key at a predetermined azimuth application_number US 94516301 A description in the following detailed description for purposes of explanation and not limitation exemplary embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present invention however it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein moreover descriptions of well known devices methods and materials may be omitted so as to not obscure the description of the present invention briefly the present invention relates to a phase shifter which selectively introduces birefringence in an optical fiber the phase shifter includes an actuator that exerts a force on an optical fiber in a transverse manner the actuator may be disposed in a mounting structure in which the optical fiber is disposed the optical fiber is illustratively a polarization maintaining fiber pmf having stress rods or other stress inducing mechanism such as an elliptical core resulting in a stress axis which will be orthogonal to the slow axis of the pmf a registration key in accordance with an exemplary embodiment.