A method to control the coupling constant of a directional coupler switch made of electro-optic polymer after completing the device fabrication is demonstrated. The method utilizes the selective postphotobleaching of the gap region to lower its effective refractive index while monitoring optical output power from each arm. The output power changes gradually and the crossover states are successively observed as the postphotobleaching proceeds. It is shown that the method can be utilized to tune the initial output to the crossover state to have a good switching extinction.
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Hwang et al. (1995) studied this question.