Linear Electro-optic Coefficients Research Articles

Electrical properties and Pockels effect in BaTiO $$_{3}$$ 3 /SrTiO $$_{3}$$ 3 superlattices

The electrical and linear electro-optical properties of BaTiO $$_{3}$$ (BT)/SrTiO $$_{3}$$ (ST) superlattices epitaxially grown on ST substrate are theoretically investigated using a microscopic quantum mechanical model based on the orbital approximation in correlation with the dipole–dipole interaction. Both the first-, second-, and third-order electronic polarizabilities were considered in this calculation in order to obtain accurate results for both the spontaneous local electric field, spontaneous polarization, relative dielectric constant, and linear electro-optic coefficients (Pockels constants) of BT/ST superlattices. The calculations show that the spontaneous local electric field, spontaneous polarization and linear electro-optic coefficients of BT/ST superlattices increase with their content in BT while the relative dielectric constant increases with their content in ST. Moreover, we have shown that significant enhancement of the linear electro-optic coefficients can be achieved in BT/ST superlattices. This enhancement, which concerns the ST as well as the BT layers, arises from the combined effects of strain, induced in the BT layers by the epitaxial growth, and internal polarizing electric field originating in the BT layers and acting on the electronic clouds of the polarizable constituent ions of the system.

Real-Time Investigation of Thermal Poling Process in Optic Fiber

Thermal poling could make centrosymmetric fused silica optical fibers generate second-order nonlinearity effect and linear electooptic effect. In order to investigate the influence of thermal poling parameters on linear electooptic effect, a real-time test system, which mainly consists of an all polarization maintaining fiber Mach-Zehnder interferometer, has been utilized to monitor the whole thermal poling process in fibers. The processing parameters in thermal poling, such as applied poling voltage, poling duration and temperature, have been measured in real time. Based on those measurements, their influence on the linear electrooptic effect has been discussed. Experiment results show that the linear electrooptic coefficient would increase when a stronger electric field is applied on fibers. Considering the anti-high-voltage breakdown capability of fibers, a DC voltage from 3KV to 4KV is suitable for polarization in thermal poling. When using 3KV, the optimum poling duration is about 16 minutes and the best temperature for thermal poling is around 190°C. Keywords: electro-optic effect, poled fiber, thermal poling, real time test system, fiber optic interferometer

A strong electro-optically active lead-free ferroelectric integrated on silicon

The development of silicon photonics could greatly benefit from the linear electro-optical properties, absent in bulk silicon, of ferroelectric oxides, as a novel way to seamlessly connect the electrical and optical domain. Of all oxides, barium titanate exhibits one of the largest linear electro-optical coefficients, which has however not yet been explored for thin films on silicon. Here we report on the electro-optical properties of thin barium titanate films epitaxially grown on silicon substrates. We extract a large effective Pockels coefficient of r(eff) = 148 pm V(-1), which is five times larger than in the current standard material for electro-optical devices, lithium niobate. We also reveal the tensor nature of the electro-optical properties, as necessary for properly designing future devices, and furthermore unambiguously demonstrate the presence of ferroelectricity. The integration of electro-optical active films on silicon could pave the way towards power-efficient, ultra-compact integrated devices, such as modulators, tuning elements and bistable switches.

Ab initio study of elasticity, piezoelectricity, and nonlinear optical performance in monoclinic NaAsSe2

Monoclinic NaAsSe2 (γ-NaAsSe2) has been reported to be a potential IR nonlinear optical material due to the very strong second harmonic generation (SHG). Here, we present a systematic density functional theory (DFT) study on the elasticity, SHG response, linear electro-optical (EO) effect, and piezoelectricity of this compound and analyze the microscopic origins of these properties. We find that γ-NaAsSe2 has smaller values of elastic moduli than those of AgGaSe2, and behaves in a ductile manner. The strong SHG response observed experimentally is well predicted by the 2n+1 theorem andthe “sum over states” expressions based on the DFT. As with the strong SHG response, γ-NaAsSe2 also presents large linear EO coefficient (r11=32.7pm/V, as large as that of LiNbO3), and piezoelectric coefficient (e11=1.27C/m2, about seven times larger than that of α-quartz). The highly distorted structure and the strong hybridizations between As and Se sp orbitals are identified as the chief sources of these unique properties. Our results demonstrate the potential applications of γ-NaAsSe2 in piezoelectric, electro-optical, and nonlinear optical devices.

