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 Ypropagating 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. 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.
Optical measurement of voltage because of its excellent advantages is studied by several research groups. In this paper, two optically voltage measurement method based on periodic structure have been introduced. First one is based on Bragg reflection effect. The coefficient of reflection from a periodic layered medium depends on properties of periodic structure. In this work a periodic structure on LiNbO3 substrate was considered and under a high voltage electric field perpendicular to surface of layers, refractive indices of substrate have been changed. Performance of reflection versus applied electric field was calculated. Second method was based on Guided-mode resonance effect. Guided mode resonance effects in waveguide grating structures results in sharp variations in the intensity of the observable propagation waves. When a waveguide grating structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is diffracted and trapped in waveguide layer. The trapped light is then rediffracted and it
can interfere destructively with the transmitted or reflected light and show transmission or reflection anomalies. This phenomenon is sensitive to constitutive parameters of structure; therefore, it can be used in order to electro-optic voltage measurement.