Electro-optic spectral filter based on optical superlattice LiNbO₃

Electro-optic (EO) effect of optical superlattice LiNbO₃ (OSLLN), a single crystal with periodic ferroelectric domain structure was studied theoretically and experimentally. Because the electro-optic coefficient has different signs in different domains, the refractive index ellipsoid deforms periodically in the presence of an electric field applied along the Y-axis, which results in the coupling between the extraordinary wave and ordinary wave. Under specific conditions, the polarization of a light may be rotated to 90°, which means that the optical material could act as a precise spectral filter. The influence on the transmission spectrum of an OSLLN EO filter when there is another electric field along the Z-direction was also studied. It was demonstrated that the transmission peak could move with the electric field along the Z-axis if the duty cycle of the periodic structure is not 50%. Based on this effect, a tunable filter may be constructed.