Effect of optical activity on electro-optic measurements in crystals of the potassium dihydrogen phosphate family

Crystals of the potassium dihydrogen phosphate family in their paraelectric phase belong to point group \overline 4 2m, which allows for natural optical activity and electric field-induced optical activity related to the linear and nonlinear electrogyration effects. This work presents a theoretical analysis of the influence of these effects on measurements of the linear, quadratic and fourth-order electro-optic coefficients. Both the polarimetric technique and a method based on Michelson interferometry are considered. A number of configurations of the light path and the electric field directions were analyzed, and it was found that the influence, when it appears, is usually negligibly small. Thus, no previously reported experimental data need a new interpretation. However, in future measurements of some effective coefficients of the quadratic electro-optic effect using the dynamic polarimetric technique, the contribution of the quadratic electrogyration may no longer be negligible after improving the resolution from 10−21to 10−22 m2 V−2. This work also shows that the quadratic electrogyration described by the β31coefficient may be decoupled from the linear and quadratic electro-optic effects in measurements performed by the polarimetric method.

Measurement of the linear electro-optic tensor of cubic boron nitride single crystals

The transverse electro-optic (EO) modulation system is built based on cubic boron nitride (cBN) single crystals unintentionally doped and synthesized at a high pressure and high temperature. The photoelectric output of the system includes two parts that can be measured respectively and the value of elements in the linear EO tensor of the cBN crystal can be obtained. This method does not need to measure the absolute light intensity. All of the surfaces of the tiny cBN crystals whose hardness is next to the hardest diamonds are {111} planes. The rectangular parallelepiped cBN samples are obtained by cleaving along {110} planes and subsequently grinding and polishing f112g planes of the tiny octahedral cBN flakes. Three identical non-zero elements of the EO tensor of the cBN crystal are measured via two sample configurations, and the measured results are very close, about 3.68 and 3.95 pm/V, respectively, which are larger than the linear EO coefficients of the general III-V compounds.

High-Speed InAs Quantum-Dot Electrooptic Phase Modulators

In this letter, we report results of direct current (dc) and radio-frequency (RF) characteristics of self-assembled InAs quantum-dot (QD) electrooptic modulators. Although dc modulation results have been reported in the literature, these are the first high-frequency designs and measurements. These QD modulator wafers were grown by molecular beam epitaxy (MBE) and phase modulator devices were fabricated with coplanar traveling-wave electrodes. For the 800-μm-long modulators, the half-wave voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> was measured as 11.4 V at 1.55 μm and 7.34 V at 1.32 μm. The phase variation is 21.9°/(mm·V). The linear electrooptic coefficient T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">41</sub> is calculated to be 35.4 pm/V for QDs. These modulators have a 3-dB bandwidth of 10 GHz. A signal-to-noise ratio of 9 dB was measured at 20 GHz.

Hot-pressed K 0.48Na 0.52Nb 1− xBi xO 3 ( x = 0.05–0.15) lead-free ceramics for electro-optic applications

Bismuth-modified potassium sodium niobate K 0.48Na 0.52Nb 1− x Bi x O 3 ( x = 0.05–0.15) transparent lead-free ceramics were fabricated by a hot-pressing method. Both hot-pressing conditions (pressure, temperature and duration) and Bi-content were found to have strong influences on the density, transparency, electro-optical coefficient, and electrical properties of the ceramics. Under the typical hot-pressing conditions of 1060 °C for 5 h at 5.5 MPa, the optimum Bi-content was found at 7.5 at.% in the system under study. These ceramics display good optical transmission in the visible and particularly in the infrared regions. For visible light, the highest transmission value of a polished 0.5-mm thick plates is about 60% at a wavelength of 800 nm; while for infrared, the transmission value is about 80% at 4000 nm. The effective linear electro-optic coefficient of the ceramics was found to be 42 pV m −1. The dielectric permittivity and loss tangent of the KNNB ( x = 0.075) ceramics were found to be 716 and 0.031 at room temperature.

