Learn details of Lithium niobate

Lithium niobate (chemical formula: LiNbO3) is a meta-niobate. Its single crystals are optical waveguides, important materials for cell phones, piezoelectric sensors, optical modulators and various other linear and nonlinear optical applications.

Properties of Lithium Niobate

Lithium niobate is a colorless solid that is insoluble in water. It has a tripartite crystal system that lacks inversion symmetry and shows ferroelectricity, bubble kerstral effect, piezoelectric effect and photoelasticity. Lithium niobate has negative uniaxial birefringence, which is slightly dependent on the temperature as well as the stoichiometric ratio of the crystal. It can transmit waves with wavelengths between 350 and 5200 nm.  

Lithium niobate can be doped with magnesium oxide at its optical damage threshold to enhance its resistance to photodamage (often referred to as photoreflective damage). Other available dopants are Fe, Zn, Hf, Cu, Gd, Er, Y, Mn and B.  

Lithium niobate nanoparticles

Nanoparticles of lithium niobate and niobium pentoxide can be prepared at low temperatures. The complete experimental report shows the reduction of NbCl5 by LiH and subsequent in situ spontaneous oxidation to low-valent niobium nanoxides. These niobium oxides are exposed to an air atmosphere to produce pure Nb2O5. finally, the stable Nb2O5 is converted to lithium niobate LiNbO3 nanoparticles in a controlled hydrolysis of excess LiH. Lithium niobate spherical nanoparticles with a diameter of about 10 nm can be prepared by impregnating a porous silica matrix with an aqueous mixture of LiNO3 and NH4NbO(C2O4)2 followed by heating in an IR furnace for 10 min.

Applications of lithium niobate

Lithium niobate is widely used in the telecommunications market, for example in cell phones and optical modulators. It is an optional material for the manufacture of surface acoustic wave devices. For some applications it can be replaced by lithium tantalate, LiTaO3. Other uses are in laser frequency doubling, nonlinear optics, bubble kerlix boxes, optical parametric oscillators, Q-switched lasers, and other acousto-optic effect devices, gigahertz frequency optical switches, etc. It is an excellent material for the fabrication of optical waveguides.  

It is also used in the fabrication of spatial low-pass (anti-aliasing) filters for optics.

Periodically poled lithium niobate (PPLN)

Periodically poled lithium niobate (PPLN) is a lithium niobate crystal designed and manufactured in magnetic domains, mainly for quasi-phase matching in nonlinear optics. The ferroelectric domains point alternately in the +c and -c directions, with periods typically ranging from 5 to 35 µm. The shorter periods in this range are used for second harmonic generation, while the longer periods are used for optical parametric oscillations. Periodic polarization can be achieved by electrodepolarization using electrodes with periodic structures. Controlled heating of the crystal can be used to fine-tune the phase matching in the medium due to the small variations of the dispersion with temperature.  

Periodic polarization uses the nonlinear tensor maximum of lithium niobate, d33= 27 pm/V. Quasi-phase matching gives a maximum efficiency of 2/π (64%) of the full d33, which is about 17 pm/V.  

Other materials used for periodic polarization are wide-bandgap inorganic crystalline KTP (which can produce periodically polarized KTP, i.e., PPKTP), lithium tantalate, and some organic materials.  

Periodic polarization techniques can also be used to form nanostructures on surfaces.  

However, due to its low light reflection destruction threshold, PPLN finds only limited applications at very low power levels. However, MgO-doped lithium niobate is fabricated by the periodic polarization method. Therefore, periodically polarized magnesium oxide-doped lithium niobate (PPMgOLN) extends the application to medium power levels.