| 1. |
- Canalias, Carlota, et al.
(författare)
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In situ visualization of domain kinetics in flux grown KTiOPO4 by digital holography
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:6, s. 064105-
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Tidskriftsartikel (refereegranskat)abstract
- The fast dynamic evolution of ferroelectric domains during electric field poling in flux grown KTiOPO4 crystals was investigated online by a digital holography based technique. The dependence of the ferroelectric domain kinetics on the electric field temporal wave form and poling history was studied. High-speed imaging by means of a complementary metal-oxide-semiconductor image sensor camera allowed in situ measurement of the domain wall propagation speed under different poling conditions. The results also give evidence of the strong influence of the dielectric surface layer in this material.
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| 2. |
- De Angelis, M., et al.
(författare)
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Evaluation of the internal field in lithium niobate ferroelectric domains by an interferometric method
- 2004
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Ingår i: Applied physics letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85:4, s. 2785-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the evaluation of internal electric field of a ferroelectric engineered-domain in a LiNbO3 wafer crystal by detecting optical path length variation with a noninvasive interferometric inspection method. The lithium niobate wafer has been patterned and subjected to electric field poling to obtain two antiparallel ferroelectric domains separated by a single domain wall. The crystal has been mounted into one arm of a Mach-Zehnder-type interferometer to study the phase map and evaluate the effects of domain reversion by a digital holographic technique. Evaluation of the internal field and consequent variation of the electro-optical properties of the different domains is analyzed.
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| 3. |
- Ferraro, P., et al.
(författare)
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Surface topography of microstructures in lithium niobate by digital holographic microscopy
- 2004
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Ingår i: Measument science and technology15. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 15:5, s. 961-
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Tidskriftsartikel (refereegranskat)abstract
- We report here on the application of digital holographic microscopy as a metrological tool for the inspection and the micro-topography reconstruction of different microstructures fabricated in bulk lithium niobate by differential etching of reversed ferroelectric domain patterned crystals. These structures have a range of applications in optical ridge waveguides, alignment structures, V-grooves, micro-tips and micro-cantilever beams and precise control of the surface quality and topography is required. The technique allows us to obtain digitally a high-fidelity surface topography description of the specimen with only one image acquisition allowing us to have relatively simple and compact set-ups able to give quantitative information on object morphology. The advantages of this technique compared to traditional microscopy are discussed.
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| 4. |
- Grilli, Simonetta, et al.
(författare)
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A Mach-Zehnder interferometric system for measuring the refractive indices of uniaxial crystals
- 2002
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Ingår i: Optics communications. - 0030-4018. ; 202, s. 9-15
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Tidskriftsartikel (refereegranskat)abstract
- We report a new interferometric technique for measuring the ordinary and extraordinary refractive indices of uniaxial crystals. The technique is based on the measurement of the rotation-dependent phase changes of the optical path length in crystal plates. Accurate measurement of the phase shift as a function of the rotation of the sample is achieved by using a fast-Fourier-transform based fringe analysis method for phase retrieval. The principle of the method is discussed and measurements of the ordinary and extraordinary refractive indices of a lithium niobate crystal are reported.
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| 5. |
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| 6. |
- Grilli, Simonetta, et al.
(författare)
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Control of lateral domain spreading in congruent lithium niobate by selective proton exchange
- 2006
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Ingår i: Applied physics letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:3, s. 032902-
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Tidskriftsartikel (refereegranskat)abstract
- Proton exchange was observed to increase the poling voltage for congruent lithium niobate. Patterned proton exchange was then used to control domain nucleation and inhibit broadening of reversed domains. Periodically proton exchanged samples were used to form domain gratings by electric field poling just using planar electrodes and without need for poling current control. The reversed domain gratings had a duty cycle faithfully reproducing that of the proton exchanged pattern with straight domain walls parallel to the x face, thus demonstrating that high-fidelity reversed domain patterning is possible to obtain by a relatively simple process.
