Spectral Efficiencies of Channel-Interleaved Bidirectional and Unidirectional Ultradense WDM for Metro Applications

We measure spectral efficiencies of ultra-dense (UD) wavelength-division multiplexing (WDM) channels for metro applications. We change the channel spacing in 500-MHz step using a beat-frequency-locking method. Applying both a polarization control (PC) and a forward-error correction (FEC), we achieve spectral efficiencies as high as 1.54 and 0.91 b/s/Hz in back-to-back operations for channel-interleaved (CI) bidirectional and unidirectional UD-WDM, respectively. If we use the PC and the FEC separately for the CI-bidirectional UD-WDM, the PC enhances the spectral efficiency over the FEC by 4.6%-21.2% as the transmission distance is increased.