Employing concatenated-FEC to mitigate polarization-sensitivity in all-optical wavelength-conversion

Wavelength-conversion is an essential block in building all-optical networks. Currently, all-optical wavelength-conversion can quite efficiently be performed by means of SOA. In this approach however, a significant shortcoming is the high sensitivity of error-performance to the relative polarization of optical-signals, which imposes rigid tuning requirements. To make conversion insensitive to random fluctuations of polarization, we employ a standard outband-FEC method, in combination with a novel inband-FEC method. The latter, called ldquoFOCUSrdquo, is best suited for combating burst-form errors. This particular property of ldquoFOCUSrdquo matches the error-distribution generated by the associated outband-FEC code, when the two are combined in serial-concatenation. We demonstrate the corrective-power of this FEC-concatenation scheme in protecting a 10 Gb/s lightwave-channel, which undergoes wavelength-conversion by means of an all-optical, SOA-based Mach-Zehnder Interferometer (MZI) switch. In this experiment, the MZI switch was purposely misadjusted, in order to increase the polarization sensitivity. We show error-free 10 Gb/s wavelength-conversion and no need for polarization-control before the converter.