Longitudinal Electro-optic Effect Research Articles

Examining the change of half-period voltage in longitudinal electro-optic modulation and residual stress of potassium dihydrogen phosphate crystal.

In this paper, the voltage-transmittance curvesKDP crystals were measured accurately between two crossed or parallel polarizers using longitudinal electro-optic effect. The end faces of rectangular KDP samples were coated with ring-shaped electrodes using conductive silver paint (CSP). The change of half period voltage U i has been investigated. A method for quantitative characterization of residual stress has been proposed, based on deviation voltage U d. The results demonstrate that loading voltage is close to the integration of electric field intensity in crystal along the optical path when the CSP ring electrodes have a large outer radius R, small inner radius r, and long-distance d. The half-period voltage U i is also close to longitudinal half-wave voltage U π in these circumstances. The unclamped electro-optic coefficient γ63σ of KDP crystal at room temperature was measured as 10.24±0.05p m/V at the wavelength of 632.8nm.

Development and Pilot Operation of a Three-Phase Fully Optical Measuring Voltage Transformer of 220 kV with Digital Output

An electronic three-phase fully fiber-optic measuring voltage transformer (FOVT) of accuracy class 0.2 for a nominal voltage of 220 kV with a digital output for operation at power system facilities, including electrical substations, is described. The operation principle of the device is based on the use of a longitudinal linear electro-optical effect (Pockels effect) for measuring AC voltage. The fiber-optic measurement scheme based on low-coherent interferometry is connected via a fiber cable to an optical high-voltage primary converter (HVPC) with an electro-optical crystal placed in it; there are no additional voltage dividers inside. The digital signal processing unit (DPU) contains optical and electronic circuits for generating, detecting, and processing an electro-optical signal. FOVT has a digital interface that complies with the IEC 61950-9-2 LE standard, and can be used as a component for the Digital Substation and Smart Power Grid technologies. The design features of the HVPC and the DPU are described and the results of the metrological characteristics of FOVT-220, based on the data obtained during the certification and pilot operation at the 220 kV electrical substation, are presented.

Mechanism of Optical Charge Exchange of Magnetic Centers in BSO : Fe

High-resistance photosensitive crystals of Bi12SiO20 (BSO) doped with iron ions were studied. X-ray diffraction analysis reveals the compression of a unit cell in a BSO : Fe crystal with increasing impurity concentration. Electron paramagnetic resonance demonstrates a decrease in the intensity of the EPR signal when the BSO: Fe crystal is exposed to light that generates photocarriers. It is found that the characteristic time of the EPR signal decrease is close to the value of the Maxwellian relaxation time measured with the help of the longitudinal electrooptical effect. A physical model of the mechanism of optical charge exchange of magnetic iron centers is discussed, based on the statement that the nature of the crystal bonds of the iron ion with ligands without structural modification of the crystal lattice changes during the photogeneration of carriers. A physical model is proposed, according to which a trivalent Fe3+ ion transforms into a divalent state of Fe2+ with a change in the total spin from 5/2 to 2. The compression of the unit cell with increasing iron ion concentration in the framework of the model under discussion is due to the transformation of atomic orbitals upon replacement of silicon ions by iron ions. The transformation process affects the cells unoccupied by iron, which is proved by the absence of a bifurcation of X-ray reflections and indicates the long-range nature of the intracrystalline interactions in sillenites.

