Lithium Niobate Single Crystals Research Articles

ОЦЕНКА ПРИМЕНИМОСТИ КРИСТАЛЛОВ НИОБАТА ЛИТИЯ Z-СРЕЗА С ЗАДАННЫМ РАСПРЕДЕЛЕНИЕМ ПРИМЕСЕЙ ДЛЯ ИЗГОТОВЛЕНИЯ ПРОТОНООБМЕННЫХ ВОЛНОВОДОВ

Different methods (optical, laser, and electron microscopy) used to compare of the structural features of the near-surface layers of single-crystal lithium niobate plates with a predetermined distribution of impurities along its length and lithium niobate from Crystal Technology (USA). Investigation of optical characteristics (refractive index and depth of planar waveguide) was performed using the method of mode spectroscopy, and also the obtained characteristics were compared with the parameters sample of Crystal Technology. It is shown that the characteristics of planar proton-exchange waveguides are very similar in their values to each other. However, the state of the near-surface layers of the investigated single-crystal lithium niobate plates with a predetermined distribution of impurities along its length is significantly different from the quality of the plates produced by Crystal Technology. The investigated samples of lithium niobate with a predetermined distribution of impurities along its length contain many scratches and points defects on the surface, as well as defective near-surface layer with a depth of 15 μm, which is significantly worse than sample produced by Crystal Technology. It is impossible to use such lithium niobate plates in the manufacture of integral optics elements (channel waveguides, electrodes). Multiple surface defects will significantly reduce the quality of structures, up to their complete rejection.

Bottom-Up Assembly of Molecular Nanostructures by Means of Ferroelectric Lithography.

Here, we report on the photochemical deposition of Rhodamine 6G (Rh6G) and Alexa647 molecules from aqueous and methanolic solution along 180° ferroelectric (FE) domain walls (DWs) of z-cut lithium niobate (LNO) single crystals. Molecules and FE domains were investigated by means of dynamic-mode AFM, piezoresponse force microscopy (PFM), and confocal scanning fluorescence microscopy. A high deposition affinity for 180° DWs on the LNO surface is observed, leading to the formation of molecular nanowires. Additionally, a more complex deposition pattern for Rh6G adsorbed to the domain areas of freshly poled samples was equally observed, being associated with the DW dynamics. These results are explained by considering contributions from screening-charge-dependent photochemistry as confined to the DWs, UV-induced DW motion, and transient electrostatic fields arising from the metastable defect distribution shortly after poling. Hence, tuning these effects offers the possibility for accurately controlling the complex bottom-up assembly of functional molecular nanostructures through domain-structured ferroelectric templates.

IR absorption spectra in the region of stretching and deformation vibrations of hydrogen bond in pure and alloyed single crystals of LiNbO3

We have measured infrared absorption spectra of the stretching and bending vibrations of the hydrogen bond of pure and alloy additives Me (Me = Mg, Zn) single crystals of lithium niobate (LiNbO 3 ) grown using various technologies. Preliminary studies of the spectra showed that the frequency of stretching vibrations in the IR spectra of single-crystal samples obtained from the homogeneously doped charge differ significantly (more than 50 cm −1 ). However, no difference in the IR spectra of single crystals obtained using other doping techniques, we have found. It is assumed that the observed differences in the absorption spectra of single crystals due to the different character of the formation of hydrogen bonds in the preparation of precursors Nb 2 O 5 : Me.

Controlling optical inhomogeneity of LiNbO3 single crystals

Different ways of inducing changes in the optical inhomogeneity of single crystals of lithium niobate are described. These include the application of a conductive coating in combination with the heating of samples and exposure to the field of a corona discharge, to UV radiation from a Nd:YAG laser, and to the electron beam of an electron microscope. All such effects can be used to record images.

