Wavelength Conversion and All-Optical Regeneration: Achievements and Open Issues

All-optical wavelength conversion and regeneration have, since 20 years, attracted a lot of interest thanks to their potential applications and sophisticated working principles; however, they have not yet led to practical products that could be deployed in the real networks. We present here a critical review of the greatest achievements and main type of solutions that have been demonstrated. We then discuss the still-open issues that should be addressed in order to see the practical implementations.