Publications

2007
Aharon J Agranat, Roy Kaner, Galina Perepelitsa, and Yehudit Garcia. 2007. “Stable electro-optic striation grating produced by programed periodic modulation of the growth temperature..” Applied Physics Letters, 90, 19, Pp. 192902. Publisher's Version Abstract
Electrically controlled Bragg gratings implemented by periodic striations that were produced during the crystal growth are demonstrated in potassium lithium tantalate niobate crystals. The striations were generated by blowing air with periodic flow at the flux surface. The gratings were investigated by measurements of the diffraction efficiency versus the applied electric field. It was found that the composition grating induced correlated gratings of the refractive index and the low frequency dielectric constant. The latter, under the application of a uniform electric field, produced an electrically controlled birefringence grating through the quadratic electro-optic effect. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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A Pierangelo, E DelRe, A Ciattoni, G Biagi, E Palange, and A Agranat. 2007. “Separating polarization components through the electro-optic read-out of photorefractive solitons.” Optics Express 15 (21), Pp. 14283 - 14288. Publisher's Version Abstract

Analyzing the propagation dynamics of a light beam of arbitrary linear input polarization in an electro-activated photorefractive soliton we are able to experimentally find the conditions that separate its linear polarization components, mapping them into spatially distinct regions at the crystal output. Extending experiments to the switching scheme based on two oppositely biased solitons, we are able to transform this spatial separation into a separation of two distinct guided modes. The result is a miniaturized electro-optic polarization separator. (c) 2007 Optical Society of America.

2006
P Ben Ishai, AJ Agranat, and Y Feldman. 2006. “Confinement kinetics in a KTN:Cu crystal: Experiment and theory.” Physical Review B - Condensed Matter and Materials Physics, 73, 10. Publisher's Version
Accession Number: edselc.2-52.0-33644787901; (Physical Review B - Condensed Matter and Materials Physics, 2006, 73(10)) Publication Type: Academic Journal; Rights: Copyright 2012 Elsevier B.V., All rights reserved.
A Bitman, N Sapiens, G Bartal, L Secundo, M Segev, and AJ Agranat. 2006. “Electroholographic Tunable Volume Grating in the g44 Configuration.” Optics Letters , 31, 19, Pp. 2849-2851. Abstract
The g(44) grating is an electroholographic transmission grating in which the applied field is perpendicular to both the grating vector and the wave vector of the incident beam. It is argued that in this configuration the incident beam traverses through a periodically rotating index ellipsoid. It is shown that in the g(44) configuration the Bragg condition is fulfilled for a specific value of the applied field and for a diffracting beam polarization that is perpendicular to that of the incident beam. Consequently, the g(44) grating can be used as an electrically controlled filter. Tunability of 7 nm is demonstrated in a 2mm thick grating.
Angelo Pierangelo, E DelRe, E Palange, A Ciattoni, Y Garcia, and AJ Agranat. 2006. “Pinning-induced round solitons with symmetric nonlinear response for electroactivated optical circuitry..” Applied Physics Letters, 89, 12, Pp. 121123. Publisher's Version Abstract

The authors experimentally and theoretically study the formation of transient two-dimensional photorefractive spatial solitons in a striated paraelectric potassium lithium tantalate niobate crystal. The partial pinning to the built-in slablike index structures activates an interplay between the linear and nonlinear responses that leads to round solitons through a highly symmetric anisotropic nonlinearity, the means to self-write compact undistorted optical circuitry. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Accession Number: 23073383; Pierangelo, Angelo 1 DelRe, E. 2 Palange, E. 2; Email Address: palange@ing.univaq.it Ciattoni, A. 3 Garcia, Y. 4 Agranat, A. J. 4; Affiliation: 1: Dipartimento di Fisica, Università di Roma “La Sapienza,” 00185 Roma, Italy 2: Laboratorio di Ottica e Fotonica, Dipartimento di Ingegneria Elettrica e dell’Informazione, Università dell’Aquila, Monteluco di Roio, 67040 L’Aquila, Italy and CNISM, Università dell’Aquila, Monteluco di Roio, 67040 L’Aquila, Italy 3: Consiglio Nazionale delle Ricerche-Laboratorio Regionale CASTI, Università dell’Aquila, 67010 L’Aquila, Italy and Dipartimento di Fisica, Università dell’Aquila, 67010 L’Aquila, Italy 4: Department of Applied Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel; Source Info: 9/18/2006, Vol. 89 Issue 12, p121123; Subject Term: SOLITONS; Subject Term: LITHIUM niobate; Subject Term: ANISOTROPY; Subject Term: CRYSTALS; Subject Term: CRYSTALLOGRAPHY; Number of Pages: 3p; Illustrations: 2 Black and White Photographs, 1 Graph; Document Type: Article