Raman spectra of lithium niobate crystals heavily doped with zinc and magnesium

We have examined the Raman spectra of heavily doped lithium niobate single crystals (at close-to-threshold concentrations of doping cations): LiNbO3:Zn (4.5 mol % ZnO), LiNbO3:Mg (5.01 mol %):Fe (0.005 mol %), LiNbO3:Mg (5.1 mol %), and LiNbO3:Mg (5.3 mol % MgO). Low-intensity lines with frequencies at 209, 230, 298, 694, and 880 cm–1 have been revealed for the first time. Analysis of the data from the literature on lattice dynamics calculations from first principles (ab initio) does not make it possible to unambiguously state that these lines correspond to fundamental vibrations of the А2 symmetry species, which are forbidden for the С3V6 (R3c) space group. At the same time, ab initio calculations unambiguously indicate that the experimentally observed low-intensity “superfluous” lines with the frequencies at 104 and 119 cm–1 cannot correspond to vibrations of the А2 symmetry species. It is most likely that they correspond to two-particle states of acoustic phonons with a total wave vector equal to zero.

Formation of a bidomain structure in lithium niobate wafers for beta-voltaic alternators

The possibility of increasing the efficiency of a beta-voltaic generator due to using a single-crystal bimorph element made of lithium niobate as a piezoelectric converter. The known beta voltaic alternators consist of a piezoelectric cantilever and a source of β-electrons. The cantilever represents a resilient member made, for example, of silicon, on which a piezoelectric element made of PZT piezoceramics is mounted. It is proposed to replace the silicon cantilever structure with a piezoelectric element by a uniform cantilever that represents a thin wafer made of a bidomain single-crystal lithium niobate. Due to this, the efficiency of the mechanical oscillation conversion into electrical power, the system Q-factor, and the stability of the operating parameters simultaneously increase; and the operation temperature range also significantly increases (by several hundred degrees). The solution of the main problem—the formation of a bidomain structure in a thin wafer of lithium niobate—is considered in detail. A method for the high-temperature annealing of samples in a nonuniform electric field is proposed. It is demonstrated that one can predict the domain structure based on the developed model. Samples are obtained having the occurrence depth of the interdomain boundary ranging from 120 to 150 μm. At the same time, it is shown that the sharpness of the boundary depends on the potential difference between the striated electrodes of the technological cell and the external electrode. The method is efficient for manufacturing a bidomain structure in a wafer up to 300 μm thick.

Chip-scale cavity optomechanics in lithium niobate.

We develop a chip-scale cavity optomechanical system in single-crystal lithium niobate that exhibits high optical quality factors and a large frequency-quality product as high as 3.6 × 1012 Hz at room temperature and atmosphere. The excellent optical and mechanical properties together with the strong optomechanical coupling allow us to efficiently excite the coherent regenerative optomechanical oscillation operating at 375 MHz with a threshold power of 174 μW in the air. The demonstrated lithium niobate optomechanical device enables great potential for achieving electro-optic-mechanical hybrid systems for broad applications in sensing, metrology, and quantum physics.

Surface polishing of lithium-niobate single crystals

The polishing of a lithium-niobate single crystal is considered. Specifically, the influence of the applied pressure and relative speed on the productivity and the quality of the machined surface is studied. A formula is given for the total depth of the surface layer removed in finishing and the polishing time required for its removal.

Polishing tool for optical materials

The influence of various abrasive materials on the polishing of lithium-niobate single crystals is studied experimentally. In the analysis of the polishing tool, the tool life, the productivity, and the quality of the machined surface are taken into account.

Finishing technologies for processing of optical microelectronic items

This article discusses comparative studies of the influence of specific pressure and speed of relative motion of tool and item on polishing capacity and quality of processed surface of lithium niobate single crystal. The equation for calculation of total depth of layer destroyed upon finishing and time of polishing required for its removal. Analysis of polishing tool has accounted for strength properties of the polishing material, removal capacity, and quality of processed surface of lithium niobate single crystal. It is experimentally established that upon basic pressure both for woven and unwoven polishers with the highest capacity the lower limit of grain coarseness of polishing suspension is 1/0.5 μm. A reserve of increase in shape accuracy and polishing quality is the use of polishers with equal thickness and structure of working surface.

