General model for a multimode Nd-doped fiber laser. I: Construction of themodel

We present a general modeling of a multi-longitudinal-mode bipolarized Nd-d oped fiber laser which keeps both vectorial (polarization) and longitudinal properties in the dynamical equations. We use an approach based on random orientation of the microscopic dipoles and demonstrate that it is isomorphi c to the model derived assuming a transverse two-site distribution function for the ions. This result is also true under the mean-field approximation. At steady-state, the model is the generalization of Rigrod's theory to the case of a bipolarized laser.