H Ilan, A Gumennik, R Fathei, AJ Agranat, I Shachar, and M Hass. 2006. “Submerged waveguide constructed by implantation of 12C ions in electrooptic crystals.” Applied Physics Letters, 89, 24. Abstract
Waveguide structures were fabricated in potassium lithium tantalate niobate crystals by the implantation of high energy C12 ions. The implantation forms an amorphous layer with a lowered index of refraction within the depth of the crystal, which serves as the cladding of the waveguides. Two amorphous layers were fabricated at 18.8 and 25.6 μm below the surface of the crystal by implantation at 30 and 40 MeV, respectively. This formed a submerged slab waveguide sandwiched between the two amorphous layers and two slab waveguides that were formed between the surface of the crystal and each of the amorphous layers. Coupling between those waveguides was observed and investigated, and confinement of the light in the sandwiched waveguide was demonstrated. © 2006 American Institute of Physics.
2005
Eugenio DelRe, Angelo D'Ercole, Elia Palange, and Aharon J Agranat. 2005. “Observation of soliton ridge states for the self-imprinting of fiber-slab couplers..” Applied Physics Letters, 86, 19, Pp. 191110. Publisher's Version Abstract

We investigate experimentally the energy exchange patterns and consequent propagation dynamics of an extended hybrid-dimensional interaction between a one-dimensional and a two-dimensional spatial soliton in a biased photorefractive crystal. Results show that conditions can be found in which the coupling manifests propagation invariant features. The mechanism hinges on mutual distortion through spatially nonlocal components of response, as opposed to standard wave overlap, which would lead to a diffusion of the needle into the slab mode. These nonlocal-nonlinearity-driven ridge modes represent the instrument for writing fiber-slab couplers, the key to attaining soliton-based wavelength selectivity with electroactivated features. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Alexander Gumennik, Aharon J Agranat, Igal Shachar, and Michael Hass. 2005. “Thermal stability of a slab waveguide implemented by α particles implantation in potassium lithium tantalate niobate..” Applied Physics Letters, 87, 25, Pp. 251917. Publisher's Version Abstract
A slab waveguide was fabricated in a potassium lithium tantalate niobate crystal by the implantation of He2+ ions at 2.26 MeV. The waveguide profile and loss were evaluated by measuring the dark mode TE spectrum using the prism coupling method at λ=1.3 μm. The implantation generated amorphous cladding layer 5 μm below the surface of the crystal with a refractive index lower by 3.9% then that of the substrate. The propagation loss of the waveguided modes was found to be 0.1–0.2 dB/cm. Thermal stability of the waveguide was obtained by isothermal annealing at 351 and 446 °C. Following the annealing the waveguide index profile remained unchanged when subjected to annealing at 150 °C for one week. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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P Ben Ishai, CEM de Oliveira, Y Ryabov, AJ Agranat, and Y Feldman. 2005. “Unusual glass-like systems - relaxation dynamics of Cu+ ions in ferroelectric KTN crystals.” J. Non-Cryst. Solids 351 (33-36), Pp. 2786 - 2792. Publisher's Version Abstract
We present a broadband dielectric spectroscopy study of potassium tantalate niobate (KTN) crystals, doped with varying amounts of Cu ions. The dielectric landscape in frequency and temperature is rich, with multiple processes in different temperature phases of the crystals. Of particular interest are the processes resulting from Cu and Nb ions in the paraelectric phase of the crystal and from Cu ions in the ferroelectric phase. The linear dependence of the ferroelectric transition temperature in KTN crystals (KTa0.62Nb0.38O3Cu) on the concentration of Nb, as well as the dielectric behavior of the ferroelectric phase transition in these crystals, are well known. We concentrate of the dielectric relaxation resulting from the Cu ions in the crystal lattice. Cu dopants in very small concentrations have been added in the past to enhance the photoreftractive properties of KTN crystals. However the small ionic radius of such dopants, relative to their lattice site, results in virtual dipoles exhibiting dielectric relaxation. The random nature of their distribution throughout the ordered KTN lattice leads to relaxation behavior reminiscent of glass formers. In particular Vogel Fulcher Tammann relaxation of these ions is evident in the paraelectric phase of the crystal. This cooperativity is broken at a critical temperature (T = 354 K) and the relaxation becomes Arrhenius in nature. An explanation in terms of Adam-Gibbs theory is presented where the cooperative cluster is realized by polarized Nb ions linking the widely space Cu ions. At the phase transition (T-c = 295.6 K) this relaxation is 'frozen' by large internal fields caused by the structural shift of the Nb ion in the unit cell. As the temperature drops the Cu ions undergo a reorganization about the multiwell potential leading to a saddle-like process characteristic of liquids in confined systems. An explanation for this behavior is proposed based on free volume concepts, where the relatively small ionic radius of the Cu ions provides the free volume for the relaxing species. The role of the oxygen octahedra as the relaxing species is discussed. (c) 2005 Published by Elsevier BV.
2004
Eugenio DelRe, Elia Palange, and Aharon J Agranat. 2004. “Fiber-launched ultratight photorefractive solitons integrating fast soliton-based beam manipulation circuitry,” 7. Publisher's Version Abstract

