Potassium Lithium Tantalate Niobate Research Articles

Anomalous Optical Properties of KTN:Li Ferroelectric Supercrystals.

We report a spectroscopic investigation of potassium-lithium-tantalate-niobate (KTN:Li) across its room-temperature ferroelectric phase transition, when the sample manifests a supercrystal phase. Reflection and transmission results indicate an unexpected temperature-dependent enhancement of average index of refraction from 450 nm to 1100 nm, with no appreciable accompanying increase in absorption. Second-harmonic generation and phase-contrast imaging indicate that the enhancement is correlated to ferroelectric domains and highly localized at the supercrystal lattice sites. Implementing a two-component effective medium model, the response of each lattice site is found to be compatible with giant broadband refraction.

Electro-optic active Q-switched Tm:YLF laser based on polarization modulation.

An electro-optic active Q-switched Tm:YLF laser (1880 nm) employing a novel, to the best of our knowledge, switching scheme is presented. The switching is done by a potassium lithium tantalate niobate (KLTN) crystal operated slightly above the ferroelectric phase transition, cut in a trapezoidal shape for reducing acousto-optic oscillations. The novel switching scheme exploits the emission cross section difference between the π and σ polarizations in the Tm:YLF and overcomes the residual oscillation effects even at high repetition rates. The laser exhibited stable operation yielding pulses of 0.81 mJ and pulse duration of 30 ns at 5 kHz, and pulses of 1.25 mJ and pulse duration of 19 ns at 500 Hz.

Enhanced electro-optic effect in potassium lithium tantalate niobate at the paraelectric phase near Tc

The electrooptic effect in potassium lithium tantalate niobate (KLTN) at the paraelectric phase in close proximity to Tc was investigated, and was found to be exceptionally large. At Tc+3°C, the electrically induced change in the refractive index was measured to be ≈0.014 while high optical quality was maintained. It is also shown that at the paraelectric phase, close to Tc, the electrooptic behavior deviates from being directly proportional to the square of the electrically induced polarization P2. This is attributed to the influence of dipolar clusters that are formed upon cool-down towards Tc. Taking this influence into account, it was shown that the electrooptic effect close to Tc remains quadratic, enabling the inhibition of photorefractive optical damage by employing a bi-polar driving voltage.

Super-crystals in composite ferroelectrics.

As atoms and molecules condense to form solids, a crystalline state can emerge with its highly ordered geometry and subnanometric lattice constant. In some physical systems, such as ferroelectric perovskites, a perfect crystalline structure forms even when the condensing substances are non-stoichiometric. The resulting solids have compositional disorder and complex macroscopic properties, such as giant susceptibilities and non-ergodicity. Here, we observe the spontaneous formation of a cubic structure in composite ferroelectric potassium–lithium–tantalate–niobate with micrometric lattice constant, 104 times larger than that of the underlying perovskite lattice. The 3D effect is observed in specifically designed samples in which the substitutional mixture varies periodically along one specific crystal axis. Laser propagation indicates a coherent polarization super-crystal that produces an optical X-ray diffractometry, an ordered mesoscopic state of matter with important implications for critical phenomena and applications in miniaturized 3D optical technologies.

Miniaturized electro-optic infrared beam-manipulator based on 3D photorefractive funnels

We demonstrate tunable electro-optic guiding, shaping, and switching of beams in the near infrared spectrum ( 980 nm), typical of VCSEL technology, using biomimetic 3D funnel waveguides miniaturized into a sample of potassium–lithium–tantalate–niobate. The switchable waveguides are written using the slow photorefractive build-up of a 3D volume space-charge field caused by a diffracting continuous wave low intensity λ = 532 nm beam, and electro-optic functionality is supported by the quadratic electro-optic effect of the high-symmetry paraelectric phase.

Volume integrated phase modulator based on funnel waveguides for reconfigurable miniaturized optical circuits.