Механизм оптической перезарядки магнитных центров в BSO:Fe

AbstractHigh-resistance photosensitive crystals of Bi_12SiO_20 (BSO) doped with iron ions were studied. X-ray diffraction analysis reveals the compression of a unit cell in a BSO : Fe crystal with increasing impurity concentration. Electron paramagnetic resonance demonstrates a decrease in the intensity of the EPR signal when the BSO: Fe crystal is exposed to light that generates photocarriers. It is found that the characteristic time of the EPR signal decrease is close to the value of the Maxwellian relaxation time measured with the help of the longitudinal electrooptical effect. A physical model of the mechanism of optical charge exchange of magnetic iron centers is discussed, based on the statement that the nature of the crystal bonds of the iron ion with ligands without structural modification of the crystal lattice changes during the photogeneration of carriers. A physical model is proposed, according to which a trivalent Fe^3+ ion transforms into a divalent state of Fe^2+ with a change in the total spin from 5/2 to 2. The compression of the unit cell with increasing iron ion concentration in the framework of the model under discussion is due to the transformation of atomic orbitals upon replacement of silicon ions by iron ions. The transformation process affects the cells unoccupied by iron, which is proved by the absence of a bifurcation of X-ray reflections and indicates the long-range nature of the intracrystalline interactions in sillenites.

Langasites as electro-optic materials for high-voltage optical sensors

Electro-optic properties and linear birefringence of langasite (LGS), langataite (LGT), and catangasite (CTGS) single crystals are measured in the temperature range of 115 ~310 K, along with room-temperature refractive indices of CTGS at 1540 nm. Lanthanum-containing LGS and LGT have 5 times larger unclamped electro-optic constant r11 and 1 ~2 orders of magnitude less thermal coefficient for longitudinal half-wave voltage than rare-earth free CTGS. Temperature dependence of natural birefringence in LGS is non-monotonic with a maximum at 158 K and a temperature derivative of birefringence within ± 3.3 × 10−8 K−1 in the range of 115 ~172 K. Rare-earth containing langasites like LGS can be considered as promising electro-optic materials for AC high-voltage optical sensors because of the existence of a longitudinal electro-optic effect with weak temperature dependence.

Influence of Misfit Strain on Longitudinal Electro-optic Properties in Preferentially Oriented (Pb,La)(Zr,Ti)O3 Films

We successfully fabricated single-crystal-like (Pb,La)(Zr,Ti)O3 (PLZT) films with preferred (100), (110), and (111) orientations on Al-doped ZnO (AZO) coated on (100), (110), and (111) SrTiO3 (ST) substrates. The longitudinal electro-optic (LEO) effect according to crystal orientation was investigated to find the birefringence origin of the LEO effect in oriented PLZT films. The PLZT films with (100) and (111) orientations exhibit promising LEO properties, while in the case of (110)-oriented PLZT films, the LEO effect is very small. From the strain-induced EO effect, this difference in LEO properties in these three kinds of preferentially oriented PLZT films may be attributed to changes in the strain effect from in the PLZT/AZO interfaces. Consequently, we believed that a misfit strain in interfaces between EO films and transparent conductive oxide films is a birefringence origin in oriented films, and control of the misfit strain is a key factor for improving the LEO effect.

Longitudinal electro-optic effect of highly (100) oriented (Pb,La)(Zr,Ti)O<sub>3</sub> film grown on a transparent Al-doped ZnO electrode

Longitudinal electro-optic effect of highly (100) oriented (Pb,La)(Zr,Ti)O<sub>3</sub> film grown on a transparent Al-doped ZnO electrode

Bragg diffraction of light by a hypersound in gyrotropic cubic crystals

Noncollinear acousto-optical interaction of light beams in acoustically gyrotropic cubic crystals is considered. The dependences of the diffraction efficiency of the parameters of the optical and acoustical gyrotropy have been established. The attainability of the optimal efficiency of diffraction by shear ultrasonic waves due to the anisotropy electrically induced by the external field under conditions of longitudinal electro-optical effect is shown.

