94 research outputs found
Electric surface potential and frozen-in field direct measurements in thermally poled silica
No full textWe report measurements of the electric surface potential (SP) and its temporal evolution in thermally poled silica samples, thus, providing a direct quantitative evidence of the frozen-in voltage. The SP value is found to be directly related to the voltage across the depletion layer and there is a clear link between frozen-in electric field and nonlinear optical coefficient, inferred from SP and second harmonic generation measurements respectively. Our studies also show the presence of screening surface charge layers. We have calculated the space charge distribution making evident that the thinner the sample, the larger the screening surface charge density
Simultaneous guidance of slow photons and slow acoustic phonons in silicon phoxonic crystal slabs
No full textThis paper was published in OPTICS EXPRESS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OE.19.009690. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law[EN] We demonstrate theoretically that photons and acoustic phonons can be simultaneously guided and slowed down in specially designed nanostructures. Phoxonic crystal waveguides presenting simultaneous phononic and photonic band gaps were designed in perforated silicon membranes that can be conveniently obtained using silicon-on-insulator technology. Geometrical parameters for simultaneous photonic and phononic band gaps were first chosen for optical wavelengths around 1550 nm, based on the finite element analysis of a perfect phoxonic crystal of circular holes. A plain core waveguide was then defined, and simultaneous slow light and elastic guided modes were identified for some waveguide width. Joint guidance of light and elastic waves is predicted with group velocities as low as c/25 and 180 m/s, respectively. © 2011 Optical Society of America.This research has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number 233883 (TAILPHOX).Laude, V.; Beugnot, J.; Benchabane, S.; Pennec, Y.; Djafari-Rouhani, B.; Papanikolaou, N.; Escalante Fernández, JM.... (2011). Simultaneous guidance of slow photons and slow acoustic phonons in silicon phoxonic crystal slabs. Optics Express. 19(10):9690-9698. https://doi.org/10.1364/OE.19.009690S969096981910Kushwaha, M. S., Halevi, P., Dobrzynski, L., & Djafari-Rouhani, B. (1993). Acoustic band structure of periodic elastic composites. Physical Review Letters, 71(13), 2022-2025. doi:10.1103/physrevlett.71.2022Maldovan, M., & Thomas, E. L. (2006). Simultaneous localization of photons and phonons in two-dimensional periodic structures. Applied Physics Letters, 88(25), 251907. doi:10.1063/1.2216885Maldovan, M., & Thomas, E. L. (2006). Simultaneous complete elastic and electromagnetic band gaps in periodic structures. Applied Physics B, 83(4), 595-600. doi:10.1007/s00340-006-2241-yAkimov, A. V., Tanaka, Y., Pevtsov, A. B., Kaplan, S. F., Golubev, V. G., Tamura, S., … Bayer, M. (2008). Hypersonic Modulation of Light in Three-Dimensional Photonic and Phononic Band-Gap Materials. Physical Review Letters, 101(3). doi:10.1103/physrevlett.101.033902Sadat-Saleh, S., Benchabane, S., Baida, F. I., Bernal, M.-P., & Laude, V. (2009). Tailoring simultaneous photonic and phononic band gaps. Journal of Applied Physics, 106(7), 074912. doi:10.1063/1.3243276Papanikolaou, N., Psarobas, I. E., & Stefanou, N. (2010). Absolute spectral gaps for infrared light and hypersound in three-dimensional metallodielectric phoxonic crystals. Applied Physics Letters, 96(23), 231917. doi:10.1063/1.3453448Mohammadi, S., Eftekhar, A. A., Khelif, A., & Adibi, A. (2010). Simultaneous two-dimensional phononic and photonic band gaps in opto-mechanical crystal slabs. Optics Express, 18(9), 9164. doi:10.1364/oe.18.009164Pennec, Y., Rouhani, B. D., El Boudouti, E. H., Li, C., El