Lithium Niobate

Lithium niobate (LiNbO3) is a compound of niobium, lithium and oxygen. Its single crystal is an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linear and nonlinear optical applications.

　　Chemical properties: Lithium niobate crystal is abbreviated as LN, belongs to the trigonal crystal system, ilmenite type (distortion perovskite type) structure. Relative density 4.30, lattice constant a=0.5147 nm, c=1.3856 nm, melting point 1240℃, Mohs hardness 5, refractive index n0=2.297, ne=2.208 (λ=600 nm), dielectric constant ε=44, ε =29.5, ε=84, ε=30, primary electro-optical coefficient γ13=γ23=10×10pm/V, γ33=32×10pm/V. Γ22=-γ12=-γ61=6.8×10pm/V, nonlinear coefficient d31=-6.3×1p0 m/V, d22=+3.6×10pm/V, d33=-47×10pm/V. Lithium niobate is a ferroelectric crystal with a Curie point of 1140°C and a spontaneous polarization of 50×10C/cm'. The distorted lithium niobate crystal has multiple properties such as piezoelectric, ferroelectric, optoelectronic, nonlinear optics, pyroelectric and so on. It also has a photorefractive effect.

　　Production method: the pulling method uses lithium carbonate and niobium pentoxide as raw materials to prepare lithium niobate: Put lithium carbonate and niobium pentoxide in a platinum crucible, and grow crystals along the (001) direction. In order to obtain a high-quality colorless and transparent cylinder, when the temperature of the two end faces in the two directions of crystal growth is slightly higher than the Curie temperature, an appropriate electric field is added to form the crystal and then the crystal is cooled to room temperature. Obtain lithium niobate crystals.

　　 Uses: Used in microwave technology for Q-switching, photoelectric modulation, frequency doubling, and optical parametric oscillation; LN crystal doped with a certain amount of iron and other metal impurities can be used as a holographic recording medium material. It is also used in phase modifiers, non-volatile memories, second harmonic generators, phase grating modulators, and large-scale integrated optical systems. It is also widely used in infrared detectors, high frequency and wide band filters, etc.

　　 Related extension: The electro-optic effect refers to the effect that the refractive index of the crystal changes when an electric field is applied to the crystal. Some crystals have inherent electric dipole moments due to spontaneous polarization. When an electric field is applied to this kind of crystals, the external electric field makes the orientation of the inherent dipole moments in the crystal tend to be consistent or a certain dominant orientation. Therefore, the crystal will inevitably be changed. The refractive index of, that is, the external electric field causes the optical power of the crystal to change. In optical communications, electro-optical modulators are made using the principle that an electric field changes the refractive index of a crystal. The electro-optic crystal is located between the polarizer and the analyzer. When no electric field is applied, the polarizer and the analyzer are perpendicular to each other. After the natural light passes through the polarizer, the analyzer blocks and cannot pass. When an electric field is applied, the light rate body changes, and the light can pass through the analyzer. The intensity of the light passing through the analyzer is controlled by the magnitude of the voltage applied to the crystal, so as to achieve the purpose of modulating the intensity of the light by controlling the voltage.