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.

中文翻译：

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三角铌酸锂中的线性电光效应：第一性原理研究

铌酸锂$\mathrm{铌酸锂}{\mathrm{氧}}_3$（LN）已成为一种有前途的电光（EO）材料，在硅光子学中得到应用。它表现出较大的线性 EO 响应，通常称为普克尔斯效应。我们报告了对普克尔斯响应起源的第一性原理调查$右3C$液化天然气。我们研究了普克尔斯张量的三个贡献，即其电子、离子（拉曼）和压电分量，并证明拉曼磁化率的大值可以追溯到特定的$A_1$影响 Nb-O 键合的模式。为了检查压电普克尔斯响应的起源，我们计算了弹光张量和压电张量。重要的是，普克尔斯张量的最大分量$r_{33}$主要由离子响应决定，这解释了 LN 中 EO 效应对频率的不敏感性。