Linear Electro-optic Coefficients Research Articles

Electro-optic coefficients of ferroelectric PMACB and PMABB crystals

Temperature dependences of linear electro-optic coefficients in two isomorphous ferroelectric crystals (CH3NH3)Bi2Cl11 (PMACB) and (CH3NH3)5Bi2Br11 (PMABB) have been measured around temperatures of their ferroelectric-paraelectric phase transitions. The employed external reference measuring method (Mach-Zehnder interferometer) allowed for determination of values of all main free Pockels coefficients at room temperature.

Temperature dependence of photorefractive properties of Cr-doped potassium sodium strontium barium niobate

Photorefractive two-beam coupling gain and speed of Cr-doped potassium sodium strontium barium niobate are measured as a function of crystal temperature. It is found that the saturated coupling gain coefficient has strong temperature dependence near the ferroelectric phase transition. It is also found that the photoconductivity-dominant build-up time for the space-charge field exhibits temperature dependence. These behaviors are found quite different from the dark-conductivity dominant case and can be explained in terms of power-law dependence of a dielectric constant and a linear electrooptic coefficient on the crystal temperature.

Measurement of the linear electro-optic coefficient in poled amorphous silica

We report measurements of the linear electro-optic coefficients of temperature- and/or static-electric-field-poled bulk fused silica. The values for r31 and r33 are 0.1 ± 0.03 and 0.3 ± 0.1 pm/V, respectively, in agreement with extrapolations from measured second-harmonic generation coefficients. Measurements were performed by use of a Mach–Zehnder interferometer with LiNbO3 as a reference material.

Identification and quantitative characterization of antiparallel domains using an interferometric method

We present a method to identify antiparallel domains through the use of an optical interferometric technique. In contrast to etching techniques, this method is nondestructive and provides a quantitative measure of the linear electro-optic coefficient. Comparisons with the etching technique show that the two methods are in good agreement. This interferometric technique can be generalized to identify other types of domain structures as well.

High-performance Mach-Zehnder modulators in multiple quantum well GaAs/AlGaAs

We demonstrate Mach-Zehnder interferometric waveguide intensity modulators which employ electrorefraction due to the quantum-confined Stark effect in multiple quantum well (MQW) GaAs/AlGaAs. These devices exhibit average half-wave voltage-length products as low as 3.0 V/spl middot/mm and extinction ratios greater than 23.8 dB, which are superior to any MQW devices of this type. An effective index based model is developed to extract linear and quadratic electro-optic coefficients from the modulation data. Also, the power handling limitations of MQW modulators are discussed in terms of device performance and catastrophic electrical failure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermally stable poled polymers: Highly efficient heteroaromatic chromophores in high temperature polymides

In this paper, we report our recent developments in achieving thermally stable polyimides that possess large second order nonlinear optical activity. We have developed several classes of novel chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. Through these developments, we have synthesized chromophores that possess nonresonant βμ values as high as 9100 × 10-48 esu measured at 1.9 µm. These chromophores also possess improved thermal and chemical stabilities. The incorporation of these chromophores in high temperature polyimides produces E-0 materials with high linear electro-optic coefficients (in excess of 15 μm/V at 1.3 μm) and long-term temporal stability at an elevated temperature of 150°C for more than 750 h.

Calculation of phase-matching electro-optical modulation of SHG in KTP

The electric field required to modulate type II SHG efficiency in KTP using the linear electro-optical effect is calculated. It is found that 16 kV/cm for the conversion 1.064 μm→0.532 μm and 31.5 kV/cm for the conversion 1.32 μm→0.66 μm, applied along the binary axis, allow a phase-mismatch equal to π for a crystal length of 1 cm along the phase-matching direction. From the general point of view, the required electric field is expressed as function of the angular acceptance and of the electro-optical dispersion of the phase-matching direction. This treatment allows a well understanding of the respective contributions of the refractive indices and of the linear electro-optical coefficients.

Electro-optic coefficient determination in stratified organized molecular thin films: application to poled polymers

We describe a method which enables us to determine the linear and quadratic electro-optic coefficients (real and imaginary parts) of thin stratified films even inside the absorption range. The principle is based on the interferences between the electric-field-induced modulation of the transverse electric and transverse magnetic reflected waves. Experiments performed on a poled polymer yield microscopic parameters such as the excited and fundamental state permanent moments and the difference and transition moments which are in a very good agreement with other determinations. The presence of an excited state not detected by linear spectroscopy was revealed.

