Study of thermo-optic and thermo-polarizability coefficients of ions in congruent LiNbO₃ open-type optical waveguide using point dipole approximation

The thermo-optic coefficients (TOCs), thermo-polarization coefficients (TPCs) and dn/dT, dα/dT of congruent lithium niobate LiNbO₃ / LN (mole ratio Li/Nb = 0.946) are tested within the temperature range of 293–773 K at λ = 0.4358 µm, λ = 0.6328 µm and λ = 1.15232 µm employing the point dipole approximation. The refractive indices, n_o and n_e, were first determined at these temperatures and wavelength ranges, by iterating the electronic polarizabilities of Nb⁵⁺ and O²⁺ ions. It has been found that the polarizability of Nb⁵⁺ ions drops and that of O²⁻ ions increases when temperature rises for a particular wavelength. Both Nb⁵⁺ and O²⁻ lose polarizability with increasing wavelength for a given temperature. TOCs for n_o and n_e rise as the temperature rises. The TOC rises as wavelength for n_o and n_e decreases. TPCs of O²⁻ rise in ions and temperature causes Nb⁵⁺ ions to decrease. At a particular temperature, TPCs of O²⁻ions become less while Nb⁵⁺ ions grow as wavelengths rise. Generally, it is used in potential electronic polarizabilities and thermal refraction applications.