We present an extension of an early work on external optical feedback in semiconductor lasers. A more general formalism has been developed, which takes into consideration the anisotropy properties of an external cavity. The expressions are derived for description of the feedback phenomena in a system composed of a laser diode and a Fabry-Perot cavity which is optically birefringent. We show that the emission behavior of such a system can be strongly affected by the polarization states of the feedback waves, and that therefore multiple solutions become possible for stabilization of a composite mode. Particular attention is paid to the angle-dependent phase condition. Examples are given for a laser emitting at the wavelength of 1.54 µm and for an external cavity made of a quartz crystal.