Properties Of Lithium Niobate Crystals Research Articles

New insights into refractive indices and birefringence of undoped and MgO-doped lithium niobate crystals at high temperatures

The lithium niobate single crystal is a well-known optical material that has been employed in a wide range of photonic applications. To realize further applications of the crystal, the birefringence properties need to be determined over a large range of temperatures. We report refractive indices and birefringence properties of undoped and MgO-doped lithium niobate crystals with high accuracy using spectroscopic ellipsometry in the spectral range from 450 to 1700 nm and a temperature range from ambient temperature to 1000 °C. The birefringence results indicate a transition temperature, where the crystal transforms from an anisotropic to isotropic property, and the advance of MgO doping in the crystal, which is related to the optical damage threshold of the materials. In addition, the lattice dynamics of the crystals have been analyzed by revisiting the Raman spectroscopy. The results establish the foundation of optical properties of lithium niobate crystals, providing pathways for their photonic applications.

Research progress in lithium niobate on insulator lasers

<p indent="0mm">Lithium niobate on insulator (LNOI) is considered one of the most competitive integrated photonics platforms due to the excellent optical properties of lithium niobate crystal and their compatibility with semiconductor micro/nano processing. Based on the continuous improvement of micro-nano fabrication technology, various transmission and control devices, such as low-loss waveguides and high-quality factor micro-cavities, showing better performance than traditional bulk materials devices, have been realized on LNOI. However, as an essential part of integrated photonics, the research of LNOI laser has made a breakthrough recently. Lithium niobate is an indirect bandgap material and thus tough for electroluminescence. It is a feasible and straightforward scheme to realize optically pumped laser based on rare-earth ion doping. This paper summarizes our research group’s recent research progress on realizing microdisk, microring, and single-mode lasers based on rare-earth-ion-doped LNOI and related works from other groups. We hope this review could benefit the related research on the active devices on LNOI.

Nonlinear optical properties of lithium niobate crystals doped with alkaline earth and rare earth elements

Nonlinear optical properties of lithium niobate crystals doped with alkaline-earth (Zn2+) and rare-earth (Er3+) elements were quantitatively studied from the chemical bond viewpoint of crystal. The different influences of Zn and Er dopants on the dielectric response of LiNbO3 were compared. The value of nonlinear optical second-harmonic generation coefficients was determined mainly by the Li–O bonds both in LiNbO3:Zn and LiNbO3:Er crystals. We observed sharp changes in the second order nonlinear optical response of Zn-doped LiNbO3 single crystals at 1064 nm with increasing Zn concentration in the crystal. The calculated values of the nonlinear optical coefficients for the LiNbO3:Zn crystals exceed those for the LiNbO3:Er crystals. The LiNbO3:Zn crystal with dopant concentration 5.48 mol.% is the most suitable crystal for the second-harmonic conversion.

Anisotropy of elastic and photoelastic properties of lithium niobate crystals

The elastic and photoelastic constants of lithium niobate crystals and the attenuation coefficients of acoustic waves at room temperature have been determined by the Bragg diffraction of light by sound. The components of the photoelasticity tensor were determined by the modified Dixon method. The obtained values of the constants were used to determine the anisotropy of the effective elastic and photoelastic constants with a change in the direction of propagation of acoustic waves in the (100) symmetry plane, for different directions of the wave vector and polarization of light relative to the sound wave vector. It is shown that, for certain geometries of the Bragg light diffraction, there is a correlation between the orientation dependences of the effective elastic and photoelastic constants in the investigated plane. The results of the study can be used to analyze the anisotropy of the photoelastic properties of lithium niobate crystals and determine the diffraction geometry with the highest efficiency of Bragg light diffraction.

Estimating the Degree of Unipolarity of LiNbO3 Crystals Using Static and Dynamic Piezoelectric Measurements

In this paper, we describe improved methods for assessing the static and dynamic piezoelectric properties of lithium niobate crystals. The results can be used for evaluating results of conversion of large lithium niobate crystals to a single-domain state under mass production conditions. We present main calculated relationships for assessing the degree of unipolarity and the relative volume of antiparallel domains in large lithium niobate crystals. The described techniques are applicable to other piezoelectric materials as well.