Measuring the parameters of photorefractive crystals by an electrooptical compensation method

A new compensation method, based on the longitudinal electrooptical effect in a modified Pockels cell accommodating two crystal plates instead of a single plate, is proposed for measuring the parameters of photorefractive crystals. The plates are oriented so that their surfaces are perpendicular to the optical axis and the long semiaxes of the electric-field-induced birefringence ellipsoids are rotated 90° relative to one another around this axis. The proposed method was used to measure the Maxwell relaxation time in the Bi12SiO20:Al crystal (0.2% Al) as a function of the photoexcitation intensity Iex in the green-blue spectral region (λ=5145 A). For Iex=10 mW/cm2, the Maxwell relaxation time decreases by 6±1 s as compared to the dark value (80±10 s).

Electro-optic potassium-tantalate-niobate films prepared by pulsed laser deposition from segmented pellets

Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser deposition and investigated with a number of analytical techniques, including electrical and electro-optical measurements. For applications in longitudinal electro-optic modulators, a transparent electrode is required between substrate and electro-optic layers. Suitable electrode materials, which at the same time permit epitaxial growth of KTN, were identified and prepared. The resulting layered samples were not only of good epitaxial and optical quality, but also exhibited the expected maximum of the longitudinal electro-optic effect at temperatures between the phase transitions from cubic to tetragonal and from tetragonal to orthorhombic. However, the maximum achievable electro-optic phase shift was found to be limited to roughly τ/100 for KTN films in the thickness range around 1 μm. Therefore, much thicker films are probably necessary for most practical applications, which requires significant improvements in the long-term stability and homogeneity of the deposition process.

Electro-optic and electrostrictive properties of the low-temperature phase of barium borate BaB2O4 *

All components of the linear electro-optic tensor [r σ ijk] (unclamped) of low-temperature BaB2O4 and the liner electrostrictive tensor [d ijk] were determined (T= 293 K; λ= 633 nm). In its electro-optic and electrostrictive behaviour low-temperature BaB2O4 resembles the tetraborates Li2B4O7 and PbB4O7. The maximum value of the longitudinal and transversal electro-optic effects is only one fourth of that in KDP. This reduces the importance of BaB2O4 for electro-optic applications.

Longitudinal Electrooptic Effects and Photosensitivities of Lead Zirconate Titanate Thin Films

The feasibility of storing and reading high‐density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure the longitudinal electrooptic effects and the photosensitivities of the films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a longitudinal linear electrooptic rc coefficient, and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and rc coefficients are about an order of magnitude less than the transverse R and rc coefficients of bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence of the films after poling (>10−2) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used in this paper for evaluating the photosensitivities of thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (as in bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be significantly higher than those of bulk ceramics of similar compositions. The high photosensitivities coupled with the substantial longitudinal electrooptic coefficients combine to establish the feasibility of using PZT or PLZT thin films for optical information storage applications.

Picosecond electro-optic sampling of electron-hole vertical transport in surface space charge fields

The longitudinal electro-optic effect in GaAs(100) is used to measure the dynamics of electron-hole pair separation in surface space charge fields present at GaAs/oxide interfaces. At low photocarrier injection, the rise time in the E field transient is a direct measurement of the charge transport across the space charge field which is found to be faster than 500 fs. The results demonstrate that the charge carriers are energetically unthermalized at the surface prior to the surface chemistry. This method is also found to be sensitive to 10 −5 of a monolayer of charged surface states.

Linear longitudinal electro-optic effect in oxygen octahedra ferroelectrics

Abstract Electro-optic half-wave voltages have been calculated for a longitudinal geometry in crystals of point group symmetry mm2 (orthorhombic) and 4mm (tetragonal). The solution for an arbitrary direction of light propagation and parallel electric field is given. The predicted minimal longitudinal half-wave voltages range from 194 V in KNbO3, 100 V in Sr0.75Ba0.25Nb2O6 and 40 V in BaTiO3 to 9 V in KTal-x Nb x O3. The angular, wavelength and temperature dependences of the half-wave voltage have been determined. In KNbO3 measurements of the minimal longitudinal half-wave voltage at room temperature reach (195 ± 8) V and (118 ± 7) V with red (Λ = 633 nm) and blue light (Λ = 458 nm) respectively. At–40°C, close to the orthorhombic-rhombohedral phase transition, the half-wave voltage for red light reduces to (135 ± 6) V. From the measurements we determine a negative sign of the electro-optic coefficient r 42 = – 380 pm/V. The possibility of spatial light modulation by the longitudinal electro-optic effect is discussed.

