Performance of Ti:LNB directional coupler for optical high voltage measurement

Coupling efficiency in a directional coupler is influenced by the change. of refractive index of substrate. It can be modulated by applying electric field and changing the coupling constant in an electro optic substrate. In this work. a Y-propagating Ti:LiNbO3 channel waveguide fabricated in a Z-cut LiNbO3 substrate is simulated. Then, two waveguides with an enough separation gap are considered. Solving Maxwell's equations and applying boundary conditions yields new eigenmodes of this structure. Using these new eigenmodes, coupling constant is obtained. For obtaining eigenmodes of coupled system, a recently reported variational approach has been used [1]. Then, performance of the sensor was studied by applying electric field. It changes refractive indices in this structure, which gives new eigenmodes and new coupling constants. Simulation results show variations in coupling constant with the change of electric field; these changes of output optical power level can be used to measure the applied electric field.