Current flow in doped and undoped electro-optic polymer films during poling

Abstract

Electric-field poling is used to achieve a macroscopic alignment of the chromophores responsible for the electro-optic (EO) effect in polymer films.1 In EO polymer devices this chromophore doped layer, referred to as the “core” layer, is usually stacked between two polymer “cladding” layers of lower index which confine transmitted light to the core layer. These polymer films are formed by spin coating using standard semiconductor equipment and manufacturing processes. The polymer films are amorphous as spun and cured, so the polarizable chromophores are randomly arranged, and therefore no second-order electro-optic effects occur. Electric-field poling has been used to make a variety of EO polymer devices2,3,4,5, but the process is not well understood. In electric field poling the EO polymer is heated above its glass transition temperature Tg, a voltage is applied by electrodes to align the nonlinear chromophore molecules in the direction of the field, and the material is cooled back to room temperature under the influence of the electric field. While the voltage is applied to the cladding/core/cladding stack of films, the electric field divides in some manner so that a portion of the applied voltage appears across each of the film layers, as illustrated in Figure 1.