Linear electro-optic effect in trigonal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>LiNb</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>: A first-principles study
Inhwan Kim, Alexander A. Demkov
Abstract
Lithium niobate $\mathrm{LiNb}{\mathrm{O}}_{3}$ (LN) has emerged as a promising electro-optic (EO) material with applications in silicon photonics. It demonstrates a large linear EO response, often referred to as the Pockels effect. We report on a first-principles investigation of the origins of the Pockels response in $R3c$ LN. We examine three contributions to the Pockels tensor, its electronic, ionic (Raman), and piezoelectric components, and demonstrate that the large value of Raman susceptibility can be traced to specific ${A}_{1}$ modes that affect the Nb-O bonding. To examine the origin of the piezoelectric Pockels response, we compute the elasto-optic and piezoelectric tensors. Importantly, the largest component of the Pockels tensor ${r}_{33}$ is dominated by the ionic response, which explains the insensitivity of the EO effect in LN to frequency.