Effects of strain on electronic and optical properties of LiNbO3: a first principles study

The exchange-correlation functions of local density approximation and generalized gradient approximation using density functional theory were performed to calculate electronic and optical properties of lithium niobate crystal. To correct the underestimated value of band gap, a reverse scissor correction procedure was performed based on the experimental refractive index value because it is more suitable for compound with polar crystal. It is found that underestimated electronic band gap ∼4.76 eV was generated due to nature of generalized gradient approximation (GGA) exchange correlation. Based on density of states calculation, Li ion tends to diffuse into substrate as it possesses pure ionic character. Thus, the chemical bonding in LiNbO3 crystal has a mixed covalent-ionic character. The effect of strain on a-axis of the crystal and thus, its electronic and optical properties were investigated. The a-axis of the crystal is more sensitive towards the strain compared to c-axis as the band gap largely changes upon the applied strain. The optical properties such as dielectric function, refractive index, extinction coefficient, and absorption were calculated and explained in detail. The positive and negative strains do shift the optical spectrum either to higher or lower frequency depending on specific properties. These results would assist to provide the fundamental explanation about the effect of strain on the properties of lithium niobate crystal.

Structural, electronic and optical properties of LiNbO3 using GGA-PBE and TB-mBJ functionals: A DFT study

In the present work, first-principles calculations were performed to obtain the structural, electronic and optical properties of lithium niobate crystal using two exchange-correlation functionals (GGA-PBE and TB-mBJ). The calculated structural parameters were very close to the experimental values. TB-mBJ functional was found to be good when compared to LDA and GGA functionals in case of bandgap energy of 3.715 eV of lithium niobate. It was observed that the upper valence and lower conduction bands consist mainly the O-2p and Nb-4[Formula: see text] states, respectively. Furthermore, calculations for real and imaginary parts of frequency-dependent dielectric function [Formula: see text] of lithium niobate crystal were performed using TD-DFT method. The ordinary refractive index n[Formula: see text], extraordinary refractive index n[Formula: see text], its birefringence and absorption peaks in imaginary dielectric function [Formula: see text] were also calculated.

Selective Photorefractive Light Scattering in Rh-Doped LiNbO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; Crystals

The photorefractive properties of lithium niobate crystals depend strongly on the kind of doping admixture. Study of LiNbO3 crystals with various doping admixtures using photorefractive light scattering allows insight into the processes taking place in the crystals. This paper presents new experimental results of non-selective and selective photorefractive light scattering investigations into rhodium-doped lithium niobate crystals and proposes a model to explain the experimental data.

Electrical and electromechanical properties of stoichiometric lithium niobate at high-temperatures

Electrical and electromechanical properties of lithium niobate crystals with various compositions from congruent to stoichiometric are analyzed in the temperature range from 500°C to 900°C and in the oxygen partial pressure range from 10−14bar to 0.2bar. The total conductivity is found to decrease with increasing lithium concentration while the activation energy of the conductivity increases. The oxygen partial pressure dependence results in a slope of −0.22 in the plot log(σ) vs. log(pO2). Ionic and electronic conductivity and the lithium diffusion coefficient are determined using this data. The piezoelectric properties of lithium niobate allow the excitation of thickness and shear vibration modes depending on the crystal orientation at temperatures up to 900°C. For both modes the temperature dependence is observed and the inverse Qf product determined, which represents the loss.

Anomalies in the pyroelectric properties of LiNbO3 crystals of the congruent composition

A number of anomalies are revealed in the temperature dependence of the primary pyroelectric coefficient for single-domain crystals of lithium niobate LiNbO3 in the temperature range 310–330 K. It is shown that these anomalies are associated with the transformation of the domain structure of the lithium niobate crystals. The problem regarding the correct performance of the pyroelectric measurements and the possible influence of the observed effects on the optical properties of lithium niobate crystals and on the recording of optical phase holograms are discussed.