The deterministic and reliable singlemode fiber integration with spatial solitons through ultratight needs in photorefractives have been demonstrated. Efficient electro-optic beam handling was allowed where the fiber carried the information sequence and also delivered the photorefractively active control beam that configured the circuitry.

Item Citation: Journal of Applied Physics. April 1, 2004, Vol. 95 Issue 7, 3822-3824Accession Number: edsgcl.123305906; Publication Type: Academic Journal; Source: Journal of Applied Physics; Language: English; Publication Date: 20040401; Rights: Copyright 2004 Gale, Cengage Learning. All rights reserved.; Imprint: American Institute of Physics, Inc.

P Ben Ishai, CEM de Oliveira, Y Ryabov, Yu. Feldman, and AJ Agranat. 2004. “Glass-forming liquid kinetics manifested in a KTN: Cu crystal.” Physical Review B - Condensed Matter and Materials Physics, 70, 13, Pp. 132104-1-132104-4. Publisher's Version
Accession Number: edselc.2-52.0-37649030903; (Physical Review B - Condensed Matter and Materials Physics, October 2004, 70(13):132104-1-132104-4) Publication Type: Academic Journal; Rights: Copyright 2008 Elsevier B.V., All rights reserved.
A D’Ercole, E Palange, E DelRe, A Ciattoni, B Crosignani, and AJ Agranat. 2004. “Miniaturization and embedding of soliton-based electro-optically addressable photonic arrays..” Applied Physics Letters, 85, 14, Pp. 2679. Publisher's Version Abstract

