EN
In this work we present results of calculations concerning bistability of optical polarisation in birefringent media. Second-order optical nonlinearity is assumed to be dominant and represented by one parameter. In our model the second-harmonic generation regime is assumed. Light transmission is analysed in terms of standard Fabry-Perot model of feedback. We derived formulas for the Stokes parameters describing the polarisation state. Numerical results showed that three parameters may exhibit bistable behaviour. This creates new possibilities for optical switching.