Optical Link Tomography: First Field Trial and 4D Extension

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Publication Date: 12/15/2025

Event: Journal of Lightwave Technology

Reference: 43(24):10776-10787, 2025

Authors: Takeo Sasai, NTT Network Innovation Laboratories; Giacomo Borraccini, NEC Laboratories America, Inc.; Yue-Kai Huang, NEC Laboratories America, Inc.; Hideki Nishizawa, NEC Laboratories America, Inc.; Zehao Wang, Duke University; Tingjun Chen, Duke University; Yoshiaki Sone, NTT Network Innovation Laboratories; Minami Takahashi, NTT Network Innovation Laboratories; Tatsuya Matsumura, NTT Network Innovation Laboratories; Masanori Nakamura, NTT Network Innovation Laboratories; Etsushi Yamazaki, NTT Network Innovation Laboratories; Koichi Takasugi, NTT Network Innovation Laboratories; Ting Wang, NEC Laboratories America, Inc.; Yoshiaki Kisaka, NTT Network Innovation Laboratories

Abstract: Optical link tomography (OLT) is a rapidly evolving field that allows the multi-span, end-to-end visualization of optical power along fiber links in multiple dimensions from network endpoints, solely by processing signals received at coherent receivers. This paper has two objectives: (1) to report the first field trial of OLT, using a commercial transponder under standard DWDM transmission, and (2) to extend its capability to visualize across 4D (distance, time, frequency, and polarization), allowing for locating and measuring multiple QoT degradation causes, including time-varying power anomalies, spectral anomalies, and excessive polarization dependent loss. We also address a critical aspect of OLT, i.e., its need for high fiber launch power, by improving the power profile signal-to-noise ratio through averaging across all available dimensions. Consequently, multiple loss anomalies in a field-deployed link are observed even at launch power lower than the system-optimal level. The applications and use cases of OLT from network commissioning to provisioning and operation for current and near-term network scenarios are also discussed.

Publication Link: https://ieeexplore.ieee.org/document/11199900