We achieved the soliton-based miniaturized integration of electro-optic devices in a photorefractive paraelectric bulk crystal, by driving self-trapping through an external bias field in a top-sided electrode geometry. The ensuing spatially resolved electric field manifests a localized voltage-dependent region in which a quasi-uniform field leads to screening-like self-trapped waves at considerably low voltages without sample miniaturization, along with their electro-optic beam manipulation. By replicating the electrode structure, our achievements constitute the basic building block that paves the way to digitally addressable volume photonic manipulator arrays. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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CEM de Oliveira, G Orr, N Axelrold, and AJ Agranat. 2004. “Controlled composition modulation in potassium lithium tantalate niobate crystals grown by off-centered TSSG method.” J. Cryst. Growth 273 (1-2), Pp. 203 - 206. Publisher's Version Abstract
Off-centered top-seeded solution growth (TSSG) method is demonstrated as an effective and simple way to generate controlled composition modulation in potassium lithium tantalate niobate (KLTN) single crystals. The changes in concentration were measured by differential interference contrast (DIC) microscopy. Large length with periodic modulations ranging from 1 to 5 mum in period was grown along a KLTN sample with period dispersion lower than 2%. (C) 2004 Elsevier B.V. All rights reserved.
M Ivker and AJ Agranat. 2004. “Resistance degradation due to interstitial hydrogen in photorefractive potassium lithium tantalate niobate single crystals.” J. Applied Physics 96 (11), Pp. 6405 - 6408. Publisher's Version Abstract
Resistance degradation in potassium lithium tantalate niobate (KLTN) doped with iron and titanium was measured in a single sample containing various concentrations of interstitial hydrogen. In this crystal the degradation arose from the migration of interstitial hydrogen and not oxygen vacancies, as reported in previous research. Interstitial hydrogen and oxygen vacancy defects both arise to compensate the valence shortfall of the substitutional iron impurities and the thermodynamic balance between the two compensation mechanisms can be controlled using reaction chemistry techniques. Through appropriate annealing treatments a single crystal of KLTN was prepared in three states: hydrogen-rich oxidized, hydrogen-poor reduced, and hydrogen-rich reduced. The characteristic degradation times for the three cases were 29, 2710, and 26 min, respectively. The degradation rate is correlated with hydrogen concentration and not oxidation state of the crystal. Infrared absorption from near the two electrodes of the hydrogen-rich reduced crystal after degradation confirmed polarization of the hydrogen concentration. Electrocoloration was also found to correlate with hydrogen-it was observed in both hydrogen-rich states, but was absent from the hydrogen-poor crystal. (C) 2004 American Institute of Physics.
2003
E DelRe, A D'Ercole, and AJ Agranat. 2003. “Emergence of linear wave segments and predictable traits in saturated nonlinear media.” Optiocs Letters 28 (4), Pp. 260 - 262. Publisher's Version Abstract

We find the key behind the existence traits of asymptotic saturated nonlinear optical solitons in the emergence of linear wave segments. These traits, produced by the progressive relegation of nonlinear dynamics to wave tails, allow a direct and versatile analytical prediction of self-trapping existence conditions and simple soliton scaling laws, which we confirm experimentally in saturated-Kerr self-trapping observed in photorefractives. This approach provides the means to correctly evaluate beam tails in the saturated regime, which is instrumental in the prediction of soliton interaction forces. (C) 2003 Optical Society of America.

2002
E DelRe and AJ Agranat. 2002. “Dielectric nonlinearity in photorefractive spatial soliton formation.” Physics Review A 65 (5). Publisher's Version Abstract

We find that the anomalous behavior of optical spatial screening solitons observed in the high-symmetry paraelectric phase is a consequence of nonlinear dielectric effects. These, coupled to space charge in saturated conditions, change the effective optical nonlinearity even far from the phase-transition regime.

E DelRe, B Crosignani, P Di Porto, E Palange, and AJ Agranat. 2002. “Electro-optic beam manipulation through photorefractive needles.” Optics Letters 27 (24), Pp. 2188 - 2190. Publisher's Version Abstract

We demonstrate electro-optic spatial two-dimensional mode switching in a bulk sample of potassium lithium tantalate niobate. Spatial confinement, mode coupling, and electro-optic functionality are mediated by two photorefractive needle solitons of opposite electroholographic charges embedded together in their anisotropic lobular structure. (C) 2002 Optical Society of America.

