Structural, electrical and piezoelectric properties of LiNbO3 thin films for surface acoustic wave resonators applications

In this work, 0.30 μm thick LiNbO₃ layers have been deposited by sputtering on nanocrystalline diamond/Si and platinised Si substrates. The films were then analyzed in terms of their structural and optical properties. Crystalline orientations along the (0 1 2), (1 0 4) and (1 1 0) axes have been detected after thermal treatment at 500 °C in air. The films were near-stoichiometric and did not reveal strong losses or diffusion in lithium during deposition or after thermal annealing. Pronounced decrease of the roughness on top of the LiNbO₃ layer and at the interface between LiNbO₃ and diamond was also observed after annealing, compared to the bare nanocrystalline diamond on Si substrate. Furthermore, ellipsometry analysis showed a better density and a reduced thickness of the surface layer after post-deposition annealing. The dielectric constant and losses have been measured to 50 and less than 3.5%, respectively, for metal/insulator/metal structures with 0.30 μm thick LiNbO₃ layer. The piezoelectric coefficient d₃₃ was found to be 7.1 pm/V. Finally, we succeeded in switching local domain under various positive and negative voltages.     

Crystal-Physical Model of Ion Transport in Nonlinear Optical Crystals of KTiOPO<Subscript>4</Subscript>

The ionic conductivity along the principal axes a, b, and c of the unit cell of the nonlinear-optical high-resistance KTiOPO₄ single crystals (rhombic syngony, space group Pna2₁), which are as-grown and after thermal annealing in vacuum, has been investigated by the method of impedance spectroscopy. The crystals were grown from a solution-melt by the Czochralski method. The as-grown KTiOPO₄ crystals possess a quasi-one-dimensional conductivity along the crystallographic c axis, which is caused by the migration of K⁺ cations: σ_║c = 1.0 × 10^–5 S/cm at 573 K. Wherein the characteristics of the anisotropy of ionic conductivity of the crystals is equal to σ_║c/σ_║a= 3 and σ_║c/σ_║b= 24. The thermal annealing at 1000 K for 10 h in vacuum increases the magnitude of σ_║c of KTiOPO₄ by a factor of 28 and leads to an increase in the ratio σ_║c/σ_║b= 2.1 × 10³ at 573 K. A crystal-physical model of ionic transport in KTiOPO₄ crystals has been proposed.     

Jahn-Teller效应和LiNbO3的结构相变(Ⅱ)

本文在文献[1]的基础上,研究LiNbO₃,中对称单元“Nb—Li—Nb”的静态Jahn-Teller畸变,计算材料在相变点(T_c=75℃)处的热膨胀系数跳跃值,结果定量与实验符合。 关键词：     

A compact, robust and versatile moiré interferometer

A moiré interferometer was designed and constructed based on a general system design using a reflective crossed-line diffraction grating to produce the four beams of light necessary for moiré interferometry. The design concept, basic design and tuning procedures are discussed. The important features of the interferometer, i.e. compactness, versatility, polarization insensitivity, relaxed collimation requirements, low laser power and remote optics, are addressed. Several such interferometers have been constructed and successfully applied to engineering problems. These include examining the displacement fields surrounding drilled and preformed holes in composite laminates loaded in tension, and the evaluation of nonhomogeneous behavior in textile composites.     

Experimental analysis of thermal displacement and strain distributions in a small outline J-leaded electronic package by using wedged-glass phase-shifting moiré interferometry

To evaluate the influence of a printed wiring board (PWB) with a high coefficients of thermal expansion (CTE) on the thermal deformation of a small outline J-leaded electronic package (SOJ), a newly developed phase-shifting method was applied to moiré interferometry. This phase-shifting moiré interferometry method uses a wedged glass plate as a phase shifter to obtain displacement fields with a sensitivity of 100 nm/line. This technique also enabled the quantitative determination of strain distributions in all observation areas. Thermal loading was applied from room temperature (25 °C) to an elevated temperature (100 °C), and then the thermal strains of SOJ with and without the PWB were compared. The results showed that the concentrations of the longitudinal strains ε_xx and ε_yy became increasingly prominent when mounted on the PWB, and the shear strains γ_xy were concentrated at the corners of the silicon chip. The values of these strains increased by about 50% when the SOJ was mounted on the PWB.     

White light interferometry test and analysis of LiNbO3 polarizer

White light interferometer can be used to measure the amplitude extinction ratio (ER) of polarizer and coupling distribution in fiber. A LiNbO₃ polarizer coupled with a polarization maintaining fiber and a silica planar waveguide at the two ends was measured using white light interferometer. According to the principles of optical coherence domain polarimeter (OCDP) technique, the test scheme is analyzed and presented to measure the ER of LiNbO₃ polarizer with its apparatus proposed correspondingly. By analyzing the interference intensity, both the ER of LiNbO₃ polarizer and its coupling crosstalk with optical fiber and waveguide are obtained. The results illustrate that the ER of a 5 mm-long LiNbO₃ polarizer is 71 dB and the crosstalk of the coupling points are around 40 dB. The results have good agreement with analysis.     