Nanoscale pillar hypersonic surface phononic crystals

We report on nanoscale pillar-based hypersonic phononic crystals in single crystal Z-cut lithium niobate. The phononic crystal is formed by a two-dimensional periodic array of nearly cylindrical nanopillars 240 nm in diameter and 225 nm in height, arranged in a triangular lattice with a 300-nm lattice constant. The nanopillars are fabricated by the recently introduced nanodomain engineering via laser irradiation of patterned chrome followed by wet etching. Numerical simulations and direct measurements using Brillouin light scattering confirm the simultaneous existence of nonradiative complete surface phononic band gaps. The band gaps are found below the sound line at hypersonic frequencies in the range 2--7 GHz, formed from local resonances and Bragg scattering. These hypersonic structures are realized directly in the piezoelectric material lithium niobate enabling phonon manipulation at significantly higher frequencies than previously possible with this platform, opening new opportunities for many applications in plasmonic, optomechanic, microfluidic, and thermal engineering.

Deformation anisotropy of Y + 128° –cut single crystalline bidomain wafers of lithium niobate

Bidomain single crystals of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are promising material for usage as actuators, mechanoelectrical transducers and sensors working in a wide temperature range. It is necessary to take into account anisotropy of properties of crystalline material when such devices are designed. Inthis study we investigated deformations of bidomain round shapedY+ 128°-cut wafers of lithium niobate in an external electric field. Dependencies of piezoelectric coefficients on rotation angles were calculated for lithium niobate and lithium tantalate and plotted for the crystal cuts which are used for bidomain ferroelectric structure formation. In experiment, we utilized external heating method and long-time annealing with lithium out-diffusion method in order to create round bidomain lithium niobate wafers. In order to obtain dependencies of the bidomain crystals’ movements on the rotation angle with central fastening and external electric field application optical microscopy was used. We also modeled a shape of the deformed bidomain wafer with a suggestion that the edge movement depends on the radial distance to the fastening point quadratically. In conclusion, bidomainY+ 128°-cut lithium niobate wafer exhibits saddle-like deformation when DC electric field is applied.

Back Cover: Ann. Phys. 5'2016

Annalen der PhysikVolume 528, Issue 5 p. 434-434 Back CoverFree Access Back Cover: Ann. Phys. 5'2016 First published: 03 May 2016 https://doi.org/10.1002/andp.201670031AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Surface phonon cavities that are homogenous in both mechanical and dielectric properties are reported. The cavities are formed by the placement of a defect of a single domain within periodic domain inversion of single crystal piezoelectric lithium niobate that exhibits a surface phononic bandgap through the phonon-polariton coupling. Surface cavity resonances are observed within the bandgap, which correspond to entrapment of the phonon-polariton within the defect. In addition to demonstrating that the observed resonances are non-radiative and decoupled from bulk radiation, which is critical for high Q cavities, the possibility to tune the surface cavity resonance spectra simply by varying the defect width is also shown. Such an ability to excite a surface cavity resonance that is non-radiative with simultaneous localization of the electric field, together with the advantage of a cavity that is physically formed from a completely monolithic and uniform material, offers unique opportunities. Volume528, Issue5May 2016Pages 434-434 RelatedInformation

The electronic conductivity in single crystals of lithium niobate and lithium tantalate family

ABSTRACTThe electronic conductivity was measured in single crystals of lithium niobate and lithium tantalate family at elevated temperatures using direct electrometric method with original technique of compensation of pyroelectric current. Experimentally measured temperature dependences of the bulk electrical conductivity along the polar direction followed the Arrhenius law with activation energy ranging from 1.0 to 1.2 eV. It was shown that bulk intrinsic conductivity became the main mechanism of screening at the temperatures above 160°C. The conductivity anisotropy was studied in MgOLN single crystals.

Domain kinetics in LiNbO3 and LiTaO3 with modified bulk conductivity

ABSTRACTThe switching in the bulk only in lithium tantalate single crystals with modification of the surface layer by short-time low energy ion irradiation has been studied experimentally. It was shown by us earlier that in lithium niobate single crystals such irradiation led to spatially inhomogeneous increase of the bulk conductivity and allowed us to create by polarization reversal the stable domain structure with charged domain walls. In this paper, we compare the features of the domain structure evolution and growth of the charged domain walls in modified crystals of lithium tantalate and lithium niobate.

