On the Cascadability of All-Optical Wavelength Converter for High-Order QAM Formats

With the evolution to ever more complex modulation formats for optical signals, all-optical wavelength converters offer great benefits to optical networks, thanks to the possibility of translating the wavelength of an optical signal regardless of its data rate or modulation format. To deliver its full advantages over conventional optical-electrical-optical conversion, an all-optical wavelength converter has to possess important features in terms of transparency, bandwidth, and cascadability for practical applications in real systems. In this paper, we review a recent development of an all-optical wavelength converter, which exhibits seamless conversion in the C-band with a low noise figure of 6.2 dB for dual-polarization (DP) phase-modulated signals. We then carry out an investigation by both experiment and calculation of the cascaded operation of the developed wavelength converter for high-order quadrature amplitude modulation (QAM) formats. A cascadability comparable to an erbium-doped fiber amplifier is achieved for DP-QPSK, DP-16QAM, and DP-64QAM signals, thanks to the exemplary characteristics of the wavelength converter.