We demonstrate the integration of a miniaturized 30(x) μm×30(y) μm×2.7(z) mm electro-optic phase modulator operating in the near-IR (λ=980 nm) based on the electro-activation of a funnel waveguide inside a paraelectric sample of photorefractive potassium lithium tantalate niobate. The modulator forms a basic tassel in the realization of miniaturized reconfigurable optical circuits embedded in a single solid-state three-dimensional chip.

Electro-optical modulation with immunity to optical damage by bipolar operation in potassium lithium tantalate niobate.

A method for suppressing the formation of optical damage in quadratic electrooptic devices operated at short wavelengths is presented. Formation of optical damage is attributed to the generation of a trapped space charge induced by photoionization of impurity ions by the propagating beam. It is shown that in potassium lithium tantalate niobate where the electrooptic effect is quadratic, operating the electrooptic device by a bipolar driving voltage prevents the space charge from accumulating, which inhibits the formation of the optical damage. A 6 hours continuous operation of electrooptic modulator for a 30 W/cm(2) at λ = 445 nm input beam is demonstrated.

Construction of waveguiding structures in potassium lithium tantalate niobate crystals by combined laser ablation and ion implantation

A generic methodology for constructing complex integrated electro-optic circuits in waveguided configurations is presented. The method is based on combining two techniques, “laser ablation” and “refractive index engineering by ion implantations.” The constructed circuits are side-cladded by air trenches that were produced using laser ablation and bottom-cladded by a layer with a reduced refractive index which is generated through the implantation of He+ ions. This fabrication technique enables the construction of circular structures with complex geometry featuring small radii of curvature, and further can be employed to construct microfluidic channels on the same substrate. The research demonstrates waveguides in both linear and circular configurations that were constructed in a potassium lithium tantalate niobate (KLTN) substrate using the aforementioned method, proving that this substrate is a suitable candidate for use in creating laboratories-on-a-chip with multifunctional capabilities. The proposed techniques used in the research are generic and applicable to a wide range of substrates.

Upconversion Emission Properties of Erbium- and Ytterbium-Doped Potassium Lithium Tantalate Niobate Ceramics

We investigate the luminescence properties of erbium-doped and erbium-ytterbium-codoped potassium lithium tantalate niobate ceramics prepared by the solid phase syntheses method. The crystalline structure and surface morphology of these ceramics are tested by x-ray diffraction and scanning electron microscopy. The green, red, and near-infrared upconversion photoluminescence properties are analyzed by the steady-state spectra under 975 nm and 800 nm excitations. These ceramics are well sintered and tetragonal tungsten type crystalline structure with the 4mm point group and the P4bm space group. The Er3+ upconversion emission integrated intensities increase with the increase in Er3+ ion concentration, while the green emission decreases with the increase in Yb3+ ion concentration under the 800 nm excitation. An effective energy back transfer process from the Er3+ 4S3/2 state to Yb3+ ground state plays an important role in enhancing the red emission and weakening the green emission.

Electrical properties of lead-free Fe-doped niobium-rich potassium lithium tantalate niobate single crystals

Lead-free, 0.025 wt% Fe-doped niobium-rich potassium lithium tantalate niobate Fe: K0.95Li0.05Ta1−xNbxO3 single crystals have been grown by the top-seeded melt growth method. All the transition temperatures have been determined by the dielectric constant and loss-dependent temperature. The spontaneous polarizations computed by the integration of pyroelectric coefficients over all the temperatures are consistent with the results of the P-E hysteresis loops. The piezoelectric constants and electromechanical coupling factors are attractive among lead-free piezoelectric materials. With suitable Fe-doping, the electrical properties of KLTN single crystals have been improved overall and can be compared to those of the current important lead-based piezoelectric materials.