Hassouani, Y., Vasseur, J. O., … Martinez, A. (2010). Simultaneous existence of phononic and photonic band gaps in periodic crystal slabs. Optics Express, 18(13), 14301. doi:10.1364/oe.18.014301Safavi-Naeini, A. H., & Painter, O. (2010). Design of optomechanical cavities and waveguides on a simultaneous bandgap phononic-photonic crystal slab. Optics Express, 18(14), 14926. doi:10.1364/oe.18.014926El Hassouani, Y., Li, C., Pennec, Y., El Boudouti, E. H., Larabi, H., Akjouj, A., … Djafari Rouhani, B. (2010). Dual phononic and photonic band gaps in a periodic array of pillars deposited on a thin plate. Physical Review B, 82(15). doi:10.1103/physrevb.82.155405Khelif, A., Aoubiza, B., Mohammadi, S., Adibi, A., & Laude, V. (2006). Complete band gaps in two-dimensional phononic crystal slabs. Physical Review E, 74(4). doi:10.1103/physreve.74.046610Hussein, M. I. (2009). Reduced Bloch mode expansion for periodic media band structure calculations. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 465(2109), 2825-2848. doi:10.1098/rspa.2008.0471Johnson, S. G., Fan, S., Villeneuve, P. R., Joannopoulos, J. D., & Kolodziejski, L. A. (1999). Guided modes in photonic crystal slabs. Physical Review B, 60(8), 5751-5758. doi:10.1103/physrevb.60.5751Xu, T., Wheeler, M. S., Nair, S. V., Ruda, H. E., Mojahedi, M., & Aitchison, J. S. (2008). Highly confined mode above the light line in a two-dimensional photonic crystal slab. Applied Physics Letters, 93(24), 241105. doi:10.1063/1.3046124Laude, V., Achaoui, Y., Benchabane, S., & Khelif, A. (2009). Evanescent Bloch waves and the complex band structure of phononic crystals. Physical Review B, 80(9). doi:10.1103/physrevb.80.092301Laude, V., Khelif, A., Benchabane, S., Wilm, M., Sylvestre, T., Kibler, B., … Maillotte, H. (2005). Phononic band-gap guidance of acoustic modes in photonic crystal fibers. Physical Review B, 71(4). doi:10.1103/physrevb.71.045107Dainese, P., Russell, P. S. J., Joly, N., Knight, J. C., Wiederhecker, G. S., Fragnito, H. L., … Khelif, A. (2006). Stimulated Brillouin scattering from multi-GHz-guided acoustic phonons in nanostructured photonic crystal fibres. Nature Physics, 2(6), 388-392. doi:10.1038/nphys31
Band gaps and cavity modes in dual phononic and photonic strip waveguides
No full text[EN] We discuss theoretically the simultaneous existence of phoxonic, i.e., dual phononic and photonic, band gaps in a periodic silicon strip waveguide. The unit-cell of this one-dimensional waveguide contains a hole in the middle and two symmetric stubs on the sides. Indeed, stubs and holes are respectively favorable for creating a phononic and a photonic band gap. Appropriate geometrical parameters allow us to obtain a complete phononic gap together with a photonic gap of a given polarization and symmetry. The insertion of a cavity inside the perfect structure provides simultaneous confinement of acoustic and optical waves suitable to enhance the phonon-photon interaction. © 2011 Copyright 2011 Author(s).This work was supported by the European Commission Seventh Framework Programs (FP7) under the FET-Open project TAILPHOX No 233883.Pennec, Y.; Rouhani, BD.; Li, C.; Escalante Fernández, JM.; Martínez Abietar, AJ.; Benchabane, S.; Laude, V.... (2011). Band gaps and cavity modes in dual phononic and photonic strip waveguides. AIP Advances. 1(4):41901-41908. https://doi.org/10.1063/1.3675799S41901419081
Integrated acousto-optic polarization converter in a ZX-cut LiNbO3 waveguide superlattice
No full textInternational audienceWe report an integrated acousto-optic polarization converter exploiting a novel surface acoustic superlattice (S-ASL) transducer. The S-ASL transducer is made of a ZX-cut periodically poled lithium niobate (PPLN) crystal with uniform coplanar electrodes for surface acoustic wave (SAW) generation. For a PPLN period of 20 mu m the SAW is excited at an rf of about 190 MHz, while the phase matching occurs at an optical wavelength of around 1456 nm. The measured mode conversion efficiency of 90% at an input rf power of 1 W and the 3 dB optical bandwidth of 2.5 nm confirm the confinement of the SAW between the electrode gap and the constructive interaction along the whole 10 mm electrode length
