Quasibound states in a one-dimensional grating for electro-optic modulation

For modulation in free space using the linear electro-optic effect, a narrow-linewidth resonance is favorable when a minimal voltage is preferred to fully shift the resonance. Here a method is proposed to engineer the quasibound states in a slab waveguide consisting of electro-optic polymer and metal gratings, in order to achieve narrow-linewidth resonances for electro-optic modulation. This quasibound state features a strong out-of-plane electric field component located at the position of the metal strips constituting the grating, which also work as the interdigitated electrodes, and thus, the optical mode can interact with the electrostatic field efficiently. The radiation damping of the quasibound state can be controlled by changing the relative position of the neighboring metal strips, while the optical mode can maintain the same periodicity as the electrostatic field. This method also offers prospects for engineering narrow-linewidth resonances for other applications.