Scalable single-fiber CWDM ring networks with stackable ROADMs

Stackable reconfigurable optical add-drop multiplexers (S-ROADMs) have been proposed for single-fiber coarse wavelength division multiplexing (CWDM) ring networks so as to perform lightpath reconfiguration remotely. The S-ROADM consists of some modules with different wavelengths required in the node, and with this facility manual ROADM reconfiguration can be performed for low-cost transmission systems. The experimental results clarified that the S-ROADM could multiplex and demultiplex the wavelengths successfully without limiting the wavelengths passing through, making the network's wavelength transparent. The self-healing performance was investigated during a fiber cut in the single-fiber ring networks. Insertion of a new module inside the in-service S-ROADM was also accomplished to increase bandwidth for new users. The experimental results clarify that S-ROADMs provide more flexible CWDM networks in terms of reconfigurability and scalability.