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| 7. |
- Grilli, Simonetta, et al.
(författare)
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Double-face and submicron two-dimensional domain patterning in congruent lithium niobate
- 2006
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Ingår i: IEEE photonics technology letters. - 1041-1135. ; 18, s. 541-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the simultaneous fabrication of two-dimensional submicron engineered domain patterns on both crystal faces, in congruent lithium niobate. The fabrication technique is based on interference photolithography, which allows short pitch over large areas, followed by electric field poling performed in overpoling regime. Experimental results for different domain pattern geometries, on the two crystal faces, are reported. These structures could be useful for short-wavelength frequency conversion and Bragg gratings applications. The moire effect is used in the lithographic process to fabricate more complex structures which could find application in photonic bandgap devices.
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| 8. |
- Grilli, Simonetta, 1974-
(författare)
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Ferroelectric domain engineering and characterization for photonic applications
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium niobate (LiNbO3) and KTiOPO4 (KTP) are ferroelectric crystals of considerable interest in different fields of optics and optoelectronics. Due to its large values of the nonlinear optical, electro-optic (EO), piezoelectric and acousto-optical coefficients, LiNbO3 is widely used for laser frequency conversion using the quasiphase matching (QPM) approach where the sign of nonlinearity has been periodically modulated by electric field poling (EFP). In the microwave and telecommunication field LiNbO3 is used for surface acoustic devices and integrated optical modulators. KTP and its isomorphs, on the other hand, exhibit slightly lower nonlinear coefficients but have much higher photorefractive damage thresholds, so that it is mainly used in the fabrication of QPM devices for both UV, IR and visible light generation and in high power applications. This thesis focus on different key issues: (1) accurate characterization of specific optical properties of LiNbO3, which are of interest in nonlinear and EO applications; (2) in-situ visualization and characterization of domain reversal by EFP in LiNbO3 and KTP crystals for a through understanding of the ferroelectric domain switching; (3) fabrication of periodic surface structures at sub-micron scale in LiNbO for photonic applications. An interferometric method is used for accurate measurement of ordinary and extraordinary refractive indices in uniaxial crystals, which is of great interest in the proper design of QPM crystals. A digital holography (DH) based method is presented here for 2D characterization of the EO properties of LiNbO , which is considerably interesting in the applications where the proper design of the EO device requires a spatially resolved information about the EO behaviour and the existing pointwise techniques are not sufficient. A DH method for novel in-situ monitoring of domain reversal by EFP in both LiNbO3 and KTP, is also presented here. The technqiue could be used as a tool for high fidelity periodic domain engineering but also provides information about domain kinetics, internal field and crystals defects. 3 3 3 Finally this thesis presents novel results concerning nanoscale periodic surface structuring of congruent LiNbO3. Holographic lithography (HL) is used for sub-micron period resist patterning and electric overpoling for surface domain reversal. Surface structures are obtained by selective etching. Moiré effect is also used in the HL to fabricate complicated structures with multiple periods. The depth compatibility with waveguide implementation allows foreseeing possible applications of these structures for Bragg gratings or innovative photonic crystal devices, exploiting the additional nonlinear and EO properties typical of LiNbO3.
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| 9. |
- Grilli, Simonetta, et al.
(författare)
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Investigation on reversed domain structures in lithium niobate crystals patterned by interference lithography
- 2003
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Ingår i: Optics express. - 1094-4087. ; 11, s. 392-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography. Furthermore we investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature. We show the possibility for realizing submicron-scaled three-dimensional domain patterns that could be applied to the construction of photonic crystals and in nonlinear optics. We show that high etch-rate applied to such structures allows to obtain pyramidal-like submicron relief structures which in principle could find application for waveguide construction in photonic bandgap devices
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| 10. |
- Grilli, SImonetta, et al.
