F. Abdi

Band structure treatment of the influence of nonstoichiometric defects on optical properties in LiNbO3

We present a band structure approach in connection with a molecular dynamics cluster optimization that accounts for various structural modifications related to the nonstoichiometry of LiNbO3 crystals. Variation of optical properties with the deviation from the stoichiometric composition can be understood within this approach. The particular role of the electron-phonon contributions to the electro-optic coefficient is shown. Model calculations yield a large dependence of the electro-optic coefficient r22 on the crystal composition, in agreement with the experimental data. The observed minimum of the r22 coefficient versus nonstochiometry is explained within a microscopic approach. The r33 tensor component shows substantially different behavior versus the stoichiometry.

ELECTRO-OPTICAL PROPERTIES OF A SINGLE DOMAIN PBTIO3 CRYSTAL

The electro‐optic coefficient rc has been measured at low frequency in a single crystal of PbTiO3. Linear and quadratic polarization optic coefficients are derived from this value of rc and from the electric properties measured on the same crystal. Figures of merit for modulator application and the thermo‐optic coefficient are determined in PbTiO3 and are compared with those in other electro‐optic materials. Results show that PbTiO3 can be interesting for electro‐optic applications.

DiP223: Strongly temperature dependent electro-optic coefficients in BaTiO3

Abstract By means of a Senarmont set up and a very sensitive method, electrooptic coefficients in BaTiO3 are accurately determined from the phase measurement of the retardation Γ due to the electric field induced birefringence of the crystal. Electro-optic properties are investigated as a function of temperature around room temperature. A very large value of the coefficient r42 is found, in agreement with previous investigations. In addition, this coefficient is shown to be very sensitive to the temperature even for a very small change. The importance of both the thermo-optic effect and the thermal variation of electro-optic properties is pointed out for device applications of BaTiO3.

Accurate measurements of the electro-optic coefficients and birefringence changes using an external modulation signal

We propose a new method to measure within a high accuracy both the electro-optic properties and the birefringence changes in bulk crystals. This technique is based upon the frequency doubling electro-optic modulation (FDEOM) method in which an external modulator is inserted in the experimental Senarmont setup. We present a complete analysis of the optical response of a Senarmont setup within Jones formulation. The FDEOM method possesses as main advantages a high accuracy and sensitivity in the measurements due to a direct determination of the electric field-induced phase retardation in the crystal under study. The measurements are recorded with an adjustment of the shape of the output beam at a frequency double the frequency of the ac applied voltage. The external modulation version of this method allows us to perform measurements with a higher modulation depth and to avoid any additional dynamical perturbation in the electro-optic crystal under study. Therefore, even small values of the electro-optic coe...

Accurate Measurement Of The Electro-Optic Coefficients : Application To LiNbO 3

A technique issued from the Senarmont method is developped in order to determine the electro-optic (E/0) coefficients of solid compounds. The transfer function of the transmitted beam is given by : I/Io=(1/2)[1±sin(Γ-2B], where Γ is the phase shift induced by the natural birefringence and the applied (AC +DC) electric field in the sample I and Io are, respectively, the output and input beam intensities, while B represents the analyser azimuthal angle. We show the various methods derived from the Senarmont arrangement which can be used to determine the E/0 coefficients. The method which provides both good accuracy and correctness is based on a direct determination of the phase shift when the DC and AC fundamental components of I are equal to zero and the frequency of the demodulated output transmitted beam is double of the AC frequency. The measurements take into account of the optical absorption of the set-up and the temperature dependence of the natural birefringence. This method is applied to the determination of the rc coefficient in LiNbO3 around room temperature.

Electro-optic measurements in PbTiO3 single crystals

Abstract Electro-optic properties are investigated in tetragonal PbTiO3 single crystals at room temperature with a technique based upon the Senarmont method. The linear and quadratic electro-optic coefficients are determined from the measurements of the birefringence as function of applied DC electric field. The values of the linear rc and quadratic Rc electro-optic coefficients are given for a wavelength λ = 633 nm. Further, a large memory effect is detected when the electric field is switched off.

Influence of the non-stoichiometry on the electro-optic properties in pure LiNbO3

Abstract We report, for the first time a complete set of electro-optic measurements of the rc and r22 coefficients and of their corresponding dielectric permittivities in pure LN as function of the concentration of intrinsic defects related to the deviation from the stoichiometry. Non monotonous dependences of EO coefficient rc and r22 are found to be closely linked to similar dependences of their corresponding dielectric permittivities. This behaviour can be attributed to the partial occupation by Nb ions of Li sites. The role of intrinsic defects are discussed to explain these behaviours. Particularly, the electromechanical contributions are considered

Study of contributions to temperature dependence of the phase shift in an electro-optic crystal

The spontaneous and electric field induced phase retardations have been measured as a function of temperature in a KDP crystal using an accurate method. The plots of these retardations versus temperature reveal unexpected undulations. We consider the various contributions which could be involved in these dependences, such as the thermo-optic effect, crystal dilatation and temperature dependence of the electro-optic coefficient. By means of calculations, the undulations are shown to be caused by an interference phenomenon related to light reflections on the surface of the crystal.