Electrooptical and electrostrictive PLZT ceramics light modulators for infrared

Abstract The studies of modulators for infrared made of transparent PLZT ceramics are reported. Two types of light modulators are discussed: 1) using the transversal electrooptic effect and 2) using the longitudinal electrooptic (EO) effect and electrostriction. The latter has been made as an electric field controllable Fabry-Perot interferometer. The characteristics of the modulators are provided.

Growth of ferroelectric tungsten bronze crystals and thin films

Abstract In this paper, we review the state-of-art for the growth of ferroelectric tungsten bronze single crystals in optical quality and large size. The Czochralski technique has been optimized for various bronze solid solution crystals such as Sr1−xBaxNb2O6 (SBN), Ba2−xSrxK1−yNayNb5O15 (BSKNN) and Sr2−xCaxNaNb5O15 (SCNN) with properties specifically tailored for electro-optic, pyroelectnc and more recently for photorefractive applications. SBN solid solution crystals are found to be easiest to grow in series up to 1′′ in diameter with excellent transverse electro-optic effects; whereas BSKNN crystals, which exhibit excellent longitudinal electro-optic effects are more difficult to grow in large sizes and optical quality. BSKNN crystals exhibit ferroelectric and optical properties similar to perovskite BaTiO3 and are found to be particularly useful for photorefractive applications. The SCNN solid solution crystals are orthorhombic at room temperature and are much more difficult to grow; currently, crysta...

Experiments on electro-optic effects with a ceramic dielectric

An experimental investigation of the Kerr effect is described which uses the optical ceramic PLZT, instead of the poisonous nitrobenzene, as a birefringent medium. Both the transverse and the longitudinal electro-optic effect can be demonstrated. A wide range of further quantitative measurements may be performed using the optical ceramic. As examples we describe how temperature-dependent properties and hysteresis characteristics of the material can be examined, and demonstrate technical applications such as in welding goggles or for the intensity modulation of a light beam.

Experiments on electro-optic effects with a ceramic dielectric

An experimental investigation of the Kerr effect is described which uses the optical ceramic PLZT, instead of the poisonous nitrobenzene, as a birefringent medium. Both the transverse and the longitudinal electro-optic effect can be demonstrated. A wide range of further quantitative measurements may be performed using the optical ceramic. As examples the authors describe how temperature-dependent properties and hysteresis characteristics of the material can be examined, the demonstrate technical applications such as in welding goggles or for the intensity modulation of a light beam.

Optical parallel logic gate using spatial light modulators with the Pockels effect

This paper describes a new optical gate for logical processing in parallel. The gate consists of two spatial light modulators which spatially modulate a lightwave by the longitudinal electrooptic or Pockels effect. The gate can perform in parallel all sixteen logic functions of two binary variables in both the bright-true logic and the dark-true logic. The gate has the capability of operating on large arrays of binary variables.

Preparation and properties of thin ferroelectric films of PLZT

PLZT films are prepared by r f diode sputtering from a target, eight inches in diameter, manufactured by hot pressing of ceramic powder. The parameters of this process, e.g. gas pressure, substrate bias, power and excess PbO built into the target, have a great influence on the stoichiometry of the films. Substrate temperatures above 500°C during the process are necessary to obtain perovskite ferroelectric films in situ. A thermal annealing destroys the surface of the films and they can no longer be used for optical application. The ferroelectric behaviour is examined by dielectric measurements versus temperature and frequency and by studies of hysteresis loops respectively. The results are compared with the values of ceramics. The longitudinal electro-optic effect of the films is measured in transmission.