I. Introduction
Estimating the quality of transmission (QoT) of lightpaths prior to their establishment is capitally important for ensuring the reliability of lightpaths in optical networks. Recently, machine learning (ML), especially the artificial neural network (ANN), becomes a promising technology for QoT estimation. As for the ANN-based QoT estimator, a large set of training samples from lightpaths' observations are required to ensure its accuracy [1]. Unfortunately, the acquisition of the training samples is hindered by practical limitations, such as the shortage of monitorable lightpaths in the early stage of optical network deployment or/and the absence of optical monitors in partial network nodes. Therefore, how to obtain a high-precision QoT estimator with few training samples becomes a crucial problem.