Frequency and wavelength dependences of electro-optic coefficients in inorganic crystals

The frequency dependence of electro-optic coefficients in congruent and stoichiometric LiNbO₃, LiTaO₃, β-BaB₂O₄ and KTiOPO₄ was determined and compared to each other for the first time in a wide frequency range from DC up to 150 MHz. The measurements have been investigated as a function of laser wavelength from 0.5 to 1.3 μm. Clamped and unclamped electro-optic coefficients as well as the acoustic contribution have been established for each crystal.     

Measurement of nonlinear refractive index of Ag and Au nano-particles using moiré technique

In this paper we have measured second order nonlinear refractive index of Ag and Au nano-particles using the moiré deflectometry with a CW He-Ne laser at wavelength of 632.8 nm. The main advantages of this technique are its extreme experimental simplicity and low sensitivity to external distribution in comparison with other interfrometric methods that need very stable experimental set-up. Because of self-focusing (or self-defocusing) that is due to intensity dependent refractive index, presence of sample in the moiré deflectometry set-up lead to rotation of moiré fringes. By moving the sample in set-up we have measured these rotation angles in different displacements from focus point of lens used in this set-up and then we have calculated the nonlinear refractive index of Ag and Au nano-particles using their values. Also we have obtained the sign of n₂ regard to the direction of rotations. Consequently by using the Mathematica software we have exhibited the suitable fitness of theoretical curve with experimental results.     

Anisotropic properties of self-flux grown LiB3O5 single crystals

In this paper, we report the existence of anisotropic behavior along the crystallographic axes in optical, electrical and thermal properties of lithium tri borate, a recently developed vacuum UV-NLO material. The variation of refractive index with the wavelength along the crystallographic axes was investigated by prism coupling method. The results of impedance spectroscopy measurement reveal the presence of a strong anisotropy in ionic conductivity and dielectric constant along the axes and also show the super-ionic conduction behavior along the c-axis with the activation energy of Δ∼0.20 eV. A thermo-mechanical study in the temperature range of 300-900 K indicates the existence of a strong variation in the linear thermal expansion coefficient (positive value along the a-axis, and negative value along the c-axis) of LiB₃O₅ crystals.     

Photorefractive Fourier transform profilometer for the measurement of 3-D object shapes

In the present work dynamic moiré-like fringe patterns, produced by photorefraction with low spatial frequencies, applied for profile determination of small objects is proposed. Basically, a Fourier transform profilometry technique is developed for an automated profile determination. This means, as far as we know, a new experimental procedure that exploits the real time holographic two wave mixing in Bi₁₂TiO₂₀ crystal sample. Besides, the mainly advantages of this procedure are, comparatively to the classical fringe projection method using the Michelson interferometer, best fringe pattern contrast, less speckle noise, absence of noises produced by spurious reflections and, the most significant, a pure sinusoidal shape obtained by dynamic holographic moiré-like process using photorefraction.     

Effect of electron and gamma irradiation on elastic characteristics of KTiOPO4 crystals

The elastic moduli C ₁₁ and C ₃₃ of KTiOPO₄ crystals unirradiated and irradiated by electrons and gamma quanta in the temperature range 100–330 K have been measured by the echo-pulse technique. It has been shown that C ₁₁ < C ₃₃ and, with increasing temperature, their values smoothly decrease; moreover, in the temperature range of the second-order phase transition at T ～ 281 K, the curves C ₁₁ = f(T) and C ₃₃ = f(T) exhibit anomalies in the form of a kink. It has been established that, under electron irradiation, the elastic moduli decrease and the phase transition temperature increases. Irradiation of KTiOPO₄ crystals by gamma quanta with a dose of 10⁷ R has no substantial effect on the dynamic characteristics of this crystal.     

New large-aperture and high- accuracy lateral shearing interferometer

The principle of a new large-aperture high-accuracy interferometer for flow visualization is presented. The interferometer uses a Twyman-Green interferometer as a beam-splitter, a grating as a detector, and a real-time moiré fringe method to eliminate systematic errors. The interferometer has been used to measure the flow fields in a shock tunnel and obtained satisfactory results.     

A study on the 3-D measurement by using digital projection moiré method

Moiré topography method is a well-known non-contacting 3-D measurement method. Recently, the automatic 3-D measurement technique by moiré topography has been developed in order to apply to the engineering and medical fields. The projection moiré topography is very attractive because of its high measuring speed and high sensitivity. In this paper, using the two-wavelength methods of projection moiré topography was investigated to measure the 3-D shape of an object with 2π-ambiguity problems. Rapid measurement can be accomplished by the synchronization between CCD camera and projector. The experimental results prove that the proposed scheme is capable of finding absolute fringe orders, so that the 2π-ambiguity problems can be effectively overcome so as to treat large step discontinuities in measured objects.     

