Poincare Sphere Method for Optimizing the Wavelength Converter Based on Nonlinear Polarization Rotation in Semiconductor Optical Amplifiers

We present a Poincare sphere (PS) model to optimize the wavelength converter (WC) based on nonlinear polarization rotation (NPR) in semiconductor optical amplifiers (SOA). The PS method is applied to describe the variations of ellipticipy angle and azimuth of SOA output state of polarization (SOP) induced by polarization-dependent gain (PDG) and polarization-dependent phase shift, respectively. The theoretical results reveal that the polarization dependence of the linewidth enhancement factor (LEF) and the variation of SOA gain are significant factors for the NPR. The evolutions of output SOP on the PS under quasi-continuum condition have been demonstrated experimentally. The experimental results agree well with our analysis.