Photonic applications of lithium niobate crystals

In this paper the most important properties of lithium niobate crystals for photonic applications are reviewed. We will summarize how acting on the stoichiometry, sample structure, doping and domain structure of the crystals, these properties are governed, and can be taylored for each specific application. Finally we present a review of photonic applications in a wide spectrum of fields as lasers and non-linear optics, optical communications, optical memories, and diffractive optics. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Review Article: Photonic applications of lithium niobate crystals

In the Review Article [1], a comprehensive overview on the most important properties of lithium niobate crystals as well as photonic applications of this material for lasers and non-linear optics, optical communications, optical memories, and diffractive optics is given. The cover picture illustrates the scheme of two wave mixing for holographic recording, one of the most promising applications of LiNbO3. The review is based on an invited presentation at the E-MRS 2003 Fall Meeting, Symposium A: Novel Wide Bandgap Materials for Optoelectronic and Electronic Applications, held in Warsaw, Poland, 15–19 September 2003. The full Proceedings of the E-MRS 2003 Fall Meeting, Symposia A and C, are published in physica status solidi (c) – conferences and critical reviews1, No. 2 (February 2004) (ISBN 3-527-40504-6).

Photorefractive properties of lithium niobate crystals doped with manganese

The photorefractive properties of lithium niobate crystals doped with manganese (Mn) have been investigated. It is found that the effect of dark decay due to electron tunneling, which is the limiting factor of the highest practical doping level, is less in LiNbO_3:Mn than in LiNbO_3:Fe , and higher doping levels can be used in LiNbO_3:Mn to achieve larger dynamic range and sensitivity for holographic applications. The highest practical doping level in LiNbO_3:Mn has been found to be ~0.5 wt.% MnCO_3, and refractive-index changes and sensitivities up to 1.5X10^-3 and 1.3 cm/J are measured for extraordinarily polarized light of the wavelength 458 nm. It has been found that, in terms of both dynamic range (or refractive-index change) and sensitivity, the optimal oxidation state is highly oxidized. The distribution coefficient of Mn has been determined to be ~1. Absorption measurements are used to obtain more information about charge-transport parameters. The material is excellently suited for holographic recording with blue light. The hologram quality is outstanding because holographic scattering is much weaker compared with that in, e.g., iron-doped lithium niobate. Thermal fixing has been successfully demonstrated in LiNbO_3:Mn crystals.

Crystallographic modifications of physical properties of lithium niobate crystals by the cation location

On the basis of crystallographic data of various pure and doped lithium niobate crystals, Pauling's rules, the bond valence sum model and the chemical bond method are employed to understand crystallographic modifications of physical properties of lithium niobate crystals. The physical properties such as dielectric responses (including the principal refractive indices and second-order nonlinear optical coefficients), the spontaneous polarization and the spontaneous strain are quantitatively or qualitatively studied. The present work shows that the vacant site in the lithium niobate crystallographic frame constructs a useful buffer for Li + and Nb 5+ cations to balance their strong interaction, which is not energetically available for any cation; the Nb 5+-site can give a strong effect on the mechanical properties of crystals, which is tremendously important for the crystal growth; the Li +-site is closely correlated to the dielectric properties of crystals, which is an active and sensitive lattice site available for various dopants with the valence ranging from +1 to +5.

Influence of zinc doping on the photorefractive properties of lithium niobate

The photorefractive properties of lithium niobate crystals containing zinc dopants as well as iron ions are studied to obtain quantitative information on the influence of Zn. Elementary holographic gratings are recorded and erased using light intensities from 10 2 to about 10 11 W/m 2 . The experiments indicate that nonlinear contributions to the bulk photovoltaic effect and to the photoconductivity as well as light-induced absorption changes at high intensities can be diminished by Zn doping. Additionally, Zn dopants considerably increase the photoconductivity and thus reduce light-induced refractive index changes. Results are discussed using a two-center charge transport model recently proposed to describe the photorefractive properties of LiNbO 3 :Fe at high light intensities.