High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

In this paper we report on a continuous-wave (CW) intracavity singly resonant optical parametric oscillator (ICSRO) based on periodically poled LiNbO₃ (PPLN) pumped by a diode-end-pumped CW Nd:YVO₄ laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406~nm to 1513~nm is obtained. At a PPLN grating period of 29~μ m and a temperature of 413~K, a maximum signal output power of 820~mW at 1500~nm is achieved when the 808~nm pump power is 10.9~W, leading to an optical-to-optical conversion efficiency of 7.51%.     

Realization of high sensitivity displacement field from moiré interferometer with rough phase shifting mechanism and pattern matching technique

In this study, phase shifting method is used to modify moiré system into micro moiré interferometer which can measure displacement field with highly improved sensitivity. Apart from existing micro moiré technique, a low cost and less precise translation stage with rough resolution (10 μm resolution) is adapted for the phase shifter. Least square algorithm is applied to estimate the arbitrary phase shifted amount and to minimize the errors induced by lowering the cost. Moreover, specimen grating is phase shifted instead of reference grating which enables simple construction from given moiré system. To compensate for rigid body in-plane translation of specimen that may occur during phase shifting, pattern matching algorithm is put into practice to ensure pixel correspondence for each phase shifted images. To verify the newly constructed micro moiré technique, local displacement fields of Fine pitch Ball Grid Array package and Wafer Level Chip Size Package with elevated sensitivity up to 26 nm per fringe was acquired.     

Magnetoelastic properties of Nd6Fe13Cu intermetallic compound

Magnetoelastic properties of Nd₆Fe₁₃Cu intermetallic compound are reported. To study the magnetoelastic behaviour of this compound, the thermal expansion as well as the longitudinal (λ_l) and transverse (λ_t) magnetostriction were measured by using the strain gauge method in the selected temperature range of 80-500 K under applied magnetic fields up to 1.5 T. An anomaly and invar-type effects are observed in the linear thermal expansion and α(T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic-paramagnetic transition occurs. In the low field region, the absolute values of the anisotropic magnetostriction are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.     

Electro-optic characterization of tetragonal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals by a modified Sénarmont setup

The refractive indices of tetragonal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals were measured with a prism coupler and their linear electro-optic (EO) properties were investigated from 20 to 80 °C by the automated scanning Sénarmont system with an ac field. The composition and temperature effect on the EO coefficients were also discussed. It has been found that their EO coefficients are much larger than that of widely used LiNbO₃ single crystal and the calculated half-wave voltages are also much lower, which enable the operation at lower voltages and the smaller device dimensions. Since the excellent EO properties are very stable and such high quality single crystals with large-size have been obtained, the PMN-xPT single crystals are a very promising candidate for EO modulation applications. By linking to the polarization-related quadratic EO coefficients, we find that the linear EO properties are related with the spontaneous polarization and dielectric constants.     

Effects on absolute moiré contouring by using gratings with different period and profile and rotating angles

Effects on the absolute moiré contouring systems from using different period and profile gratings and rotating angles are described in this paper. It was found that by choosing a different period of the grating or the rotating angle, different resolution and accuracy of the measurement can be obtained. So, for objects with different height or depth, different period of grating or rotating angle should be chosen to ensure accuracy of the measurement. The square wave intensity grating with small period can be treated as a sinusoidal wave intensity grating in the absolute moiré contouring system. A few objects with different shapes and dimensions have been used as samples to verify the above conclusion.     

Improved algorithm for image encryption based on stochastic geometric moiré and its application

A technique based on optical operations on moiré patterns for image encryption and decryption is developed. In this method, an image is encrypted by a stochastic geometric moiré pattern deformed according to the image reflectance map. The decryption is performed using pixel correlation algorithm in the encrypted image and the stochastic geometrical moiré pattern. The proposed technique has a number of advantages over existing encryption techniques based on moiré gratings. No original moiré grating can be reconstructed only from the encrypted image. Stochastic moiré grating can be deformed in any direction what is an important factor of encryption security. Finally, the quality of the decrypted image is much better compared to decryption methods based on the superposition of the regular and deformed moiré gratings. The proposed technique has a great potential, because the process is performed using computational algorithms based on optical operations and optical components are avoided.     

Analysis of moiré fringes for measuring the focal length of lenses

We describe a technique based on fast Fourier transform and least-squares fit for automated analysis of moiré fringe patterns for accurately measuring the focal length of lenses. An interference fringe pattern is produced by a reflective diffraction grating interferometer and illuminates the test lens. Moiré fringes are generated by digitally superimposing the magnified fringe pattern imaged by the lens on the interference fringe pattern without the test lens. We analyze two common ways to generate the digital moiré effect: multiplication and subtraction with successive rectification of the two digitally stored intensity distributions, and we show that in the latter case by means of the described technique it is possible to determine the moiré spatial frequency by a simple and fully automated procedure.