Optical channel defragmentation technology for flexible optical networks

For an effective use of the limited spectral resources, optical channel defragmentation is one of the important technologies, where the fragmented optical channels are consolidated to make useful white space. The optical channel defragmentation node need to be transparent with respect to the modulation format, baud-rate, and the wavelength of signals, to deal with any kind of optical signals. We have experimentally demonstrated an optical channel defragmentation node by using IQ modulator-based frequency shifters, which is transparent to the optical signal formats. Spectrally efficient Nyquist wavelength division multiplexed channels are successfully defragmented and achieved Add operation for different modulation formats with power penalty of less than 2.5 dB. In addition, a multi-hop Add-Drop network is also demonstrated, where the four nodes are connected by 50 km fiber link and two nodes are the defragmentation nodes. The system shows error-free operation with low power penalty less than 4 dB.