## 1 Introduction  
Future optical networks will adopt advanced modulation formats to increase bit rate and improve spectral efficiency [1]. The eventual introduction of coherent detection for reception will also facilitate innovations such as filterless networks. Adding wavelength conversion to the mix achieves the most flexible, dynamically-reconfigurable network [2; 3; 4]. Wavelength converters must be able to support both legacy intensity modulation systems and more challenging formats incorporating phase modulation. Several wavelength conversion technologies have been proposed; however, semiconductor optical amplifiers (SOAs) offer many advantages over other solutions, such as ultra-fast response time, cost-effectiveness, compactness and the possibility of photonic integration [5]. Four-wave mixing (FWM) in SOAs for wavelength conversion preserves both the signal phase and amplitude, hence offering compatibility across modulation formats, as well as supporting high bit rates [6; 7; 8]. The use of dual pumps provides wide tunability [9; 10]. For example, a \(100\) nm tuning range was achieved in [11] with a quantum dot semiconductor optical amplifier. We recently proposed a wavelength conversion scheme exploiting a quantum-dash mode-locked laser (QD-MLL) combined with a frequency selective filter to provide two tunable wavelength pumps for FWM in SOAs. This scheme offers wide wavelength coverage for conversion; it is tunable, modulation-format-independent and provides stable phase. Our previous experiment [12] demonstrated wavelength conversion of 10 Gb/s on-off keying (OOK) based on FWM in SOAs. We did not assess the conversion efficiency of our technique for phase modulated sources. Tunability of wavelength converters is typically predicated upon tunable laser sources. Support of phase modulated signals with such sources can lead to elevated phase noise levels until the laser stabilizes following tuning [13; 14; 15]. The use of a multi-wavelength source based on QD-MLLs, combined with a tunable filter to select wavelengths, avoids this transient increase in laser phase noise. QD-MLLs are multi-wavelength sources that exhibit low-noise, high thermal stability, narrow linewidth, broad gain spectrum and reasonable output power [16]. The optical spectrum of the QD-MLLs presents multiple modes with spacing of 100 GHz, thus providing a gamut of wavelengths for the two pumps. Instead of two tunable lasers for pumps for wide spectral coverage, we proposed [12] the use of one multi-wavelength source and two tunable filters. As all concerned devices (tunable lasers, SOAs, tunable filters and QD-MLLs) can be integrated, we assume they are equal cost/complexity solutions. In this paper we examine intensity modulated, OOK and differential phase shift keying (DPSK) signals. DPSK exhibits various advantages over conventional OOK, such as better receiver sensitivity, improved tolerance to chromatic dispersion, and robustness to optical filtering and fiber impairments [1; 17; 18; 19]. We previously demonstrated high conversion efficiency of OOK at low pump powers when adopting a strategy of locating one pump as close as possible to the input signal while avoiding filtering effects on the converted signal. The significant sidelobes of the DPSK spectrum (relative to OOK), are aggravated during FWM and post-filtering, leading us to identify a modest penalty in bit error rate (BER) performance for DPSK. While DPSK was examined in [8] for a cascade, wide tunability and direct comparison of OOK and DPSK were not investigated. We demonstrate wavelength conversion at 40 Gb/s based on FWM in an extremely nonlinear SOA (XN-SOA) with a QD-MLL as a dual pump source for OOK and DPSK signals. Wavelength conversionis examined from a fixed input signal to a set of 16 output wavelengths with 100 GHz spacing, for a conversion range of 12 nm. Error-free transmission (BER below \(10^{-9}\)) with power penalty less than 2 dB for OOK and less than 3 dB for DPSK is observed.