Experimental Investigation of Long-Haul Transport at 42.7-Gb/s through Concatenated Optical Add/Drop Nodes

A detailed experimental study was made where a single channel was transported over a long haul network with optical add/drop multiplexers (OADMs) spaced at different distances. On-off- keyed formats (non-returm-to-zero, return-to-zero, and carrier- supressed-return-to-zero) as well as differential phase shift keyed formats (33% and 67% return-to-zero) were investigated. When OADMs are spaced close together, the successive node filtering effects dominate and do not influence the propagation characteristics. 

However, as the distance between OADM nodes is increased, the node-to-node propagation characteristics are additionally impaired by the amount of optical filtering the channel suffered in the preceding nodes. The incremental transmission penalty from node to node increases faster than when no OADMs are in the transport path. Formats that are robust to filtering are seen to propagate better in the presence of OADMs.