Analysis in the Measurement of Optical Signal-Noise-Ratio Degradation of an Optical Node

The optical signal-Noise-Ratio(OSNR) degradation (OSNRD) induced by an optical network node is studied in the paper. It is shown that the difference of OSNRs detected before and after the node depends not only on internal parameters of the optical node to be measured, but also on the external condition. This kind of difference can not be used to evaluate the optical performance of the node unless either gain condition or power condition is met during the measurement. It also found that the relationship between OSNRDs and internal parameters of the node obtained under the two conditions are reverse. In the view of optical networking, the power condition is considered more reasonable for the reason that the relationship between OSNRD and the node under this condition is corresponding to the case where the node is used in optical networks.