Linear electro-optic dispersion in (-)-2-(α-methylbenzylamino)-5-nitropyridine single crystals

The variation of the linear electro-optic effect in (-)-2-(α-methylbenzylamino)-5-nitropyridine with the wavelength of the incident light at room temperature has been measured. The reduced half-wave voltages have been found to have the values 2.1, 2.8, and 6.0 kV at 488, 514.5, and 632.8 nm respectively and the corresponding values of the linear electro-optic coefficient have been evaluated. The interpretation of the results in terms of the structures of the molecule and the crystal is discussed. The thermal variation of the birefringence has also been investigated and the coefficient for the temperature variation of the refractive index difference is found to have the value (dΔn/dT)=9.3×10−5 K−1.

Characterization of the poling process in zinc diffused lithium tantalate optical waveguides

Abstract A model for the poling process of Zn diffused LiTaO3 optical waveguides that is based on the thermodynamic theory of ferroelectrics is presented. The effect of oppositely oriented domain regions are related to the linear electrooptic coefficient by the approximation that the polarization inside the crystal is proportional to the external electric field applied during poling. The model predictions agree well with experimental optical phase shift data of electrooptic waveguide modulators produced by diffusions above the Curie temperature then repoled under different electric field values.

Photoluminescence and electro-optic properties of small (25–35 nm diameter) quantum boxes

The luminescence and electro-optic properties of buried 25–35 nm quantum boxes have been measured. The quantum boxes were defined by a combination of molecular beam epitaxial growth and regrowth, electron beam lithography, and dry etching. The photoluminescence from 35 nm boxes shows a blue shift of ∼15 meV compared to the bulk luminescence and an enhancement, taking into account the fill factor. An enhanced effective linear electro-optic coefficient, rl, is observed for the quantum boxes.

Refractive Indices, Permittivities, and Linear Electrooptic Coefficients of Tetragonal Potassium Tantalate-Niobate Crystals

The refractive indices no and ne, the linear electrooptic coefficient r33, and the relative (low frequency) permittivities e3 and e2 = e2 of nominally pure KTN crystals with tetragonal symmetry (4 mm) are measured at different temperatures. In the case of the optical properties (no, ne, and r33) the light wavelength is varied, too.

Theory of electro-optic effect in the tetragonal phase of BaTiO3

Abstract The microscopic mechanism of electro-optic effect in tetragonal phase of BaTiO3 is discussed taking account of the piezoelectric effect due to the lattice deformation and the spontaneous Kerr effect as to a cause of the to the strong local field acting in the constituant ions. It is found that the birefringence σn and the linear electro-optic coefficients (Pockels constants) r33 and r13 obtained are in good agreement with the experimental data.

Thermally Stable Poled Polymers: Highly Efficient Heteroaromatic Chromophores In High Temperature Polyimides

ABSTRACTIn this paper, we report our recent developments in achieving thermally stable polyimides that possess large second order nonlinear optical activity. We have developed several classes of novel chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. Through these developments, we have synthesized chromophores that possess non-resonant βμ values as high as 9,100 × 10−48 esu measured at 1.9 μm. These chromophores also possess improved thermal and chemical stabilities. The incorporation of these chromophores in high temperature polyimides produces E-O Materials with high linear electro-optic coefficients (in excess of 15 pm/V at 1.3 μm) and long-term temporal stability at an elevated temperature of 150°C for more than 800 hours.

