We calculate the pump laser linewidths required to achieve specific system performance when undertaking wavelength conversion of DQPSK data signals at 10 and 25 Gbaud using four-wave mixing in a semiconductor optical amplifier. The results highlight the class of laser that can be used to implement this scheme. We show that the limits are consistent with expected theories and indicate guidelines for implementing multiple wavelength conversions using this scheme in an optical network. © 2013 Elsevier B.V.