Surface acoustic wave generation in ZX-cut LiNbO3 superlattices using coplanar electrodes
No full textWe report on a configuration to generate surface acoustic waves (SAWs) in acoustic superlattices based on ZX -cut periodically poled lithium niobate. The coplanar electrode configuration allows inducing Rayleigh type SAWs with the elastic energy mainly concentrated in between the electrodes gap and under the crystal surface. With respect to standard interdigitated transducers using the same crystal orientation, the efficiency of the SAW generation in the proposed designs are similar, while, for the same grating period, the resonance frequency that can be achieved is two times larger
Simultaneous Existence of Phononic and Photonic Band Gaps in Phoxonic Crystal Slabs
No full textWe discuss the simultaneous existence of phononic and photonic
band gaps in a periodic array of holes drilled in a Si membrane. We investigate in detail both the centered square lattice and the boron nitride (BN) lattice with two atoms per unit cell which include the simple square, triangular and honeycomb lattices as particular cases. We show that complete phononic and photonic band gaps can be obtained from the
honeycomb lattice as well as BN lattices close to honeycomb. Otherwise, all investigated structures present the possibility of a complete phononic gap together with a photonic band gap of a given symmetry, odd or even, depending on the geometrical parameters
Adduden n yiselmaden n tmaziɣt akked yinelmaden n ulmud alemmas ɣef udlisfus n uswir wis ukkuẓ
No full text67p.; Table.; 30cm.(+cd)Tutlayt n tmaziɣt tudef ɣer uɣerbez azzayri deg useggas 1995, aselmed-is ur yeqqim
ara akken yebda, imi tger asurif ɣer sdat. Abeddel deg unagraw n usegmi i d-yellan deg
useggas n 2003, yegla-d s usutteb n kra n wallalen n tsensegmit, ad nebder gar-asen ahilen
d yidlisfusen i d-iheyya uɣlif n usegmi i kraḍ n yiswiren. Adlisfus n tmaziɣt ɣur-s azal d
ameqqran deg usnerni n tmusniwin n unelmad. Aṭas n yimsikden d yimussnawen n
tesnalmudt i yerran lwelha ɣer lexṣas n yigburen n wahilen d yidlisfusen n tmaziɣt, aladɣa
deg uswir n ulmud alemmas.
Deg umahil-a, neɛreḍ ad d-nesbeggen tilawt n udlisfus n useggas wis ukkuẓ n ulmud
alemmas, akken ad d-nerr ɣef yiseqsiyen igejdanen iɣef tbedd tezrawt-a. Ad d-nesmekti,
nexdem amahil-a s usentel “Adduden n yiselmaden n tmaziɣt akked yinelmaden n ulmud
alemmas ɣef udlisfus n useggas wis ukkuẓ”, i ibedden ɣef kraḍ n yiseqsiyen igejdanen
yellan deg tmukrist, aseqsi amenzu d andi ɣef tmuɣli n yinelmaden d yiselmaden n useggas
wis ukkuẓ ɣef udlisfus n tmaziɣt, aseqsi wis sin ɣef wuguren i d-ttemlilen deg usemres-is
deg uselmed d ulmad.
Deg tezrawt-a i nga, nessaweḍ ad d-nessisen timuɣliwin yemgaraden n yinelmaden d
yiselmaden ɣef udlisfus akked usemres-is. Akken ad d-negmer ugar n tmuɣliwin d yisallen
i yerzan asentel-nneɣ, nheyya-d sin yimseqsiyen, amenzu i yinelmaden, ma d wis sin i
yiselmaden n sin wasunen deg lwilaya n Tizi Wezzu (Buzgan d Yiferḥunen).
Tuget n yiselmaden iɣer d-negmer isalan d imuzzag n taɣult, imi akk sɛan agerdas n
turagt n tutlayt d yidles amaziɣ.
Tasleḍt n yiseqsiyen i d-nefka deg yimseqsiyen, tessaweḍ-aɣ ad nẓer igemmaḍ ɣef
wayen i nettnadi, imi s umata adlisfus iɣef nga tazrawt ixus deg lebni-s almend n talɣa d
tɣra. Ad t-naf yebḍa ɣef kraḍ n yiḥricen i yuran s yisekilen n tira yemgaraden, d ayen ur
yettɛawanen ara inelmaden. Iselmaden ur asen-teɛǧib ara talɣa d tɣara n udlisfus-a, d ayen
ara aɣ-yeǧǧen ad d-nessentem turda tamezwarut.
