Polarization-Insensitive Wavelength Converters Based On Four-Wave Mixing In Semiconductor Optical Amplifiers

Future high capacity all-optical telecommunications systems will use avariety of techniques to access the enormous available bandwidth of opticalfibre. The advanted WDM(wavelength division multiplexing) technologyrepresents the developing way of future optical telecommunication networks.And in WDM systems, all optical wavelength converters are expected to bekey components and plays a major role in avoiding wavelength blocking.Many schemes, such as cross gain modulation(XGM), cross phasemodulation(XPM) and four-wave mixing(FWM), have been proposed torealize wavelength conversion based on SOA. But four-wave mixing in SOAis one of promising approaches because it is the only wavelength conversiontechnique demonstrated so far that is transparent to bit rate and modulationformat and is fully tunable over a wide range of wavelengths.Much researchhas been focused on the investigation of the single-pump FWM technique,however, the conversion efficiency drops rapidly with wavelength detuning,causing a reduction in the intensity of the converted signal and a degradationin the optical signal-to-noise ratio(SNR). A polarization-diversity schemeusing two-orthogonal pump configuration provide a large tuning range hasbeen demonstrated. In this paper,we propose a simple configuration of wavelength converterto realize the wanted polarization-diversity and constant conversion efficiencyover a large range. In fig.1, the pump1 is amplified by the EDFA then mixed with the signal,with random polarization, at the input-port of a polarizationbeam-splitter(PBS1) through polarization controller(PC), optical coupler(OC)and circulator(C). At the output-port, they have perpendicular polarization.The pump2 is sent to polarization beam-splitter(PBS2) then is divided intotwo perpendicular parts reciprocal with respect to the other part. P2 PBS2 P2 P2 P1 SOA S S P2 S P1 S P2 P1 P1 PBS1 S P1 Fig.1. Scheme of two-pump polarization-diversity configuration The experimental setup is shown in fig.2. The pump2 is generated by atunable semiconductor laser. The other two semiconductor lasers are used togenerate P1(λ1 =1553.6nm) and S(λs =1554.0nm) . The frequency separation( ?λ = 0.4nm )between and S which is fixed is selected accoding to theadvicement of the international telecom union. The small-signal gain of theSOA we use is 25dB. The saturation output power is 9dBm. The powerinjected in the SOA is:-15.9dBm for S ,-4.8dBm for P1. Fig.3 shows the experimental results obstained with an optical spectrumanalyzer(OSA). The conversion interval is over 100nm with smaller than a1.3dBm variation of the conversion efficiency. Compared with the result of PBS2 P2 PC3 PC6 SOA PC2 PC5 OC2 OC3 Signal C PC4 OC1 PBS1 P1 EDFA PC1 OSA Fig.2. Experimental setup -10 -20 dB) ( 率 -30 效 换 转 -40 -50 1520 1540 1560 1580 1600 1620 波 长 (nm) Fig.3. relationship betwe...