(författare)
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Surface nanoscale periodic structures in congruent lithium niobate by domain reversal patterning and differential etching
- 2005
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Ingår i: Applied physics letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87, s. 233106-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterization of one- and two-dimensional periodic structures down to 200 nm size, in congruent lithium niobate crystal samples. Periods from 2 mu m to 530 nm are investigated. Interference photolithography is used to obtain short pitch insulating gratings, and subsequent electric-field poling, at the overpoling regime, is performed for periodic domain inversion. Nanoscale structures are obtained by selective chemical etching, and topographic investigations are performed by atomic force microscope. The fabricated structures are attractive in nonlinear optics for short-wavelength conversion and in the field of photonic crystals for Bragg and band-gap applications
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| 11. |
- Grilli, Simonetta, et al.
(författare)
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Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography
- 2005
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Ingår i: Optics letters. - 0146-9592. ; 30:13, s. 1671-1673
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.
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| 12. |
- Grilli, Simonetta, et al.
(författare)
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Visualization of optical deflection and switching operations by a domain-engineered-based LiNbO electro-optic device
- 2003
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Ingår i: Optics express. - 1094-4087. ; 11, s. 1212-
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Tidskriftsartikel (refereegranskat)abstract
- An electro-optic device applied as an optical beam deflector and switch at different wavelengths has been built and tested. The electro-optic device is based on domain-engineered lithium niobate (LiNbO3). In this paper, for the first time, its operation has been visualized by an imaging camera. The device has been characterized both at the visible wavelength (632.8 nm) and at a typical telecom wavelength (1532 nm). Furthermore, the device has been tested as an amplitude modulator in the mid-infrared region as well, at a wavelength of similar to4.3 mum, where no Pockels cells are available. A detailed description of this device is given, and the experimental results are discussed.
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| 13. |
- Grilli, Simonetta, et al.
(författare)
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Whole optical wavefields reconstruction by digital holography
- 2001
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Ingår i: Optics express. - 1094-4087. ; 9:6, s. 294-302
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Tidskriftsartikel (refereegranskat)abstract
- n this paper, we have investigated on the potentialities of digital holography for whole reconstruction of wavefields. We show that this technique can be efficiently used for obtaining quantitative information from the intensity and the phase distributions of the reconstructed field at different locations along the propagation direction. The basic concept and procedure of wavefield reconstruction for digital in-line holography is discussed. Numerical reconstructions of the wavefield from digitally recorded in-line hologram patterns and from simulated test patterns are presented. The potential of the method for analysing aberrated wave front has been exploited by applying the reconstruction procedure to astigmatic hologram patterns.
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| 14. |
- Paturzo, M., et al.
(författare)
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Investigation of electric internal field in congruent LiNbO3 by electro-optic effect
- 2004
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Ingår i: Applied physics letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85, s. 5652-5654
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of the defect-induced internal field on the electro-optic behavior of z-cut congruent lithium niobate crystals. We measure, by a spatially resolved interferometric technique, the phase retardation due to an external applied voltage occurring in two regions with opposite ferroelectric polarization. When measurements are performed just after electrical poling, the two opposite domains show a different electro-optic behavior. We interpret this as due to an elastic component of the internal field. In fact, the asymmetric behavior disappears when the sample is thermally annealed, i.e., when the internal field vanishes
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| 15. |
- Paturzo, M., et al.
(författare)
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On the origin of internal field in lithium niobate crystals directly observed by digital holography
- 2005
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Ingår i: Optics express. - 1094-4087. ; 13:14, s. 5416-
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Tidskriftsartikel (refereegranskat)abstract
- We show the defect dependence of the internal field in Lithium Niobate using a full-field interferometric method and demonstrate that it can be directly measured on some clusters of defects embedded in a stoichiometric matrix. Results show that the value of the internal field grows in proximity of defects and vanishes far from them, which addresses the long-standing issue about its origin in Lithium Niobate crystal.
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