Near- and far-field verification of electro-optic effect enhancement on a tunable lithium niobate photonic crystal

In this paper, we present the optical response of a tunable lithium niobate photonic crystal (PC) using the electro-optic effect of the material. The band gap tunability is 300 times higher than what one could expect for a bulk lithium niobate device of the same characteristics. Theoretical calculations based on the finite-difference time domain technique have allowed us to determine the physical origin of this enhanced electro-optic coefficient. Indeed, the effective second-order susceptibility in the LN nanostructure increases, giving rise to an ultra-compact low-voltage photonic crystal modulator when it operates at its band edge. In addition, the theoretical and far-field transmission results are confirmed by near-field optical microscopy images of the structure at different excitation voltages.