I. Introduction
Fiber OPTICAL parametric amplifiers (FOPAs) have been used in several applications, e.g., as wavelength converters [1], amplifiers [2], and pulse sources [3]–[8]. Based on four-wave mixing (FWM) with exponential gain, the FOPA can (when used as a pulse source) generate short return-to-zero (RZ) pulses at the input signal wavelength and the converted idler wavelength. This is due to the fact that the peak of the pump pulse, which has higher gain than its wings, results in a signal pulse compressed with respect to the pump pulse [3]. Using a tunable continuous-wave (CW) signal and an amplitude-modulated pump, a tunable pulse source can be realized [4]. This was later upgraded to 40 GHz, with the demonstration of a pulse source based on optical parametric amplification capable of emitting 2-ps pulses with high power and high quality [5]. The pulse source was later evaluated when generating 10-GHz pulse trains at three wavelengths simultaneously [6]. Transmission experiments were also performed at bit rates from 10 to 40 Gb/s to quantify the transmission properties of these pulse sources. Both signal and converted idler wavelengths were used in a 10-Gb/s experiment over 650 km [7]. The idler suffered from timing jitter due to the frequency-modulated pump, arising from the frequencies used to suppress stimulated Brillouin scattering (SBS). Timing jitter on the idler arises due to the combination of frequency jitter and dispersion. The signal was transmitted at a bit rate of 40 GHz over a 320-km transmission link. The output pulse from the FOPA was also measured versus residual dispersion and found to have a nonnegligible chirp [7]. The FOPA pulse source has also been used in transmission at bit rates of 160 Gb/s [8].