Photobleaching for the formation of nonlinear optical polymer waveguide devices

A simple but realistic kinetic model has been developed to delineate the refractive index profiles formed by photochemical reaction in nonlinear optical polymers. The effects of the absorption due to the unconverted reactant and the photoproduct are included in the model. The parameters required in the model are obtained from simple transmission experiments. The experimental results are consistent with the model. The refractive index profile is steeper when nonlinear optical polymeric materials are bleached by light with higher absorption. The rate of the bleach depth change becomes slower as the bleaching proceeds. Small absorption of bleaching light due to the photoproduct has significant effect on the resulting refractive index profiles. The photobleaching process is shown to be accelerated by the addition of a photosensitizer. Photobleaching time has been effectively reduced by a factor of 3-5. Linear and nonlinear optical properties of the polymer were little affected by the addition of the photosensitizer. It has also been demonstrated that the photobleaching technique can be utilized to tune the initial state of a directional coupler switch after completing the fabrication of the device. It was shown that successive cross states are passed from the initial cross state by selective bleaching of the gap region. The evolution of the refractive index profiles is successfully applied to predict the evolution of output state.