-accuracy multi-channel optical transfer delay measurement using time-gated phase-based ranging

Accurate measurement of optical transfer delay (OTD) in multiple channels is crucial for applications such as optical phased array antennas, distributed fiber-optic sensors, and high-capacity multichannel optical communications. However, conventional high-accuracy microwave photonic phase-derived measurement techniques are limited to single-channel operation, where multi-channel measurements are typically performed sequentially via optical switching, resulting in low measurement efficiency. In this paper, we propose and experimentally demonstrate a high-accuracy, parallel multi-channel OTD measurement technique based on time-gated phase-based ranging. Wavelength division multiplexing (WDM) is employed to distribute multi-wavelength probe signals to multiple channels. Each wavelength corresponds to a specific channel, enabling parallel excitation and single-receiver detection, which significantly simplifies the system architecture. Although reflections from multiple channels overlap in the frequency domain, the proposed method separates individual channel responses in the time domain. The phase response of each channel is then retrieved via time-domain gating and frequency-domain processing, allowing high-accuracy delay extraction through the linear slope of the unwrapped phase. Experimental results demonstrate simultaneous parallel measurement of 8 channels with a measurement precision of ±0.25 ps. Featuring a simple architecture, high precision, and multi-channel scalability, the proposed technique provides an efficient solution for the characterization of complex optical networks and multi-core fiber systems.