IEEE Photon. Tech. Lett. 25, 791–794 (2013)

Wavelength conversion, whereby data is transferred from one carrier wavelength to another, is a potentially useful functionality in optical networks. In the optical domain, conversion can be performed by nonlinear optical processes such as four-wave mixing and it is routinely applied to intensity-modulated data. Now, Giampiero Contestabile and co-workers from Scuola Superiore Sant'Anna in Italy and Osaka University in Japan have demonstrated that the technique can also be applied to various coherent, phase-modulated data formats such as QPSK, 8-PSK and 16-QAM. The team used an InAs/InGaAsP/InP quantum-dot semiconductor optical amplifier to perform four-wave mixing. They report a conversion efficiency of more than −10 dB and an output optical signal-to-noise ratio in excess of 20 dB over a wavelength band of about 30 nm. An optical signal-to-noise ratio penalty of around 1 dB — which varies according to the data format used — is reported for the conversion process.