Modeling of nonlinear polarization rotation in tensile-strained semiconductor optical amplifiers using Mueller matrices and carrier density induced refractive index change calculations

A model of nonlinear polarization rotation in a tensile-strained bulk SOA is presented. The model uses a wideband steady-state SOA model to determine the SOA carrier density and the polarization dependent gain. The carrier density distribution is used to determine the phase difference between the TE and TM components of an amplified CW probe signal in the presence of a counter-propagating pump. The active waveguide polarization dependent effective index difference is determined using the Marcatili method and the carrier induced refractive index changes are calculated using a detailed material band structure model. The SOA Mueller matrix, which is modeled as the product of an diattenuator and phase shifter, is used to predict the Stokes vector of the amplified signal. This allows a simple comparison with experiment as the Stokes vector can be easily measured using a polarization analyzer. The model is used to predict the polarization rotation of a probe signal induced by a counter-propagating pump. The model can be used to aid in the design of all-optical signal processing functions such as wavelength conversion and optical logic that use SOA polarization rotation effects.