A NOVEL LEAD-FREE TRANSPARENT CERAMIC WITH HIGH ELECTRO-OPTIC COEFFICIENT

A novel lead-free transparent electro-optic ceramic (K0.5Na0.5)0.95 Li0.05Nb0.95Bi0.05O3+ 2 mol % excess Bi2O3 has been fabricated by hot-press sintering. The ceramic possesses a dense, fine-grained and pure-perovskite structure. Owing to the decreases in optical anisotropy of the crystal structure and optical scattering by the fine grains, the ceramic becomes visually clear. It exhibits a high transmittance of 60% in the near-IR region as well as a high effective linear electro-optic coefficient of 102 pm V-1. Although a relaxor behavior is induced, the ceramic exhibits reasonably good ferroelectric and piezoelectric properties (d33 = 64 pC N-1).

Organic electro-optic thin films by simultaneous vacuum deposition and laser-assisted poling

Organic materials with a high second-order optical nonlinearity have an important application for the next generation of computing, telecommunications, and other industries. Because of a high electro-optic coefficient and low dielectric constant, N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals have been grown and their optical properties have been extensively studied. In this Letter, a poled BNA thin film material was prepared through simultaneous vacuum evaporation and laser-assisted electrical poling. The linear electro-optic coefficients of BNA were measured by a Young's two-slit interference electro-optic measurement method. The dependence of the resulting electro-optic properties on optical power was explored. Enhancement induced by laser illumination was demonstrated. The BNA thin film can exhibit an r(33) value comparable to that of BNA single crystals.

Measurement of optical and surface properties of PLZT thin films

Lanthanum-modified lead zirconate titanate (Pb 0.93La 0.07(Zr 0.3Ti 0.7) 0.93O 3, PLZT7/30/70) thin films with and without a seeding layer of PbTiO 3 (PT) were successfully deposited on indium-doped tin oxide (ITO) coated glass substrate via spin coating in conjunction with a sol–gel process, and a top transparent conducting thin film of SnO 2 was also prepared in the same way. The thicknesses of PLZT and PT layers are 0.5 μm and 24 nm, respectively. The retardance of PLZT film was measured by a new heterodyne interferometer and enhanced by application of a seeding layer of PT. The Pockels linear electro-optical coefficient of PLZT film with a PT layer was determined to be 3.17 × 10 −9 m/V when the refractive index is considered as 2.505, which is one order larger than 1.4 × 10 −10 m/V for PLZT12/40/60 doped with Dy reported in the literature. The root-mean-square (rms) roughness of PLZT thin film with a PT layer ( R rms = 6.867 nm) was larger than that of PLZT film ( R rms = 0.799 nm). From the comparisons, the average transmittance of PLZT film with a PT seeding layer was 77.01%, which was a little smaller than that of PLZT film (around 80.75%). Experimental results imply that the PT seeding layer plays a key role in the increase of retardance value, leading to a higher Pockels coefficient.

Simultaneous evaluation of the linear and quadratic electro-optic coefficients of the nonlinear optical polymer by attenuated-total-reflection technique

A method of simultaneously evaluating the linear electro-optic and quadratic electro-optic coefficients of the nonlinear polymer poly (9,9-dioctyl-2,7-fluorene-co-benzo[c][1,2,5]thiadiazole-co-9-hexyl-3,6-carbazole) (PF8-BT-CZ) was proposed based on the attenuated-total-reflection (ATR) technique. The measurement was sensitively carried out without the lock-in amplifier due to the prism-waveguide configuration of the sample and only one single optical path was applied, which simplified the experimental setup.

