A high output transmission and high quality factor, compact LiNbO3 -based Fabry-Perot-type photonic crystal cavity is reported that can be used in electro-optical modulators at optical communication wavelengths. The electro-optic effect is 123 times enhanced as compared to the bulk material as a result of the slow light effect. The transmission wavelength is found to depend linearly on the applied voltage with 1.2 nm/V modulation sensitivity. Moreover, an externally switchable dual mode regime with high quality factors and transmissions is realized. High transmissions and high quality factors are also obtained for both transverse-electric and transverse-magnetic polarizations simultaneously. © 2017 TÜBITAK.