AJ Agranat. 2002. “Optical lambda-switching at telecom wavelengths based on electroholography .” Topics in Applied Physics , 89, Pp. 129-156. Abstract
Electroholography is a wavelength-selective optical switching method based on governing of the reconstruction process of volume holograms by means of an electric field. Electroholography is based on the voltage-controlled photorefractive effect in the paraelectric phase. The basic switching device is an electrically controlled Bragg grating or a volume hologram stored in a volume of a paraelectric crystal by the photorefractive process. The basic electroholographic switching operation is the reconstruction of a volume grating (hologram), which requires that the Bragg condition be satisfied, and therefore is wavelength selective. In addition the applied field governs the efficiency of the reconstruction. Consequently, electroholographic switching includes grouping, multicasting, power management and non-intrusive data as an integral part of the switching operation. In preliminary measurements the performance envelope of the electroholography-based switch, is a cube of 1.8 mm3 was found to be as follows: The minimum net insertion loss is 0.5 dB per switching operation. The minimum loss when a beam propagates through a latent grating is 0.2%. The Polarization-Dependent Loss (PDL) in a device that includes diversity architecture is less than 0.4 dB and the Polarization Mode Dispersion (PMD) is less than 0.07 ps. Bit-error rate (BER) in a switch operating at 40 Gb/s was measured to be 10-13. These features make electroholography ideal for circuit switching applications. Finally, response times of approximately 10 ns were measured, opening the way to burst switching applications.
Vladimir A Trepakov, Lubomir Jastrabik, Siegmar Kapphan, Enrico Giulotto, and Aharon J Agranat. 2002. “Phase transitions, related properties and possible applications of (K,Li)(Ta,Nb)O3 crystals.” Optical Materials, 19, Photonic Materials for the 21st Century. Proceedings of the 2nd International Symposium on Laser, Scintillator and Nonlinear Opt, Pp. 13 - 21. Publisher's Version Abstract
It is shown that doping the highly polarizable KTaO3 perovskite simultaneously by Li and Nb (K1−xLixTa1−yNbyO3, KLTN) gives rise to new impressive dipole ordering effects, very unusual physical properties and strong responses with respect to doping parameters. Besides, KLTN has outstanding perspectives of application in electrically controlled holographic and compositionally graded pyroelectric devices.
Accession Number: S0925346701001963; Author: Trepakov, Vladimir A. (a, ∗); Author: Jastrabik, Lubomir (b); Author: Kapphan, Siegmar (c); Author: Giulotto, Enrico (d); Author: Agranat, Aharon J. (e); Affiliation: A.F. Ioffe Physical and Technical Institute, 194 021 St. Petersburg, Russia; Affiliation: Institute of Physics AS CR, 182 21 Praha 8, Czech Republic; Affiliation: FB Physik, University of Osnabrück, 49069 Osnabrück, Germany; Affiliation: Dipartimento di Fisica “A. Volta”, Università di Pavia and INFM, 27100 Pavia, Italy; Affiliation: Department of Applied Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel; Number of Pages: 9; Language: English;
G Bitton, Y Feldman, and AJ Agranat. 2002. “Relaxation processes of off-center impurities in KTN : Li crystals.” J. Non-Cryst. Solids 305 (1-3), Pp. 362 - 367. Publisher's Version Abstract
The dielectric and ferroelectric properties of K1-xLixTa1-yNbyO3 (KLTN) crystals as functions of temperature, frequency, and electric field are presented. Measurement of the polarization as a function of temperature indicates the existence of polarized microregions at temperatures well above the phase transition (PT) temperature. In the vicinity of the PT those microregions respond cooperatively and contribute to the observed macroscopic polarization. This cooperative behavior was also evident from dielectric relaxation measurements. Two relaxation processes were observed, one at high frequency and the other at low frequency. In both processes the relaxation time and the relaxation step (DeltaE) were found to increase as the PT temperature was approached. Those processes originate from movement of off-center ions in a multi-well potential. In the vicinity of the PT the correlation length of the host lattice is increased and the movements of the off-center ions become more and more correlated. The increased number of cooperatively relaxing ions increases the relaxation time and the relaxation amplitude. (C) 2002 Published by Elsevier Science B.V.

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