rotation of the faraday rotator mirror 210 although the phase drift compensating means provides environmental stability a polarization transformation is necessary for non linear polarization evolution to be optimized for modelocking this action is performed by including a means for transforming linear polarization of energy such as the incorporation of 1 or more bulk waveplates 214 within the laser cavity 200 for introducing a linear phase delay the cavity of fig1 also includes the polarizer 216 polarization eigenmodes interfere at the polarizer 216 in the cavity the polarizer 216 can be any optical polarizing element the polarization change induced by the waveplate 214 depends on the tilt and rotation of the waveplate or waveplates although use of a single waveplate will minimize scattering of light two waveplates can be used to provide independent control of the ellipticity and rotation angle of elliptically polarized light the polarization change induced by the waveplate or by any arbitrary number of such waveplates or any arbitrary polarization transformer is considered with respect to the polarization axis of the polarizer 216 the erbium doped fiber of gain medium 202 can be aligned at any axis with respect to the polarizer polarization transformation is then uniquely.