Исследование структурного совершенства монокристаллов ниобата лития разного состава и генезиса методом ИК спектроскопии в области валентных колебаний водородных связей

We have analyzed complex defects due to the presence of hydrogen bonds in the crystal structure in nominally pure lithium niobate crystals with different Li/Nb ratio, in crystals alloyed with magnesium and zinc in a wide concentration range (LiNbO3 : Mg (0.19-5.91 mol.% MgO) and LiNbO3 : Zn (0.04-6.5 mol. % ZnO)) and in the double-alloyed crystals (LiNbO3 : Y(0.24) : Mg(0.63 wt. %) and LiNbO3 : Gd (0.25) : Mg(0.75 wt. %)), obtained by technology of direct melt alloying, and also in the double-alloyed crystal (LiNbO3 : Mg(5. 05 mol.% MgO) : Fe(0.009 mol.% Fe2O3)) grown from a charge synthesized using the technology of homogeneous alloying with magnesium and iron Nb2O5. We revealed the influence of doping impurities on the concentration of OH-groups, the type and localization of complex defects in the crystal structure. The change in the number of hydrogen atom positions in the structure of the LiNbO3 crystal allow us to judge with sufficient accuracy whether the crystal composition is stoichiometric or congruent. For doped crystals of different compositions data were obtained testifying to changes in the character of complexation of OH-groups with point defects of the cationic sublattice with formation of defects: MеLi-OH-, MеLi-MеNb-OН. A change in the mechanism of entry of the dopant cation into the structure dramatically affects the change in the properties of the crystal.The difference in the frequencies (and, correspondingly, in the values of the quasi-elastic constants of the O-H bonds) in the spectrum of a congruent crystal and doped crystals can also be contributed by differences in the electronegativity and ionic radii of the principal and doping cations.

Photoluminescence in near ir-region of lithium niobate crystals of different composition and genesis

The dependence of photoluminescent of lithium niobate crystals of different composition and genesis in the near IR- region on stoichiometry, Zn concentration, doping method was observed. It was found that increasing in stoichiometry leaded to decreasing in the photoluminescence. At Zn = 6.5 mol. % in the LiNbO3 crystal an intense emission was observed at 1.45 eV with simultaneous quenching of the NbLi emission. Homogeneous doping method of LiNbO3:Mg,Zn crystal allowed to enhance the luminescence in the region of 1.3–1.5 eV relative to the crystals obtained by direct doping method of the melt.

Reduction in DC-Drift in LiNbO3-Based Electro-Optical Modulator

This study involves the results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is measured in minutes, and for a long-term drift it is measured in hours and days. DC-drift was measured by applying bias voltage and changing crystal temperature. The obtained results show significant impact on the stability of operating point in EO-modulators after treatment of defective structure of the near-surface layer of a LiNbO3 crystal. Treatment of the disturbed near-surface layer of a LiNbO3 crystal results in the simultaneous reduction in short-term DC-drift and increase in operation stability of electro-optical modulators during long-term measurement of temperature by activation energy calculation.

Optical properties of Er: LiNbO3 ceramics on Yb, Er: LiNbO3 substrate

The present research focuses on the study of the polarization and temperature dependences of the luminescent kinetic spectral properties of Er: LiNbO3 ceramics deposited on Yb,Er: LiNbO3 crystal substrate by laser ablation.

Reduction of DC-drift in LiNbO3-based Electro-optical Modulator

This work involves results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is minutes, and for a long-term drift, hours and days. DC-drift was measured by applying bias voltage and changing crystal temperature. Obtained results shows significant impact on stability of operating point in EO-modulators after treatment of defective structure of the near-surface layer of a LiNbO3 crystal. Treatment of the disturbed near-surface layer of a LiNbO3 crystal results in twice reduction of short-term DC-drift and increase of operation stability of electro-optical modulators during long-term measurement of temperature by activation energy calculation.

Scanning Electron Microscopy Investigation of Surface Acoustic Wave Propagation in a 41° YX-Cut of a LiNbO3 Crystal/Si Layered Structure

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO3 crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration mode, made it possible to visualize the SAW and PSAW in the LiNbO3/Si layered structure. The process of the SAW and PSAW propagation in a LiNbO3/Si layered structure and in a bulk 41° YX-cut of a LiNbO3 crystal were compared. It was demonstrated that the SAW velocities in the layered LiNbO3/Si structure exceed the typical SAW velocities for LiNbO3 and Si single crystals. In the layered structure, the SAW and PSAW velocities were 4062 m/s, 4731 m/s, and 5871 m/s. It was also demonstrated that the PSAW velocities are the same in the LiNbO3/Si layered structure and in the bulk 41° YX-cut of a LiNbO3 crystal.