Conoscopic interferometry for probing electro-optic coefficients of strontium calcium barium niobate crystal

The relation between the linear electro-optic effect and conoscopic interference has been investigated in a biased electro-optic crystal strontium calcium barium niobate (CSBN). Based on the change of interference patterns with applied field, an interferometric method for probing electro-optic coefficients of electro-optic crystals has been proposed. In our case, the linear electro-optic coefficients of CSBN:50 was first probed at γ 33 =(141.0±0.5)×10 −12 m/V and γ 13 =(85.0±0.5)×10 −12 m/V. ► A interferometric method for probing electro-optic coefficients of CSBN has been proposed. ► The linear electro-optic coefficients of CSBN was first calculated to be γ 33 =(141.0±0.5)×10 −12 m/V and γ 13 =(85.0±0.5)×10 −12 m/V. ► Investigation on conoscopic interference in biased CSBN.

Electron–phonon coupling in the molecular charge transfer crystal 2-(α-methylbenzylamino)-5-nitropyridine

Orientated single-crystal infrared, Raman and terahertz measurements have been carried out for the molecular charge transfer material 2-(α-methylbenzylamino)-5-nitropyridine. This information, together with experimental frequency doubling data and theoretical calculations of the electro-optic coefficient, was used to deduce the optical phonon contribution to the linear electro-optic coefficient. The optical phonon spectra are dominated by three intense bands attributed to vibrations of the ring, NO 2 substituent and N–H bond. The most intense scattering arose from the α bb component of the polarisability tensor. This implied that the most significant contribution to the transition polarisability arises from the electronic transition near 435 nm, polarised along the b-axis of the crystal. The strongest bands in the infrared spectra are also associated with the same three bands. This implies that efficient electron-phonon coupling (or electronic delocalization) in the conjugated system. DFT calculations of optical phonon frequencies and eigenvectors were used to help assign relevant vibrational features and to derive useful information about the molecular structure. The information obtained from this study is important for assessing the suitability of this material for generating terahertz frequencies by optical rectification.

Simultaneous characterization of the electro-optic, converse-piezoelectric, and electroabsorptive effects in epitaxial (Sr,Ba)Nb2O6 thin films

Implementation of the linear electro-optic (EO) effect in thin film waveguides is expected to allow drastic reductions in the drive voltage, power, and dimensions of devices devoted to light modulation. It should also enable the realization of electrically tunable photonic crystal devices. In this paper we introduce a method which eliminates systematically the sources of the unreliability which strongly affects thin film EO characterization. Based on a Fabry–Perot reflective configuration, the method enables characterizing simultaneously the EO, converse-piezoelectric, and electroabsorptive effects in a film. It provides the magnitude and sign of each of the involved coefficients, and allows accounting for the whole of experimental data versus angle of incidence for both transverse-electric and transverse-magnetic polarizations. At λ=633 nm and room temperature, the results obtained with an epitaxial strontium barium niobate (SrxBa1−xNb2O6, x=0.60) ferroelectric thin film, are: r13=+8.5±1.3 pm/V, r33=+38.9±0.5 pm/V, d33=Δe/ΔV=+21±4 pm/V, and Δko/ΔV=(+9.8±0.6)×10−6, where r13 and r33 are two linear EO coefficients, d33 is a converse-piezoelectric coefficient, and e, ko, V represent, respectively, the film thickness, film ordinary extinction coefficient, and applied voltage. Converse-piezoelectric and electroabsorptive effects are found significant in the film response at a frequency below piezoelectric resonance. Diagonal and effective EO coefficients of the (Sr,Ba)Nb2O6 (SBN) film explored in the present work are larger than those of a crystal of lithium niobate (LN) at the same wavelength λ=633 nm. Taking into account the significant difference in dielectric permittivity between the two materials, advances and potential of LN and SBN thin film paths are compared.

