Ferroelectric lithium niobate (LiNbO3) is widely used in integrated and guided-wave optics because of its favorable optical, piezoelectric, electro-optic, elastic, photoelastic, and photorefractive properties. However, detailed summaries of its pertinent physical properties and crystal structure are not readily available. In this tutorial paper, the important tensor physical properties and their mathematical descriptions are compiled and presented. The essential features of the structure of lithium niobate, including its hexagonal and rhombohedral unit cells, are illustrated and the principal (Cartesian) axes used in the description of the anisotropic properties are specified relative to the crystal structure. Errors in property coefficient values and structure information that have been propagated in the literature are corrected.

Lithium niobate: Summary of physical properties and crystal structure

The absorption coefficient and the index of refraction of undoped and Mg-doped stoichiometric and congruent LiNbO3 crystals were determined for polarization parallel to the z axis in the far-infrared (FIR) 30−180-cm−1 frequency range for different Mg-doping levels and temperatures down to 10 K. For stoichiometric LiNbO3, smaller absorption and index of refraction were found, than for congruent samples. At a Mg content near the photorefractive threshold, the FIR absorption coefficient has the lowest value in the stoichiometric crystals, which are most suitable for efficient pulse generation in the terahertz range.

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO3 in the THz range

The absorption coefficient and the index of refraction of Mg-doped LiNbO/sub 3/ crystals with different compositions are determined in the 30 - 200 cm-1 frequency range. We find that stoichiometric LiNbO/sub 3/ has smaller absorption and index of refraction than congruent samples.

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO/sub 3/ in the THz range

Surface acoustic waves (SAWs) serving as universal interfaces are intriguing for hybrid systems with classical and quantum components. This study demonstrates a method for designing a high-quality SAW resonator using phononic band structure engineering. The SAW resonator presents a quality factor $Q$ g 104 at gigahertz frequencies, yielding a figure of merit (the product of frequency and $Q$) of 10${}^{13}$ at room temperature. Improvements in $Q$ at cryogenic temperatures are also observed. The presented methodology paves the way for hybrid classical-quantum phonon networks.

https://link.aps.org/accepted/10.1103/PhysRevApplied.12.014022

Phononic Band Structure Engineering for High- Q Gigahertz Surface Acoustic Wave Resonators on Lithium Niobate

The low temperature electrical properties of some anisotropic crystals

Coefficients of linear thermal expansion are reported, in the range 60 K to room temperature, for eight optical materials: Polytran potassium chloride and Polytran calcium fluoride—Harshaw; chemical-vapor-deposited (CVD) zinc sulfide and zinc selenide—Raytheon; germanium (single-crystal and polycrystal); crystalline magnesium fluoride, potassium dihydrogen phosphate (KDP), and lithium niobate—Harshaw. The last three are anisotropic crystals; thermal expansion was measured both parallel and perpendicular to the c axis.

James Steve Browder

Papers

Thermal expansion data for eight optical materials from 60 K to 300 K