Electrooptic coefficient measurements in LiTaO/sub 3/ and LiNbO/sub 3/ waveguides

The magnitudes of linear electrooptic coefficients r/sub 13/ and r/sub 33/ in Zn:LiTaO/sub 3/ repoled channel waveguides are reported. The measurements were made at 0.633- mu m wavelength using a Fabry-Perot interferometer. The waveguides were produced by diffusion from the vapor phase at a temperature above the Curie temperature. For full recovery of the Pockels effect, an electric field of 200 V/cm is needed during repoling. The measured values of r/sub 13/ and r/sub 33/ at 32-MHz modulation frequency are 7.2 and 30.3 pm/V, respectively. The difference between unclamped and clamped coefficients is comparable to that from bulk crystals. Measurements were also made on Ti:LiNbO/sub 3/ waveguides that did not require repoling, and good agreement with bulk crystal values was obtained. >

Dispersion of the linear electro-optic coefficients in GaAs

A phenomenological expression is derived for the calculation of the spectral dependence of the linear electro-optic coefficients in zinc-blende-type semiconductors. Analyses are presented for GaAs, and results are in good agreement with published experimental data when a lifetime broadening effect is taken into consideration in the model. It is also found that the E0 gap (lowest-direct gap) strongly contributes to the dispersion of the linear electro-optic coefficients, but not to its absolute value.

Grain Size Dependence of Optical Transmittances and Linear Electrooptic Coefficients of Hot-Pressed Ba(La1/2Nb1/2)O3-PbZrO3-PbTiO3 Ferroelectric Ceramics

In order to study the grain size dependence of optical transmittances and linear electrooptic coefficients of the ferroelectric ceramics with the composition 0.1Ba(La1/2Nb1/2)O3-0.9Pb(Zr0.5Ti0.5)O3, specimens having various grain sizes were prepared by the hot-pressing method under different sintering conditions, namely by varying the temperature, the time and the pressure, independently. The results obtained show that the transmittance increases as the grain size increases, and that it decreases very slightly in the phase change from the paraelectric to the ferroelectric tetragonal phase. The linear electrooptic coefficient rc shows a slight decrease with increasing grain size.

Optical Properties of Gd2(MoO4)3 Studied by High Accuracy Universal Polarimeter (HAUP) Method*

Birefringence Δnc of the improper ferroelectric Gd2(MoO4)3 was accurately measured by using the HAUP (high accuracy universal polarimeter) method as a function of temperature and electric field. Electric field dependence of Δnc was found to show unique behaviour in the vicinity of Tc. It is of importance that the linear electrooptic coefficient r63 changes its sign and manifests a sharp peak in the close vicinity of Tc. This result coincides qualitatively with the result reported by Kobayashi and Miyazaki, but disagrees with other reports.

Enhanced linear electro-optic response and enhanced stability of thermo-poled 'guest-host' polycarbonate thin films

Fixed electrode poling of 20% DAN doped bisphenol-A polycarbonate at moderate poling temperature (80 degrees C) gives a linear electro-optic (EO) coefficient, r33 of 1.12 pm V-1 for an applied poling field, Ep, of 27 V mu m-1. This value is found to be ten times larger than that predicted using a simple thermodynamic model. The long term stability of the EO response was found to be unexpectedly good for a guest-host system and approaches that of some side-chain-type materials. At room temperature, a decrease of only 25% was seen in the linear EO response over a period of 21 days. The enhanced response and its unexpected stability is thought to be due to guest-host interactions and particularly to hydrogen bonding. Poling is performed 70 degrees C below the glass transition temperature of the host and is assisted by a beta -relaxation process identified at 80 degrees C.

The electro-optic coefficients of GaAs: Measurements at 1.32 and 1.52 μm and study of their dispersion between 0.9 and 10 μm

The linear (r41) and quadratic (R11 and R12) electro-optic coefficients of GaAs have been measured at the wavelengths 1.32 and 1.52 μm using single-mode AlGaAs/GaAs strip-loaded waveguides. The results are r41=−(1.54±0.08)×10−10 cm/V, R11=−(9.3±2.8)×10−17 cm2/V2 and R12=−(5.1±l.9)×10−17 cm2/V2 at 1.32 μm and r41=−(1.50±0.08)×10−10 cm/V, R11=−(3.2±2.3)×10−17 cm2/V2 and R12=−(5.1±2.6)×10−17 cm2/V2 at 1.52 μm. These results, together with those previously measured at different wavelengths, are compared with published theoretical models. The linear electro-optic coefficient r41 is slightly dispersive near the band gap and roughly constant for longer wavelengths, in good agreement with the models. The quadratic electro-optic coefficients drop rapidly with increasing wavelength, in good agreement with a model based on electroabsorption.