Optical parametric oscillator based on the periodically poled MgO:LN crystal with 4.1 μm wavelength and varied pulse duration

ABSTRACTThe generation of optical parametric oscillator (OPO) at 4.1 μm in the periodically poled MgO doped congruent lithium niobate (MgOLN) single crystal was studied and tested. The stable domain structure with period 28.48 μm was produced in 2-mm-thick wafer by multi-pulse periodical poling at elevated temperature. The Nd:YAG laser was used as a pumping source. The OPO was realized by single resonant scheme with two-mirror cavity. The average power at the generated idler wavelength 70 mW was achieved for 5 W average pump power and pulse duration 10 ns. The produced OPO can be used for diagnostic equipment.

Growth of Large Size Lithium Niobate Single Crystals of High Quality by Tilting-mirror-type Floating Zone Method

Large size high quality LiNbO3 single crystals were grown successfully by tilting-mirror-type floating zone (TMFZ) technique. The grown crystals were characterized by X-ray diffraction, etch pits density measurement, Impedance analysis, Vibrating sample magnetometry (VSM) and UV-Visible spectrometry. The effect of mirror tilting during growth on the structural, electrical, optical properties and defect density of the LiNbO3 crystals were investigated. It was found that the defect density in the crystals reduced for tilting the mirror in the TMFZ method. The chemical analysis revealed that the grown crystals were of high quality with uniform composition. The single crystals grown by TMFZ method contains no low-angle grain boundaries, indicating that they can be used for high efficiency optoelectronic devices.

Site-selective measurement of relaxation properties at 980 nm in Er $$^{3+}$$ 3 + -doped congruent and stoichiometric lithium niobate crystals

A pump-probe-type saturation spectroscopic experiment has been performed at 980 nm to measure the homogeneous linewidth of the $$^4$$ I $$_{11/2}$$ – $$^4$$ I $$_{15/2}$$ transition and the lifetime of the $$^4$$ I $$_{11/2}$$ state of erbium embedded into lithium niobate single crystals. There are several non-equivalent Er $$^{3+}_{\mathrm{Li}^+}$$ –V $$_{\mathrm{Li}^+}$$ sites with differently oriented defect structure for charge compensation. These non-equivalent centers differ in their transition energies. Hence, our measurements have been done at two nearby frequencies, addressing groups of erbium ions located at non-equivalent sites. The results are compared with lifetime calculations and measurements found in the literature and with the predictions of our simple model calculation.

Bidomain structures formed in lithium niobate and lithium tantalate single crystals by light annealing

The bidomain structures produced by light external heating in z-cut lithium niobate and lithium tantalate single crystals are formed and studied. Interdomain regions about 200 and 40 μm wide in, respectively, LiNbO3 and LiTaO3 bidomain crystals are visualized and studied by optical microscopy and piezoresponse force microscopy. Extended chains and lines of domains in the form of thin layers with a width less than 10 μm in volume, which penetrate the interdomain region and spread over distances of up to 1 mm, are found.

Electric-optical property of the proton exchanged phase modulator in single-crystal lithium niobate thin film.

The electric-optical property of the proton exchanged phase modulator in an x-cut single-crystal lithium niobate thin film was studied. Proton exchanged waveguides generally suffered from a deteriorated electric-optical coefficient. By introducing a shallow proton exchange layer (thickness = 0.165 μm), most energy of the optical mode was allowed to guide in the untouched single-crystal lithium niobate film, making contribution to the effective electric-optical coefficient as high as 29.5 pm/V, which was very close to that of the bulk lithium niobate (r33 = 31 pm/V). A 12 V voltage applied to the electrodes located on the two sides of the waveguide induced a 0.097 nm shift of the Fabry-Perot resonant peak. Considering the wavelength difference of the neighboring resonant peaks (0.228 nm) and the length of the electrodes (2.3 mm), the voltage-length product was as low as 6.5 V·cm, indicating the efficient electric-optical modulation.