We experimentally study four-wave mixing in highly nonlinear fibers using two independent and partially coherent laser pumps and a third coherent signal. We focus our attention on the Bragg-scattering frequency conversion. The two pumps were obtained by amplifying two Intracavity frequency-shifted feedback lasers working in a continuous wave regime. 1. Introduction Over the last decades, the nonlinear phenomena of parametric four-wave mixing (FWM) have been intensively studied in view of their great potential to provide a large variety of all-optical functionalities for ultrafast signal processing [1–4]. In particular, optical parametric amplification, frequency conversion, phase conjugation, and nonlinear switching have been widely explored. The main interest was developed for FWM with coherent pumps, since this technique may provide high conversion efficiencies with appropriate dispersion curves [5]. Nevertheless, in recent years, FWM in optical fibers with incoherent or partially coherent pumps has attracted great attention, in view of its polarization-independent gain and increased resilience to stimulated Brillouin scattering (SBS) [6, 7]. Let us remember that SBS limits the direct use of intense and narrowband lasers in nonlinear fiber. For the specific case of highly nonlinear fibers (hereafter HNLF) the Brillouin threshold may be in the order of few tens of milliwatt for a fiber length of 500？m. The common way to increase the Brillouin threshold requires the adoption of phase modulation of pumps. For the case of two-pump parametric devices, optimal architectures of phase modulations have been proposed to suppress SBS. These solutions are based on phase modulators, generally driven by a pseudorandom bitsequence generator [4, 5, 8, 9] at GHz repetition frequency. With pure phase modulation the pumps can be spectrally broadened without affecting the time domain intensity. The adoption of incoherent pumps may represent a cost-effective solution to study FWM in different scenarios and may open a novel kind of applications, even if this may take place at the expense of low conversion efficiency and spectral broadening of the converted signal. The interplay between four-wave mixing processes with mixed coherent-incoherent pumps may also open entirely new features as reported very recently in [10]. Till now, most of investigations on nonlinear effects with incoherent pumping have been conducted for single pump FWM processes and so far, little attention has been paid to a specific type of FWM generally called Bragg-scattering FWM (BS-FWM) [6, 10]. The
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