Abstract-Four-wave mixing (FWM) in semiconductor optical amplifiers is an attractive mechanism for wavelength conversion in wavelength-division multiplexed (WDM) systems since it provides modulation format and bit rate transparency over wide tuning ranges. A series of systems experiments evaluating several aspects of the performance of these devices at bit rates of 2.5 and 10 Gb/s are presented. Included are single-channel conversion over 18 nm of shift at 10 Gb/s, multichannel conversion, and cascaded conversions. In addition time resolved spectral analysis of wavelength conversion is presented.

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Abstract-Time-resolved spectral analysis is performed on 10-Gb/s signals wavelength converted by four-wave mixing (FWM) in semiconductor optical amplifiers. A pattern-dependent chirp resulting from parasitic gain modulation by the signal is measured and characterized as a function of the converter's pumpto-probe ratio. This chirp is found to be insignificant for pumpto-probe ratios exceeding 9 dB.

Electroabsorption Modulator IOGHzRFCTuH5 Fig. 1 Laser cavity schematic. SLA: semiconductor laser amplifier, FI: Faraday isolator, PC: polarization controller.monolithic semiconductor lasers with intracavity electroabsorption modulator (EAM) sections5 and hybrid external-cavity semiconductor lasers. The nonlinear attenuation with applied voltage characteristic of EAMs results in short temporal transmission windows, making them attractive for modelocking applications, as the "effective" modulation frequency can be much higher than the applied electrical driving frequency. They tend, however, to be damaged by the high peak powers that can occur within erbium fiber lasers, particularly in the case of Q-switching. We report a novel 10-GHz actively modelocked unidirectional ring laser constructed from discrete components that uses a semiconductor laser amplifier as the gain medium and a short temporal switching window EAM as an amplitude modulator. The laser cavity configuration is shown schematically in Fig. 1. It was composed entirely from fiber-pigtailed devices. Gain was provided by an InGaAsP semiconductor laser amplifier (SLA). Following the SLA a fEed 6-nm bandpass filter was included to constrain the lasing wavelength. A polarization controller (PC) was added to adjust the state of polarization injected to the EAM. The loop was completed with a fused fiber coupler, which provided a 10% output. The output pulses produced were measured using a scanning autocorrelator and optical spectrum analyzer, and in all cases the pulse shape was assumed to be Gaussian, as predicted by AM active modelocking theory.The output pulses were found to be -5 ps long with a time-bandwidth product of 0.73, indicating that they were significantly chirped. Previous studies have shown that EAMs can provide large degrees of approximately linear chirp and by splicing a length of dispersion compensating fiber to the output of the laser it was possible to compress these pulses down to 2.01 ps. The spectral FWHM was 2.0 nm, yielding a time-bandwidth product of 0.50, which indicates that these compressed pulses were close to transform-limited. Figures 2a and 2b show the autocorrelation trace and spectrum of these pulses, respectively.The use of a tunable fdter with a bandwidth of 2.65 nm resulted in the generation ofslightly longer 3-ps pulses, but had the advantage that the central wavelength could be selected. Adjustment of this filter and the EAM driving frequency allowed tuning ofthe laser output. It was possible to produce pulses of 13.5 ps duration over a continuously tunable range from 1548-1565 nm. These lower and upper wave- length limits were determined by the gain bandwidth of the SLA and the operating range of the EAM respectively. Despite the fact that no active stabilization techniques were employed and the entire cavity was composed of non-polarization-maintaining fiber the laser was found to be stable under laboratory conditions for timescales of an hour or more. In summary, we report the generation of 2-ps transform-limited p...