Ayen yerzan uguren i d-ttemlilen yinelmaden d yiselmaden deg usemres n udlisfus,
deg tazwara d iḍrisen i yellan deg-s, imi iselmaden s umata ur ttafen ara ayen ḥwaǧen i
uselmed acku ttwatun s tantaliwin-nniḍen n tmaziɣt deg-s tacawit d temẓabit. Iḍrisen-a
xussen deg usummen, imi llan wid ur nesɛi ara tugniwin neɣ ur laqent ara, d ayen i ten yeǧǧan ur ttilin ara d imalɣaden. Ma d inelmaden yesɛan adlisfus, semrasen-t i tɣuri n
yinzan d yisefra, ula d wi tikwal kan i teqqaren.
Tin ɣer-s d iferdisen n tutlayt, xas ttɛawanen anelmad akken ad xedmen asenfar,
maca ad naf amur ameqqran n yirmad i yellan ur llin ara deg tgezmin d yisenfaren
iwulmen, llan wid ilaqen i tesnawit. S yisalan-a i d-negmer sɣur yinelmaden d yiselmaden,
nessaweḍ ad d-nessentem turda tis snat i d-nefka “ Iselmaden d yinelmaden ttemlilin-d
uguren deg usemres n udlisfus ”.
Almend n yisalan i d-negmer, igburen n udlisfus mačči d ufrinen ilaqen i uselmed
deg uswir-a.
Aselmed n tutlayt n tmaziɣt, d amaynut deg tmurt n Lezzayer, ɣef waya ilaq ad ilin
ugar n yinadiyen ɣef tesnalmudt n tutlayt-a, imi aṭas n wuguren i d-ttemlilen yiselmaden d
yinelmaden. Tazrawt-nteɣ terza asentel n udlisfus, nessaram d tin ara d-igen iberdan i
tezrawin-nniḍen, ara yilin d afud i tutlayt n tmaziɣt
Characteristics of Speed Sensorless Vector Controlled Induction Motor with High Efficiency Taking Core Loss into Account
No full textAbstractThis paper presents the characteristics of a speed sensorless vector control method of an induction motor operating at high efficiency and high response, in which core loss is taken into account. An improved method of speed estimation that operates on the principle of speed adaptive flux and current observer has been proposed. An observer is basically an estimator that uses a plant model and a feedback loop with measured stator voltage and current. Simulation results show that the proposed direct field oriented control with the proposed observer provides good performance characteristics. The IM is fed by an indirect power electronics converter. This indirect converter is controlled by a pulse width modulation PWM technique that enables minimization of harmonics introduced by the line converter, as well as the control of the power factor and DC-link voltage. We study the robustness of the overall system- using simulation of different modes to operating modes and varied parameters
Low power consumption integrated acousto-optic filter in domain inverted LiNbO_3 superlattice
No full textInternational audienceWe report on an integrated acousto-optic filter in domain inverted LiNbO(3) using a coplanar electrode configuration, which can achieve complete optical switching at electrical powers as low as 50mW. These values are more than one order of magnitude lower than previously reported results [Opt. Lett. 34, 3205 (2009)]. In order to design the low power consumption devices, we have calculated surface acoustic wave excitation, propagation and acousto-optic interaction in the domain inverted LiNbO(3) superlattice using scalar approximation and FEM analysis. Results from both modeling techniques are in good agreement with the experiments, including direct measurement of the acoustic displacement using laser interferometry and acousto-optic performance
Diffraction less and strongly confined surface acoustic waves in domain inverted LiNbO3 superlattices
No full textInternational audienceWe show that an appropriate mass-loading, placed on the surface and in between the electrodes of a coplanar acoustic LiNbO3 superlattice, can counteract lateral diffraction of surface acoustic waves (SAWs). The strong confinement corresponds to a SAW mode, whose displacement is measured using laser interferometry. The proposed SAW confinement method has also potentials in acousto-optic devices, as we demonstrate a threefold reduction in the electrical power required for complete optical switching in mass-loaded superlattice with respect to similar unloaded structure. The devices have also the advantage not to suffer additional acoustic or optical loss due to the mass-loading structure
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