Measurement of nonlinear polarization rotation in a highly birefringent optical fibre using a Faraday mirror

We present both a theoretical and experimental analysis of nonlinear polari zation rotation in an optical fibre. Starting from the coupled nonlinear Sc hrodinger equations an analytical solution for the evolution of the state o f polarization, valid for fibres with large linear birefringence and quasi cw input light with arbitrary polarization, is given. It allows us to model straightforwardly go-and-return paths as in interferometers with standard or Faraday mirrors. In the experiment all the fluctuations in the linear bi refringence, including temperature- and pressure-induced ones, are successf ully removed in a passive way by using a double pass of the fibre under tes t with a Faraday mirror at the end of the fibre. This allows us to use long fibres and relatively low input powers. The match between the experimental data and our model is excellent, except at higher intensities where deviat ions due to modulation instability start to appear.