Modeling the electrooptic evolution in thermally poled germanosilicate fibers

We formulate a simple quantitative three-species charge-carrier transport m odel, consisting of two distinct positive ions and a single negative ion, t o describe the dynamics during thermal poling of a germanosilicate optical fiber. We numerically solved the equations and report one-dimensional space -time solutions for the electrooptic (EO) coefficient. In the two-cation mo del, our findings show the EO coefficient initially dips near the anode and then monotonically rises to a steady-state value, higher than that produce d by the initial applied poling field. However, at the cathode, the electri c field quickly dropped to zero where it remained zero for the poling durat ion. The introduction of a moving negative ion clearly shows the existence of a dead time characteristic appearing at the cathode, resulting in a gain in the initial EO coefficient. This model also reveals that the resulting EO evolution in a thermally poled germanium-boron codoped fiber can be attr ibuted to the movement of just two ions of opposite polarity. To explain th e increase in the EO coefficient in boron codoped germanosilicate fiber, we found it necessary to allow for an increase in the third-order susceptibil ity by a factor of similar to3.4.