Piezoelectric and ferroelectric properties of lead-free niobium-rich potassium lithium tantalate niobate single crystals

Lead-free potassium lithium tantalate niobate single crystals with the composition of K0.95Li0.05Ta1−xNbxO3 (abbreviated as KLTN, x=0.51, 0.60, 0.69, 0.78) were grown using the top-seeded melt growth method. Their piezoelectric and ferroelectric properties in as-grown crystals have been systematically investigated. The phase transitions and Curie temperatures were determined from dielectric and pyroelectric measurements. Piezoelectric coefficients and electromechanical coupling factors in thickness mode, length-extensional mode and longitudinal mode were obtained. The piezoelectric properties are very attractive, e.g. for x=0.60 composition, kt≈70%, k31≈70%, k33≈77%, d31≈230pC/N, d33≈600pC/N are comparable to the lead-based PZT composition. The polarization versus electric field hysteresis loops show saturated shapes. In short, lead-free niobium-rich KLTN system possesses comparable properties to those in important lead-based piezoelectric material nowadays.

A Bragg grating embedded in a slab waveguide fabricated by the implantation of high-energy light ions in KLTN substrate

Electro-optically tunable transmission grating was imprinted in potassium lithium tantalate niobate by irreversible spatial patterning of the dielectric constant. While embedded into waveguided architecture, it provides a reliable and versatile building block for opto-electronic circuitry, capable of both active switching and multiplexing. Realization of such a block is critical for the fabrication of integrated photonic circuits in electro-optic substrates by means of Refractive Index Engineering by fast ion implantation.

Thermal expansion behavior and polarization properties of lead-free ferroelectric potassium lithium tantalate niobate single crystals

Abstract Lead-free ferroelectric niobium-rich potassium lithium tantalate niobate K 0.95 Li 0.05 Ta 1− x Nb x O 3 (KLTN) single crystals were grown by the top-seeded melt method. Thermal expansion properties of K 0.95 Li 0.05 Ta 1− x Nb x O 3 ( x =0.78, 0.69, 0.60, and 0.52) single crystals were investigated in the temperature range of 140 K–800 K using a dilatometer. According to the thermal expansion data, phase transition temperatures of all compositions were determined, and temperature dependence of local polarization was calculated. In addition, the results were discussed in combination with the composition and crystallographic orientation.

Low-frequency–dependent electro-optic properties of potassium lithium tantalate niobate single crystals

A series of lead-free ferroelectric potassium lithium tantalate niobate K0.95Li0.05Ta1−xNbxO3 (x = 0.78, 0.69, 0.60, 0.52) single crystals were grown using the top-seeded melt growth method. The low-frequency–dependent linear electro-optic properties of K0.95Li0.05Ta1−xNbxO3 single crystals in the tetragonal state were investigated using the Senarmont method, autoscanning Mach-Zehnder interferometer technique and AC measurement method at room temperature. The electro-optic measurements were taken with continuous low frequency (from 1 kHz to 100 kHz) of a sinusoidal electric field, and large electro-optic responses were observed. For every component, the values of the electro-optic coefficients γ33, γ13 and γc decrease with the increase of frequency. However, the γ51 shows low sensitivity to the change of frequency. γ33, γ13 and γc increase with tantalum content, but γ51 decreases with the increase of tantalum content. The electro-optic properties of high-optical-quality K0.95Li0.05Ta1−xNbxO3 single crystals forecast their outstanding potential in various electro-optic applications.

Structure and dielectric properties of niobium-rich potassium lithium tantalate niobate single crystals

Abstract The structure and lattice parameters of high quality niobium-rich potassium lithium tantalate niobate (K 0.95 Li 0.05 )(Ta 1− x Nb x )O 3 ( x =0.44–0.66) single crystals were determined by the X-ray powder diffraction technique. Dielectric properties were studied in the temperature range from 20 to 500 K. The transition temperatures were determined, and the Curie temperatures adjusted between 330 K and 480 K through the suitable selection of Ta-to-Nb ratio. The degree of relaxation ( γ ) has been estimated using the modified Curie–Weiss law. The (K 0.95 Li 0.05 )(Ta 1− x Nb x )O 3 single crystals have also shown strong dc electric field dependent dielectric behavior, and high dielectric tunability (∼43%) for x =0.44.

