Dispersion-Monitoring in WDM Systems by Injecting Modulated ASE

We demonstrate a technique for measuring the residual dispersion in wavelength-division-multiplexing links by injecting a low level of broadband amplified spontaneous emission that has been modulated with a radio-frequency (RF) tone into the start of the link to be monitored. The residual dispersion at the end of the link is then determined by measuring the RF phase shifts in this tone across different wavelengths. A benefit of this technique is that it does not require integration into the channel transponder and is not constrained to monitoring a fixed wavelength, but instead can be implemented as an independent unit capable of monitoring the link across the band irrespective of channel presence.