We present a model for the polarization states of a quasi-isotropic laser. The model includes the polarization competition among the gain medium, general cavity anisotropies, and the anisotropy arising from weak but arbitrarily polarized feedback. Three examples of linearly polarized feedback are given, one with the axes of the internal and external anisotropies parallel to each other and two other examples with the axes inclined at 45°. The new calculations are in agreement both with earlier calculations based on a more restricted model and with existing experimental results for a He–Ne laser operating at 3.39 μm. An important feature of the calculations is a method of finding all the stationary solutions, even in the general case. For the three examples considered we find many stationary polarization states. A linear stability analysis shows that only two are stable and permits us to relate our calculations to additive pulse mode locking, to Casperson instabilities, and to Hopf bifurcations.
© 1992 Optical Society of America
Original Manuscript: August 6, 1991
Revised Manuscript: November 18, 1991
Published: April 1, 1992
P. Paddon, M. Bourouis, G. Stéphan, E. Sjerve, and A. D. May, "Polarization modes in a quasi-isotropic laser: a general anisotropy model with applications," J. Opt. Soc. Am. B 9, 574-589 (1992)