Frequency Dependent Electro-Optic Properties of Potassium Lithium Tantalate Niobate Single Crystal

Single crystals K0.95Li0.05Ta1-x Nb x O3 (KLTN) - x = 0.6 are grown and the transmission spectra show the UV absorption edge is about 400 nm for the transparent KLTN crystal sample. The refractive index and the frequency dependent of linear electro-optic coefficients of KLTN single crystals in the tetragonal phase are characterized at room temperature. The minimum deviation method is used for the refractive index measurements and the electro-optic properties have been investigated using the senarmont method and the auto scanning mach-zehnder interferometer technique. The EO measurements were taken with the continuous low frequency of applied ac field from 100 Hz to 100 KHz. Large electro-optic responses are observed and the coefficients, γ33 = 216.7 pm/V, γ13 = −21.2 pm/V, and γc = 242.9 pm/V at 1 kHz are measured for the crystals. The E-O properties show that the high quality KLTN single crystals have the potential in the field of optical modulation and deflection field devices.

Influence of crystal phase and transparent substrates on electro-optic properties of lead zirconate titanate films

Pb ( Zr x Ti 1 − x ) O 3 [x=0.52, PZT(52) near morphotropic phase boundary], tetragonal PZT(65), and rhombohedral PZT(20) thin films have been fabricated on different transparent substrates by radio frequency sputtering. The optical studies show that the band gap energies and refractive indices of the PZT thin films are crystal phase dependent. The largest electro-optic (EO) coefficient of 219.6 pm/V has been achieved by controlling the crystal phase of the PZT thin films. The linear EO coefficients of PZT(52) films on the (Pb0.86La0.14)TiO3-coated glass, indium tin oxides, and MgO substrates are also studied. Such study could contribute to the crystal phase and substrate dependent PZT films for electro-optic devices and multifunctional integrated circuits.

Reduction of electro-optic half-wave voltage of 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 single crystal through large piezoelectric strain

The influence of converse piezoelectric effect on the electro-optic coefficient of single domain relaxor-based 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 (PZN-0.07PT) has been quantified under ambient conditions. It was found that the large piezoelectric constants d31 and d33 have significant influence to the half-wave voltage of electro-optic modulators. For single domain PZN-0.07PT crystal, Vπ13T is reduced by a factor of 8 and Vπ13L can be decreased by more than an order of magnitude due to the large piezoelectric effect. Compared to commonly used electro-optic crystal LiNbO3 and BaTiO3, PZN-xPT single crystal is much superior for optic phase modulation applications because they have much higher linear electro-optic coefficients and much lower half-wave voltage when piezoelectric strain influence is considered.

Electro-optic polymer film light modulator model based on grating-coupled long-rangesurface plasmon resonance

An electro-optic (EO) polymer film light modulator based on grating-coupledlong-range surface plasmon resonance is proposed and numerically investigated.Near the resonance condition, the incident light can be absorbed to excite thesurface plasmon on both sides of a thin metal layer, sandwiched between a claddinglayer and the EO polymer. The reflected light intensity is highly sensitive to therefractive index of the EO polymer. For the structure with optimal thickness, themodulator is able to vary the reflectance from 0 to 0.6 by applying 10.61 V across a5 µm thick EO polymer film with a linear electro-optic coefficient of200 pm V − 1.

Electro-optic characterization of epitaxial Ba 0.7Sr 0.3TiO 3 thin films using prism coupling technique

In this work, we present our study on evaluating electro-optic properties of Ba 0.7Sr 0.3TiO 3 thin films by prism coupling technique. Ferroelectric Ba 0.7Sr 0.3TiO 3 thin films were epitaxially deposited on LaNiO 3 electroded MgO (001) single-crystal substrates using pulsed laser deposition. Refractive indices and thickness of the Ba 0.7Sr 0.3TiO 3 thin film were determined with a rutile prism (Metricon 200-P-2) under zero electric field at a wavelength of 632.8 nm. The angular shift of guided mode was observed subsequently with a conductive prism (Metricon 200-P-4aC) when electric field was applied to the thin film sample. The ordinary refractive index n o changes 2.2% under a dc voltage of 4 V ( E ∼ 11 V/μm). The linear electro-optic coefficient tensor r 13 is thus calculated to be about 780 pm/V, showing the excellent potential of Ba 0.7Sr 0.3TiO 3 thin films for use in active optical devices.