Pyroelectric properties of lead-free ferroelectric niobium-rich potassium lithium tantalate niobate single crystals

The pyroelectric properties of niobium-rich potassium lithium tantalate niobate K0.95Li0.05Ta1−xNbxO3 (x=0.46, 0.51, 0.55, and 0.62) single crystals have been investigated. The pyroelectric coefficients (pi), the computed spontaneous polarizations (Ps) and the pyroelectric figures of merit (FOMs) have been determined. The typical values of pi (632 μC/cm2 K), Ps (13.3 μC/cm2) and FOM (243 pm/V) are attractive, and can be compared to the classical pyroelectric materials. The transition temperatures also have been determined from dielectric and pyroelectric measurements. These good pyroelectric properties as well as the possibility to produce large-size and high-quality single crystals make this kind of single crystal very promising for infra-red detectors and other pyroelectric applications.

Electrically controlled absorption in a slab waveguide formed by the implantation of protons in a potassium lithium tantalate niobate substrate

Electrically controlled absorption was observed in a slab waveguide, fabricated in a potassium lithium tantalate niobate substrate by proton implantation, at an energy of E=1.15 MeV and a fluence of 6.1×1016ions/cm2. The implantation created an amorphous layer which acted as the cladding with an adjacent proton doped layer at its bottom. It is suggested that a n-i junction is formed at the interface between the proton layer and the substrate, which is the core of the waveguide. The electrically controlled absorption is attributed to changes in the width of the depletion area of the n-i junction induced by the applied field.

Investigation of the conduction in an implanted layer of protons in a potassium lithium tantalate niobate substrate

The electrical conductivity in the amorphous layer formed by the implantation of protons at 1.15 MeV with fluence of 1.1×1017 ions/cm2 within the depth of potassium lithium tantalate niobate is investigated by four probes and Hall effect measurements. It is shown that the conductivity originates from electrons that are induced by “Hydrogen donors” that reside in a band structure 0.22 eV below the conduction band. It is claimed that this phenomenon enables the construction of conductive structures with submicron features within the depth of the substrate that can be used as embedded electrodes in electrooptical devices integrated in this substrate.

Electric field controlled higher-order diffraction images of paraelectric potassium lithium tantalate niobate

We report some electric field controlled photorefractive higher-order diffraction phenomena of a paraelectric phase potassium lithium tantalate niobate crystal doped with iron. In experiments, a p-polarized semiconductor laser (532nm) was used to record grating at a small incident angle. Higher-order diffraction images were observed when the signal beam was focused behind and in front of the crystal. Then the higher-order diffraction images were reconstructed by a p-polarized He–Ne laser (632.8nm) in the direction perpendicular to the surface. The higher-order diffraction images could be controlled by the external electric field. A theory about the higher-order diffraction images of the K and 2K grating is developed. The results show that the even order diffraction images of the K grating and the odd order diffraction of the 2K grating overlap each other. The odd order diffraction images of the K grating are diffracted in unattached direction. The electric field controlled higher-order diffraction image provides a useful method for optical information processing.

Growth, characterization and upconversion properties of erbium-doped potassium lithium tantalate niobate single crystals under 975 nm laser excitation

Potassium lithium tantalate niobate single crystals doped with erbium ions are grown by top-seeded solution growth method. The crystals are characterized by X-ray diffraction and differential thermal analysis. The refractive indices of the crystal are measured using ellipsometry method and fitted by Sellmeier equation. The as-grown crystals are tetragonal phase tungsten bronze-type structure with Curie temperature of 271.3°C. Characteristic Er3+ absorption bands are observed from 350 to 1100nm in ultraviolet–visible-near infrared absorption spectra. These crystals emit brightly green and red upconversion fluorescence under 975nm LD laser excitation, and the steady state upconversion spectra are obtained at room temperature. The red emission intensity increases as the erbium ions concentration increases in crystals. Processes of excited state absorption and energy transfer are responsible for upconversion luminescence. The emission intensities are quadratic dependences on pump power from pump power dependence analyses and deduction of transition rate equation model.