Spatial anisotropy of linear electro-optic effect in crystal materials: II. Indicative surfaces as efficient tool for electro-optic coupling optimization in LiNbO3

The electro-optic (EO) properties of pure and MgO-doped LiNbO₃ crystals are characterized by indicative surfaces (IS) describing the spatial anisotropy of the longitudinal and transverse linear EO effects. By analyzing the IS and their stereographic projections, we have determined the geometries with maximum EO coupling. The maximum magnitudes of the linear EO effect are revealed in the longitudinal and transverse geometries along the directions that substantially deviate from the principal crystallographic axes of both crystals. Spatial analysis of the IS thus yields a set of the optimized sample geometries recommended for designers who develop EO modulators or deflectors. Just by switching from the standard cell geometry to the optimized cell geometry, as determined in the present work, one may improve almost three times the modulation efficiency of EO devices based on lithium niobate crystals. This results in a corresponding reduction of their driving voltages being evidently of great practical importance for many applications.     

Anisotropy of the electro-optic effect in magnesium-doped LiNbO3 crystals

Specific features of constructing indicatory surfaces of the electro-optic effect (EOE) are described. The generalized case for the symmetry class 3m and all three possible indicatory surfaces under orthogonal experimental conditions, when the directions of light propagation and electric field are orthogonal, is considered. The EOE surfaces are constructed for magnesium-doped lithium niobate crystals. The specific features of anisotropy of these surfaces are discussed and their extreme values and corresponding angular coordinates are found. To construct the indicatory surfaces, all absolute coefficients of the linear electro-optic effect are determined by the interferometric method. The difference in the electro-optic coefficients of pure and magnesiumdoped crystals does not exceed 10%. An advantage of doped crystals is their high durability to high-power laser radiation.

     

Spatial anisotropy of linear electro-optic effect in crystal materials: I—Experimental determination of electro-optic tensor in LiNbO3 by means of interferometric technique

The paper presents a technique suitable for the determination of linear electro-optic effect (LEOE) tensor components in crystal materials of any symmetry. The method is based on the Michelson interferometer, where the sample being studied is set into one of its arms to measure the electro-induced changes of the optical path. We describe in detail the sample geometries that are needed to determine a complete set of the LEOE tensor components and derive the corresponding equations. The experimental technique has been tested and verified on lithium niobate crystals as well as applied to MgO-doped LiNbO₃ crystals to study their electro-optic properties. The developed method can be useful for optical engineering, which deals with new materials being used in design or production of devices, such as, e.g., modulators or deflectors.     

Relaxation of static photoelasticity in triglycine fluoroberyllate crystals

The relaxation of the static photoelasticity in triglycine fluoroberyllate crystals has been studied. The anisotropy of the relaxation amplitudes and their anomalies near the phase transition have been revealed. The photoelastic relaxations and peculiarities of their temperature behavior have been explained in terms of the piezocaloric mechanism.     

Effect of heat treatment of the D16 alloy on its mechanical properties at low stresses

The elastic hysteresis and residual deflection of the aluminum D16 alloy samples corresponding to the model of a circular plate clamped along its perimeter have been studied at low (the beginning of the Hooke region) mechanical stresses. It has been shown that these characteristics depend substantially (change several times) on the sample state provided by different heat treatment conditions. The non-destructive method used in this work has a high accuracy and can be used to estimate the strength, yield stress, and fatigue life of metals.