Stackable reconfigurable optical add/drop multiplexers (S-ROADMs) have been proposed for use in IP over coarse wavelength-division multiplexing (CWDM) networks so as to provide capabilities of remote lightpath reconfiguration and manual ROADM reconfiguration under the best effort transmission specified by the service level agreement. The S-ROADM can be constructed by connecting modules with different wavelengths required in the node. The experimental results clarify that the S-ROADM can add/drop or pass through the wavelengths successfully, providing no limit to the passing-through (PT) wavelengths, that is, ensuring the wavelength transparency in the network. The S-ROADMs could remove congestions by adding a lightpath remotely within a recovery time with degraded SLA. The transmission break time was also within the recovery time when adding a module manually to the in-service S-ROADM to increase bandwidth to be provided to new users. As a result, the S-ROADMs provide more flexible CWDM networks in terms of scalability and reconfigurability. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.