Verification of a System for Calibrating Optical Transmission Path Asymmetry

This work addresses the calibration of asymmetry in optical transmission paths for precise time and frequency distribution. Specifically, we focus on calibrating White Rabbit technology, where local calibration is not possible due to the considerable distance between synchronized nodes. We developed an automatic calibration system using micro-electromechanical optical switches, which we verified under laboratory conditions. The verification process utilizes a basic calibration method, employing an auxiliary communication channel to transmit the 1PPS signal from a remote synchronized White Rabbit node for local comparison. The remote 1PPS signal’s transmission direction is time-multiplexed. Experimental results from a laboratory model of a real optical transmission system demonstrated the alignment between the automatic calibration system and our verification chain. The change in optical system asymmetry, simulated by adding additional optical fiber to the existing path, resulted in measured asymmetry changes of 101.5 ps by the automatic system and 102.6 ps by the verification chain. The overall difference between these two calibration methods was 1.1 ps. These findings confirm that the automatic system provides reliable results for calibrating asymmetry in optical transmission systems.