Upgrading WDM networks using ultradense WDM channel groups

In order to upgrade conventional wavelength-division-multiplexing (WDM) networks, we propose to use ultradense (UD) WDM channel groups. One UD-WDM channel group replaces one WDM channel and traverses the WDM network following the same path as the original WDM channel. We show experimentally that each conventional 100-GHz-spaced WDM channel can be upgraded in this way to have the transmission capacity of 20-40 Gb/s.